3Fibers The predominant collagens of the PDL are type I, III and XII. Those types have a short half-life and means that they have less time for fibrilar assembly.The fiber bundles are able to adapt to continual stress placed on them through continual remodeling.
4Principal fibersThey are present in a wavy course and arranged in 3 ligaments:Alveolo-dental ligamentGingival ligamentTranseptal (interdental) ligament!!!
5Alveolo-dental ligament Fiber bundles running between tooth and alveolar bone are termed alveolo-dental and can be subdivided in:Alveolar crest groupHorizontal groupOblique groupApical groupInterradicular group
7Alveolar crest groupThe fibers radiate from the crest of alveolar process (lower level) to attach cervical part of cementum (higher level).cementum
8Horizontal groupThe fibers run from cementum to bone with perpendicular angle to the long axis of the toothcementum
9Oblique groupThey run obliquely from bone (higher level) to cementum (lower level).They form a major part of alveolo-dental ligament.They support the tooth against (vertical) masticatory forces.cementum
14Gingival ligamentThe fiber bundle passes from cementum to interlace with gingival fibrous tissue at the level of free and attached gingival and can be subdivided into:Dentogingival groupAlveologingival groupCircular groupDentoperiosteal groupTransseptal group
15Dentogingival groupThe most numerous fibers in this group radiate from the cervical cementum into the lamina propria of the free and attached gingiva.
16Alveolo-gingival group The fibers radiate from the bone of he alveolar crest and extend into the lamina propria of the free and attached gingiva.
17Circular groupThis small group forms a band around the neck of the tooth, interlacing with other groups of fibers helping to bind the free gingiva to the tooth
18Dentoperiosteal group Running apically from the cementum over the periosteum of outer cortical plate of the alveolar process to insert in it.
20Transseptal groupThe fibers run interdentally from the cervical cementum of one tooth over the alveolar crest and insert into a comparable area of the cementum of the neighboring tooth.This group is also termed: interdental/transseptal ligament.
28Accessory fibersIt 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.
29Oxytalan fibersThey are bundles of elastic fibers which run vertically in the PDL.They run from the cementum downward to the walls of arteries, veins and lymphatics.They form a three dimensional network and are associated with neural elements.In the cervical region they are dense and run parallel to the gingival group of fibers.
32Oxytalan fibersThe function of the oxytalan fibers is thought to be the regulation of the vascular flow in relation to tooth function.
33Ground substanceThe space between the cells, fibers, blood vessels and nerves in the PDL is occupied by ground substance.It is made up of water (70%) and two major groups of substances, proteoglycans and glycoproteins.
34Ground substance The ground substance has many important functions: Ion, water and growth factors binding and exchange,Control of collagen fibrilogenesis and fiber orientation.
35Ground substanceTissue fluid pressure has been found to be high in the PDL (being 10 mm Hg above atmospheric pressure) and this has been implicated in the tooth support, withstanding stress loads and eruptive mechanisms.
36Ground substanceThe ground substance also contains inhibitors of the mineralization process that explain why the PDL width remains constant between two mineralized tissues (bone and cementum).
37Blood supplyThe PDL is exceptionally well vascularized connective tissue. This reflects the high turnover of its cellular contents.The maim blood supply is from the inferior and superior alveolar arteries, which are branches of the maxillary artery.Those arteries give off the interalveolar branches.
38Blood supplyFrom those branches numerous branches run horizontally to perforate the alveolar bone and enter the PDL space.Because they enter the ligament through the alveolar bone, they are termed the perforating arteries.They are more abundant in posterior teeth than anterior teeth and more in the gingival and apical region than in the middle region.
39Blood supplyThey course in an apical-occlusal direction with numerous transverse connections.coronalThe thickened venous network at the apexapical
40Blood supply Other sources for blood supply in the PDL are: Branches from the gingival vesselsBranches from the apical vessels that supply the dental pulp
41Blood supplyBlood supply of the PDL from the gingival and intra-alveolar branches
42Nerve supplyAll nerves that innervate the PDL are branches from the trigeminal nerve. The architecture of the nerve supply is applicable for all teeth:Nerve fibers that run from the apical area toward the gingival margin. Other Nerve fibers enter the PDL from the foramina of the alveolar wall to join the first group.
43Nerve supplyThe regional variation occurs in the termination of the neural elements. The apical region contains more nerve endings than elsewhere, except the upper incisor.
45Nerve supply There are four types of neural terminations: Treelike terminations of free nerve endings. They are the most frequent type and are located in regular intervals along the length of the root, suggesting that each one controls its own territory and extend to the cementoblast layer. They are largely from unmyelinated fibers. They are thought to be mechanoreceptors and nociceptors.
46Nerve supplyThe second type of nerve terminals is found around the root apex and resemble ruffini's corpuscles. The appear dendritic and end in terminal expansions among the fiber bundles. Their function is thought to be mechanoreceptors.
47Nerve supplyThe third type of endings is a coiled form found in the mid region of the PDL.The fourth type consists of spindle like endings and are found associated with the root apex. The are the less frequent group.
48Function of the PDLThe periodontal ligament serves primarily a supportive function by attaching the tooth to the surrounding alveolar bone proper. This function is mediated primarily by the principal fibers of the periodontal ligament.
49Function of the PDLIt also serves as a shock-absorber by mechanisms that provide resistance to light as well as heavy forces:Light forces are cushioned by intravascular fluid that is forced out of the blood vessels. Moderate forces are also absorbed by extravascular tissue fluid that is forced out of the periodontal ligament space into the adjacent marrow spaces.The heavier forces are taken up by the principal fibers.
50Function of the PDLIt also serves a major remodeling function by providing cells that are able to form as well as resorb all the tissues that make up the attachment apparatus, i.e. bone, cementum and the periodontal ligament
51Function of the PDLUndifferentiated ectomesenchymal cells, located around blood vessels, can differentiate into the specialized cells such as osteoblasts, osteoclasts, cementoblasts, cementoclasts and fibroblasts.Bone- and tooth-resorbing cells are generally multinucleated cells derived from blood-borne macrophages.
52Function of the PDLThe periodontal ligament also serves a sensory function.The periodontal ligament provides a nutritive function that maintains the vitality of its various cells.