Defensive macrophage, lymphocytes and cells mast cellsepithelial cells remnants of the epithelial root sheath of Hertwig
Extracellular substances The fibers of the periodontal ligament are . mainly collagen :They are divided into .A) The principal fibers .B) The accessory fibers .C) The oxytalan ( elastic ) fibers
.a) Gingival fibers.b) Transseptal or interdental ligamentc) Alveolodental ligament which is subdivided into the:following five groups. Alveolar crest group- 1. Horizontal group- 2. Oblique group- 3. Apical group- 4. Interradicular group- 5
1- Dentogingival group : extend from the cervical cementum into the lamina propria of the gingival.2- Alveologingival group: extends from the alveolar crest into the lamina propria.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 and then incline apically between the periosteum of the alveolar bone to the lamina propria of the gingiva.
Functions of the gingival fibersThey hold the marginal gingiva against the tooth .They provide the marginal gingiva with enoughrigidity to withstand the forces of masticationwithout distorting .
*It connects two adjacent teeth.*The ligament runs from the Denti cementum of one tooth over the n crest of the alveolus to the cementum of the adjacent tooth. Bone Dentin
1-Alveolar crest group: radiate from the crest of the alveolar process and attach to the cervical part of the cementum.2-Horizontal group: Bone DentinThe fiber bundles run from the cementum to the bone at right angle to the long axis of the tooth.
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 bone fiber bundles found in this group. dentinThey perform the main support of the tooth against masticatory force.
4- Apical group: denti nThe bundles radiate from the apical region of the root to the surrounding bone. bone5- Interradicular group:The bundles radiate from the interradicular septum to the denti furcation of the multirooted n tooth. bone
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.
Oxytalan Fibers Immature elastic fibers. Run in axial or oblique direction. One end being embedded in cementum or bone and the other end in the wall of b.v. 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.
Some of the b.vs., lymphatics, and nerves of the PDL are surrounded by loose C.T. These areas have termed interstitial tissue. Fibroblasts histiocytes, UMC, and lymphocytes are also found in interstitial tissue. Biological significance: unknown.
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 constitue the main blood supply. 3- Branches from the apical vessels that supply the dental pulp.
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
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 of the collagen fibers gradually straightening out *Also periodontal fibers being non elastic prevent the tooth from being moved too far.
The periodontal ligament having the mechanoreceptor contributes to the sensation of touch and pressure on the teeth.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 theformation of new periodontal ligament fibersand dissolution of the old fibers Cementoblasts and osteoblasts are essential inbuilding up cementum and bone.
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 form of a coil and attached to bone and cementum through the oxytalan 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.c- The nerves:By its mechanoreceptors nerves.
*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 calcosphrite as degenerated cells, area of hemorrhage and epithelial rests 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.