Periodontal Ligaments PDF

Periodontal ligaments (PDL) By dr. Sally Sakr  Periodontal Ligaments “PDL” Definition: The periodontal ligament (PDL) is a soft, specialized dense fibrous connective tissue that is noticeably cellular & vascular. It is covering the root of the tooth & the bone forming t...

Periodontal ligaments (PDL) By dr. Sally Sakr  Periodontal Ligaments “PDL” Definition: The periodontal ligament (PDL) is a soft, specialized dense fibrous connective tissue that is noticeably cellular & vascular. It is covering the root of the tooth & the bone forming the socket wall. “alveolar bone”.  Width of Periodontal Ligament: The thickness of the PDL varies in different individuals , in different teeth in the same person, and different locations on the same tooth. Generally, its width ranges from 0.15 to 0.38 mm. It is widest at its cervical & apical extremities, and narrowest at the mid-root region. With advancing age, the thickness of the PDL decreases mainly due to increased amount of cementum formation.  Development of the periodontal ligament Development of the periodontal ligaments occurs in association with the development of the root. It developed from cells of dental follicle  to fibroblasts which synthesize the fibers and ground substance. At the onset of the ligament formation, its space consists of unorganized connective tissue with short fibers bundles extending into it from the bone and cemental surfaces.  Development of the periodontal ligament Next, ligament cells secrete collagen type 1 which assembles as collagen bundles extending from bone to cementum and secure tooth attachment. Also, several non-collagenous proteins are secreted and play a role in maintaining the PDL space. Development of the periodontal ligament Development of the periodontal ligament Eruption as well as tooth reaching occlusion will modify the PDL initial attachment. Before tooth erupts, the crest of alveolar bone above CEJ and developing fiber bundles are directed obliquely root wise.  Development of the periodontal ligament With eruption, the level of the alveolar crest coincide with CEJ, and fiber bundles become horizontally aligned. When tooth in occlusion, the alveolar crest is apical to CEJ, and the alveolar crest fiber group is oblique, in coronal direction, opposite to the beginning. Structure of the PDL The periodontal ligament consists of: 1. Cells (fibroblasts, osteoblasts, osteoclast, cementoblast , epithelial cell of Malassez , macrophages, undifferentiated mesenchymal cells, stem cells). 2. Extracellular matrix made of ( fibers & ground substance ). 3. Also, the PDL contains neurovascular elements comprising nerves , blood vessels & lymphatics. 4. Cementicles may be present in PDL.  I. Cells of the PDL 1. Fibroblast. 5. Epithelial cell of Malassez. 6. Macrophages. 2. Osteoblast. 7. Undifferentiated mesenchymal 3. Osteoclast. cells. 4. Cementoblast. 8. Stem cells.  Fibroblasts The principal cells of PDL, characterized by high rate of turnover of proteins “in particular collagen”. Fibroblasts are large cells with an extensive cytoplasm containing an abundance of organelles associated with protein synthesis ( REE, Golgi complex, and many secretory granules). It appears as ovoid or elongated cells oriented along the principal fibers , exhibiting pseudopodia like processes.  Fibroblasts PDL fibroblasts have a well-developed cytoskeleton with prominent actin network for the cell to change shape and migration. Fibroblast’s contractility has a great significance through functional movement during mastication, accommodation of jaws growth, and compensation of occlusal and proximal wear. Actin filaments in fibroblast  Fibroblasts Fibroblasts and the collagen align parallel to the direction of the principal strain in the matrix lead to high ordered arrangement of bundles. Because of high rate of turnover of collagen in PDL, any interference with fibroblast function by a disease  rapidly produce loss of the supporting tissues of a tooth. Fibroblast/Fibroclast & possibly functional pathways  Fibroblasts Fibroblasts respond to change in tension and compression in the matrix, by formation or resorption of bone and cementum. Bone formation Bone resorption  Fibroblasts Bone formation Bone resorption  Osteoblasts: They appear as cuboidal cells having large nuclei and abundant cytoplasm. They differentiate from the dental follicle cells. They are found on the periodontal surface of the alveolar bone. They are rich in alkaline phosphatase (ALP) activity.  Cementoblasts: They appear as cuboidal cells having a distribution on the cementum surface similar to the distribution of osteoblast cells on the bone surface. They differentiate from the mesenchymal cells of the tooth follicle.  Resorptive cells of PDL Osteoclasts. Cementocasts. Both are rich in acid phosphatase (TRAP) activity.  Epithelial cell rest of Malasses There are epithelial cells in the PDL that are remnants of the root sheath of Hertwig form discrete masses surrounded by a basement membrane close to cementum. They persist as a cluster, strands, or tubule- like structure near and parallel to the surface of the root ,easily recognized in H&E stains by deeply stained nuclei.  Epithelial cell rest of Malasses The epithelial rests appear as small clusters of epithelial cells which are located in the periodontal ligament adjacent to the surface of cementum. They are cellular residues of the embryonic structure known as Hertwig's epithelial root sheath. Epithelial cell rest of Malasses Epithelial cell rest of Malasses Epithelial cell rest of Malasses  Progenitor cells All connective tissues including PDL contain progenitors' cells that have the capacity to undergo mitotic division. They are the undifferentiated mesenchymal cells that have a perivascular location within 5 micrometres of blood vessels. When stimulated appropriately, these cells undergo mitotic division and can differentiate into fibroblast , osteoblast or cementoblast. STEM CELLS: Pluripotent stem cells are present in PDL, which easily accessible than those found in pulp. These postnatal mesenchymal stem cells have the capacity of self renewal and have the potential to differentiate into any type of cells. Defensive cells of PDL 1. Macrophage 2. Mast cells 3. Lymphocytes II. Extracellular matrix of the PDL The extracellular substance of the PDL comprises the following: A. Fibers B. Ground substance 1. Collagen fibers 1. Proteoglycans “glycosaminoglycan-protein 2. Oxytalan fibers complex”. 3. Elastic fibers 2. Glycoproteins. 4. Elaunin fibers  A. Fibers: 1. Collagen Fibers: The predominant collagens of PDL are type I, type III and XII with individual fibrils having smaller diameter than tendon’s collagen fibrils. This difference is thought to reflect the short half- life of ligament collagen and less time for fibrillar assembly “remodellig. Most collagen fibrils in PDL arranged in definite & distinct fiber bundles each bundle resembles a spliced rope.  1. Collagen Fibers: Individual strands can be remodelled continually , whereas the overall fiber maintains its architecture & function. In this way the fiber bundles are able to adapt to the continual stresses placed on them. “functional adaptation” Principal fibers of periodontal ligament  Principal fibers of periodontal ligament Principal fibers of periodontal ligament are arranged in 5 particular groups: 1. Alveolar crest group 2. Horizontal group 3. Oblique group 4. Apical group 5. Interradicular group  Principal fibers of periodontal ligament 1. Alveolar crest group : Attached to cementum just below cementoenamel junction and running downward & outward into rim of the alveolus. These fibers limit vertical & intrusive movement. 2. Horizontal group : Attached just apical to alveolar crest group & running at right angles to the long axis of the tooth from cementum to bone. These fibers resist horizontal & tipping forces.  Principal fibers of periodontal ligament 3. Oblique group : The most numerous in PDL & running from cementum in an oblique direction to insert into bone coronally. These fibers resist vertical &intrusive forces. 4. Apical group: Radiating from cementum around the apex of root to bone, forming the socket base. These fibers resist vertical forces.  Principal fibers of periodontal ligament 5. Interradicular group: only between roots of multirooted teeth & running from cementum to bone of the crest of interradicular septum. These fibers resist vertical & lateral movements.  Attachment of Collagen Fibers: At each ends, all the principal fibers of the PDL are embedded in cementum & alveolar bone and the embedded portion referred to as “Sharpey's fibers ”.  Sharpey's fibers Colored enhanced Scanning electron micrograph showing cementoblast in between the collagen fibers Transmission electron micrograph (TEM) showing embedded in the AEFC to form the sharpey’s fibers cementoblast (Cb), cementoid , sharpey’s fibers Sharpey's fibers  Sharpey's fibers Sharpey's fibers in primary acellular cementum are fully mineralized , in cellular cementum & bone are partially mineralized “only partially “ at their periphery. S.E.M showing insertion site of sharpey’s fibers. These S.E.M showing insertion site of sharpey’s fibers in cellular fibers in primary acellular cementum are fully mineralized. cementum. Peripheral portions of Sharpy’s fibers are more mineralized than their center.  Gingival group of ligament: Although they are not part of PDL, other groups of collagen fibers are associated with maintaining the functional integrity of the periodontium. These groups are found in the lamina propria of the gingiva and collectively form the gingival ligaments. 1. Dentogingival group 2. Alveolo-gingival group 3. Circular group 4. Dento-periosteal group 5. Transseptal group  Gingival group of ligament 1. Dento-gingival group : most numerous fibers extending from cervical cementum to lamina propria of free & attached gingiva. 2. Alveolo-gingival group : radiate from the bone of the alveolar crest & extend into the lamina propria of free & attached gingiva. 3. Circular group : this small group of fibers forms a band around the neck of the free gingiva to the tooth. 4. Dento-periosteal group : running from cementum over the periosteum of the outer cortical plates of the alveolar process.  Gingival group of ligament 5. Trans-septal group : Running interdentally from cementum just above the alveolar crest & insert into cementum of adjacent tooth. Together these fibers constitute the transseptal fiber system , forming an interdental ligament connecting all of the arch. These fibers are a major cause of post-retention relapse of orthodontically positioned teeth.  5. Trans-septal group : Cause of post retention relaps ?? The inability of transseptal fibers to undergo physiologic rearrangement Although the rate of turnover of gingival fibers is not as rapid as in PDL, studies improved the trans- septal fiber system is capable of turnover & remodelling under normal physiologic conditions & during therapeutic orthodontic tooth movement. A sufficiently prolonged retention following orthodontic tooth movement allow reorganization of trans- septal fiber system to ensure clinical stability of tooth. Trans-septal fiber system Elastic fibers : The three types of elastic fibers are: 1. Elastin, 2. Oxytalan , 3. and Elaunin. Only oxytalan fibers are present within the PDL, however, elaunin may be found within fibers of the gingival ligament. The presence of elastic fibers in the human PDL is restricted to the walls of blood vessels , but in some animals, these fibers may constitute a considerable part of the ligament fibers.  Oxytalan Fibers: They are bundles of microfibrils distributed extensively in the PDL. They run vertically from cementum surface of the root apically forming a three- dimentional branching meshwork surrounds the root & terminates in the apical complex of arteries, veins &lymphatics. Purple oxytalan fibers (arrowheads) connect forming cementum with alveolar bone. Blood vessel (BV). (b) Near the root apex many oxytalan fibers have an apico-occlusal orientation, with thick fibers (arrow) running along vessels near the alveolar bone. Other finer fibers (arrowheads) branch from the thicker fibers to insert into the cementum.  Oxytalan & Elaunin Fibers: These fibers are also associated with neural and vascular elements. Oxytalan fibers are numerous & dense in the cervical region of the ligament where they run parallel to the gingival group of collagen fibers. Their functions are thought to regulate vascular flow in relation to tooth function.  Ground Substance of the PDL Ground substance is an amorphous background material that binds tissue and fluids , the later serving for the diffusion of gases and metabolic substances. It is present everywhere between the cells , the fibers & the fibrils as well as between the blood vessels & nerves. Similar to all connective tissue the ground substance is made up of two major groups of substances, Proteoglycans and Glycoprotein.  Dermatan sulfate is the principal glycosaminoglycan (GAGs) of PDL. PDL ground substance estimated to be 70% water to withstand stress loads on tooth. In areas of injury & inflammation an increase in tissue fluids occurs within the amorphous matrix of the ground substance.  Interstitial Tissues: They are areas consisting of loose connective tissue and contain some of the blood vessels, lymphatics and nerves.  Blood supply and lymphatics Derived from 3 sources: 1. Branches from apical vessels that supply the pulp (from apical direction). 2. Branches from intra-alveolar vessels called perforating arteries (run horizontally). 3. Branches from gingival vessels (from coronal direction). Blood supply and lymphatics  Blood supply and lymphatics Perforating arteries more in posterior teeth than anterior and in greater numbers in mandibular than maxillary teeth. In single rooted teeth more in gingival third followed by apical third. This of clinical importance in healing of extraction wound, new tissue invades from the perforation , blood clot is more rapid in gingival & apical areas. Vessels course in an apical- occlusal direction with numerous transvers connections.  Blood supply and lymphatics Arteriovenous anastomoses occur within PDL. Fenestrated capillaries occur. Venous drainage is achieved by axially directed vessels that drain into a networks in the apical portion of PDL consisting of large diameter venules. Lymphatic vessel follow venous drainage The flow is from PDL toward & into the adjacent alveolar bone. Extensive vasculature of the periodontal ligament. Many transverse connections and the thickened venous network at the apex are visible.  Nerve supply of PDL: The nerve supply to the PDL comes from either the inferior or superior alveolar nerves. Branches supply the ligament in two ways: Small bundles of nerve fibers run from the apical region of the root towards the gingival margin and are joined by fibers entering laterally through foramina in the socket wall. These lateral fibers divide into two branches, one apically & one gingivally. Regional variation occurs in neural termination with apical region containing more nerve ending than elsewhere. ??  Nerve supply of PDL: Four types of neural terminations: 1. Free nerve ending: “most frequent” They are most frequent. Ramifying in a tree like configuration”. Are thought to be nociceptors & mechanoreceptors. 2. Ruffini's corpuscles (dendritic): They found around root apical area. Appear dendritic & end in terminal expansion among PDL fiber bundles. Their function is mechanoreceptors.  Nerve supply of PDL: 3. Coiled ending: Found in mid region of PDL. Thought to be mechanoreceptor at mid root region. 4. Spindle- like-ending “encapsulated” (lowest frequent): Lowest frequency , surrounded by fibrous capsule. Found at root apex. Pressure & vibration.  Nerve supply of PDL: In the PDL, the sensations includes pain, heat, cold & localization of pressure due to the variations in the receptors , while in the pulp, there is only one type of receptors which are the free nerve ending s for perception of pain sensation “nociception”. Cementicles : They are calcified bodies that sometimes found in the PDL. They are seen in older individuals. They may either remain free in the PDL or they become attached to the cementum surface forming exocementonsis , or even become completely embedded in the cementum due to the continuous deposition of cement and increase in its thickness.  Functions of PDL 1. Supportive Attachment: The most important function of the periodontal ligament is support of the teeth in its socket. At the same time, they permit them to withstand the considerable force of mastication. Failure of this function results in tooth loss. 2. Sensory: The PDL act as sensory receptor which is necessary for the proper positioning of the jaw during normal function. “proprioceptors”. PDL contributes to the sensation of touch and pressure on tooth. “mechanoreceptor”. In addition, the especial distribution of ligament receptors is significant, as stimulation of the teeth causes a relax jaw opining and stimulation of PDL mechanoreceptors initiates this response.  Functions of PDL 3. Nutritive: The blood vessels of the ligament provide the essential nutrients for the ligament's vitality and the hard tissue of cementum and alveolar bone. All cells require nutrition, which is carried by the blood vessels to the ligament. 4. Formative & Maintenance: Remarkable capacity of PDL is it maintains its width more or less over time. Balance between formation and maintains of mineralized tissue bone and cementum verses soft connective tissue of the PDL requires finely regulated control over cells in the local area. If balance disturbed results in pathologic conditions for example: 1) lack of tooth eruption by ankylosis. 2) lack of cementum formation resulting of tooth exfoliation as observed in hypophosphatasia (hereditary disease no cementum development in lower incisor deciduous teeth).  PDL also has capacity to adapt to functional changes?? In areas of increased function: The width of PDL can increase as much as 50%. The principal fibers bundles increase in thickness. Alveolar bone thickened. Reduction in function leads to: Narrowing of the ligament. Fiber bundles decrease in number & thickness. Bone trabeculae fewer. Reduction in width by cementum deposition. Functioning Non-functioning Age changes of the periodontal ligaments Detachment of cervical PDL fibers apically. Decrease cellularity and vascularity. Decrease thickness as well as activity. Cementicles may be found. Clinical considerations Apical pulp inflammation cause granuloma and cyst lesions in PDL. Gingivitis cause destruction of PDL and bone. Traumatic injury cause ankylosis.  Clinical considerations The primary role of the periodontal socket is to support the tooth in the bony socket. Its thickness varies in different individuals in different teeth in the same person and in different locations on the same tooth. Acute trauma to the periodontal ligament , accidental blows or rapid mechanical destruction may produce pathologic changes such as fractures or resorption of the cementum, tears of fiber bundles , haemorrhage and necrosis.  Clinical considerations In inflammatory situations an increased expression of Matrix Metalloproteinases “MMPs” occurs that aggressively destroys collagen. Attractive therapies for controlling tissue destruction may include host-modulators that capable to inhibit MMP.