Tissue of the teeth Periodontium (cont.) Dr Jamal Naim PhD in Orthodontics Periodontium (cont.)

Fibers

Fibers 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.

Principal fibers They are present in a wavy course and arranged in 3 ligaments: Alveolo-dental ligament Gingival ligament Transeptal (interdental) ligament!!!

Alveolo-dental ligament Fiber bundles running between tooth and alveolar bone are termed alveolo-dental and can be subdivided in: Alveolar crest group Horizontal group Oblique group Apical group Interradicular group

Alveolo-dental ligament

Alveolar crest group The fibers radiate from the crest of alveolar process (lower level) to attach cervical part of cementum (higher level). cementum

Horizontal group The fibers run from cementum to bone with perpendicular angle to the long axis of the tooth cementum

Oblique group They 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

Apical group They radiate from the apex of the root to the surrounding bone.

Interradicular group They radiate from crest of interradicular septum to the area of bi- or trifurcation.

Gingival ligament The 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 group Alveologingival group Circular group Dentoperiosteal group Transseptal group

Dentogingival group The most numerous fibers in this group radiate from the cervical cementum into the lamina propria of the free and attached gingiva.

Alveolo-gingival group The fibers radiate from the bone of he alveolar crest and extend into the lamina propria of the free and attached gingiva.

Circular group This 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

Dentoperiosteal group Running apically from the cementum over the periosteum of outer cortical plate of the alveolar process to insert in it.

Transseptal group The 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.

Transseptal group

Transseptal group

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.

Oxytalan fibers They 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.

Oxytalan fibers

Oxytalan fibers

Oxytalan fibers The function of the oxytalan fibers is thought to be the regulation of the vascular flow in relation to tooth function.

Ground substance The 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.

Ground substance The ground substance has many important functions: Ion, water and growth factors binding and exchange, Control of collagen fibrilogenesis and fiber orientation.

Ground substance Tissue 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.

Ground substance The ground substance also contains inhibitors of the mineralization process that explain why the PDL width remains constant between two mineralized tissues (bone and cementum).

Blood supply The 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.

Blood supply From 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.

Blood supply They course in an apical-occlusal direction with numerous transverse connections. coronal The thickened venous network at the apex apical

Blood supply Other sources for blood supply in the PDL are: Branches from the gingival vessels Branches from the apical vessels that supply the dental pulp

Blood supply Blood supply of the PDL from the gingival and intra-alveolar branches

Nerve supply All 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.

Nerve supply The regional variation occurs in the termination of the neural elements. The apical region contains more nerve endings than elsewhere, except the upper incisor.

Nerve 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.

Nerve supply The 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.

Nerve supply The 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.

Function of the PDL The 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.

Function of the PDL It 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.  

Function of the PDL It 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

Function of the PDL Undifferentiated 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.

Function of the PDL The periodontal ligament also serves a sensory function. The periodontal ligament provides a nutritive function that maintains the vitality of its various cells.