JOURNAL TRANSCRIPT

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Periodontal ligament

The periodontium The periodontium includes: The gingiva Cementum Periodontal ligament Alveolar bone

Def: The periodontal ligament is the dense fibrous connective tissue that occupies the periodontal space between the root of the tooth and the alveolus.

The periodontal ligament characterized by: 1- The highest rate of turnover in the body. 2- Large volume of ground substance. 3- The presence of oxytalen fibers. 4- High cellularity.

Width of the periodontal ligament: It ranges from 0.15-0.21 mm. The region at the alveolar crest is the widest followed by the (apical region) and the narrowest area is at Fulcrum (midroot)

The space is reduced in non-functional and unerupted teeth, Bone

Dentin while is increased in teeth subjected to heavy occlusal stress and in deciduous teeth

Development of periodontal ligament •The periodontal ligament originates from the progenitor cells of the dental sac surround the enamel organ just after root formation. •The innermost cells differentiate into cementoblasts and lay down cementum. •The outermost cells differentiate into osteoblasts and lay down bone. •The centrally located cells differentiate into fibroblast that produce collagen fibers of the P.L that their ends embedded inside the cementum & bone .

Histological structure The periodontal ligament is formed of: 1- Cells Synthetic

2- Intercellular substances 3-Fibers,

Resorpative Progenitor Defensive Epithelial

4- ground substances 5- blood vessels, nerves & lymphatic.

The cells Synthetic cells

fibroblasts, osteoblasts ,cementoblasts.

Resorptive cementoclasts , osteoclasts, fibroblasts. cells

Progenitor undifferentiated mesenchymal cells (Stem Cells) cells epithelial cells remnants of the epithelial Defensive macrophage, root sheath of Hertwig lymphocytes and cells mast cells

- Epithelial rests of Malassez: **deeply stained cuboidal cells surrounded by basal lamina.

** They may proliferate to form cysts or tumors.

II- The fibers *The fibers of the periodontal ligament are mainly collagen. They are divided into: A) The principal fibers. B) The accessory fibers. C) The oxytalan fibers.

*Elastic fibers are restricted almost entirely to the walls of blood vessels.

A- The principal fibers of periodontal ligament are formed of collagen bundles, which are wavy in course and are arranged mainly in three ligaments. a) Gingival ligament. b) Transseptal or interdental ligament. c) Alveolodental ligament which is subdivided into the following five groups: 1- Alveolar crest group. 2- Horizontal group. 3- Oblique group. 4-Apical group. 5- Interradicular group.

1- The principal fibers: a- The gingival ligament: 1- Gingival fibers: extend from the cervical cementum into the lamina propria of the gingiva. 2- Alveologingival group: extends from the alveolar crest into the lamina propria.

Dentogingiva l Circular fibers

3- Circular group: a small group of fibers that encircles the tooth and interlaces with the outer fibers & bone. 4- Dentoperiosteal fibers: they extend from the cementum direct over the crest of the alveolar bone then inserted in periosteum of the labial surface of the alveolar bone.

Dentoperiosteal

Alveologingival

Gingival fibers form a rigid cuff around the tooth that can add stability.

b- The Transseptal fibers: *It connects two adjacent teeth so it is called interdental group of fibers. *The ligament runs from the cementum of one tooth over the crest of the alveolus to the cementum of the adjacent tooth. * Responsible for the mesial shift of the teeth.

Dentin

Bone

Dentin

Transseptal Fibers

c- The alveolodental fibers: 1-Alveolar crest group: radiate from the crest of the alveolar process and attach themselves to the cervical part of the cementum. 2-Horizontal group: The fiber bundles run from the cementum to the bone at right angle to the long axis of the tooth.

Bone

Dentin

3- Oblique group: The fiber bundles run obliquely. Their attachment in the bone is somewhat coronal than the attachment in the cementum. It is the greatest number of fiber bundles found in this group. They perform the main support of the tooth against masticatory force.

bone dentin

4- Apical group: The bundles radiate from the apical region of the root to the surrounding bone. 5- Interradicular group: The bundles radiate from the interradicular septum to the furcation of the multirooted tooth.

dentin

bone

dentin

bone

a l v e o l o d e n t a l

P r i n c i p l e f i b e r s

B- Accessory fibers: It is collagenous in nature and run from bone to cementum in different planes, more tangentially to prevent rotation of the tooth and found in the region of the horizontal group.

C- Oxytalan fibers These are immature elastic (pre-elastic) fibers. They need special stains to be demonstrated. They tend to run in an axial direction, one end being embedded in bone or cementum and the other in the wall of blood vessels.

The function of the oxytalan fibers has been suggested that they play a part in supporting the blood vessels of the periodontal ligament during mastication i.e., it prevents the sudden closure of the blood vessels under masticatory forces.

Interstitial tissue It is found between the fibers of the periodontal ligament. They are areas containing some of the blood vessels, lymphatics and nervs and surrounded by loose connective tissue.

Blood supply The arterial blood supply of the periodontal ligament is derived from 3 sources: 1- Branches from the gingival vessels. 2- Branches from the intra-alveolar vessels, these branches run horizontally and these constitutes the main blood supply.

3- Branches from the apical vessels that supply the dental pulp.

Nerve supply: The nerve supply of periodontal ligament comes from either the inferior or superior dental nerves. 1- Bundles of nerve fibers run from the apical region of the root towards the gingival margin. 2- Nerves enter the ligament horizontally through multiple formatina in the bone.

Small fibers

pain sensation mechanoreceptors

large fibers

touch & pressure

Functions of the periodontal ligament:

1- Supportive: *periodontal ligament permits the teeth to withstand the considerable forces of mastication. *As the force is applied on the teeth, the wavy course collagen fibers are transmitting tension to the wall of the alveolus instead of pressure. *Also periodontal fibers being non elastic to prevent the tooth from being moved too far.

2- Sensory: • The periodontal ligament having the mechanoreceptor contributes to the sensation of touch and pressure on the teeth.

sudden overload

proprioceptive reflex inhibition of the activity

of the masticatory muscles

Opening the mouth

3- Nutritive: The blood vessels in the periodontal ligament provide nutrient supply required by the cells of the ligament and to the cementocytes and the most superficial osteocytes.

4- Formative: The fibroblasts are responsible for the formation of new periodontal ligament fibers and dissolution of the old fibers Cementoblasts and osteoblasts are essential in building up cementum and bone.

5- Protective: The protective function of the periodontal ligament is achieved by: a- The principal fibers. b- The blood vessels. c- The nerves. a- The principal fibers: The arrangement of the fiber bundles in the different groups is well adapted to fulfill the functions of the periodontal ligament. The alveolodental ligament transforms the masticatory pressure exerted on the tooth into tension or traction on the cementum and bone. If the exerted force on a tooth is transmitted as pressure this will lead to differentiation of osteoclasts in the pressure area and resorption of bone.

b- The blood vessels: The capillaries form a rich network, they are arranged in the form of a coil and attached to bone and cementum through the oxytalen fibers. This arrangement makes it possible when pressure is exerted on the tooth, the blood does not escape immediately from the capillaries and thus buffering the pressure action before it reaches the bone. The behavior of the blood in the capillaries may be simulated to a hydraulic brake. c- The nerves: By its mechanoreceptors nerves.

Age Changes of periodontal ligament The periodontal ligament through aging shows

• Vascularity • Cellularity • Thickness *It may contain cementicles.

The cementicles appear near the surface of cementum may be free , attached or embedded in the cementum. They have nidus favoring the deposition of concentric layers of calcospherite as degenerated cells,

area of hemorrhage and epithelial rest's of Malassez. Cementicles are usually seen in periodontal ligament by aging but in some cases they may be seen in a younger person after local trauma.

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