JOURNAL TRANSCRIPT
Mineral Trioxide Aggregate: A review of clinical usage and investigations of the effects of modifying particle size William Nguyen Ha BDSc GradCert Research Commercialisation
A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2017 School of Dentistry
Abstract Introduction Mineral trioxide aggregate (MTA) is a dental cement used in various endodontic and pulp therapy procedures. MTA takes longer to set than other dental cements or bulk dental restoratives such as glass ionomer cement (GIC). The long setting time and the cost of the material are often described as problems of MTA. A method to accelerate reaction speed is to reduce particle size. As a smaller particle size will accelerate the setting reaction, the next consideration was how particle size influences the physical properties of the set MTA cement. In the literature on MTA, the setting time has been assessed using an indentation method involving arbitrary weights and needle diameters as defined by the International Organization for Standardization (ISO), in particular, ISO 9917-1 for water-based cements and ISO 6876 for endodontic cements. Both of these standards define a dental cement as ‘set’ based on arbitrary needle weights applied to the MTA, to which a complete indentation is ‘set’ and an incomplete indentation is ‘unset’. This resulting definition of set versus unset lacks validity, since the response to indentation pressure does not relate to the material’s clinical properties nor its progress in hydration. Elastic modulus is a parameter which can be measured over time as a material sets which can be used to test MTA and other dental cements. Methods To understand MTA, a review of the chemistry of MTA and its relationships with other related dental cements was performed. As MTA is 80% Portland cement, a review was performed utilising knowledge from the concrete industry. A review of the clinical knowledge of MTA was performed as well as a review of the testing methodology used in the literature. To understand how MTA was used by clinicians, a survey was performed of general dentists (GDs), endodontists (EDs) and paediatric dentists (PDs) in Australia. Laser diffraction analysis (LDA) was used to assess the particle size distribution (PSD) of ProRoot MTA (MTA-P) and MTA Angelus (MTA-A). The data obtained were analysed using the non-linear least squares method to deconvolute the PSD into the constituents of Portland cement (PC) and bismuth oxide (BO). The three key parameters of PSDs, namely the 10th percentile (D10), the 50th percentile (D50) and the 90th percentile (D90) were plotted against the setting times of 11 commercial MTA cements, 6 PC products and against the cumulative heat release of the PC products.
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To assess the influence of reduced particle size on setting time, experimental MTAs with varying particle size had their indentation setting time measured, elastic modulus tested over time and comparisons of strength over time. Results The review of MTA and related cements revealed the use of vague or inaccurate terms in the literature, which led to a formal creation of the term ‘hygroscopic dental cement’ (HDC). New MTA-like cements, often called ‘bioceramics’, fall under the category of HDCs and share similar properties, all of which, can be influenced by storage, mixing, placement and curing. The testing of HDCs often does not correlate well to the clinical usage of HDCs as its setting time and curing is not considered. A lack of experience with MTA was the greatest barrier to its use for GD (48.7%), followed by its high cost (31.6%). A majority of GD (82.5%) desired additional hands-on training in the use of MTA. LDA documented a different PSD for each material, and also showed that because of the hygroscopic nature of the cement, there were changes in the PSD when the powder was exposed to room air. This point has important implications for how MTA powder is packaged. MTA-P was shown to have both fine and large PC particles, with intermediate size particles for BO. On the other hand, MTA-A had small BO with large PC particles. Of the three key markers, the D90 showed the strongest correlation with the setting time and the cumulative heat release. Curing under dry conditions gave a lower CS than when samples were cured under wet conditions (in PBS). Cements with smaller particle sizes gave greater initial CS and FS. However, this advantage was lost over time (1-3 weeks). The cements tested were Fuji VII, Fuji IX, MTA-P, Biodentine, AH 26, AH Plus Jet and Real Seal SE Sealer. Discussion Despite proposed advantages in handling, ‘bioceramics’ illustrate compromises in their resultant properties which could have implications on clinical outcomes. These compromises can be difficult to identify as the results of many published tests for MTA and ‘bioceramics’ are not reflective of clinical use of the material.
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Significant differences existed in how MTA was being used between GDs and EDs that was reflected in the different levels of training. Thus, lack of knowledge of the material is a larger barrier to its use, rather than its high cost or any inherent problems with the material. The use of smaller particle sizes in MTA and PC correlate with faster setting times. Elastic modulus provides a better method for testing setting time than indentation testing. Our testing with experimental MTA illustrated faster setting times with no advantages to the final strength of the cement. Testing of endodontic cements using rheology illustrated that the proposed setting time by manufacturers can be an underestimation as the material is still reacting.
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Declaration by author
This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis.
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Publications during candidature Peer-reviewed papers
1. Ha WN, Kahler B, Walsh LJ. Classification and nomenclature of commercial hygroscopic dental cements. Euro Endod J. In press 2017 (accepted 9 Sep 2017). 2. Ha WN, Kahler B, Walsh LJ. Clinical manipulation of mineral trioxide aggregate: Lessons from the construction industry and their relevance to clinical practice. J Can Dent Assoc 2015;81:f4. 3. Ha WN, Nicholson T, Kahler B, Walsh LJ. Mineral trioxide aggregate – a review of properties and testing methodologies. Materials. In press 2017 (accepted 26 Sep 2017). 4. Ha WN, Kahler B, Walsh LJ. Dental material choices for pulp therapy in paediatric dentistry. Eur Endod J; 2017, 2:1-7. 5. Ha WN, Duckmanton P, Kahler B, Walsh LJ. A survey of various endodontic procedures related to MTA usage by members of the Australian Society of Endodontology. Aust Endod J; 2016; 42; 132-138. 6. Ha WN, Kahler B, Walsh LJ. Particle size changes in unsealed mineral trioxide aggregate powder. J Endod 2014;40:423-426. 7. Ha WN, Shakibaie F, Kahler B, Walsh LJ. Deconvolution of the particle size distribution of ProRoot MTA and MTA Angelus. Acta Biomater Odontol Scand 2016;2:7-11. 8. Ha WN, Bentz DP, Kahler B, Walsh LJ. D90: The strongest contributor to setting time in mineral trioxide aggregate and Portland cement. J Endod 2015;41:11461150. An abstract from this also appeared in the Australian Dental Journal Research Supplement 2015; S11-12. 9. Ha WN, Kahler B, Walsh LJ. The influence of particle size and curing conditions on testing Mineral Trioxide Aggregate cement. Acta Biomater Odontol Scand 2016;2:130-137. 10. Ha WN, Nicholson T, Kahler B, Walsh LJ. Methodologies for measuring the setting times of mineral trioxide aggregate and Portland cement products used in dentistry. Acta Biomater Odontol Scand 2016;2:25-30. Database publication
1. Ha WN. Registrant of GMDN Term ‘Hydraulic dental cement’, (now Hygroscopic dental cement), Term P60510. Available from https://www.gmdnagency.org/
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Conference proceedings
Australian and New Zealand College of Veterinary Scientists (Dental Section) Gold Coast, Australia
2015
Conference abstracts
UQ School of Dentistry Research Day presentations UQ School of Dentistry Brisbane, Australia
2011, 2012, 2013, 2014, 2015, 2016, 2017
Storage of MTA IADR Conference, Asia Pacific Region Bangkok, Thailand
2013
Setting time of MTA IADR Conference, Australia and New Zealand Division Brisbane, Australia
2014
Survey on the usage of MTA by members of the Australian Society of Endodontology Annual Meeting of the Japanese Association of Dental Research Fukuoka, Japan
2015
Rheology of MTA IADR Conference, Australia and New Zealand Division Dunedin, New Zealand
2015
Dental material choices for pulp therapy by ANZSPD members World Congress on Dental Traumatology Brisbane, Australia
2016
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Publications included in this thesis 1. Ha WN, Kahler B, Walsh LJ. Classification and nomenclature of commercial hygroscopic dental cements. Euro Endod J. In press 2017 (accepted 9 Sep 2017). - Incorporated in Chapter 1 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (50%) Design methodology (100%) Data collection (100%) Analysis (100%) Literature review (100%) Writing of manuscript (50%)
Bill Kahler
Writing of manuscript (50%) Critical review (50%) Supervision (50%)
Laurence J Walsh
Construct idea (50%) Critical review (50%) Supervision (50%)
2. Ha WN, Kahler B, Walsh LJ. Clinical manipulation of mineral trioxide aggregate: Lessons from the construction industry and their relevance to clinical practice. J Can Dent Assoc 2015;81:f4. - Incorporated in Chapter 1 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (50%) Design methodology (100%) Data collection (100%) Analysis (100%) Literature review (100%) Writing of manuscript (50%)
Bill Kahler
Writing of manuscript (50%) Critical review (50%) Supervision (50%)
Laurence J Walsh
Construct idea (50%) Critical review (50%) Supervision (50%) viii
1. Ha WN, Nicholson T, Kahler B, Walsh LJ. Mineral trioxide aggregate – a review of properties and testing methodologies. Materials. In press 2017 (accepted 26 Sep 2017). - Incorporated in Chapter 1 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (50%) Design methodology (100%) Data collection (100%) Analysis (100%) Literature review (100%) Writing of manuscript (50%)
Bill Kahler
Writing of manuscript (50%) Critical review (50%) Supervision (50%)
Laurence J Walsh
Construct idea (50%) Critical review (50%) Supervision (50%)
3. Ha WN, Kahler B, Walsh LJ. Dental material choices for pulp therapy in paediatric dentistry. Eur Endod J; 2017, 2017; 2:1-7. - Incorporated as Chapter 2 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (50%) Design methodology (100%) Data collection (100%) Analysis (100%) Literature review (100%) Writing of manuscript (50%)
Bill Kahler
Writing of manuscript (50%) Critical review (50%) Supervision (50%)
Laurence J Walsh
Construct idea (50%) Critical review (50%) Supervision (50%)
ix
4. Ha WN, Duckmanton P, Kahler B, Walsh LJ. A survey of various endodontic procedures related to MTA usage by members of the Australian Society of Endodontology. Aust Endod J; 2016; 42; 132-138. - Incorporated as Chapter 3 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (50%) Design methodology (100%) Data collection (100%) Analysis (100%) Literature review (100%) Writing of manuscript (50%)
Peter Duckmanton
Construct idea (25%) Critical review (25%) Supervision (25%)
Bill Kahler
Writing of manuscript (50%) Critical review (25%) Supervision (50%)
Laurence J Walsh
Construct idea (25%) Critical review (50%) Supervision (25%)
x
5. Ha WN, Kahler B, Walsh LJ. Particle size changes in unsealed mineral trioxide aggregate powder. J Endod 2014;40:423-426. - Incorporated as Chapter 4 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (50%) Design methodology (100%) Data collection (100%) Analysis (100%) Literature review (100%) Writing of manuscript (50%)
Bill Kahler
Writing of manuscript (50%) Critical review (50%) Supervision (50%)
Laurence J Walsh
Construct idea (50%) Funding (100%) Critical review (50%) Supervision (50%)
xi
6. Ha WN, Shakibaie F, Kahler B, Walsh LJ. Deconvolution of the particle size distribution of ProRoot MTA and MTA Angelus. Acta Biomater Odontol Scand 2016;2:7-11. - Incorporated as Chapter 5 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (50%) Data collection (100%) Literature review (100%) Writing of manuscript (50%)
Fardad Shakibaie
Analysis (100%) Design methodology (100%) Writing of manuscript (50%)
Bill Kahler
Writing of manuscript (50%) Critical review (50%) Supervision (50%)
Laurence J Walsh
Construct idea (50%) Critical review (50%) Supervision (50%)
xii
7. Ha WN, Bentz DP, Kahler B, Walsh LJ. D90: The strongest contributor to setting time in mineral trioxide aggregate and Portland cement. J Endod 2015;41:11461150. An abstract from this also appeared in the Australian Dental Journal Research Supplement 2015; S11-12. - Incorporated as Chapter 6 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (75%) Design methodology (75%) Data collection (75%) Analysis (75%) Literature review (75%) Writing of manuscript (75%)
Dale Bentz
Construct idea (25%) Design methodology (25%) Data collection (25%) Analysis (25%) Literature review (25%) Writing of manuscript (25%)
Bill Kahler
Writing of manuscript (50%) Critical review (50%) Supervision (50%)
Laurence J Walsh
Construct idea (50%) Funding (100%) Critical review (50%) Supervision (50%)
xiii
8. Ha WN, Kahler B, Walsh LJ. The influence of particle size and curing conditions on testing Mineral Trioxide Aggregate cement. Acta Biomater Odontol Scand 2016;2:130-137. - Incorporated as Chapter 7 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (50%) Design methodology (100%) Data collection (100%) Analysis (100%) Literature review (100%) Writing of manuscript (50%)
Bill Kahler
Writing of manuscript (50%) Critical review (50%) Supervision (50%)
Laurence J Walsh
Construct idea (50%) Funding (100%) Critical review (50%) Supervision (50%)
xiv
9. Ha WN, Nicholson T, Kahler B, Walsh LJ. Methodologies for measuring the setting times of mineral trioxide aggregate and Portland cement products used in dentistry. Acta Biomater Odontol Scand 2016;2:25-30. - Incorporated as Chapter 8 Contributor
Statement of contribution
William Ha (Candidate)
Construct idea (75%) Design methodology (75%) Data collection (75%) Analysis (75%) Literature review (75%) Writing of manuscript (75%)
Tim Nicholson
Construct idea (25%) Design methodology (25%) Data collection (25%) Analysis (25%) Literature review (25%) Writing of manuscript (25%)
Bill Kahler
Writing of manuscript (50%) Critical review (50%) Supervision (50%)
Laurence J Walsh
Construct idea (50%) Funding (100%) Critical review (50%) Supervision (50%)
10. Ha WN. Registrant of GMDN Term ‘Hydraulic dental cement’, (now Hygroscopic dental cement), Term P60510. Available from https://www.gmdnagency.org/ Incorporated in the Appendix Contributor
Statement of contribution
William Ha (Candidate)
Application and submission (100%)
xv
Contributions by others to the thesis No contributions by others.
Statement of parts of the thesis submitted to qualify for the award of another degree None.
xvi
Acknowledgements I would also like to acknowledge the assistance, collaboration and advice of the following: o Prof Laurence Walsh, Professor of Dental Science, School of Dentistry - UQ, for his assistance in everything dental and research related; o Associate Prof Bill Kahler, Honorary Associate Professor of Endodontics, School of Dentistry - UQ, for his specialist knowledge in endodontics and dental materials; o Dr Tim Nicholson, Senior Researcher, School of Chemical Engineering - UQ, for his help in rheology; o Dr Mingyuan Lu, Post-doc, School of Mechanical & Mining Engineering - UQ, for her assistance in indentation setting time testing, compressive strength testing and flexural strength testing; o Dr Fardad Shakibaie, Post-doc, School of Dentistry - UQ, for his assistance in mathematical deconvolution; o Dale Bentz, Chemical Engineer, Materials and Structural Systems Division National Institute of Standards and Testing (USA) for collaborating research; o Adjunct Associate Professor Peter Duckmanton - University of Sydney for the opportunity to present to ASE-NSW and undertake collaborative research; o Michael Archer, General Manager, Si Powders Pty Ltd for cement samples, particle size testing and technical advice; o Shane Shipperley, Lab manager, Cement Australia for assistance with particle size testing; o Bobbie Jennings, Corporate Services, School of Dentistry - UQ, for organising payments of grant monies; o Dr Lei Chai, Postdoc, School of Dentistry - UQ, for SEM images of MTA; o Queensland University of Technology - for preparing MTA for SEM imaging; o ATA Scientific - for use of their scanning electron microscopes; o the Australian Dental Research Foundation - for the Early Career Researcher Grant 2012; o the Australian Society of Endodontology - for the Endodontic Research Grants 2014 and 2016; o the members of the Australian Society of Endodontology – for completing a survey on MTA usage; o the International Association of Dental Research - for a travel grant to Bangkok, Thailand, to present my research;
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o the Japanese Association for Dental Research - for the travel grant to Fukuoka, Japan, to present my research; o the members of the Australian and New Zealand Society of Paediatric Dentistry - for completing a survey on MTA usage; and o Dentsply, Gunz, Angelus, Septodont, Henry Schein Halas, Maruchi, Micromega, BioMTA, Bisco and VladMiVa - for providing samples of dental materials.
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Keywords Particle size analysis, International Organization for Standardization, elastic modulus, compressive strength, indentation tests, Portland cement, calcium silicate, bismuth oxide, setting time, laser diffraction.
Australian and New Zealand Standard Research Classifications (ANZSRC) ANZSRC code 110503, Endodontics, 60% ANZSRC code 090301, Biomaterials, 30% ANZSRC code 110507, Paedodontics, 10% Fields of Research (FoR) Classification FoR code 1105, Dentistry, 60% FoR code 0903, Biomedical Engineering, 30% FoR code 0912, Materials engineering, 10%
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Dedication
To my friends, particularly those who laugh that I’d become twice the doctor, but not a medical doctor. To my family, who never understood my research, but supported me anyway. And, to my field, which has given me the opportunity to continually challenge my hands and my brain.
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Table of Contents Abstract
........................................................................................................................ ii
Declaration by author......................................................................................................... v Publications during candidature...................................................................................... vi Peer-reviewed papers ...................................................................................................................... vi Database publication ........................................................................................................................ vi Conference proceedings .................................................................................................................. vii Conference abstracts ....................................................................................................................... vii
Publications included in this thesis .............................................................................. viii Contributions by others to the thesis............................................................................ xvi Statement of parts of the thesis submitted to qualify for the award of another degree ..................................................................................................................... xvi Acknowledgements ........................................................................................................ xvii Keywords
..................................................................................................................... xix
Australian and New Zealand Standard Research Classifications (ANZSRC) ............ xix Dedication
...................................................................................................................... xx
Table of Contents ............................................................................................................ xxi List of Figures ................................................................................................................ xxvi List of Tables ................................................................................................................ xxvii List of Equations ........................................................................................................... xxix Appendices ................................................................................................................... xxix List of Symbols and Abbreviations .............................................................................. xxx List of dental materials described in the thesis ....................................................... xxxiii Introduction ........................................................................................................................ 1 Chapter 1
Literature Review .......................................................................................... 6
1.1
Introduction ............................................................................................................................ 6
1.2
A review of hygroscopic dental cements – MTA, bioceramics and calcium silicate cements10
1.2.1
Introduction .................................................................................................................. 10 xxi
1.2.2
Methods ....................................................................................................................... 11
1.2.3
Review ......................................................................................................................... 11
1.2.4
Clinical and research consequences ........................................................................... 23
1.2.5
Conclusions ................................................................................................................. 23
1.3
Review of the placement of cements in the construction industry ....................................... 25
1.3.1
Introduction .................................................................................................................. 25
1.3.2
Water and the setting reaction ..................................................................................... 25
1.3.3
Exposure of the set material to acids ........................................................................... 26
1.3.4
Acids present at the time of mixing .............................................................................. 26
1.3.5
Interactions with EDTA ................................................................................................ 27
1.3.6
Interactions with phosphoric acid ................................................................................. 28
1.3.7
Presence of contaminants such as blood .................................................................... 28
1.3.8
Variations in the liquid component of MTA .................................................................. 29
1.3.9
Curing of the cement ................................................................................................... 29
1.3.10
Storage of MTA ............................................................................................................ 30
1.3.11
Summary ..................................................................................................................... 31
1.4
The properties of MTA and how it can be manipulated ....................................................... 32
1.4.1
Aims ............................................................................................................................. 32
1.4.2
MTA formulation .......................................................................................................... 32
1.4.3
CH & MTA .................................................................................................................... 34
1.4.4
pH and Calcium hydroxide release .............................................................................. 35
1.4.5
Clinical properties ........................................................................................................ 36
1.4.6
Commercial brands of MTA ......................................................................................... 37
1.4.7
Clinical uses ................................................................................................................. 45
1.4.8
Handling MTA .............................................................................................................. 48
1.4.9
Conclusions ................................................................................................................. 50
1.5
Review of properties and testing methodologies ................................................................. 51
1.5.1
Introduction .................................................................................................................. 51
1.5.2
Aims ............................................................................................................................. 52 xxii
1.5.3
Methods and materials ................................................................................................ 53
1.5.4
Results ......................................................................................................................... 54
1.5.5
Discussion ................................................................................................................... 62
1.5.6
Conclusion ................................................................................................................... 68
Chapter 2
How do paediatric dentists use MTA? ...................................................... 69
2.1
Introduction .......................................................................................................................... 69
2.2
Methods ............................................................................................................................... 70
2.3
Results ................................................................................................................................. 71
2.3.1
Respondent characteristics ......................................................................................... 71
2.3.2
MTA Usage .................................................................................................................. 71
2.3.3
Education regarding MTA usage ................................................................................. 73
2.3.4
IPCs ............................................................................................................................. 75
2.3.5
DPCs ........................................................................................................................... 76
2.3.6
Pulpotomies ................................................................................................................. 76
2.4
Discussion ........................................................................................................................... 77
2.5
Conclusions ......................................................................................................................... 80
Chapter 3
How do endodontists use MTA? ............................................................... 81
3.1
Introduction .......................................................................................................................... 81
3.2
Methods ............................................................................................................................... 82
3.3
Results ................................................................................................................................. 83
3.3.1
Membership ................................................................................................................. 83
3.3.2
Education on MTA use ................................................................................................ 85
3.3.3
MTA Usage .................................................................................................................. 85
3.4
Discussion ........................................................................................................................... 90
3.5
Conclusions ......................................................................................................................... 92
Chapter 4
What is the particle size of MTA? .............................................................. 93
4.1
Introduction .......................................................................................................................... 93
4.2
Materials and methods ........................................................................................................ 95
4.3
Results ................................................................................................................................. 96 xxiii
4.4
Discussion ........................................................................................................................... 98
4.5
Conclusion ......................................................................................................................... 100
Chapter 5
What constitutes the particle size of MTA? ............................................ 101
5.1
Introduction ........................................................................................................................ 101
5.2
Materials and methods ...................................................................................................... 102
5.2.1
Particle size assessment ........................................................................................... 102
5.2.2
Statistical analysis ..................................................................................................... 102
5.2.3
SEM ........................................................................................................................... 103
5.3
Results ............................................................................................................................... 103
5.3.1
Backscatter SEM ....................................................................................................... 106
5.3.2
Energy dispersive X-ray spectroscopy ...................................................................... 106
5.4
Discussion ......................................................................................................................... 107
Chapter 6
How does the particle size correlate with the setting time of MTA and
PC?
.................................................................................................................... 109
6.1
Introduction ........................................................................................................................ 109
6.2
Materials and Methods ...................................................................................................... 114
6.2.1
PSD ........................................................................................................................... 114
6.2.2
Materials .................................................................................................................... 114
6.2.3
Heat of hydration ....................................................................................................... 117
6.3
Results ............................................................................................................................... 117
6.4
Discussion ......................................................................................................................... 120
Chapter 7
What are the strength implications for set MTA if the particle size was
changed?
.................................................................................................................... 122
7.1
Introduction ........................................................................................................................ 122
7.2
Material and Methods: ....................................................................................................... 123
7.2.1
Sample Preparation ................................................................................................... 123
7.2.2
PSD ........................................................................................................................... 123
7.2.3
Curing conditions and CS .......................................................................................... 124
7.2.4
Curing conditions and FS .......................................................................................... 125 xxiv
7.2.5
Particle size effects on CS ......................................................................................... 126
7.2.6
Particle size effects on FS ......................................................................................... 126
7.2.7
Statistical analysis ..................................................................................................... 126
7.3
Results ............................................................................................................................... 126
7.3.1
PSD ........................................................................................................................... 126
7.3.2
Effect of curing and testing conditions on CS ............................................................ 127
7.3.3
Effect of curing and testing conditions on FS ............................................................ 129
7.3.4
Effect of particle size on CS ....................................................................................... 131
7.3.5
Effects of particle size on FS ..................................................................................... 132
7.4
Discussion ......................................................................................................................... 132
Chapter 8
How is the setting time measured? What if the particle size was
changed to hasten the setting time? ............................................................................ 135 8.1
Introduction ........................................................................................................................ 135
8.2
Material and methods: ....................................................................................................... 137
8.2.1
Determination of PSD ................................................................................................ 138
8.2.2
Indentation testing ..................................................................................................... 138
8.2.3
Rheology testing ........................................................................................................ 138
8.3
Results ............................................................................................................................... 139
8.3.1
PSDs: ......................................................................................................................... 139
8.3.2
Indentation setting times ............................................................................................ 140
8.3.3
Rheological testing .................................................................................................... 140
8.4
Discussion ......................................................................................................................... 142
8.5
Conclusion ......................................................................................................................... 143
Chapter 9
Can the rheological method of setting time assessment be used for
other cements? ............................................................................................................... 145 9.1
Introduction ........................................................................................................................ 145
9.2
Materials and methods ...................................................................................................... 148
9.2.1
Sample Preparation ................................................................................................... 148
9.2.2
Rheological testing .................................................................................................... 148 xxv
9.3
Results ............................................................................................................................... 149
9.4
Discussion ......................................................................................................................... 152
9.5
Conclusions ....................................................................................................................... 154
Chapter 10 General Discussion ................................................................................... 156 Chapter 11 Clinical Implication Summary .................................................................. 162 11.1
Chapter 1 Literature Review .............................................................................................. 162
11.2
Chapter 2 Use of MTA in paediatric dentistry .................................................................... 163
11.3
Chapter 3 Use of MTA in endodontics ............................................................................... 163
11.4
Chapter 4 Particle size of MTA .......................................................................................... 163
11.5
Chapter 5 What constitutes the PSD of MTA .................................................................... 163
11.6
Chapter 6 Correlation of particle size with setting time ..................................................... 163
11.7
Chapter 7 Strength and particle size ................................................................................. 163
11.8
Chapter 8 How is the setting time measured? ................................................................... 164
11.9
Rheology for other cements............................................................................................... 164
Chapter 12 Conclusions ............................................................................................... 164 Chapter 13 References ................................................................................................. 167 Chapter 14 Appendix .................................................................................................... 209
List of Figures Figure 1 Flow of literature review and surveys with corresponding chapters .................................... 3 Figure 2 Flow of experiments and corresponding chapters .............................................................. 5 Figure 1-1 pH of setting MTA .......................................................................................................... 36 Figure 1-2 Applications of MTA ....................................................................................................... 45 Figure 2-1 Proportions of clinicians who perform IPC ..................................................................... 73 Figure 2-2 Proportions of clinicians who perform DPC ................................................................... 74 Figure 2-3 Proportions of clinicians who perform DPCs .................................................................. 74
xxvi
Figure 4-1 PSD of MTA-P (above) and MTA-A (below) when fresh and 2 y after having the packaging opened ................................................................................................................... 97 Figure 4-2 BSE imaging of MTA-P. ................................................................................................. 98 Figure 5-1 Normalised PSD for BO and three PC samples of differing size ................................. 104 Figure 5-2 PSD of MTA-P (upper) and MTA-A (lower) and the associated deconvoluted components ........................................................................................................................... 105 Figure 5-3 SEM of MTA-P (left) and MTA-A (right) ....................................................................... 106 Figure 6-1 Setting time versus D90 of MTA .................................................................................. 118 Figure 6-2 Setting times and cumulative heat release versus particle size of PC ......................... 119 Figure 7-1 Effect of curing conditions on the physical properties on MTA .................................... 128 Figure 7-2 Influence of particle size and time on the physical properties of MTA, when stored in PBS ....................................................................................................................................... 130 Figure 8-1 G', G" and their ratio (tan_delta) .................................................................................. 141 Figure 9-1 G' of tested dental cements ......................................................................................... 150 Figure 10-1 Summary of literature review ..................................................................................... 156 Figure 10-2 Summary of surveys on MTA usage .......................................................................... 157 Figure 10-3 Summary of PSD of MTA studies .............................................................................. 159
List of Tables Table 1-1 PubMed keyword search results and comparisons with this thesis - reviews ................... 6 Table 1-2 PubMed keyword search results and comparisons with this thesis - surveys ................... 7 Table 1-3 PubMed keyword search results and comparisons with this thesis – particle size ........... 8 Table 1-4 PubMed keyword search results and comparisons with this thesis - rheology ................. 9 Table 1-5 Examples of reactions of various HDCs with water72 ...................................................... 15 Table 1-6 Commercial packable HDCs - permanent restoratives (Part 1, A-I) ............................... 16 Table 1-7 Commercial packable HDCs - permanent restoratives (Part 2, I-T) ................................ 17 Table 1-8 Commercial packable HDCs - intermediate restoratives ................................................ 19
xxvii
Table 1-9 Possible categorisation of obturation to supersede 'Endodontic filling / sealing material'. ................................................................................................................................................. 19 Table 1-10 Commercial HDCs - endodontic sealers ....................................................................... 20 Table 1-11 Clinical Techniques that influence MTA's properties ..................................................... 31 Table 1-12 Radiopacity of ProRoot MTA and dental structures ...................................................... 32 Table 1-13 Radiopacity of MTAs with different radiopacifiers (20% w/w) ....................................... 33 Table 1-14 A comparison of MTA with CH products ....................................................................... 35 Table 1-15 Comparison of MTA-P with Biodentine ......................................................................... 38 Table 1-16 Comparison of MTA-P with iRoot BP ............................................................................ 39 Table 1-17 Comparison of BioRoot RCS with AH Plus ................................................................... 40 Table 1-18 Comparison of AH Plus and TotalFill Sealer ................................................................. 41 Table 1-19 Comparison of AH Plus and ProRoot MTA ES ............................................................. 41 Table 1-20 Comparison of AH Plus and MTA Fillapex .................................................................... 42 Table 1-21 Comparative summary of popular MTA and 'MTA-like' products .................................. 43 Table 1-22 Comparison of MTA-P with Bioaggregate / DiaRoot ..................................................... 44 Table 1-23 Properties of root-end fillings ........................................................................................ 47 Table 1-24 Properties of MTA restoratives and sealers after mixing .............................................. 56 Table 1-25 Non-biological properties of MTA restoratives and sealers after setting ....................... 59 Table 2-1 MTA usage and training patterns of respondents ........................................................... 72 Table 2-2 Preferred materials for IPCs ............................................................................................ 75 Table 2-3 Preferred materials for direct pulp capping (DPCs) ........................................................ 76 Table 2-4 Preferred materials for pulpotomies ................................................................................ 77 Table 3-1 MTA usage, training and perforation repairs by GD and ED ........................................... 84 Table 3-2 Apical barrier procedures by GD and ED ........................................................................ 88 Table 3-3 MTA root-end fillings and regenerative endodontics by GD and ED ............................... 90 Table 4-1 PSD of MTA .................................................................................................................... 96 Table 5-1 PSD of PC and BO libraries, MTA-P and MTA-A .......................................................... 104 Table 5-2 Energy dispersive X-ray spectroscopy of points in Figure 7-3 ...................................... 106 Table 6-1 Comparison and composition of MTA brands ............................................................... 110 xxviii
Table 6-2 Summary of setting time standards commonly encountered in dentistry and for PC .... 112 Table 6-3 Summary of PSDs of PC, MTA, their setting times and cumulative heat release ......... 116 Table 7-1 PSDs of experimental cements and their constituents .................................................. 127 Table 8-1 PSDs of PC, experimental MTA and bismuth oxide used to produce MTA .................. 139 Table 8-2 Indentation testing initial and final setting times ............................................................ 140 Table 8-3 Plateau G’ and the time to reach 95% .......................................................................... 141 Table 9-1 Plateau G’ of various dental cements (in MPa) ............................................................. 151 Table 9-2 Time to reach 90% of plateau G’ (in minutes) ............................................................... 151 Table 9-3 Comparison of marketed setting times against setting times using the time to reach 90% of the plateau G’ .................................................................................................................... 152
List of Equations Equation 4-1 Degree of Hydration ................................................................................................... 94 Equation 5-1 Normalised frequency at a given particle size ......................................................... 102 Equation 6-1 Function of setting time with D90 ............................................................................. 117 Equation 6-2 Function of initial setting time with D90 .................................................................... 118 Equation 6-3 Function of final setting time with D90 ..................................................................... 118 Equation 6-4 Function of cumulative heat with D90 ...................................................................... 118 Equation 5 Formula for compressive strength ............................................................................... 125 Equation 6 Formula for flexural strength ....................................................................................... 125
Appendices Appendix 1 GMDN Registration for Hygroscopic Dental Cement ................................................. 209 Appendix 2 Dental material choices for pulp therapy by ANZSPD members ................................ 210
xxix
List of Symbols and Abbreviations a
Degree of hydration
°C
Degrees Celsius
μm
Micrometres
AAE
American Association of Endodontists
ADA 57
American Dental Association’s specification 57 for endodontic filling materials
ADRF
Australian Dental Research Foundation
ANOVA
Analysis of Variance
ANZSPD
Australian and New Zealand Society of Paediatric Dentistry
ASE
Australian Society of Endodontology
ASTM
American Society for Testing and Materials
ASTM C 191
ASTM test method for time of setting of hydraulic cement (Vicat needle)
ASTM C 266
ASTM test method for time of setting of hydraulic cement (Gillmore needle)
ASTM C 1608
ASTM test method for chemical shrinkage of hydraulic cement
BC
Bioceramic
BO
Bismuth oxide
BSE
Scanning electron microscopy with backscatter imaging
CH
Calcium hydroxide
CHC
Calcium hydroxide cement
CHX
Aqueous solution containing chlorhexidine gluconate
CHP
Calcium hydroxide paste
CPD
Continuing professional development
CS
Compressive strength
CSH
Calcium silicate hydrate
D10
Particle size at the 10th percentile (smaller size)
D50
Particle size at the 50th percentile (median size)
D90
Particle size at the 90th percentile (larger size)
DPC
Direct pulp cap
ED
Endodontist
EDX
Energy dispersive X-ray spectroscopy
EDTA
Aqueous solution containing Ethylenediaminetetraacetic acid
F
Normalised frequency
FeSO4
Ferric sulphate xxx
FC
Formocresol
FS
Flexural Strength
G’
Elastic modulus
G”
Viscous modulus
g/L
Grammes per litre
GD
General dentist
GIC
Glass ionomer cement
GMDN
Global Medical Device Nomenclature
GP
Gutta Percha
h
Hour
h (J/g)
Heat (Joules per gramme)
HDC
Hygroscopic dental cement
Hz
Hertz
IPC
Indirect pulp cap
ISO
International Organization for Standardization
ISO 4049
ISO for testing polymer based restorative materials
ISO 6876
ISO for testing root canal sealing materials
ISO 9917-1
ISO for testing water-based cements
ISO 13320
ISO for Particle size analysis (Laser diffraction)
ISO 15223
ISO for symbols for medical devices
k
Rate constant
kg
Kilogramme
kV
Kilovolts
LDA
Laser diffraction analysis
m
Metres
M1
Experimental MTA 1 (Smaller sized particles)
M2
Experimental MTA 2 (Standard sized particles)
mm
Millimetres
MPa
Megapascals
MTA
Mineral Trioxide Aggregate
MTA-A
MTA Angelus
MTA-P
ProRoot MTA
NaOCl
Aqueous solution containing sodium hypochlorite
P
P-value
P1
Experimental PC 1 (Smaller sized particles) xxxi
P2
Experimental PC 2 (Standard sized particles)
PBS
Phosphate buffered saline
PC
Portland cement
PC1
Reference Portland cement 1
PC2
Reference Portland cement 2
PC3
Reference Portland cement 3
PD
Paediatric dentist
PSD
Particle size distribution
r
Pearson’s product-moment correlation coefficient
r
Radius of the particle
rad/s
Radians per second
RI
Refractive index
RMGIC
Resin-modified glass ionomer cement
SEM
Scanning Electron Microscopy
t (h)
Setting time (hours)
UQ
University of Queensland
UK
United Kingdom
USA
United States of America
w/w
Percentage by mass (“weight-weight percentage”)
ZO
Zirconium oxide
ZOE
Zinc oxide eugenol cement
xxxii
List of dental materials described in the thesis Hygroscopic Dental Cements Product (Supplier, City, Country)
Page
Apatite Root Sealer I (Dentsply Sirona, York, USA)
20
Apatite Root Sealer II (Dentsply Sirona, York, USA)
20
Apatite Root Sealer III (Dentsply Sirona, York, USA)
20
iRoot® BP (Innovative Bioceramix Inc. Vancouver, Canada)
16
EndoSequence® RRM (Putty)
see iRoot BP
EndoSequence® RRM Fast Set (Syringe Putty)
see iRoot FS
TotalFill® RRM (Putty)
see iRoot BP
TotalFill® RRM Fast Set (Syringe Putty)
see iRoot FS
BioAggregate® (Innovative Bioceramix Inc, Vancouver, Canada)
16
Biodentine® (Septodont, Saint-Maur-des-Fossés, France)
16
BioRootTM (Septodont, Saint-Maur-des-Fossés, France)
20
CEM Cement® (BioniqueDent, Tehran, Iran)
16
TM
Cavit
(3M, St Paul, USA)
19
CavitTM G (3M, St Paul, USA)
19
CavitTM W (3M, St Paul, USA)
19
Coltosol® F (Coltene, Altstätten, Switzerland)
19
DiaRoot® BioAggregate
see BioAggregate
DuoTEMP® (Coltene, Altstätten, Switzerland)
19
Endobinder® (Binderware, São Carlos, Brazil)
12
Endocem MTA (Maruchi, Wonju-si, South Korea)
16
Endocem Zr (Maruchi, Wonju-si, South Korea)
16
EndoCPM Sealer (EGEO Dental, Buenos Aires, Argentina)
20
Endoseal (Maruchi, Wonju-si, South Korea)
20
EndoSeal MTA (Maruchi, Wonju-si, South Korea)
20
EndoSequence® BC RRMTM
see iRoot BP
EndoSequence® BC RRM Fast Set PuttyTM
see iRoot FS
EndoSequence® BC SealerTM
see iRoot SP
Grey MTA Plus® (Avalon Biomed, Houston, USA)
16
Harvard MTA Universal OptiCaps® (Harvard Dental International GmbH, Hoppergarten, Germany)
16
Harvard MTA XR Fast OptiCaps® (Harvard Dental International GmbH, Hoppergarten, Germany)
16 xxxiii
Harvard MTA XR Flow EWT OptiCaps® Harvard Dental International GmbH, Hoppergarten, Germany)
16
Harvard MTA XR Flow Fast OptiCaps® (Harvard Dental International GmbH, Hoppergarten, Germany)
16
iRoot® BP (Innovative BioCeramix Inc, Vancouver, Canada)
16
iRoot® FS (Innovative BioCeramix Inc, Vancouver, Canada)
16
iRoot® SP (Innovative BioCeramix Inc, Vancouver, Canada)
20
MM-MTA
TM
(Micro-Mega, Besançon, France)
17
MTA Angelus® (Angelus, Londrina, Brazil)
see MTA Angelus
ChannelsTM MTA
see MTA Angelus
MTA* Caps (Acteon, Merignac, France)
17
MTA PlusTM (Prevest Denpro Ltd, Jammu, India)
17
MTA Repair HP (Angelus, Londrina, Brazil)
17
TM
NeoMTA Plus
(Avalon Biomed, Houston, USA)
NuSmile® NeoMTA®
17 See NeoMTA Plus
Ortho MTA (BioMTA, Seoul, South Korea)
17
ProRoot® ES Endo Root Canal Sealer (Dentsply Sirona, Tulsa, USA)
20
ProRoot® MTA (Dentsply Sirona, Tulsa, USA)
17
Retro MTA® (BioMTA, Seoul, South Korea)
17
Root MTA (Lotfi Research Group, Tabriz, Iran)
17
TechBioSealer Apex (Isasan, Rovello Porro, Italy)
17
TechBioSealer Endo (Isasan, Rovello Porro, Italy)
17
TechBioSealer Root End (Isasan, Rovello Porro, Italy)
17
TechBioSealer Capping (Isasan, Rovello Porro, Italy)
17
TotalFill® RRMTM TotalFill® RRM
TM
see iRoot BP Fast Set Putty
see iRoot FS
TotalFill® BC SealerTM
see iRoot SP
Trioxident (VladMiVa, Belgorod, Russia)
17
Other restoratives Fuji VII® (GC Corporation, Tokyo, Japan)
148
Fuji VII® EP (GC Corporation, Tokyo, Japan)
148
Fuji IX® (GC Corporation, Tokyo, Japan)
148
Super EBA (Harry J Bosworth Co, Skokie, USA)
89
TheraCal LC® (Bisco, Schaumburg, USA)
12 xxxiv
Other endodontic sealers AH 26® (Dentsply DeTrey, Konstanz, Germany)
145
AH Plus JetTM (Dentsply DeTrey, Konstanz, Germany)
145
MTA Fillapex® (Angelus, Londrina, Brazil)
12
RealSeal SE (SybronEndo, Amersfoort, Netherlands)
xxxv
145
Introduction MTA is an important cement that is used in endodontics and paediatric dentistry. MTA has a prolonged setting time, which is often viewed as an undesirable but fundamental property of the material. Hence the question can be raised, “How can the prolonged setting time of MTA be overcome?” This question can be answered through a series of smaller questions: •
what is MTA and why does it have a long setting time?
•
what is known about the properties of MTA and how does it correlate to the clinic?
•
based on the scientific information regarding its composition, how should clinicians use MTA to optimize its handling and physical properties?
•
how do clinicians (such as general dentists (GDs), paediatric dentists (PDs) and endodontists (EDs) use MTA?
•
what is the particle size of MTA, and what factors influence this?
•
how does particle size influence the setting time of MTA?
•
how is setting time measured? Are these methods relevant to its clinical use?
•
can a rheological method of assessing setting time provide information on the product and other dental cements? And
•
what are the implications of changing particle size in terms of the physical properties of the set cement?
The properties of MTA were first assessed through a literature review, which explored the composition and properties of the cement with those of similar cements. From this, it was evident that components found commonly in industrial cements, i.e. calcium silicates and calcium aluminates from Portland cement (PC), had a dominant influence on its properties. In attempts to provide dentists with quicker setting MTA cements, variations on this material have emerged that claim to be light-cured MTA, but are in fact resins with superfluous inclusions of MTA. Furthermore, injectable and packable cements have appeared, which are cements mixed with thickening agents. A review of the published literature on the properties of MTA and MTA variants was undertaken, and methods used to test their properties. Most of these methods are based on tests for GICs or endodontic sealers. Many of the tests in the literature have been 1
modified from the standard tests stipulated by the International Organization for Standardization (ISO). The tests results obtained for MTA and some MTA variants are inconsistent, even within studies. This has complicated meaningful comparison of how the properties differ between products. Two reviews were performed on the handling features and properties of MTA, exploring how various clinical procedures and manipulations influence the setting of MTA. Contamination from acids, medicaments and blood can retard the setting of MTA, which then raises various methods to mitigate these issues. MTA can, in fact, be ‘wet’ cured, where a glass ionomer cement (GIC) or resin is carefully placed within 10 minutes above MTA, enabling the tooth to be restored in one visit. The minimum time period of time of 10 minutes is a parameter that was examined in subsequent studies. Surveys of dental specialists (PDs and EDs) were performed. These showed which procedures MTA was the material of choice for root-end fillings, apical barrier placement, perforation repair and pulp regeneration. Although many PDs use MTA, this material is often restricted to pulpotomies. It was evident in both specialist cohorts that most specialists learnt how to handle MTA through continuing education development courses, yet they wish for more practical education focused on its clinical handling. The figure below illustrates the logical flow for the chapters relating to the general literature, and how these are linked to the surveys of MTA usage in clinical practice.
2
Figure 1 Flow of literature review and surveys with corresponding chapters
In a series of laboratory studies, the correlations between indentation-based setting time and MTA particle size were determined. This involved comparing the marketed indentation setting times of various commercial MTA products against results from analysis of the particle size using LDA. Of note, the largest particles of the cement (D90) were found to have the greatest influence on the setting time, and reductions in this size parameter have accelerated setting reactions. The D90 value for PC showed a stronger correlation to particle size than did the D90 value for MTA, indicating that commercial MTA cements contain other ingredients that influence the setting time. The PSDs within MTA were further analysed via mathematical deconvolution of PSD, using the non-linear least-squares fit method. This also established the PSDs and contributions of the respective ingredients of 80% PC and 20% BO. These respective distributions are important as there is a dynamic relationship between the setting of the PC 3
in the hydration of MTA, and in the impediment of setting from the radiopaque filler particles of BO. The slowed setting rate involving interactions of PC and BO was studied further through the use of setting time tests, using indentation and rheology. This involved testing the setting of samples of PC and comparing these against samples of PC mixed with BO. It was found that smaller PSDs of PC resulted in faster setting reactions. However, the inclusion of BO slowed the setting time. The use of rheology illustrated that accelerated setting is expected via the quicker growth of the elastic modulus (G’). However, smaller particle sizes did not result in significant increases in the final G’. A similar finding was found with the testing of the CS of MTA, whereby the final strengths were not significantly different between samples with finer versus larger particles. The use of rheology to test the setting time of other dental cements has been explored in this thesis because there is a gap in the literature assessing the change of the flow properties of a material over time as a means to express its setting rate. The results illustrate the differences in setting time of MTA against other endodontic and restorative cements. This method provides greater meaning to the understanding of setting reactions than traditional indentation tests that are based on arbitrary weights. Current tests are somewhat arbitrary with little clinical correlation to the properties of the material. Future studies will enable clinicians to have a better understanding of setting times and rates. The figure below illustrates the logical flow of the chapters relating to MTA particle size:
4
Figure 2 Flow of experiments and corresponding chapters
Although MTA has a prolonged setting time, various clinical procedures can be considered and utilised to optimise its properties to overcome the difficulties associated with a delayed setting process. Chemical additives have been considered. However, using these may compromise the performance of the material. A reduction of particle size, particularly of its 90th percentile (i.e., the larger sizes) will result in an accelerated set. However, this does not give any long-term advantages or disadvantages in terms of physical properties. Future research on modifying the radiopaque agent would be of value to improve the mechanical properties of the set MTA cement.
5
Chapter 1 1.1
Literature Review
Introduction Chapter 1 of this thesis incorporates several published articles, each of which reviews the existing literature on a specific aspect of MTA in detail. The tables below summarise the PubMed findings of relevant terms and the gaps in the literature. These gaps are addressed in chapters that have been cross-referenced. “Mineral trioxide aggregate” AND “Nomenclature” Findings: No relevant publications with these two terms. Comments: Although literature exists suggesting particular terms that could supersede ‘MTA’, and some have tried to list ingredients of commercial products, none have tried to objectively compare multiple cements by their compositions. *Refer to Subchapter 1.2 on page 6 for further detail. “Mineral trioxide aggregate” AND “clinical” AND “manipulation” AND “Review” 1
Findings: Rao reviewed MTA with a focus on manipulation of MTA for paediatric usage. Comments: While there has been one review on how MTA is handled in paediatric dentistry, there have been no reviews on the clinical use of MTA in general dentistry and endodontic practice. *Refer to Subchapter 1.3 on page 25 and Subchapter 1.4 on page 32 for further detail. “Mineral trioxide aggregate” AND “flow” OR “working time” OR “setting time” OR “film thickness” OR “dimensional change” OR “solubility” OR “radiopacity” OR “compressive strength” OR “acid erosion” OR “arsenic” OR “lead” OR “genotoxicity” OR “cytotoxicity” OR implantation”. Comments: There are multiples studies that report testing the properties of MTA. These studies 2
3
4
typically utilise ISO 9917.1, ISO 6876 and ISO 10993. Many of these tests are benchtop tests which have poor correlation to the clinical situation. *Refer to Subchapter 1.5 on page 51 for further detail. Table 1-1 PubMed keyword search results and comparisons with this thesis - reviews
6
“Mineral trioxide aggregate” AND “survey” and “paediatric 5
Findings: Walker surveyed the use of MTA, FC and FS in postgraduate programmes. Kathariya
6
7
surveyed the use of NiTi and endodontic microscopes in paediatric dentistry. Foley surveyed the 8
usage of MTA by postgraduate paediatric dentistry students for various procedures. Pitt Ford surveyed undergraduate departments on which faculty members taught the use of MTA. Comments: These surveys examined the use of MTA within university programmes. No surveys have assessed the use of these materials outside the university setting. *Refer to Chapter 2 on page 69. “Mineral trioxide aggregate” AND “survey” AND “endodontics 6
9
Findings: The study of Kathariya is summarised above. Asgary reported the growth in the number of articles on MTA over time. Tanalp students. Casella
11
10
reported that MTA is not used commonly by undergraduate
reviewed the properties and usage of MTA.
Comments: As with the previous point, no prior surveys have assessed the use of these materials outside of the university setting. *Refer to Chapter 3 on page 81 for further detail. Table 1-2 PubMed keyword search results and comparisons with this thesis - surveys
7
“Mineral trioxide aggregate” AND “particle size” Findings: McMichael Khan
13
12
showed that various MTA based sealers can penetrate into dentinal tubules.
compared MTA-P against two experimental MTAs. Silva
14
illustrated that nanoparticles of
niobium pentoxide can be used as an alternative to BO as a radiopaque agent. Saghiri showed that smaller particle sizes of MTA increase calcium ion release. improved both the pushout and CS of MTA. sized MTA.
17
Komabayashi
18
16
15
Furthermore, the use of nano-sized BO
Greater bone regeneration appears to occur with nano-
showed that MTA particles enter dentinal tubules. Particle size can be
assessed with a flow particle image analyser, with 88% of particles between 0.5 and 3 μm. MTA-P has more smaller particles than MTA-A.
19
Viapiana
20
illustrated that radiopacifier particle size has a limited
effect on sealer microstructure and chemical properties. Camilleri
21
showed that MTA and Biodentine
have slightly different hydration structures. Alternative radiopacifiers (silver/tin alloy and gold) can be used to achieve high radiopacity. MTA cements. Asgary Dammaschke
25
24
22
Hwang
23
showed that PC combined with BO resembles commercial
reported that white MTA-P has smaller particles than grey MTA-P.
illustrated that MTA-P and PC are not identical with regards to surface characterization.
Comments: The work of Komabayashi is the only prior research that has attempted to assess the PSD of MTA. However, the method of assessment used was not appropriate to the range of particle sizes found in MTA. None of the articles listed above consider the bimodal effect of having two separate powders combined with different PSDs for each (namely of PC and BO). No past work has used particle size analysis to explore how humidity can change the particle size of MTA. This is reviewed in greater detail in Chapter 4 on page 93 and Chapter 5 on page 101 Although it is logical that smaller particle sizes correlates with faster setting times, this has not yet been explored for MTA. As the particles within both MTA and PC powder have a range of particle sizes, no past work has attempted to correlate setting time with particle size. Possible setting time parameters to th
th
consider are the 10 percentile particle size, the median particle size and the 90 percentile particle size. Refer to Chapter 6 on page 109 for greater detail. Lastly, there is no prior research on how curing conditions, testing conditions and particle size could alter the physical properties of MTA. This aspect has implications for how the properties of MTA are tested. Refer to Chapter 7 on page 122 for greater detail. Table 1-3 PubMed keyword search results and comparisons with this thesis – particle size
8
“Mineral trioxide aggregate” AND “Rheology” Natu
26
showed that adding propylene glycol to MTA increased the setting time, flow and calcium 18
release, but lowered the hardness and caused greater porosity. The work of Komabayashi already been summarised above. Setbon
27
has
showed that various MTA cements and MTA-like materials 8
vary in their composition. Setting time was defined as the time required to reach a CS of 8x10 Pa. Vitti
28
Silva
showed that MTA Fillapex has reduced flow, shortened working and setting times than AH Plus.
29
showed that MTA Fillapex is more cytotoxic than AH Plus but has more flow. Duarte
30
added
propylene glycol to MTA-A, which increased the setting time, flow, pH and calcium ion release. Wongkornchaowalit
31
showed that the addition of a polycarboxylate superplasticiser reduced the setting
time and increased the flow of MTA. Camilleri
32
showed that MTA is more soluble in water than PC.
The addition of a water-soluble polymer may be required for MTA to conform to the ISO standards for sealers.
33
Bernardes
34
used ADA Specification 57 to show that Sealer 26, AH Plus and MTA Obtura
(Fillapex) had flow rates greater than the specified minimum value. De Bruyne showed that all sealers are prone to leakage. However, the seal from MTA and from gutta percha (GP) improves with time. Furthermore, under laboratory conditions the seal of Fuji IX GIC was superior to MTA-P.
36
35
De-Deus
37
illustrated that all hygroscopic cements allow fluid movement when assessed using a fluid filtration leakage model. Asgary John
39
38
reported on a new endodontic cement with characteristics similar to MTA.
reported similar leakage rates for Fuji Triage and MTA-P. Martin
reacts with phosphate buffers to form apatites. Yatsushiro
41
40
demonstrated that MTA
reported that MTA provided a superior seal
to dental amalgam. Comments: Although there have been several studies of ‘flow’, these relate mainly to how it influences leakage. The change in flow of a material can be used to determine the setting time of a material such as MTA and this has not been reported previously. Refer to Chapter 8 on page 135 and Chapter 9 on page 145 for greater detail. Table 1-4 PubMed keyword search results and comparisons with this thesis - rheology
9
1.2
A review of hygroscopic dental cements – MTA, bioceramics and calcium silicate cements
This subchapter is in press: Ha WN, Kahler B, Walsh LJ. Classification and nomenclature of commercial hygroscopic dental cements. Euro Endod J. In press 2017 (accepted 9 Sep 2017). 1.2.1 Introduction A range of cements are used in clinical dental practice, including zinc oxide eugenol cements (ZOE), zinc phosphate cements, polycarboxylate cements, glass ionomer cements (GIC), and mineral trioxide aggregate (MTA) cements. The latter was introduced by Torabinejad in the early 1990s.42 There are now many types of cement on the market that, like MTA, use water as a major reagent in a setting process involving hydration reactions. Such cements differ from products where water-based solutions contain ions or compounds that react in the setting process, rather than the water itself. The Global Medical Device Nomenclature (GMDN) is a system of internationally agreed terms for identifying and categorising medical devices that is used by regulators, manufacturers and healthcare systems to objectively categorise data relating to market surveillance, adverse event reporting and other management activities.43 Under the GMDN, the newly introduced term “hygroscopic dental cement” (HDC) refers to “a nonsterile substance intended for professional use as a dental cement (e.g., luting agent, liner, base, pulp-capping material) and/or direct dental restorative material whereby the majority of the setting reaction is based on the hardening reaction of a hygroscopic inorganic compound(s) [e.g., calcium silicates, calcium aluminates, zinc sulphate, calcium sulphate] with water (hydration). It is available as a powder intended to be either mixed water prior to application or react with dentinal fluid in situ. After application, this device cannot be reused.”43 Despite increasing interest in the use of HDCs in clinical practice, many practitioners are unsure of how the various products differ one from another. Because there is no standardised nomenclature for describing these products, clinicians can easily become confused. Using the term “bioceramics” for some HDCs that require water to set into a solid form is confusing as this term also includes metal oxides and glasses used in fixed prosthodontics.44
10
The aim of this subchapter is to review recent advancements in HDC materials to propose an appropriate nomenclature to facilitate a better understanding of the similarities and differences between materials. This new classification scheme describes existing products on the global market, and can be expanded to new types of hydraulic or alkaline cements developed. The chemical additives used to modify the cements are discussed since such modifications have clinical implications. 1.2.2 Methods Commercial manufacturers of HDCs were contacted requesting detailed information on the compositions of products. Manufacturers that were unknown by the authors, unable to be contacted, or wished to be excluded in this paper, were not included. Of these products, their chemical compositions were searched in the PubMed search engine and compared with information provided by the manufacturer. 1.2.3 Review 1.2.3.1 Current terms in the literature 1.2.3.1.1 MTA While the term mineral trioxide aggregate (MTA) is in common use, it has been argued by Darvell that this has ‘no chemically-meaningful sense’.45 The origin of the term MTA is found in the early research of Torabinejad, who invented MTA,46 rather than from the original patent, which described “a cement composition in which, in a preferred embodiment, the principal composition is Portland cement’ together with ‘an additive…to render the overall cement composition radiopaque’.47 European Standard EN 197-1 defines Portland cement as consisting of “at least two-thirds by mass of calcium silicates (3CaO·SiO2 and 2CaO·SiO2), with the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass.”48
Thus, combining the patent with the original research articles on MTA one could define MTA as “Portland cement with a radiopacifier.” Under such a definition, materials such as BiodentineTM (Septodont, Saint Maur des Fossés, France) and BioAggregate® (Innovative BioCeramix, Vancouver, Canada) could be included within the grouping of MTA as their 11
composition of includes calcium silicates within the range found in Portland cement as well as radiopacifiers.49, 50 Nevertheless, there are other products that likewise contain a high percentage of calcium silicates but are not commonly referred as MTA and indeed, show significant differences in their properties.50 1.2.3.1.2 Bioceramics The term “bioceramic” appears to be first mentioned when describing a related product, BioAggregate, produced by the same manufacturer (Innovative BioCeramix).51 The term is used on all their products and often is used to collectively refer to MTA and other HDCs,52 which is problematic. As ceramics are non-metallic inorganic materials,53 the term ceramics encompasses practically all of the powdered components of MTA, zinc phosphate, zinc oxide eugenol and GICs. The term ‘bioceramics’ in a dental setting refers to prosthetic restorative materials as opposed to HDCs.53 1.2.3.1.3 Hydraulic silicate cements, calcium silicate cements, hydraulic calcium silicate cements There is a history of use in the literature for ‘hydraulic silicate cement’ ,54 ‘calcium silicate cement’55 and ‘hydraulic calcium silicate cement’.56 The term ‘hydraulic cement’ is a term which originates in the engineering literature and refers to materials which reacts “under water”, which can be extended to include GICs and related glass-based cements that set using acid-base aqueous reactions.57 As GICs contain calcium aluminium fluorosilicate, any of the terms ‘hydraulic silicate cement’, ‘calcium silicate cement’ or ‘hydraulic silicate cement’ could include GICs. Changing the descriptor from ‘hydraulic’ dental cement to ‘hygroscopic’ dental cement would clarify that the material reacts with water, which would then exclude GICs. An excessive emphasis on calcium silicates excludes other HDCs that react directly with water, particularly those that include calcium sulphate or calcium phosphate. 1.2.3.2 Confusion in the literature The ‘ideal formulation’ described within a patent is not necessarily the composition of a final commercialised product, as ongoing research and development since the patent was awarded may have revealed that a different composition may be preferred. Furthermore, the protection afforded by a patent is limited to the countries where the patent has been applied for and granted. Therefore, a product with a patent can have “copycat” products appear in other countries where protection was not applied. 12
An example of confusion in the literature is TheraCal LC® (Bisco, Schaumburg, USA). TheraCal LC is a cement-modified resin composite and has been referred to as a ‘lightcurable MTA cement’, when in fact, there is no light-initiated setting of the Portland cement.58 Rather, only the resin component (polyethylene glycol dimethacrylate) undergoes photopolymerization.59 The material is supplied as a single component, which is applied to the tooth, in the same manner as a flowable resin. The setting reaction is based on light-initiated cross-linking of the polyethylene glycol dimethacrylate, which is a slightly water-soluble di-functional methacrylic monomer.58 Thus, the setting reaction depends upon polymerization of the resin component, rather than a reaction with water, thus excluding this material from the classification of HDCs. Another example is MTA Fillapex® (Angelus, Londrina, Brazil) which is a two-paste system, within one paste contains salicylate resin, fumed silica, and bismuth trioxide (as the radiopaque agent), while the second paste contains MTA (40%), fumed silica, titanium dioxide, and 1,3-butylene glycol disalicylate resin.60 In the setting reaction, this resin reacts with calcium hydroxide released from the MTA. This same calcium hydroxide-based reaction occurs in Dycal Radiopaque Calcium Hydroxide (Dentsply Sirona, USA).60, 61 Therefore, MTA Fillapex contains a HDC but its setting reaction is not specifically based only on a reaction with water, which excludes it from being included within the HDC grouping. 1.2.3.3 Confirmation of compositions Multiple studies exist assessing the compositions of HDCs. Commonly used methods are energy dispersive x-ray spectroscopy, (EDX) X-ray powder diffraction (XRD), X-ray fluorescence (XRF),50, 62 X-ray photoelectron spectroscopy (XPS)63 and inductively coupled plasma-atomic emission spectroscopy (ICP-AES).27 All methods involve measuring interactions with electromagnetic radiation, which is dependent on the elements that are present. The atomic composition of BioAggregate when assessed using XRF,50, was found to be primarily the elements oxygen, calcium, silicon, tantalum and phosphorus. Likewise, the composition of Biodentine assessed using XRF,62 XPS,63 EDX, and ICP-AES27 all revealed that the cement is primarily the elements oxygen, calcium, silicon, and zirconium. Using EDX, EndoCem MTA was found to contain oxygen, calcium, silicon, aluminium and 13
bismuth.64 Likewise, using EDX EndoCem Zr was found to contain oxygen, calcium silicon, aluminium and zirconium.64 An EDX assessment of grey MTA Plus found this to be composed primarily of oxygen, calcium, silicon and bismuth.65 MM MTA, when assessed using EDX66 and ICP-AES,27 was found to contain primarily oxygen, calcium, silicon, bismuth and aluminium. The composition of MTA Angelus has been examined using XRF,50, 62 EDX66 67 and ICPAES27 all of which show that the major elements present are oxygen, calcium, silicon, bismuth and aluminium. Comparable studies of MTA Cap using EDX and ICP-AES27 found oxygen, calcium, silicon, tungsten and aluminium as major component elements. Likewise, studies of Neo MTA Plus using EDX also revealed oxygen, calcium, silicon and tantalum.65 Finally, the composition of ProRoot MTA, when assessed using EDX,64, 66, 68 XRD,13 XPS63 and ICP-AES27 has been found to be primarily the elements oxygen, calcium silicon, aluminium and bismuth, while BioRoot RCS, when examined using EDX,69 was found to contain primarily calcium, silicon and zirconium. For the above analyses, it must be emphasized that the all listed elements are present as compounds, rather than as the pure element. Calcium is generally present as calcium silicates, aluminium as calcium aluminate, bismuth as bismuth oxide, zirconia as zirconium oxide, tantalum as tantalum oxide, and tungsten as calcium tungstate. This has been confirmed by communications with the manufacturers. Furthermore, XRD studies have revealed the presence of different types of calcium silicates, aluminates and radiopacifiers.13, 21, 27, 50, 66-68, 70 One study has utilised Rietveld refinement to determine the quantities of these components.71 Moreover, some cements contain organic additives, such as polycarboxylic acid in Biodentine. Such organic additives can be identified with XPS, but their precise composition cannot be identified.63 For many commercial HDCs, there is no published literature on their composition. For products where there is some published data, not all components have been recorded or their presence verified. This is particularly the case when organic additives are present.
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1.2.3.4 Hygroscopic dental cement classifications The definition of HDCs includes both products with calcium silicates as well as others where components react with water to produce crystalline solid structures, ‘hydrates’. Some examples of components in HDCs are given in Table 1-5. HDC reactants
Products
Calcium silicates 2(CaO)3SiO2 + 7H2O
(CaO)3(SiO2)2•4H2O + 3Ca(OH)2
2(CaO)2SiO2 +5H2O
(CaO)3(SiO2)2•4H2O + Ca(OH)2
Calcium aluminate 2(CaO)3Al2O3 + 21H2O
2(CaO)3Al2O3•6(H2O) + 9H2O
Calcium phosphates 3Ca4•(PO4)2•O + 2H2O
Ca10•(PO4)6•(OH)2 + Ca(OH)2
Calcium sulphates CaSO4•1/2H2O + 3/2H2O
CaSO4•2H2O
Zinc sulphate & Zinc oxide
Zn2(OH)2SO4
ZnSO4•H2O+ZnO
Zn2(OH)2SO4
ZnSO4+ZnO+H2O Table 1-5 Examples of reactions of various HDCs with water
72
*This list details the most common HDC reactions. However, there are other reactions. Furthermore, when multiple HDC ingredients are present in a material, reactions may occur between the HDCs and not just with the water.
Table 1-6 and Table 1-7 summarises confirmed compositions of commercially available packable hygroscopic dental cements that are likely to be included under the GMDN term for HDCs. Grey and white formulations within brands are not listed as separate entities as their compositions are generally the same, albeit with different levels of iron and aluminium.68
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Table 1-6 Commercial packable HDCs - permanent restoratives (Part 1, A-I) ? The manufacturer withheld information, as it was commercial-in-confidence. Other additives may be present but may not be included here if the manufacturer withheld information, or if no other product featured the same additive. 16
Table 1-7 Commercial packable HDCs - permanent restoratives (Part 2, I-T) ? The manufacturer withheld information, as it was commercial-in-confidence. Other additives may be present but may not be included here if the manufacturer withheld information, or if no other product featured the same additive. 17
Most current HDCs are hybrid materials. For example, for MTA cements, the Portland cement component, which constitutes 80% of the material, contains both calcium silicate and calcium aluminate.42 Most hybrid cements are often predominately one particular type of HDC, particularly calcium silicate cements.54 Calcium sulphate, in the form of CaSO4•1/2H2O (gypsum), although a commonly used a cement in the form of dental plaster, is found mixed within other HDCs. This is illustrated in Table 1-6 and Table 1-7. Table 1-6 and Table 1-7 list the commercial packable HDC permanent restoratives. It is evident that the commercial products contain calcium silicates. However, this does not mean that calcium silicate is a mandatory ingredient. For example, calcium sulphate cements that are used for bone augmentation procedures can also be used for pulp therapy.72 These products have not been included here as the use of a bone graft material for pulp therapy is ‘off-label’ and further research is required. Also, EndoBinder® (Binderware, São Carlos, Brazil) is a calcium aluminate cement with no calcium silicates, and is a permanent restorative HDC but has not yet been commercialised.73
Table 1-8 lists the commercial packable HDC intermediate restoratives. These cements comprised of mixtures of zinc oxide and zinc sulphate. The GMDN currently has dental restorative materials divided into subcategories based on their setting reactions. Examples include HDCs, composite resins and GICs. However, all endodontic obturants are encompassed under one category of ‘Endodontic filling/sealing material,’ which includes obturation cones, thermoplastic obturation materials, endodontic sealers and root-end filling materials.
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Commercial Brands Manufacturer
Radioopacifier
Cement type Calcium sulphates
Zinc sulphate & Zinc oxide
Coltosol® F
Coltene (Altstätten, Switzerland)
•
•
DuoTEMP®
Mixing solution
Premixed with nonaqueous liquid
Methacrylate resin
ZnO
•
Coltene (Altstätten, Switzerland)
•
•
ZnO
•
•
TM
3M ESPE (St Paul, USA)
•
•
BaSO4
•
TM
3M ESPE (St Paul, USA)
•
•
BaSO4
•
TM
3M ESPE (St Paul, USA)
•
•
BaSO4
•
Cavit Cavit G Cavit W
Table 1-8 Commercial packable HDCs - intermediate restoratives Other additives may be present but may not be included here if the manufacturer withheld information or if there was no other product featuring the same additive.
A material that falls under two GMDN codes, one of composition and one of clinical indication, is not ideal as medical devices should only have one identifier.43 This is the case for root-end fillings where amalgam, ethoxy benzoic acid cement, and HDC each have their own separate GMDN term but could also fall under the descriptor for endodontic filling/sealing materials.43 The existing GMDN term ‘Endodontic filling/sealing material’ could be replaced by categories for dental materials based on their composition and include possible usage in endodontics. Table 1-9 illustrates a scheme for the GMDN term ‘Endodontic filling/sealing material’ to categorise various obturation materials. Table 1-10 lists the HDC sealers that are commercially available. GP (cold or thermoplasticised) Resin obturation points Epoxy resin sealers Diketone resin sealers Methacrylate sealers CH or calcium oxide with salicylate ester sealers HDC based sealers (see Table 6) ZOE GIC Silicone (polydimethylsiloxane) Table 1-9 Possible categorisation of obturation to supersede 'Endodontic filling / sealing material'.
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Table 1-10 Commercial HDCs - endodontic sealers D
Discontinued, *MTA Fillapex is not viewed as a HDC but is listed here as it contains HDC components.
Other additives may be present but may not be included here if information was withheld by the manufacturer or if there was no other product featuring the same additive. 20
1.2.3.4.1 Property modifiers As well as differences in the composition between various subgroups of HDCs, other modifications influence their properties. These include: •
changing the particle size distribution of the reactant powder;
•
altering the radiopacifier;
•
presence of chemical accelerators;
•
inclusion of supplementary cementitious materials (SCMs);
•
inclusion of rheological modifiers and
•
the absence of mixing water.
1.2.3.4.2 PSD Altering the particle size distribution influences handling properties and the setting time.74 The smaller the particles, the greater the surface area and thus the faster the rate of reaction.75 More water is needed to adequately wet smaller particles.76 Altering the particle size also influences the flow properties of the material when it is being inserted into the tooth.77 1.2.3.4.3 Radiopacifier Although radiopacifiers are not reagents of the hydration setting reaction, they can change or impede the setting reaction leading to some changes to the physical properties of the set cement.78-80 The choice of radiopacifier has other implications, including whether the cement darkens over time or causes darkening of adjacent tooth structure, e.g. when bismuth oxide is used.81 Different radiopacifiers provide different levels of radiopacity and therefore radiopacity is expected to vary between products.82, 83 1.2.3.4.4 Accelerators With MTA cements, the most common accelerant is calcium chloride, which when used at levels up to 10% can effectively halve the initial and final setting times.84 The addition of calcium chloride increases calcium concentration available to react to form the calciumsilicate-hydrate structures.85 However, how the chloride ions interacts with calcium-silicatehydrate structures is not universally agreed.85
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1.2.3.4.5 Supplementary cementitious materials (SCMs) SCMs are mineral admixtures which do not in themselves react with water.86 However, when combined with a HDC, particularly those based on Portland cement, can react with aqueous calcium hydroxide to form compounds that will be incorporated within the hydrate structures of the HDC.86 The reaction of the aqueous calcium hydroxide from the pores of Portland cement results in lower porosity and higher strengths.86 SCMs are often rich in silica and include slag, fly ash and natural pozzolans.86 Using this approach, EndoCem MTA has achieved a faster setting time than ProRoot MTA (Dentsply Sirona, York, USA), but with similar handling characteristics to the latter.87 1.2.3.4.6 Aqueous Gels / Rheological modifiers Plasticisers, also known as water reducing agents, work by bonding to the cement particles, and applying their negative charge to the cement particles. 88 This causes the particles to spread out more evenly when mixed with water, and as a result less water is required to mix the cement.88 As less water is required to mix the material with water, the set product has greater compressive strength.89 A plasticiser has been included in Biodentine. This agent may also improve bonding to dentine and thereby increase the resistance of the material to dislodging forces.45 Thickeners can be added to HDCs for several purposes. Adding a thickener to a cement powder can produce a paste (e.g. for use as an endodontic sealer) or a putty (e.g. for a restoration).90 Thickeners are typically added to the water component of the HDC, where they alter the flow of the material when it is mixed.90 Examples of this include ProRoot Endosealer® (Dentsply Sirona, York, USA) and EndoCPM® (EGEO Dental, Buenos Aires, Argentina). ProRoot Endosealer powder has the same ingredients as conventional MTA, but the water component is enriched with a water-soluble polymer.91 EndoCPM contains Portland cement, propylene glycol alginate, propylene glycol, sodium citrate and calcium chloride.92 In this product, the propylene glycol serves as the thickening agent because of its ability to form intermolecular links that create a scaffold,93 while the calcium chloride accelerates the setting reaction.84 1.2.3.4.7 Absence of mixing water Some HDCs are supplied as a single component injectable paste with no water, and the setting reaction requires water from the dentine to diffuse through the material to enable the cement to set.94 Because the paste is water-free, a thickening agent is used to create a gel-like consistency. iRoot® SP (Innovative BioCeramix, Vancouver, Canada), is 22
supplied as a single component injectable paste, which does not contain any water. A thickening agent is used to create a gel-like consistency for the paste.94 The manufacturer claims that the typical setting time is 4 hours, but this will extend to over 10 hours when the material is placed in dry canals.95 Likewise, iRoot® BP (Innovative BioCeramix, Vancouver, Canada) is the packable version and is placed without any water to then rely upon water from an outside source (such as tooth structure surrounding the cavity preparation) to cause the material to set.96 The current GMDN term states that the HDCs are “available as a powder intended to be either mixed water prior to application or react with dentinal fluid in situ”. Some HDCs are commercially available as water-free pastes that then react with the water present in dentinal fluid once placed into the tooth. Therefore, the GMDN term should be updated to reflect these products. 1.2.4 Clinical and research consequences There are commercial products that are more like resins than HDCs, as well as HDCs that are placed without first mixing them with water. Without a functional classification of these products, clinicians would assume that all these HDCs perform identically. More research is needed to compare the subtypes of HDCs, particularly resin and HDCs that are placed without water. The terms ‘bioceramic’, ‘MTA’ and ‘calcium silicate cement’ can be misleading as not all properties are shared amongst such materials. Clinicians should be aware of the differing compositions of cements as these differences result in variations in performance. Differences in the choice of radiopacifer and its percentage composition can result in significant differences in radiopacity. 1.2.5 Conclusions HDCs, particularly those involving calcium silicates, have become an integral part of clinical practice, including endodontics and restorative dentistry. Some HDCs have then been modified to create variants, which are either flowable, for use as an endodontic sealer or highly viscous and putty-like for packing into defects. While there is a growing body of evidence supporting the use of HDCs, much of the existing literature relates to the original ProRoot MTA composition, and the data from this cannot simply be extrapolated to all HDCs, because of the influence of changes in 23
composition. One cannot simply assume equivalence even between HDCs of the same type (such as MTA) because of variations in particle size distribution, thickeners, accelerants and other components that can affect handling properties and setting reactions. There is a growing body of evidence supporting the use of HDC. However, most of this relates to the original ProRoot MTA composition. As some HDCs can be more different than others, care should be considered when assuming equivalence between products. Unlike the restorative cements, the existing GMDN scheme groups all endodontic obturation materials under the same term. The creation of separate terms based on material composition will improve the understanding of products that have similar compositions and uses, and better distinguish these from those with contrasting compositions.
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1.3
Review of the placement of cements in the construction industry
This subchapter has been published as: Ha WN, Kahler B, Walsh LJ. Clinical manipulation of mineral trioxide aggregate: Lessons from the construction industry and their relevance to clinical practice. J Can Dent Assoc 2015;81:f4. 1.3.1 Introduction The use of MTA as a dental material has become popular, despite its high cost. A typical MTA cement contains 80% PC, to which is added 20% BO to make the material radiopaque so it can easily be identified on dental radiographs. Although MTA has become a well-recognised material in endodontics, restorative dentistry and paediatric dentistry, training in its use is not common outside postgraduate continuing education courses and endodontic specialist training programmes. Despite the accepted indications for its use in the primary dentition, MTA techniques are not taught universally at dental schools, with the greatest barrier being its high cost.10, 97 Thus, information on handling and use is limited to the supplied instructions for use prepared by the manufacturer and to various published case reports.8 Although case reports and clinical trials guide clinicians as to where MTA can be used, they do not provide practical information on the rationale for the individual steps used to manipulate the material and how these steps affect clinical success. Because MTA is primarily PC, it is insightful to assess literature related to the use of PC in the construction industry to identify key factors that relate to performance to draw parallels between them and clinical practice. 1.3.2 Water and the setting reaction In the construction industry, PC is commonly combined with sand or gravel and water to produce concrete. The sand or gravel filler, which is termed aggregate, provides additional strength to the final set product, making it better suited to situations where heavy loads will be applied, such as in buildings, roads and bridges. During setting, PC reacts with the water to form calcium silicate/aluminate hydrates (such as (CaO)3•(Al2O3)•6H2O, (CaO)3(SiO2)2•4H2O), and CH water. The final set cement is a crystalline structure with voids containing water and CH. Despite appearances, the set material is not fully solid; rather there is an associated fluid state, much like water held within in a wet sponge.98 During the setting reaction, needle-like 25
crystalline hydrates form a framework connecting all the particles together and, effectively, turning the original powder–liquid mixture into a solid-like colloidal gel.98 If water is lost to the atmosphere during the setting reaction, this will significantly weaken the set material. Hence, loss of moisture while MTA is setting must be avoided.99 1.3.3 Exposure of the set material to acids When set cement is exposed to acids, the saturation of its contained fluids with CH is lost, as hydroxide ions are consumed in acid–base reactions.100 This leads to loss of some of the hydrate structure, creating a surface etching effect. A single treatment with hydrochloric acid can be used both to clean and etch concrete, exposing the aggregate as well as the matrix.101 Any other exposure of concrete to acidic environments is avoided.101 Likewise, exposure of MTA to strong acids will cause surface etching resulting from the loss of CH from the set cement, as hydroxyl ions react with the acid, and consequent dissolution of calcium silicate hydrates (CSHs).101 Fluids from the surrounding environment may enter the cement to replace the lost CH or hydrates, depending on the ions present in those fluids.102 1.3.4 Acids present at the time of mixing In the construction industry, acidic water is never used in mixing concrete, because it will cause the formation of intermediate compounds that retard hydration of the cement and limit the production of CH.103, 104 Furthermore, acids will decompose both CSH structures and CH. In the presence of acids, the compounds that form during setting are likely to be more soluble; this disrupts the formation of the mesh of interlocking crystals and also causes them to leach out of the set material.105 Before concrete is poured onto acidic soil, a process known as chemical stabilization or soil conditioning is performed.105 The soil is mixed with an alkaline material (such as calcium oxide or CH) and allowed to reach a neutral pH before placement of cement. The dental parallels to acidic soil are the presence of deep caries (indicating organic acids in the dentine), bacteria in large numbers, such as in infected root canals (accompanied by acidic waste products and metabolites) and inflammation, such as in periapical regions. An acidic pH can be expected at sites of necrosis and inflammation.106 As in construction, the presence of acids in the environment where MTA is to be placed will adversely affect the setting reaction. As the environmental pH falls from 7.4 to 4.4, 26
greater leakage can be expected at the margins of the set MTA, and its adhesion to the tooth structure will decrease.107, 108 The micro-hardness of the set MTA is reduced and its microstructure changes from cubic and needle-like crystals to eroded cubic crystal structures.109 Thus, pH should be increased back to physiological normal before placing MTA. For example, dressing the root canal of an abscessed tooth with CH for 1–2 weeks before MTA placement will improve the properties of the set MTA.110 Moreover, in a vital tooth undergoing apexification, a short treatment with CH can stimulate repair at the apex of the tooth, as well as help to disinfect the canal.111, 112 It has been suggested that pretreatment with CH paste may adversely affect the sealing ability of MTA, as it may be difficult to remove and, thus, remnants might act as a barrier to the adaptation of MTA to the root canal walls or become involved in the MTA setting reaction.113 The latter point is at odds with the literature from the construction industry that advocates the use of CH to condition acidic soil. However, CH dressings used in dentistry may contain various additives, such as methylcellulose and carboxymethylcellulose, which are known to retard the setting of PC.114, 115 Therefore, if a dressing of CH paste is used, extensive irrigation should be carried out to ensure that no remaining dressing material is present, as remnants of the cellulose thickener will retard the setting of MTA. Similarly, acidic irrigants, etching solutions and conditioners must be washed away before MTA placement. Sodium hypochlorite (NaOCl) irrigants, which have pH values above 11, should neutralise any remaining acids when used to rinse root canals.116 As discussed earlier, the presence of acids can modify the hydration of MTA, resulting in the formation of new compounds within the matrix structure that may inhibit the hydration reactions.117-119 NaOCl reacts with BO that turns the yellow powder a dark brown; therefore, the preparation should be adequately irrigated with saline to avoid unnecessary darkening of the MTA.81 As darkening of MTA may be expected, Belobrov and Parashos suggest that white MTA should not be used in the aesthetic zone, rather, CH should be considered for Cvek pulpotomies.120 1.3.5 Interactions with EDTA Some common irrigating solutions are not acidic (e.g., disodium edetate has a pH of 7.0– 7.4; and tetrasodium edetate has a pH up to 11.3). The issue with 27
ethylenediaminetetraacetic acid (EDTA) is not primarily the pH, but rather chelation. EDTA has 6 potential sites for binding positively charged ions, such as metal ions. Calcium ions are important reactants in the setting of PC and MTA. If EDTA solutions used to remove the smear layer in endodontics are not rinsed away properly, residual EDTA will chelate calcium ions and disturb the precipitation of hydration products during the setting reaction.121 This explains the finding of Lee121 who found that MTA stored in EDTA solution had no crystalline structure and a low Ca:Si molar ratio. Furthermore, EDTAtreated MTA has been shown to have reduced micro-hardness and to be less biocompatible, as gauged by reduced adhesion of fibroblasts, compared with MTA that has not been treated with EDTA.121 1.3.6 Interactions with phosphoric acid From the above discussion, it follows that phosphoric acid used for etching should be washed away thoroughly before MTA is placed. This situation is particularly relevant in a deep cavity or pulp capping application, where other acids, such as organic acids from bacteria, are also likely present. Even in small amounts, phosphoric acid will alter the MTA setting reaction and reduce the micro-hardness of the set material.122 Thus, acid etchant should be washed from the walls of the cavity preparation with water before MTA placement in a deep cavity. Alternatively, MTA can be covered with a GIC before etching of the cavity margins in the final phases of restoration placement.123 In many cases, the easiest way to address the influence of both acid etchants and EDTA will be to irrigate or rinse the area with water before placement of MTA.124 1.3.7 Presence of contaminants such as blood A general principle in the construction literature is that the higher the level of chemical impurities in the mixing water, the greater the likelihood that one or more of these impurities will interfere with the PC setting reaction, resulting in reduced CS.125 MTA set in the presence of blood has inferior physical properties, i.e., reduced CS, reduced microhardness and less resistance to displacement.126-128 Likewise, in the presence of serum, the MTA setting process is altered with a changed surface morphology, reduced microhardness and the reaction may be retarded.129 Although MTA is often described or marketed as being able to set in a wet and possibly bloody environment, it is important to minimise the ingress of any tissue fluids or blood into MTA during placement or as it is setting. This is particularly important along the margins of the preparation where leakage would occur if the MTA sets with inferior properties. 28
Clinicians should minimise a haemorrhagic contamination, as excessive blood will not only impair vision and access but will also affect the setting reaction and the quality of the end product. Contamination with blood has particular implications when MTA is used as a rootend filling. 1.3.8 Variations in the liquid component of MTA In concrete, various additives and impurities in the mixing water are known to alter the setting reaction and affect the end product. Sodium chloride (as found in saline) and many other inorganic and organic materials will likely result in slower setting due to the formation of alternative products.130 Manufacturers' instructions for use of MTA typically recommend sterile or distilled water as the liquid to be mixed with the MTA powder. For both quality control and convenience, this is often included with the MTA powder. Although MTA powder will set if mixed with local anaesthetic solutions, the reaction is slower and the set material has less CS.131, 132 NaOCl solutions will allow MTA to set faster than distilled water, but once again at the expense of CS.131, 133 However, in a confined situation where the cement is placed in a non-loading area, this would not be an issue. In many cases, the benefits of an accelerated setting reaction, i.e., less opportunity for dislodgement and disintegration of the restoration being placed, must be balanced carefully against reduced physical properties.131, 133, 134 Chlorhexidine gluconate (CHX) as an alternative to sterile water is not suitable because it completely inhibits the setting reaction of MTA.133 1.3.9 Curing of the cement The reaction of PC with water is dynamic, and water must be retained within the cement during curing to maintain the structure and ensure the strength of the final product. If water is lost to evaporation, the strength of the set cement will be reduced. In the construction industry, a range of methods are used to minimise water loss during curing, including wet curing (e.g., sprinkling water on the cement to replace water that has evaporated) and membrane curing (e.g., covering the cement with a water-tight membrane to prevent evaporation).
29
In clinical practice, the technique corresponding to wet curing is to place a damp cotton pellet on the MTA as it begins to set and leave it in place. However, if the cotton pellet is too dry, water will be drawn out of the cement, weakening it; if the pellet is too wet and is placed too soon, this will also weaken the cement. Using a cotton pellet also delays completing the clinical procedure and may compromise the quality of the seal.135 Following the industry approach of membrane curing, a material, such as GIC or resinmodified GIC (RMGIC) liner, can be placed over the MTA. Once this has been placed, the MTA is stable in terms of water loss or gain from the surface, and the clinician can proceed to restore the tooth or obturate the canal. This concept has been tested with white MTA-P (Dentsply, Johnson City, USA), which has an initial setting time of 45 minutes. GIC placed over the MTA after 45 minutes gives a shear bond strength to dentine that is the same as waiting 72 hours.123 Therefore, there appears to be no advantage in leaving MTA to set over a period of a few days compared to a one-visit restoration. However, there do not appear to be any adequate studies that assess the implications of waiting less than 45 minutes before placing GIC onto MTA. An alternative to covering MTA with GIC is to use a self-etching bonding agent system as a waterproof layer above the material. In one study,136 after allowing 10 minutes for the MTA to set, a bonding agent was placed without significantly affecting the final Vickers micro-hardness or distance between the MTA and the bonding agent, compared with waiting 1 day or 7 days before placing the bonding agent. Again, this illustrates that a single-visit restoration with composite resin can be placed over MTA.136 1.3.10 Storage of MTA Both PC and MTA powders are highly hygroscopic and, when exposed to the atmosphere, will absorb moisture and begin to hydrate. Although PC can be packaged in airtight bags and containers of appropriate size, the issue of packaging arises with MTA, as some products are sold in multiple-use bottles. Recent research has shown that opening the container causes changes in the particle size of the remaining MTA, which likely has implications in terms of delayed setting and inferior resulting material. Single-use packaging is ideal. Alternatively, airtight jars allow fewer changes in stored material.40
30
The PC setting reaction is retarded in cold temperatures. Likewise, MTA that has been refrigerated shows a significant reduction in surface hardness, greater porosity and leakage; therefore, refrigeration of MTA should be avoided.137, 138 1.3.11 Summary This analysis of certain aspects of industrial concrete provides insight into and sound principles for the clinical manipulation of MTA. The practical points from this discussion are summarised in Table 1-11. Clinical situation
Recommendation
Infected (acidic) radicular structures
Neutralise with CH paste and/or NaOCl irrigation.
Restoration in the aesthetic zone
Consider other materials and procedural alternatives; e.g., CH Cvek pulpotomy in traumatised exposures.
Endodontic medicaments present in
Remove with NaOCl or saline irrigation.
canal Etchant, conditioners and chelating
Neutralise with NaOCl irrigation.
irrigants Haemorrhage into prepared cavity
Minimise haemorrhage.
Use of local anaesthetic solution, CHX
Use distilled water.
or saline water to mix MTA Wet cure MTA using a damp cotton
Single-visit membrane cure using:
pellet
- GIC/RMGIC liner, but allow MTA to set for 45 minutes before application. - Self-etching bonding agent, but allow MTA to set for 10 minutes before application.
Storage of MTA
Do not refrigerate. Once opened, place material to be re-used in an airtight container. Keep sealed when not in use. Table 1-11 Clinical Techniques that influence MTA's properties
31
1.4
The properties of MTA and how it can be manipulated
This part of the literature review explores how MTA should be used. Parts of this chapter were published as conference proceedings for ASE-NSW, ASE-VIC and ANZCVS seminars. 1.4.1 Aims This subchapter aims to discuss the clinical properties of commercial brands of MTA, specifically: •
how MTA is made and the relevance of calcium hydroxide release;
•
the properties relating to antimicrobial activity, leakage and porosity, marginal adaptation;
•
an overview of the brands;
•
the uses of MTA; and
•
the handling of MTA.
The subsequent subchapter 1.5 on page 51 will discuss the properties of MTA as related to standard tests found in ISO 6876 and ISO 9917.1. 1.4.2 MTA formulation Many MTA cements are fundamentally the same, being a cement powder based on PC that is mixed with water, and likewise their clinical outcomes are similar.74 Different products vary in terms of particle sizes and additives, causing them to handle slightly differently. Some cements contain zirconium compounds as radiopaque agents rather than BO, which is expected to have a lower radiopacity since zirconium has a lower atomic number than bismuth. Table 1-12 illustrates the difference in radiopacity of normal PC, ProRoot MTA, dental structures as well as the international standard for radiopacity for endodontic sealers. Materials Enamel
Radiopacity (in mm Al)
139
1.8-2.0
139
0.9-1.0
Dentine
Portland cement
23
0.96
International Standard for endodontic sealers (minimum) ProRoot MTA
23
3
3.00 6.53
Table 1-12 Radiopacity of ProRoot MTA and dental structures
32
MTA is made by mixing two powders, 80% PC (w/w) and 20% BO (w/w). To achieve a similar level of radiopacity using powders that may not darken as much as BO, the following percentages of radiopacifiers can be used to replace the 20% BO: 30% ZrO2, 30% ZnO, 30% BaSO4, 10% Au or 10%Ag-Sn alloy.22, 140 Hygroscopic cements such as PC that do not have radiopacificers show a radiopacity less than dentine.83 The addition of radiopacifiers in MTA is essential for creating a radiopacity greater than dentine. Radiopacifiers are based on either: •
radiodensity. This is proportional to the density of the material; and
•
percentage of radiopacifier powder added to the cement.
Table 1-13 illustrates the differences in radiopacity when 20% (w/w) radiopacifier is combined to PC to produce MTA. Substance
Density
Radiopacity
Radiopacity
Radiopacity
(mg/cm3)
(mm Al)141
(mm Al)82
(mm Al)83
3.15
0.75
1.69
1.01
ProRoot MTA
3.65
5.72
Radiopacifier
When 20% radiopacifier is combined with
100% PC
80% PC Bismuth oxide
8.90
3.71
5.88
5.93
Tantalum oxide
8.20
2.78
Bismuth
6.86
3.25
6.06
3.11
carbonate Calcium tungstate Zirconium oxide
5.68
Zinc oxide
5.61
Barium sulphate
4.50
Iodoform
4.02
3.87
3.41 2.65
1.48
2.35
2.80
3.50
4.24
Table 1-13 Radiopacity of MTAs with different radiopacifiers (20% w/w)
The findings of one study of radiopacity cannot be reliably compared with another study, as the method of mixing, properties of the aluminium step wedge, exposure settings and assessment of radiopacity can influence the results. Nevertheless, there is a general trend that the higher the density of a material, the higher the radiopacity. In the case of MTA-P, radiopacity can vary from 2.5142 to 6.523 mm Al. This can be due to the differences in how studies place the MTA, i.e. packing123 and the water-powder ratio.143 33
Radiopacifiers are not directly involved in the setting reaction. However, their inclusion can be described as a steric hindrance. Therefore, their inclusion results in detriment to the CS, prolongs setting time and increases solubility.79, 80, 144, 145 HDCs that opt to use alternative radiopacifiers to BO may either have a substantially higher proportion of radiopacifier in their efforts to be as radiopaque as MTA-P, or may not be as radiopaque as MTA-P. While it may be said that MTA could be substituted with Portland cement,146 clinicians should be wary about such comparisons as they imply that industrial concrete can be used in teeth. In Australia, chemicals that are supplied for use in the prevention and treatment of diseases must be registered by the Therapeutic Good Administration, which has functions that parallel those of the United States Food and Drug Administration. There are studies in both animals and humans illustrating comparative positive results for MTA and PC when used for dental treatment.147, 148 Despite these findings, health care device regulations will not allow an industrial product that contains a variable number and amount of heavy metal contaminants to be used for medical purposes. Furthermore, PC is not radiopaque and therefore fails radiopacity standards for dental restorative materials. 1.4.3 CH & MTA CH paste (CHP) is a “gold standard” material for endodontic antibacterial medication. Its main antibacterial effects are due to its alkaline pH. It takes 7 days for CHP, supplied at a pH 12, to elevate the pH in the surrounding dentine from neutral to a pH of 9, a point where the growth of some bacteria is inhibited.149 CH resin-cements (CHC) do not release CH,60 rather they consume it in their setting reaction. Their pH when set is therefore less than the other CH products that do not consume CH in their setting reaction.150 Table 1-14 compares MTA with CHP and CHC.
34
Properties
CHP151
CHC61, 152
MTA122, 153
Brands
Calcipulp, Pulpdent,
Dycal, MTA
ProRoot MTA, MTA
Calyxl
Fillapex, Life
Angelus
As below
Butylene glycol
2(CaO)3(SiO2) (s) +
disalicylate(l) +
2(CaO)2(SiO2) (s)
Ca(OH)2(s)
+12H2O(l)
Calcium
2[(CaO)3(SiO2)2•4H2O] (s)
Key / Majority Reactants:
+
-
Key / Majority
Ca
Products:
Gel-like thickening
disalicylate(S) +
agent
2H2O(l)
(aq)
+ 2OH (aq) +
+ 4Ca+(aq) + 8OH-(aq)
(e.g. methylcellulose) State &
Paste
Handling
Thick paste that
Hard paste that
solidifies into
solidifies into rock-like
flaky cement
cement
Immediate pH:
12.5
9-10
12.5
Antibacterial
Strong
Mild
Strong
Soluble
Semi-soluble
Insoluble
Therapeutic dressing
Liner
Permanent restoration
effect Long term state: Clinical indication Table 1-14 A comparison of MTA with CH products
1.4.4 pH and Calcium hydroxide release The alkalinity of MTA when mixed, and hence Ca2+ and OH- release, is notable over 1-2 days.154 After this time period, the alkalinity is below antimicrobial effects and also corresponds to its increase in cytotoxicity.155, 156 This change in pH is illustrated in Figure 1-1.
35
Figure 1-1 pH of setting MTA
1.4.5 Clinical properties 1.4.5.1 Marginal adaptation A study by Shokouhinejad on the marginal adaptation of ProRoot MTA, iRoot BP and iRoot FS in simulated root end fillings illustrated that, longitudinally, the iRoot FS had larger gaps.157 The authors of this study believe that difference lies in the fact that iRoot BP and MTA can be gently compacted to reduce voids while the iRoot FS cannot be compacted as it’s applied by a syringe.157 1.4.5.2 Bacterial leakage study The bacterial leakage model appears to be the most clinically relevant method of assessing the quality of the seal.158 A study by Hirschberg compared MTA and bioceramic putty as root-end fillings in extracted teeth with no orthograde obturation.159 After 28 days from exposure to introduced E faecalis culture, 20% of MTA samples permitted bacterial leakage past the apex while 93% of bioceramic putty samples permitted bacterial leakage past the apex.159 MTA has a median leakage time of 90 days.160 This study by Hirschberg159 is notable when comparing with studies that illustrate no difference as other studies include greater setting times for iRoot BP and the placement of gutta percha coronal to the root end filling.161, 162 The greater setting time will improve the 36
setting and hence the seal of the iRoot BP. The placement of gutta percha in a leakage study can also improve the overall seal. Therefore, these two changes will increase the likelihood that an overall difference will not be found between MTA and iRoot BP. 1.4.5.3 Antimicrobial effects For a material to provide such biological effects normally requires something be released from the material. For example, if CH is being released, then the cement should be losing mass over time. This could result in a compromised seal. The exception is that some materials (e.g. MTA) may also absorb ions and hence their overall mass is not reduced.163 Against E. faecalis, when immediately placed, MTA and the iRoot BP had similar antibacterial activity.155 As the material is given time to set, the antimicrobial activity reduces and begins to match the negative control. This is similar with Candida albicans, albeit with milder activity.155 This corresponds to the setting time and cytotoxicity of the cements. If a material has set, there should be no appreciable calcium hydroxide release and therefore no antibacterial nor cytotoxic effects. 1.4.6 Commercial brands of MTA 1.4.6.1 MTA-P MTA-P is provided as sachets that are intended to be single-use only. However, many clinicians use the one sachet multiple times to lower the cost-per-use. This practice is against the manufacturer’s instructions. The advertised setting time of 4 hours for this material is based on a test where needle indentation by a force of 5 MPa is resisted.74 However, clinicians can carefully place other restorative materials above this MTA after only 10 minutes, since at this time the MTA has reached a sufficient hardness.136 1.4.6.2 MTA-A MTA-A is supplied in a re-sealable jar, which is easier to store for re-use than MTA-P. The advertised setting time of 15 minutes is based on a test that involves resisting needle indentation by a light force of only 0.3 MPa.74 It is not possible to directly compare this setting time with that of MTA-P.
37
1.4.6.3 EndoCem MTA EndoCem MTA is a relatively new product and studies on its performance are lacking. Its composition is similar to MTA-P with the difference being the inclusion of pozzolans that react with CH in the setting structure. Although this may assist in the faster setting of EndoCem, it also results in less calcium release and less apatite formation.64 MTA-P could be more biocompatible, while EndoCem MTA may have a shorter setting time.164 EndoCem Zr is likely to behave similarly to EndoCem MTA with the key difference of a change in radiopacifier from BO to ZO. Therefore, less staining is expected. 1.4.6.4 Biodentine Biodentine is supplied as a powder in a capsule with an aqueous solution that must be poured into the capsule prior to mixing. This material sets faster than conventional MTA cements. However, it is not hard enough to be a conventional bulk restorative material, unlike GIC. Table 1-15 compares MTA-P with Biodentine. ProRoot MTA
Biodentine
Superiority?
75% calcium silicates and
85% calcium silicates
ProRoot MTA is less soluble49
aluminates 5% gypsum
10% calcium carbonate
Biodentine sets faster.49
20% bismuth oxide
5% zirconium oxide
ProRoot MTA is more radiopaque49
100% distilled water
Water with 15% calcium chloride and
Biodentine has a greater
polycarboxylate
hardness49
Table 1-15 Comparison of MTA-P with Biodentine
1.4.6.5 iRoot BP (TotalFill RRM) and iRoot FS (TotalFill RRM Fast Set)) Table 1-16 compares MTA-P with iRoot BP and iRoot FS.
38
Property
MTA
iRoot BP
iRoot FS
(Putty)
(Syringe)
Radiopacity
Good
Good*
Good*
Setting time in blood165
Good
Bad
No studies
Good
Good
Not as good
Good
Best
Worst
6-week skin implantation168
Good
Good
Worst
Bone implantation169
Cytotoxicity
166
1-3-week Skin implantation
Good
No studies
No studies
155
Some
Some
Some
157
Good
Good
Worst
Good
Bad
No studies
Good
No studies
No studies
Antimicrobial effects Marginal adaptation
167
Bacterial leakage159 Solubility32 Dimensional change
32
Good
No studies
No studies
170
Good
Good
No studies
5-year clinical performance171
Good
No studies
No studies
2-year clinical performance
Table 1-16 Comparison of MTA-P with iRoot BP *Stated by manufacturer to be comparable to ProRoot MTA and appears to seem clinically suitable
1.4.6.6 Setting time of premixed putties The premixed (waterless) putties are advertised as having faster setting times than MTA cements that are mixed with water. This is because the putty structure provides indentation resistance and hence the material can appear to have set earlier. However, the putty requires diffusion of water through the apical tissues as well as the dentinal tubules to set the putty and therefore, the setting time can be variable. Furthermore, the more blood present, the more prolonged the setting time, which can increase the risk of leakage.165 1.4.6.7 Staining of premixed putties There are inconsistent reported findings regarding which products stain. The original grey MTA-P was known to darken, hence the development of white, ‘tooth-coloured’ MTA-P. This material was also found to darken somewhat over time. Caution is needed regarding claims of products being non-staining. Studies involving the application of sunlight and heat show that MTA-P will darken, while Biodentine, Total Fill Sealer, Total Fill Putty and AH Plus will not.172 A likely reason why MTA-P stains while Biodentine does not is the difference in radiopacifiers. MTA-P contains 39
bismuth oxide while Biodentine contains ZO. When radiopacifiers are excluded, PC appears to be colour stable. However, in the presence of blood, PC will stain.173 Therefore, it is expected that all HDCs used for root-end fillings will exhibit some level of darkening over time. 1.4.6.8 Properties of HDC Sealers To turn a HDC package cement into a sealer there are two options: •
adding more mixing water; and
•
having no mixing water.
Adding greater amounts of mixing water to MTA results in lower CS,174 increased solubility, increased porosity,175 lower radiopacity and longer setting time.143 Alternatively, waterless gels can be used to turn the cement into a paste, similar to the putties discussed in the section 1.2.3.4.7 on page 22. 1.4.6.9 BioRoot RCS BioRoot RCS is a new endodontic sealer from Septodont that uses a similar composition to Biodentine, with modifications to enable higher flow for use as a sealer. Table 1-17 compares BioRoot RCS with AH Plus. Property
BioRoot RCS
AH Plus
Voids176
More
Less
Solubility177
More
Less
Setting time177
324 min
612 min
Flow and film
Less flow and thicker
Complies with ISO 6876
thickness
178
consistency Table 1-17 Comparison of BioRoot RCS with AH Plus
1.4.6.10 iRoot SP iRoot SP is also known as Endosequence BC Sealer and Total Fill Sealer. The manufacturer’s directions advise that the typical setting time is 4 hours, but this will extend to over 10 hours when the material is placed in dry canals.179 Table 1-18 compares TotalFill Sealer with AH Plus.
40
Property
AH Plus
iRoot SP
Clinical Success
Commonly used in endodontic literature
Case Reports
Radiopacity
Better
Worse180
Sealing Tests
Better
Worse181
Bacteriostatic
Similar
Similar182
Push-out Strength
Better
Worse183
Solubility
Better
Worse184
(Less soluble)
(More soluble)
Table 1-18 Comparison of AH Plus and TotalFill Sealer
1.4.6.11 ProRoot MTA ES (ProRoot Endo Sealer) Unfortunately, there is little other published research available for ProRoot MTA ES. ProRoot MTA ES is mixed with water and therefore its properties may be similar to BioRoot RCS. (Table 1-19). Property
ProRoot MTA ES
AH Plus
Seal91
Similar
Similar
Table 1-19 Comparison of AH Plus and ProRoot MTA ES
1.4.6.12 MTA Fillapex MTA Fillapex is essentially Dycal™ mixed with MTA powder. It is a flowable endodontic sealer, and should not be used for endodontic repairs of teeth or for pulp therapy. It requires water to diffuse from the dentine to cause the setting reaction, and therefore the setting time is uncertain. Furthermore, it has higher solubility and greater cytotoxicity than other endodontic sealers (such as AH Plus) while the long-term seal achieved can be inferior.184-187
41
Property
AH Plus
MTA Fillapex
Clinical Success
Many and long
Lab studies and
studies
pulp caps studies
Radiopacity
Better
Worse188
Film Thickness
Better
Worse189
Cytotoxicity
Better
Worse29
Bond strength
Better
Worse190
Antibacterial
Worse
Better191
Better
Worse185
(Less soluble)
(More Soluble)
activity Solubility
Table 1-20 Comparison of AH Plus and MTA Fillapex
1.4.6.13 TheraCal LC TheraCal LC has been marketed as having high calcium ion release and as being able to create an alkaline pH.58, 192 However, the assays used involved placing the material into water and measuring changes over only a few days. TheraCal LC is not mixed with water on placement and therefore it cannot be expected to perform clinically as well as when tested in water immersion under laboratory conditions. Compared to Vitrebond and Ultrablend Plus, TheraCal LC has less cytotoxicity.193 However, there have been no comparative studies on this aspect with MTA.193
42
1.4.6.14 Differences between MTA brands and “MTA Brands” ProRoot
MTA Angelus
Biodentine
MTA
MTA
TheraCal
Fillapex
LC
What is it
Portland
Portland
Modified
Dycal &
Flowable
really?
cement &
cement &
PC & ZrO
MTA
resin & PC
bismuth
bismuth oxide
oxide Clinical
Endodontic
Endodontic
Endodontic
Endodontic
Pulp caps
Uses
repair
repair
repair
Sealer
only
Packaging
One-use
Re-sealable jar
Manually
Two-part
Single one
combined,
mixing paste
component
capsule
syringe
syringe
only sachets
mixed Setting
4 hours
15 Minutes
12 Minutes
2 hours
Light Cured
Evidence
Very
Extensive
Mostly
Performance
Mainly
base
extensive
studies.
small trials
equal to or
anecdotal
studies
Chemically
and case
less than
and lab
almost
reports.
AH26
studies
identical to
Promising
ProRoot MTA
results
Gunz
Erskine
speed*
Cost to
2 grammes
1gramme jars
5 capsules
buy
(4 sachets)
for $123
$92.40
$17.57 per use
$18.48 per
$370.51 Cost per
$92.63 for
use
one-use only
use
$26.47 for re-using packet Supplier
Dentsply
Gunz
Halas
Dental & Amalgadent Table 1-21 Comparative summary of popular MTA and 'MTA-like' products Prices are in Australian Dollars.
43
1.4.6.15 Variation between brands Many MTA cements are fundamentally the same, being a cement powder based on PC that is mixed with water, and likewise their clinical outcomes are similar.74 Different products vary in terms of particle sizes and additives, causing them to handle slightly differently. Some cements contain zirconium compounds as radiopaque agents rather than BO, which is expected to have a lower radiopacity since zirconium has a lower atomic number than bismuth. Changes in the composition of HDCs away from MTA can result in differences of performance. BioAggregate, which is a HDC with compositional differences to MTA illustrated in Table 1-6, is compared against MTA-P in Table 1-22. Property
ProRoot MTA
BioAggregate / DiaRoot
Clinical Success
Many and long studies
Lab studies and pulp cap studies
Strength
Better
Worse194
Radiopacity
Good
No studies
Setting Time
4 hours
4 hours
Sealing Tests
Good
Good195
pH / Ca(OH)2
Better
Worse
Solubility
Better
Worse196
(Less Soluble)
(More Soluble)
Table 1-22 Comparison of MTA-P with Bioaggregate / DiaRoot
44
1.4.7 Clinical uses 1.4.7.1 Clinical applications
Figure 1-2 Applications of MTA
1.4.7.2 Success Rates The reported success rates for MTA are 97.6% in pulp capping, 79% in pulpotomy in permanent teeth and >95% in pulpotomy in primary teeth.197 In apical barriers the success rate can be expected to be over 90%.198 1.4.7.3 MTA used for pulp capping Pulp capping is performed for exposures of the dental pulp where the pulp is vital and not irreversibly inflamed. Aseptic technique is mandatory and any burs used should be watercooled to prevent over heating of the pulp. Once the pulp is exposed using burs in a dental handpiece, haemostasis of the pulp is achieved via a sterile cotton pellet soaked in NaOCl. If haemostasis cannot be achieved it is likely that the area of the pulp is inflamed and the preparation should be extended until all inflamed areas of the pulp are removed, leading to a pulpotomy or a pulpectomy. Once this is done, MTA or CH can then be placed. CH has been the gold standard for pulp capping. However, this suffers from certain problems. CH when applied in a water-based paste is soluble in oral fluids and can wash out. It does not adhere to tooth structure and dislodges easily after placement. MTA has a higher success rate with less pulpal inflammation and more predictable hard dentine bridge formation than CH.199 Instead of CH, MTA can be placed, followed by a layer of
45
RMGIC over the MTA to protect it. The tooth is then etched, washed, primed, treated with adhesive and restored with a composite resin restoration.200 1.4.7.4 MTA pulpotomy Pulpotomies are performed for deep carious exposures or exposures of the pulp where the pulp is vital and not irreversibly inflamed. The clinical procedure is the same as that for pulp capping, with the key difference being the removal of all tissues in the pulp chamber.201 1.4.7.5 MTA apexification and apical barrier The larger the apex the greater the chance that the apical region of the tooth will be poorly obturated and the more difficult it is for the clinician to length control the obturation material. In the past, multiple appointments to dress the canals with CH were utilised, while with MTA, this can be done in one visit. As set MTA exerts antibacterial actions and promotes bone growth, clinicians can place MTA at the apex of a tooth with confidence the area will be well sealed. In teeth with apices wider than a 55 K-file (0.55 mm), and/or in situations when apical patency becomes difficult to achieve, MTA may be used to create an apical plug of 3-5 mm thickness, before restoring the remainder of the canal with GP or more MTA.202 1.4.7.6 MTA root-end fillings Apical infections that do not respond to conventional and adequate root canal therapy can respond to apicoectomy. In this procedure, the last 3 mm of the tooth is removed along with any pathological material, and the end of the root canal is sealed with MTA. In this procedure, MTA is used because it has excellent sealing properties and will encourage healing of the cementum repair around it, unlike the historical alternative of dental amalgam. In a survey of EDs in Australia on what was their preferred material for root-end fillings, 85.3% use MTA and 8.0% use Super EBA. Of those who use MTA, 81.5% use MTA-P and 17.3% use MTA-A. This is explained further in Chapter 3 on page 81. 1.4.7.7 Primary ideal properties of root-end fillings The properties of a desirable root-end filling are compared in Table 1-23. 46
Material
MTA
IRM 203-205
SuperEBA
~90%
203
~90%
204
Amalgam ~50%205
Success Rate
~90%
Biocompatibility*
Best206
Mid-range206
Mid-range206
Worst206
Radiopacity as per
Passable142
Passable142
Passable142
Best
Darkens root120
Nil noted
Nil noted
Corrosion
ISO standard3 Staining
but not likely to
products darken
stain soft tissue
oral soft tissues
Table 1-23 Properties of root-end fillings
MTA, IRM and SuperEBA have had comparable clinical success in the literature, with the bulk of MTA clinical evidence involving MTA-P.203-205 Nevertheless, there is a preference for MTA in root-end fillings.207 This could be attributed to its better biological properties that would instill greater confidence with clinicians for its use.206 As already mentioned, radiopacity is an important feature of dental materials as it enables identification of its placement and marginal integrity. This is of particular importance in root-end filling, where cases with good radiographic density have significant higher healing rates than those with poor density.208 1.4.7.8 Clinical trials of root end fillings 1.4.7.9 MTA vs bioceramics: There are two randomized controlled trials comparing MTA versus bioceramic putty. A prospective randomized controlled study illustrated that at 12 months, MTA and bioceramic putty had statistically similar success rates, 93.1% and 94.4% respectively.209 Success rate was defined as incomplete or complete healing on PAs. A similar study, albeit over 24 months illustrated that MTA had a success rate (incomplete or complete healing) of 95.6% on PAs, 89.3% on CBVTs while bioceramic putties had a success rate of 95.8% on PAs, 88.7% on CBVTs.170 MTA has shown similar success rates when the review period is extended to 3 years(88.8%)210 and 5 years (92.55%171 and 91%204). Of interest, of the 92.55% successful cases at 5 years, 88.1% illustrated complete healing.171 47
There are studies on the success rates of bioceramic putty past two years and no studies on bioceramic flowable putty. 1.4.7.10 Trends in Australia MTA-P is the most common MTA used in Australia, followed by MTA-A.207 Almost all EDs in Australia use MTA, while less than half of GDs in the Australian Society of Endodontology (ASE) use MTA.207 MTA is the material of choice used by EDs for perforations, apexification, apicoectomy and regenerative endodontics.207 For apexifications, ED generally perform a single visit MTA barrier placement, while GDs typically use multiple visits placing CH.207 Most EDs prefer to use NaOCl as their final irrigant prior to MTA placement.207 1.4.7.11 Staining and MTA NaOCl will react with BO to produce a dark brown precipitate. Therefore, if MTA is used in aesthetically important areas, the tooth should be adequately irrigated with saline to remove any NaOCl residues, so that darkening of MTA is reduced.22 Regardless of NaOCl use, darkening of the MTA can still be expected. Therefore, CH should be considered in aesthetic regions where darkening of the tooth would not be acceptable.120 Furthermore, MTA will darken in the presence of blood,211 which is expected for root-end fillings. 1.4.8 Handling MTA 1.4.8.1 Working time As MTA is mixed, water starts to evaporate from the reacting mass as well as being consumed by the setting MTA. Therefore, the workability dramatically changes in a short amount of time. The typical working time is 6 minutes.212 A method that extends the working time is to cover the MTA with wet gauze so that less water will evaporate from the setting MTA. 1.4.8.2 Mixing techniques Most instructions for use for these products stipulate use of 3 parts powder to 1 part water by weight. After mixing, if the working time has elapsed, extra water can be added to make
48
the MTA workable again. MTA can be mixed on a glass slab or on a paper mixing pad. However, paper mixing pads are flimsy, and thus spillage of the mix is more likely to occur. To adjust the wetness of the MTA mix, two sterile cotton rolls can be kept at hand, one dry and one wet. If the mix is dry, squeezing the wet cotton roll will gently release water into the MTA. Alternatively, a small pipette can be used to add droplets of water. If the mixture is too wet, the dry cotton roll can be used to soak up excess water. In an ideal mixture, parts of the mix collected on a flat plastic instrument neither drip off nor crumble away. 1.4.8.3 MTA carriers Amalgam carriers and normal hand instruments can be used for placing MTA for large restorations. Damp cotton pellets held by tweezers are easier to use for compacting MTA than traditional condensing instruments. For smaller restorations, MTA carriers can be used, such as the MTA Carrier, MAP MTA Carrier, or the Dovgan carrier. If excess mixed MTA is left within a carrier at the end of an appointment, the tip is likely to become clogged and unusable. If this occurs, the carrier can be submerged in vinegar (dilute acetic acid) to soften the cement. Sharp-tipped instruments such as probes and K-files can be used to remove the cement from the carrier. 1.4.8.4 Lee block (Also known as “MTA Pellet Forming Block”) Many clinicians prefer to insert MTA into a defect in the form of blocks or pillars. One simple way to shape MTA into such ideal pillars is to use a “Lee Block”.213 This plastic block has bur-sized grooves. Freshly mixed MTA is placed into the grooves, and pillars of MTA can then be lifted out from the base of each groove using a half Hollenback carver or a spoon excavator, for insertion into the tooth. Such blocks can be purchased or self-made using a fissure bur to create the channels. If several grooves are made and loaded with mixed MTA the clinician can quickly insert several pillars into the tooth without interruption. 1.4.8.5 Compacting MTA into a canal Some clinicians use ultrasonic instruments to compress and compact MTA.214 However, if ultrasonic instrument tips are applied for more than 2 seconds, the effect of such vibrations may introduce porosities and disrupt the setting structure, reducing the hardness of the set cement.215
49
1.4.8.6 Syringing bioceramic flowable putty iRoot FS is packaged in a luer-lock syringe. The plastic syringe tip may not reach into cavity preparations. However, the metal tips commonly used for dispensing etch can be used and custom bent216 As the flowable putty has low viscosity, there’s a risk that it may flow out with blood or irrigation and therefore Nasseh advocates a “lid” of normal putty placed on top of the flowable putty.216 The lid technique, advocated by Nasseh, claims that the flowable putty and a similarly packaged sealer are interchangeable.216 However, BC sealer (Total FillBC Sealer, iRoot SP, Endosequence BC Sealer) is more soluble than AH Plus.184 There is no clinical evidence to support the use of either BC flowable putty or BC sealer as a root end filling. The syringe nature of the flowable putty has handling advantages in difficult areas. Clinicians who don’t want to rely on the having a cavity mostly filled with flowable putty may use a method similar to the double mix method of crown impressions. The walls and deepest areas are lined with flowable putty. Normal putty is then placed on top, pushing out excess flowable putty. This method can hypothetically reduce the chance of voids. However, there is no evidence of this having a clinical advantage over the use of normal putty or MTA. 1.4.8.7 Removing MTA from tooth walls Unset MTA can be removed from tooth cavity walls by gentle brushing using cotton pellets or micro-brushes, by gentle irrigation with water, or by using ultrasonic instruments with water spray. Another method is to fabricate a long absorbent brush by twisting a K-file through a cotton roll. 1.4.9 Conclusions The release of calcium hydroxide from MTA as the material sets contributes to the biological properties of MTA. However, because the rate of release diminishes as the setting reaction ends any properties relating to alkalinity are likely to diminish. Variants from the original MTA composition have different properties. The handing of MTA is unique amongst dental materials.
50
1.5
Review of properties and testing methodologies
This subchapter is in press: Ha WN, Nicholson T, Kahler B, Walsh LJ. Mineral trioxide aggregate – a review of properties and testing methodologies. Materials. In press 2017 (accepted 26 Sep 2017). 1.5.1 Introduction Mineral Trioxide Aggregate (MTA) was first described in 1993 as a cement used for its use in repairing lateral root perforations.217 Its composition was described as being primarily a mixture of calcium silicates comprised of calcium oxide (CaO) (50-75% w/w) and silicon dioxide (SiO2) (15-25% w/w).42 Calcium silicates are not particularly radiopaque, and thus a radiopaque agent such as bismuth oxide was then added.42 Since its invention, MTA has been tested under laboratory conditions, then in animal studies and in clinical trials.122, 153, 218
The positive results of these investigations have resulted in MTA becoming a
commonly used material in pediatric dentistry and in endodontics.207, 219 1.5.1.1 Terminology As well as the term MTA, other words have been used to describe these types of materials. The term ‘bioceramics’, which was originally used for a material known as BioAggregate® (Innovative Bioceramix, Vancouver, BC, Canada) has been used for MTAlike cements.51 Despite the differences in terminology, these cements are similar in their elemental compositions.50, 62, 64 BioAggregate contains 38.5% calcium, 11.5% silicon and 10.6% tantalum.50 When converted to their oxide forms using element to stoichiometric oxide conversion, the respective weights of calcium oxide and silicon dioxide would be 53.9% and 24.60%. If tantalum was removed in its oxide form from the whole sample (i.e. 12.9% of Ta2O5, leaving 87.1%), the remaining percentages would be 61.8% CaO and 28.3% SiO2. These values place the material well within the definition of MTA. Another product that is not marketed as MTA but is chemically similar is BiodentineTM (Septodont, Saint Maur des Fosses, France). The elemental composition in 46.3% calcium, 9.8% silicon and 2.7% zirconium. If a similar element to stoichiometric oxide conversion is performed, the remaining cement percentages once the radiopacifier is removed are 67.2% CaO and 21.8% SiO2, values which again place the material within the definition of MTA. If one defines bioceramics as “non-metallic inorganic materials”,53 then this encompasses the powdered components of MTA, as well as zinc phosphate, zinc oxide eugenol and 51
glass ionomer dental cements, materials which do not share many similarities at the chemical level. Hence, this definition of bioceramics has little functional purpose and should not be used. Nevertheless, products which claim to be either MTA or bioceramic sealers have appeared. MTA Fillapex® (Angelus, Londrina, Brazil) is a two-paste system. One paste contains salicylate resin, fumed silica, and bismuth trioxide (as the radiopaque agent), while the second paste contains MTA (40%), fumed silica, titanium dioxide, and 1,3-butylene glycol disalicylate resin.60 Therefore, the composition is predominately salicylate resin, but with some MTA included as an additive. It is not primarily an MTA cement. Likewise, iRoot® SP (Innovative BioCeramix, Vancouver, Canada), is a single component injectable paste that does not contain any water but uses a thickening agent to create a gel-like paste.94 The lack of water for setting reaction puts this material outside the definition of MTA. 1.5.1.2 Performance testing A range of techniques have been used to assess the performance of MTA. The purpose of this paper is to explore the published literature on the testing of MTA and therefore identify key aspects of the testing methodologies used, what insights they reveal as to the behaviour of the material, and what the limitations are of widely used international testing standards and how these relate to clinical performance. Because the performance of MTA is affected by the conditions used in the testing environment, significant concerns arise when standardized testing does not represent physiological or clinical conditions. Typical international standards (ISO) that have been used to assess the properties of MTA comprise: •
ISO 6876, which tests the physical properties of endodontic sealers;3
•
ISO 9917-1, which tests the physical properties of restorative cements;2 and
•
ISO 10993 which tests the biocompatibility of medical devices.4
1.5.2 Aims This review aims to: •
Describe the commonly used ISO tests for MTA;
•
List findings from the literature on MTA using these tests;
•
Identify problems with the methods used for testing MTA; and
•
Suggest alternative testing methods.
52
1.5.3 Methods and materials A PubMed search was undertaken using ‘Mineral Trioxide Aggregate’ combined with the following terms: From testing methods for ISO 6876: •
flow;
•
working time;
•
setting time;
•
film thickness;
•
dimensional change,2 which has been removed in the latest version;
•
solubility; and
•
radiopacity.3
From testing methods for ISO 9917-1: •
setting time;
•
compressive strength;
•
acid erosion;
•
acid-soluble arsenic and lead contents; and
•
radiopacity.2
From testing methods for ISO 10993: •
genotoxicity, carcinogenicity and reproductive toxicity (ISO 10993-3);220
•
cytotoxicity (ISO 10993-5);221 and
•
local effects after implantation (ISO 10993-6).222
From the results, when multiple studies were found, studies which compared MTA products against Super EBA (Harry J Bosworth Co, Skokie, USA), glass ionomer cement, ‘bioceramics’ or AH Plus® (Dentsply DeTrey, Konstanz, Germany) were prioritized. This was done to enable meaningful comparison of MTA against its contemporary alternatives. The results of each search term were reviewed, and the methodologies were considered in light of the known properties of MTA. These properties were grouped as follows: Properties after mixing: •
flow (ISO 6876);
•
working time (ISO 6876);
•
setting time (ISO 6876 and 9917-1); and 53
•
film thickness (ISO 6876).
•
Properties after setting:
•
flow (ISO 6876);
•
dimensional change (ISO 6876);
•
solubility (ISO 6876); and
•
radiopacity (ISO 6876 and 9917-1)
•
compressive strength (ISO 9917-1);
•
acid erosion (ISO 9917-1); and
•
acid-soluble arsenic and lead contents (ISO 9917-1).
•
genotoxicity, carcinogenicity and reproductive toxicity (ISO 10993-3);
•
cytotoxicity (ISO 10993-5); and
•
local effects after implantation (ISO 10993-6).
1.5.4 Results Many of the materials that have been tested using ISO 6876 for endodontic sealers have been indicated for use as an endodontic sealer. These products are henceforth called ‘MTA sealers’, irrespective of whether the material is marketed as an MTA or as a bioceramic. Similarly, many materials that have been tested using ISO 9917.1 for restorative cements are described as ‘MTA restoratives’, irrespective of whether the material is marketed as an MTA or a bioceramic. 1.5.4.1 Properties after mixing The results of tests on MTA restoratives and MTA sealers involving properties after mixing are summarised in Table 1-24. 1.5.4.1.1 Flow This test involves placing sealer on the centre of a glass plate. After waiting for 180 s, a glass plate of placed on top of the dispensed sealer. After 10 min, the diameter of the sealer is to be measured. If the diameter is less than 17 mm, the material does not comply with the standard.3 1.5.4.1.2 Film thickness Sealer is placed on a glass plate. After 180 s, another glass plate is placed on top of the sealer, with a load of 150 N.3 The load needs to compress the sealer such that it
54
completely fills the area between the glass plates. After 10 min, the distance between the two plates is determined, to measure the thickness of the film of sealer.3 1.5.4.1.3 Working time This test is similar to the flow test ISO 6876. Instead of delaying the compression by the glass plates by 180 s, the cement is tested at longer time points, until the specimen diameter is 10% less than the tested diameter at 180 s.3 1.5.4.1.4 Setting time For MTA restoratives, cements are mixed and placed into a mould. An indentation needle with a diameter of 1 mm and a mass of 400 g is placed gently onto the setting cement at progressive time points. If a full circular indentation appears upon placement of the needle, the cement is unset. If the indentation is incomplete, it is deemed as set.2 For MTA sealers, sealers are placed into ring-shaped moulds. Sealers that require moisture to set are placed into a dental plaster mold. The mould is pre-treated by storing it in 95% humidity for 24 h prior to placing the sealer. Sealers that do not require moisture to set are placed into a metal mould.3 Of note, the ANSI/ADA standards for initial and final setting times resemble the ISO 6876 values for initial setting time and ISO 9917.1 for final setting time.2, 3, 74
55
Commercial products
ISO 6876 flow (mm)
ISO 6876 film thickness (µm)
ISO 6876
ISO 6876
ISO 9917.1
working time
setting
setting
(min)
time (min)
time (min)
MTA restoratives BioAggregate Biodentine
1260 224*
6.5
EndoCem MTA MTA Angelus ProRoot MTA
4 6.3-13.6
224,
101
226§
14.2
226†
212*
6
49,
223 87
78
87
8.5-24.3
171-175
225, 227, 228
227, 228
2.5-165
212
45-85.7
225
6.5
223
87,
212, 229
140-284
49,
87, 229, 230
MTA sealers 178*
BioRoot RCS
16
EndoSeal MTA
20.2
52
178†
231
162 iRoot SP MTA Fillapex
23.1 24.9
232
232
22
232
23.9
>1440
232
45
232
232
232‡
or
10080-
4320-6480
14400
233§
233§
66
232
Epoxy resin control AH Plus
17-21.2
178,
232
15-16
178, 232
240
232
690
232
Table 1-24 Properties of MTA restoratives and sealers after mixing *
3
Fails ISO 6876 standard for a minimum of 17 mm; 3 Fails ISO 6876 standard for a minimum of no greater than 50µm; 232 ‡ Performed using accelerated setting conditions; § As greater amounts of water (0-9%) are provided for the setting of iRoot SP, the initial setting time 233 increases from 72 h to 108 h, while the final setting time decreases from 168 h to 240 h. †
1.5.4.2 Properties after setting The results of non-biological tests on MTA restoratives and MTA sealers involving properties after setting are summarised in Table 1-25. The results for acid erosion and acid soluble arsenic and lead contents are not included in Table 1-25 as the studies are few and results are highly variable. The results of non-biological results are not summarised in a table like Table 1-25 because biological tests do not standardize precise cell lines, location for implantation or animals tested. 1.5.4.2.1 Dimensional change (ISO 6876) Materials are mixed and placed in polyethylene molds. Once set, they are removed from the mold and the length measured. After storage in distilled water for 30 days at room 56
temperature, the length is re-measured. To conform with the standard, samples should not exceed 0.1% in shrinkage or 0.1% in expansion.2 Samples that require moisture to set are mixed with 0.02 mL of water per 2 g of material prior to placement into the mold.2 This is a ratio of 0.01 g water: 1 g powder, which does not align with the manufacturer’s recommended ratio of 0.33 g water to 1 g powder. Therefore, MTA cements that are placed into the mold without mixing water will be too dry. To overcome this problem of inadequate water, in one study iRoot SP was tested by being held between two pieces of wet cloth, located between the mold and the glass plates, prior to immersing the mold into water.232 There are no known published results using the ISO 6876 test for dimensional change for MTA restoratives. As iRoot SP is highly soluble,232 the results for dimensional change are difficult to interpret in terms of what may have happened if the cement was not given added water prior to placement in the mold. 1.5.4.2.2 Solubility (ISO 6876) Solubility tests for MTA are performed by placing set samples into distilled water for 24 h to room temperature. Any residue that enters the water is then measured. To conform to the standard, sealers should not be more soluble by more than 3% by mass.3 1.5.4.2.3 Radiopacity (ISO 6876 and ISO 9917-1) A one mm thick sample of MTA placed beside an aluminum step wedge of steps of 0.5 or 1 mm is exposed to X-rays at 65 kV. The radiopacity of the sample is compared to the step wedge, and the equivalent mm thickness of aluminum (mm Al) determined.2, 3 ISO 6876 specifies that sealers must be a minimum of 3 mm Al.3 ISO 9917:2007 requires samples to be stored for no more than seven days before testing.2 1.5.4.2.4 Compressive strength (9917-1) This test involves placing samples within moulds for only one hour prior to testing.2 However, as MTA cements take longer than one hour to set, some consider curing MTA for 24 hours.2, 47 57
This test does not have a method (such as a gypsum mould) which requires diffused ambient water to aid in the setting reaction.2 Therefore, MTA cements that lack mixing water need the intentional addition of water, or otherwise they will not solidify and hence will have no compressive strength.234 Dry-stored and dry-tested ProRoot MTA has a compressive strength of 27 MPa,235 while the reported compressive strengths of MTA cements stored in water have reached 86.2 MPa,236 iRoot FS and iRoot BP, when stored using an accelerated setting method in a hot water bath, have produced compressive strengths of 96 MPa and 177 MPa, respectively.234
There are no known published results using the ISO 9917.1 test for MTA sealers. 1.5.4.2.5 Acid erosion (9917-1) Lactic acid and sodium lactate are added to water to create a demineralizing solution with pH of 2.74. Samples are placed into specimen holders and given 24 hr to set, then removed and immersed in the acidic solution for 24 h. The depth of erosion is the measured.2 There are no known published results using the ISO 9917 test for acid erosion for either MTA restoratives or MTA sealers. 1.5.4.2.6 Acid soluble arsenic and lead contents (ISO 9917-1) Cements are mixed and set for 24 h, then crushed into a powder. Two grams of the powdered cement is then added to 50 mL of HCl, and allowed to stand for 16 h. The solution is then measured for the amount of free arsenic and lead. The maximum permitted content for arsenic and lead is 2 mg/kg and 100 mg/kg, respectively.2 One study found that both ProRoot MTA and MTA Angelus had levels of arsenic levels higher than the safe limit specified by ISO 9917.237 This result was in contrast to another study that reported both cements as having safe limits of arsenic.238 Yet another study found that both ProRoot MTA and Ortho MTA (BioMTA, Seoul, Republic of Korea) had 58
safe levels of arsenic.239 Several studies have reported safe levels of lead in MTA cements.237, 239 There are no known published results for MTA sealers. Commercial products
ISO 6876
ISO 6876
dimensional
solubility
change (%)
(%)
Radiopacifier(s)
ISO 6876 and ISO 9917.1 radiopacity in mm Al
ISO 991.1 compressive strength (MPa)
MTA restoratives Bioaggregate
Ta2O5
Biodentine
4.61
ZrO2 Bi2O3
NeoMTA ProRoot MTA
Ta2O5 0.30
1.1-1.5
1.5-2.8 , 223§ 3.3-4.1 226-228, 240
4.5-5.96
16.34-29.07 223, 236
32,
227, 228†
229
223§
49, 240||
492
0.82-3.7
MTA Angelus
5.0-5.7
67.18-170.8 223, 225
19.63-41.51 225, 227
65
3.8
27
32,
Bi2O3
49, 229
6.4-8.5
49, 229, 241
229
65-86.23
144,
236, 242¶ 234#
iRoot BP
177
iRoot FS
96
234#
22
244
MTA sealers BioRoot RCS EndoSeal MTA iRoot SP
0.21 0.087
231
232*
2.9
MTA Fillapex
-0.67
232
8.3
ZrO2
9.50
ZrO2
3.0-6.68
Bi2O3
6.5-9.4
231
232‡
20.64 1.1
178
ZrO2
184†
180, 231
232‡
5.65-14.89
226, 243
184, 226†
Epoxy resin control AH Plus
-0.034
232
0.060.28
CaWO4, ZrO2
184, 232
6.9-18.4
178, 180,
231, 243
Table 1-25 Non-biological properties of MTA restoratives and sealers after setting *
232
In this study, the ISO test was modified to provide extra water to enable a complete set of iRoot SP. 3 Fails ISO 6876 standard of a maximum of 3%. ‡ The solubility test was modified by submerging the molds into heated water, hence providing more water to enable the complete setting. 223 § Radiopacity was tested at day 1 and day 28 of immersion in Hank’s balanced salt solution; || 3 Fails ISO 6876 standard of a minimum of 3 mm Al; ¶ These samples were cured in wet conditions rather than dry conditions;144, 236, 242 # 234 In this study, the ISO test was modified using an accelerated setting method in a hot water bath. †
59
1.5.4.2.7 Genotoxicity and carcinogenicity (ISO 10993-3) Genotoxicity testing is a series of in vitro and, under some circumstances, in vivo tests involving assessment of gene mutations in bacteria, chromosomal damage in mammalian cells, the mouse lymphoma tk assay and the mammalian cell micronucleus test for chromosomal damage. In vivo tests can include analysis of bone marrow cells or micronuclei in bone marrow or peripheral blood erythrocytes. For carcinogenicity, materials are implanted into tissues and assessed for tumour development.220 Numerous tests unanimously show that ProRoot MTA and MTA Angelus cause little or no DNA damage.245-247 MTA Fillapex has shown greater genotoxicity than MTA Angelus.248 MTA sealers have been modified from the original formulation to alter their handling properties, by adding in various organic (carbon-based) substances. Therefore, MTA sealers should not be assumed to give identical biological responses to the original formulation of MTA. 1.5.4.2.8 Cytotoxicity (ISO 10993-3) The agar diffusion test is a qualitative assessment of cytotoxicity involving culture medium containing serum with melted agar that is compatible with mammalian cells. The specimen is then placed in contact with one-tenth of the cell layer surface, and cytotoxicity is determined from the cellular response after 24-72 hours. A study by Miranda249 using a 5-point cytotoxicity grading system found that ProRoot MTA and Angelus WMTA received grade 1 (slight cytotoxicity). Colorimetric assays measure the activity of enzymes that reduce MTT or similar dyes (XTT, MTS, WSTs) to formazan dyes, giving a purple colour. These assays allow assessment of cell viability and proliferation in cell culture assays, which provide information on whether a material is cytotoxic. Cell viability can be compared against a negative control (a material which does not produce a cytotoxic response). ProRoot MTA that has been freshly mixed i.e. mixed within 1-12 hours, shows cytotoxicity (~50% cell survival)156, 250 while samples of ProRoot MTA and MTA Angelus that have set for 1 day or longer consistently show near 100% cell survival.166, 246, 251-254
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Samples of iRoot FS and iRoot BP Plus, when given 1 week to set166, 251, 255, or even 1 day to set,256 show negligible cytotoxicity, and in this regard, are equivalent to ProRoot MTA. However, fresh samples of iRoot FS show significantly more cytotoxicity than iRoot BP Plus and ProRoot MTA.166 Furthermore, if iRoot BP Plus is compared against ProRoot MTA in an immediate placement model, iRoot BP Plus gives greater cytotoxicity.257 MTA sealers show greater toxicity than AH Plus.258. In a four-week study, MTA Fillapex showed continual cytotoxicity.29, 259 Similarly, iRoot SP showed continual cytotoxicity in a six-week study.233 Both MTA sealers were more cytotoxic than AH Plus over the same testing period.29, 233 1.5.4.2.9 Implantation in subcutaneous and intraosseous tissues (ISO 10993-3) Implantation studies involve placing materials under the skin of rats and in their jaws and then assessing histologically the appearance of the tissues around the material at different points in time.222 ProRoot MTA and MTA Angelus cause initial inflammation, which then subsides over a 30 to 90-day period.260-263 iRoot FS implanted into subcutaneous tissues is more irritating than ProRoot MTA at 1 week and at 3 weeks.167 In contrast, iRoot BP Plus is less inflammatory than ProRoot MTA.168 For MTA sealers, there is no significant difference between iRoot SP and AH Plus.264 iRoot SP causes less severe subcutaneous connective tissue reactions than MTA Fillapex, but more than a conventional MTA cement.187, 265 The MTA sealer Endo CPM Sealer (EGEO SRL, Buenos Aires, Argentina) causes similar reactions to AH Plus, and similar reactions to MTA cements.262 When placed into bone, the initial inflammation elicited by MTA decreases over time.261, 266-271
The trend seen in studies of this type is that there is moderate inflammation at 7
days, mild inflammation at 30 days, and no inflammation from 60 days onward. For placement into bone, the MTA sealers MTA Fillapex showed comparable reactions to AH Plus over 28 days.272 Reactions to iRoot SP were not significantly different to MTA and AH Plus over 60 days.264
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1.5.5 Discussion 1.5.5.1 Properties after mixing 1.5.5.1.1 Flow (ISO 6876) For the ISO test to have an acceptable result, the glass plate above the sealer needs to apply force evenly so that the material shape remains a circle. The operator performing the test is required to balance the glass plate so that the flowing material remains in a circle. The test result is therefore directly affected by the skill and experience of the operator and is subject to bias. The purpose of the delay of 180 s is possibly an attempt to match the time between when the sealer is mixed and used in clinical practice, where the sealer is dispensed upon a mixing pad and then used to coat gutta percha points. However, some sealers are now dispensed using a syringe, the tip of which can be applied within the root canal, which removes any delay. Some newer sealers are water-based, and exposure to air can cause desiccation, resulting in a reduced flow. With such materials, a delay of 180 s is not appropriate. In clinical practice, sealers can be applied in a multitude of ways, including injection by syringe as mentioned above, direct application into the root canal using spiral rotary instruments, and by the manual manipulation of gutta percha points on the bench.273 Each method applies different types and amounts of stress on the sealer which, in turn, alters its viscosity. Sealers are often shear thinning (pseudo-plastic), and show reduced viscosity and increased flow when the shear rate (i.e. the velocity of the sealer against substrates) is increased.232 Rather than measuring how far a material flows under constant pressure over many minutes, changes in its viscosity can be measured with rheometers that apply specific shear forces to the material. This method has greater precision than the ISO flow test and thus is more likely to identify significant differences between samples.232 Furthermore, the application of different shear rates which affects the viscosities has clinical implications. Higher shear rates will lead to lower viscosity of a material and hence increase its ability adapt into voids. However, a low viscosity may also increase the likelihood of periapical
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extrusion. In this case, rapid placement under excessive pressure would increase the probability of periapical extrusion.232 When viscosity has been measured at three different shear strains, under all three testing conditions AH Plus had a lower viscosity than MTA Fillapex, which in turn had a lower viscosity than iRoot SP.232 The advantage of using a rheometer to assess endodontic sealers is that this instrument can measure the viscosity of the material as well as its other important properties such as elastic modulus and storage modulus, recording how these change over time.274 Furthermore, a strong negative correlation exists between flow using the glass plate press method, and viscosity, whereby the greater the flow, the lower the viscosity.274 This is typical of shear thinning behaviour. 1.5.5.1.2 Film thickness (ISO 6876) The ISO test implies that under a particular load, the material should flow in a certain way to produce a specific thickness. However, it does not give guidance as to how a material flows under different loads. This is relevant to endodontics as shear thinning (pseudoplastic) materials will become less viscous under increasing loads, while shear thickening (dilatant) materials will show an increase in viscosity under increasing loads. Endodontic sealers typically exhibit pseudo-plastic properties.232 Therefore, clinicians can apply excess pressure to intentionally force the material to flow into areas that are more difficult to reach. However, Portland cement, and hence MTA cements in general, typically exhibit shear thickening behavior unless substantial admixtures are present.275 MTA cements without such additives will not reliably flow these limited access areas when increased pressure is applied.90 Measuring the shear strain rate versus shear stress can identify whether a material has pseudo-plastic, dilatant, plastic or Newtonian properties. This provides greater clinical information as to which materials flow better when extra pressure is applied.232 As discussed above, using rheology the viscosity and elastic modulus can be measured, particularly as functions of time and temperature.274 1.5.5.1.3 Working time (ISO 6876) The reduction in flow to within 10% of its value does not necessarily correlate with clinical usage of the material, nor does it provide any objective data to assess the handling of the material under clinically relevant conditions of temperature and humidity. 63
Rheological studies can measure viscosity, elastic modulus and storage modulus over time. However, further research is required to determine which points in the elastic modulus curve could best be defined as the working time.274 1.5.5.2 Properties after setting 1.5.5.2.1 Dimensional change (ISO 6876) Although iRoot SP is a hygroscopic cement and will require water for its setting reaction, varying the test methods used with iRoot SP when it is compared to other cements reduces the validity of the results. Both MTA Fillapex and AH Plus absorb some water.28 If these were tested in the same modified way as iRoot SP, their values for dimensional change would likely change. When MTA cements absorb water, they expand.276 When samples are tested, they should not be submerged in water but rather in a buffered saline solution so that there are physiological concentrations of ions, and the testing conditions are more aligned to clinical conditions.32 1.5.5.2.2 Solubility (ISO 6876) MTA is more soluble in distilled water than in isotonic solutions. The ISO test uses hypotonic solutions, which increases the solubility far beyond that in the clinical situation. When MTA is tested in physiological solution, Hank’s balanced salt solution and phosphate buffered solution, BioAggregate, Biodentine and ProRoot illustrated negative values indicating that they had absorbed ions from the environment, rather than an overall loss of mass.49, 223 Hence, the clinical relevance of this method of testing is questionable.277 The test also involves giving cements the opportunity to set for a period of 50% longer than the setting time stated by the manufacturer. Those setting times often utilize ISO 6876, and thus may not reflect whether this material has reached its final hardness. As an example, ProRoot MTA when tested under ISO 6876 has a setting time of 78 min, but when tested under ISO 9917.1 has a setting time of 4 h.87, 230 Allowing a period of 50% may be insufficient if the goal is to test completely set samples. Once fully set, MTA contains calcium hydroxide and can produce some alkalinity after 28 days.154 On this basis, it could be argued that if a completely set material is desired,
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testing the cement should occur after it has aged at least 28 days. For clinical relevance, solubility should be tested immediately after placement. This could involve a slow submergence, at some arbitrary rate, preferably into a physiological solution or into blood. 1.5.5.2.3 Radiopacity (ISO 6876 and 9917-1) There is a wide range of reported values for radiopacity within various cements and some issues around the details of the method for determining radiopacity.278 Minor variations in exposure time, or in target distance within the allowed range of 300-400 mm do not significantly influence the results.279 One could expect minor variations according to the level of curing between samples280 and the type of imaging system used.281 The ISO standards describe the use of an optical density instruments on exposed films.2, 3 Digital imaging enables objective quantification with greater specificity, through the use of grayscale histogram analysis, of greyscales of radiopacity.282, 283 Regardless of the methods used, it seems the most meaningful comparisons are tests that involve several cements within the one study so that direct comparisons can be made between materials, rather than comparisons between studies where more variables are at play.282 Alternatively, a clinically relevant test based on the clinical appearance and usage of MTA in radiographs could be considered,283 possibly in a tissue simulator model with teeth and bone.284 Solubility affects radiopacity with more soluble MTAs illustrating greater loss of radiopacity over time.223 Future studies should assess changes in radiopacity as dissolution occurs. 1.5.5.2.4 Compressive strength (ISO 9917-1) MTA will expand when stored fully immersed in physiological solutions but will shrink when stored in a humid chamber.32 Therefore, it is important to know whether samples are stored dry, stored in a humid chamber, or immersed completely in water or other fluids.235, 285
For assessing compressive strength, most studies in the literature test samples of MTA once the cement has been allowed to age for 21-28 days prior to testing,144, 234, 242 which is a major difference from what is allowed in ISO 9917.2 65
Ideally, MTA should be wet cured, i.e. submerged in a physiological buffer solution, to prevent desiccation of samples, and tested in physiological solution (e.g. phosphate buffered saline), to replicate physiological conditions.79 While there is logic in testing samples that have aged for 304 weeks, there is also value in testing samples at earlier points in time, e.g. 1 day, 1 week and 3 weeks, to track how compressive strength develops over time. At any given point in time after mixing, if a cement has not set, it will have no compressive strength. This information is of value to the clinician. A further point of clinical relevance is exposure to blood. MTA that has been cured in the presence of blood has reduced compressive strength.127 1.5.5.2.5 Acid erosion (ISO 9917-1) This test is suitable for dental restoratives which are exposed to the acids in the oral environment. MTA, whether it be used as a restorative material or as a sealer, is typically located under coronal restorations, and not exposed to the oral environment. The risk of acid erosion from exposure to lactic acid produced by dental plaque biofilm is not a clinically relevant risk. Set MTA has increased solubility in acidic environments, and these conditions may occur wherever inflammation is present.286 As with solubility studies, a more clinically relevant method would be to test samples that have been exposed to weak acids immediately after mixing, rather testing the material once it has cured fully under neutral pH conditions. 1.5.5.2.6 Acid soluble arsenic and lead contents (ISO 9917-1) The results of the ISO test for acid soluble arsenic and lead content show inconsistent patterns of results. This may be due to differences in types of acids and concentrations used, as well as variations in exposure time to those acids.239 Variations in the results can also be caused by how the samples are prepared by grinding them into powder using a mortar and pestle. Materials of different hardness will be ground to different fineness, and hence will have a different surface area. This will affect how much heavy metals can be leached out from exposure to acid. The clinical relevance of this test is questionable since MTA is not exposed to the occlusion where it can undergo attrition, or be exposed to strong acids. Biological response tests, such as implantation studies, are of greater clinical relevance. There is no direct relationship between the concentration of arsenic found in MTA and the associated inflammatory response in the tissues.287 66
1.5.5.2.7 Genotoxicity and carcinogenicity (ISO 10993-1) The current panel of tests which use bacterial and mammalian cells in culture may not represent what happens in human tissues. Implantation tests in animals are more relevant, but may not be practicable for assessing long term safety issues such as carcinogenicity. 1.5.5.2.8 Cytotoxicity (ISO 10993-5) The cytotoxicity of MTA cement is affected by several variables, including storage time and storage media. The key consideration is the release of calcium hydroxide from the cement as it is setting. Initially, the speed of the setting reaction is high, and cytotoxic effects are seen from released calcium hydroxide. As the material reaches its final set, much of the alkalinity is lost and hence there is less cytotoxicity.154 Therefore, any test method where the MTA sample is fully set and then is placed into a culture or against tissues is not reflective of the clinical use of the material. On the other hand, putting freshly mixed MTA cement directly into a cell culture well will likely result in the disintegration of the material, giving greater alkaline effects from the calcium oxide components of the Portland cement. Similar considerations would apply to sealers, but with the caveat that the viscosity modifiers used in these could also affect cell viability.259 An alternative method would be to place freshly mixed MTA immediately into a simulated root-end filling that is then exposed to the testing culture.257 This prevents the disintegration of the MTA. Cytotoxicity tests employ short testing periods of typically 1-3 days. This will not identify concerns of sustained toxicity due to slow dissolution or degradation over time. This is especially important for MTA sealers which have high solubility.259 These materials should be tested over longer periods of time. Samples can be prepared, placed into a simulated root-end filling, allowed to cure in water for 1, 2 or 3 weeks, and then placed into cell culture. 1.5.5.2.9 Implantation in subcutaneous tissues and intraosseous tissues (ISO 10993-6) Results from subcutaneous implantation are considered of less relevance than those from intraosseous implantation since the clinical usage of MTA is within osseous structures. When interpreting the results of inflammation in implantation studies, it is important to understand that, as stated by Sumer,260 “when assessing the biocompatibility of a material, later harmful effects are considered to be more important than its initial effects.” The initial inflammation is partly due to the trauma of the surgical procedure to implant the material, 67
and partly due to the material itself. Review periods should account for this, and use longer intervals such as 7 days, 30 and 60 days. Although animal biocompatibility studies are considered superior to cell culture studies, it must be remembered that a material which appears to be well tolerated and which does not elicit intense inflammation may have inferior physical properties, such as high solubility or shrinkage, which compromise its performance. Studies using larger animals, e.g. beagle dogs, where MTA is placed into root-end fillings in a location where apical periodontitis has been induced, provide a method of assessing osseous healing. This is an important consideration as it goes beyond the inflammatory response. Furthermore, the use of larger animals in this manner enables not only histological assessment as per ISO 10993-6 but also the radiographic assessment of healing. However, large animal welfare can prohibit such studies being undertaken.288 1.5.6 Conclusion MTAs can be separated into two main types, MTA restoratives and MTA sealers, and feature products which are often marketed as bioceramics. These endodontic bioceramics, as with MTA, fall under the categories of MTA restoratives and MTA sealers. The results for ISO tests used for testing MTA can be biased by curing method of the MTA. MTA should be cured in a way that represents the clinical usage of the material. This typically involves immediate placement and immediate testing of samples rather than curing the cement outside of testing conditions.
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Chapter 2
How do paediatric dentists use MTA?
This chapter presents a survey of MTA usage by PDs and GD members of the ANZSPD. Although there is literature supporting the use of MTA in pulp capping and pulpotomy, within paediatric dentistry MTA is used predominately for primary molar pulpotomies. Alternative dental materials are chosen for other clinical scenarios. Although cost may contribute to the selection of alternative materials, it is known that MTA stains anterior teeth, a point that may lead clinicians to prefer alternatives such as CH. This chapter has been published as: Ha WN, Kahler B, Walsh LJ. Dental material choices for pulp therapy in paediatric dentistry. Eur Endod J; 2017, 2017; 2:1-7. 2.1
Introduction
MTA has been advocated for various paediatric dental indications such as vital pulp therapy and pulpotomy in primary and permanent teeth.153 When MTA is used in permanent teeth, there is a 97.6% success rate for DPCs,289 and a 79% success rate for pulpotomies.290 In primary teeth, the corresponding success rates are 100% for DPCs291 and 97% for pulpotomies.292 Despite these high success rates, MTA is not widely used. The high cost of the material is considered to be the major barrier to its use in clinical practice.97 However, it is also possible that lack of knowledge regarding how to use MTA could be another significant issue. The extent of teaching on the use of MTA has been limited. In 2009, across the UK and Ireland, only 2 of 14 postgraduate paediatric dentistry departments taught the use of MTA for pulp therapy in primary molars.293A similar study in the UK in 2005 of 13 dental schools reported that CH was used routinely for pulp capping, and FeSO4 for pulpotomy, with only one school teaching the use of MTA as an alternative material.8 In Europe, use of MTA is becoming more widespread as training in the use of the material has extended further. A 2013 survey of 29 postgraduate departments in Europe reported that 6 used MTA for pulp capping and 17 used MTA for pulpotomy.7 There is no published data on the use of MTA in paediatric dentistry in Australia or New Zealand. Accordingly, the aim of the present study was to assess the use of MTA by members of the Australian and New Zealand Society of Paediatric Dentistry (ANZSPD). This society is composed of both GDs with an interest in paediatric dentistry as well as 69
PDs. The study examined the choices of clinicians and assessed how well patterns of clinical use of MTA aligned with the scientific literature, focusing on pulp capping and pulpotomy, grouping both partial and complete pulpotomy into the one category. 2.2
Methods
The national office of the ANZSPD distributed information regarding a survey to all society members on November 28th of 2014 and this was followed by a reminder email sent on April 15th April 2015. The survey was conducted online using www.surveymonkey.com. The final response was received on the 21st of May 2015. The survey sought information from respondents on: •
whether the respondent was a GD, PD, or a dentist undergoing speciality training in paediatric dentistry;
•
material handling and placement preferences;
•
education and training received on MTA; and
•
preferences for materials used for IPCs, DPCs and pulpotomy in anterior and posterior primary and permanent teeth.
For each survey question, respondents were supplied with a menu of options, including an “other” option to enable short written responses. If the “other” was a listing of single responses, the first single response replaced their response. If their “other” response was equivalent to another single response, their answer was grouped with that single response. The least popular responses (i.e.