Periodontal ligament
- 1. PERIODONTAL LIGAMENT P R E S E N T E D B Y D R . M A L V I K A T H A K U R M D S I Y E A R 1/71 GUIDED BY: DR.RUPINDER KAUR
- 2. CONTENTS Introduction Definition Synonyms Extent and Shape Average Width Development of PDL Structure Blood Supply Nerve Supply Lymphatics Functions of PDL Age changes in PDL Regulation of PDL width PDL relationship with Implants Conclusion References 2/71
- 3. INTRODUCTION • The term periodontium arises from greek words “peri” meaning around and “odont” meaning tooth. Tissues that invest and support the teeth are collectively termed PERIODONTIUM. 3/71 Periodontium Gingiva Periodontal Ligament Alveolar Bone Cementum
- 4. DEFINITION • According to Carranza & Bernard “The periodontal ligament is the connective tissue that surrounds the root & connects it to the bone. It is continous with the connective tissue of the gingiva & communicates with the marrow spaces through vascular channels in the bone.” • According to Berkovitz , Holland & Moxham “ It is the dense fibrous connective tissue that occupies the periodontal space between the root of the tooth & the alveolus. It is derived from the dental follicle above the alveolar crest is continous with the connective tissues of the gingiva ; at the apical foramen it is continous with the dental pulp.” 4/71
- 5. • According to Orbans “The periodontal ligament occupies the periodontal space, which is located between the cementum and the periodontal surface of alveolar bone and extends coronally to the most apical part of the lamina propria of the gingiva.” 5/71
- 6. SYNONYMS 1. Periodontal membrane 2. Alveolo-dental ligament 3. Desmodont 4. Pericementum 5. Dental periosteum 6. Gomphosis 6/71
- 7. EXTENT • In the coronal direction it is continuous with lamina propria of gingiva & is demarcated by the alveolar crest fibers. • At the root apex it merges with the dental pulp. • It ranges in width from 0.15- 0.38mm (A.R Ten Cate) 7/71
- 8. • It is thinnest around the middle third of the root, with an hour glass appearance. • The ligament appears as a radiolucent area of 0.4- 1.5mm between the radiopaque lamina dura of the alveolar bone and cementum.(Orbans) 8/71 SHAPE
- 9. AVERAGE WIDTH Depending on age 11-16 yrs - 0.21mm 32-52 yrs - 0.18mm 51-67 yrs - 0.15mm According to functional state of the tissues Time of eruption - 0.1- 0.5mm At function - 0.2-0.35mm Hypo function - 0.1-0.15mm 9/71
- 10. DEVELOPMENT • All the periodontal tissues are derived from dental follicle • (Osborn 1984) proposed that mesenchyme deriving the periodontium may have two different compartments • Alveolar clade- fibroblasts and osteoblasts • Cemental clade- fibroblasts and cementoblasts 10/71
- 11. • Begins with root formation & prior to tooth eruption. (Tencate et al.,1972). • At Late bell stage - when amelogenesis and dentinogenesis are well advanced, the int and the ext enamel epithelium at the cervical loop of enamel organs form a doubled layered epithelial root sheath which proliferates apically map out the shape of future root. 11/71
- 12. 12/71 • HERS loses structural continuity • Epithelial rests of Malassez. • CT cells of dental follicle to migrate to the newly formed root dentin. DENTAL FOLLICULAR CELLS FIBROBLLASTS CEMENTOBLASTS OSTEOBLASTS remnants persist as this separation permits
- 13. 13/71 As the root formation continues, cells in the peri follicular mesenchyme gain their polarity, cellular volume & become widely separated Actively synthesize & deposit collagen fibrils and glycoproteins in developing PDL (Grant’s 1989; Ten Cate’s 1971) Type I collagen is secreted Assembles as collagen bundles on the bone and cementum surface Establish continuity across the ligament space
- 14. DEVELOPMENT OF PRINCIPAL FIBERS 14/71 •The alveolar bone proper (ABP) is seen to the left, the periodontal ligament (PL) is depicted in the center and the root cementum (RC) is seen to the right
- 15. • Mature PDL can be sub divided into 3 region 15/71 Bone related region - rich in cells Cementum related region - dense and ordered collagen fibers Middle zone- few cells & thinner collagen fibers
- 16. ORGANIZATION OF PDL 16/71 As the teeth begin to , erupt the orientation of ligament fibres changes according to the stage of eruption. (Grant and Bernick 1972).
- 17. PERIODONTAL LIGAMENT HOMEOSTASIS • PDL has the capacity to maintain its width overtime despite the fact that its squeezed in between 2 hard tissues. • Studies indicate that cells of PDL, both during development and regeneration secrete molecules which regulate mineralization and prevent ankylosis. • Various molecules proposed: 1. PDL cells inhibit mineralized bone nodule formation by bone stromal cells – dependent on prostaglandin production. 2. Msx2 prevents osteogenic differentiation of PDL fibroblasts by repressing transcriptional activity of Runx2 . 3. Matrix Gla Protein – inhibitor of mineralization. 4. GAGs – maintain unmineralised state of PDL. 17/71
- 18. 5. Balance b/w activities of bone sialoproteins and osteopontin – maintains unmineralized PDL region. • PDL has capacity to adapt to functional changes: 18/71 Functional demand increases Width of PDL increases by as much as 50% Fiber bundle increses in thickness Functional demand decreases Narrowing of PDL Decrease in number and thickness of fiber bundle
- 19. STRUCTURE 19/71 PDL CELLS EXTRACELLULAR SUBSTANCES 3.Progenitor cells 4.Epithelial rests of Malassez 1.Fibers Collagen fibers Oxytalan fibers 2.Ground substance Glycosaminoglycans Glycoproteins 1.Synthetic cells Osteoblasts Fibroblasts Cementablasts 2.Resorptive cells Osteoclasts Fibroblasts Cementaclasts 5.Defence cells Mast Cells Macrophages Eosinophils
- 20. • Architect, builder and caretaker • Predominant cell in the pdl . • Origin: Cementum surface: Ectomesenchyme of investing layer of dental papilla and the dental follicle Alveolar bone: perivascular mesenchyme. 20/71 1.)SYNTHETIC CELLS FIBROBLASTS • Oriented with their long axis parallel to the direction of collagen fibers . • Alligned along and between collagen fibers. • Appearance governed by surrounding matrix.
- 21. 21/71 • Fibroblasts of PDL generate an organizational pattern as they have ability to both synthesize and shape the proteins of the extracellular matrix . • Certain Fibril form bundles get inserted into tooth and bone and are known as SHARPEY’S fibers • Once embedded in the wall of alveolus or tooth, these fibers calcify to a certain degree and are associated with an abundance of non collagenous proteins found in the bone i.e. osteopontin and bone sialoprotein .
- 22. 1) Synthesize Collagen (Esterl 1961) 2) Synthesize fibrils (Stallard 1963). 3) Organize fibrous network & generate force for tooth eruption. 4) Produce extracellular matrix of PDL (Sodek 1977). 5) Have capacity to give rise to cementobalsts and osteoblasts. 6) Maintain normal width of PDL. 7) Synthesize and shape the proteins of ECM in which collagen fibrils form bundles and insert as Sharpey’s fibers. 8) Regulate collagen turnover by PHAGOCYTOSING old collagen fibers. 30 minutes are taken for the intercellular degradation of collagen. 22/71 FUNCTIONS OF FIBROBLASTS
- 23. • These cells covers the periodontal surface of the alveolar bone. • Line the tooth socket and are cuboidal in shape with a prominent round nucleus at the basal end of the cell. • RER , mitochondria , and vesicles are abundant in active cells. • Microfilaments are prominent beneath the cell membrane at secreting surface, • The cells contact one another through desmosomes and tight junctions. 23/71 OSTEOBLASTS
- 24. CEMENTOBLASTS • These cells line the surface of cementum. • They are cuboidal with a large vesicular nucleus ,with one ore more nucleoli and abundant cytoplasm. • All the organelles required for protein synthesis and secretion are present. 24 • Cells actively depositing cellular cementum exhibit abundant basophilic cytoplasm and cytoplasmic processes. • Acellular cementum- no prominent cytoplasmic processes.
- 25. 2. RESORPTIVE CELLS OSTEOCLASTS • These resorb bone and tend to be large and multinucleated but can also be small and mononuclear . • Multinucleated Osteoclasts are formed by fusion of precursor cells similar to circulating monocytes. 25/71 • The part of plasma membrane lying adjacent to bone that is being resorbed is raised in characteristic folds and is termed the Ruffled or Striated border. • Are found against the bony surface occupying shallow depression called Howship’s lacunae.
- 26. • The ruffled border is separated from the rest of plasma membrane by a zone of specialized membrane that is closely applied to the bone, the underlying cytoplasm of which tends to be devoid of organelles and has been called The Clear Zone. 26/71
- 27. CEMENTOCLASTS • As cementum does not remodel, Cementoclasts are not usually found in the ligament. • These cells only occur in certain pathologic conditions, during resorption of deciduous teeth and when regressive forces are applied on a tooth such as orthodontic therapy. 27/71 • These Cementoclasts resembles Osteoclasts and are located in depressions in cementum resembling Howship’s lacuna. • These cells not only resorb cementum, they can destroy dentin and enamel as well thus they are also called Odontoclasts.
- 28. 3.PROGENITOR CELLS • All connective tissues including PDL contain progenitors cells that have the capacity to undergo mitotic division . • 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. 28/71
- 29. 4.EPITHELIAL CELL REST OF MALASSEZ • These were first described by Malassez in 1884 and are the remnants of the epithelium of Hertwig’s epithelial root sheath. • The PDL contains epithelial cells that lie about 25 m from the cementum surface. • They persist as networks, strands, islands or tubule-like structures near and parallel to the surface of the root. 29/71
- 30. 30/71 • Their function is not yet clear but they could be involved in periodontal repair and regeneration . •Most numerous in the apical area & cervical area. (Xiong J, Gronthos S, Bartold PM ) • Presence: children – more numerous old individuals – less Dimnishes with age (Simpson HE) •These cells may proliferate to form cysts and tumors. •These cells may undergo calcification to become CEMENTICLES.
- 31. 5.DEFENCE CELLS 31/71 MACROPHAGES MAST CELLS EOSINOPHILS
- 32. EXTRACELLULAR SUBSTANCES FIBERS 1.COLLAGEN 2.ELASTIC 3.RETICULAR 4.SECONDARY 5.INDIFFERENT FIBER PLEXUS 6.OXYTALAN 32/71 GROUND SUBSTANCE 1.PROTEOGLYCANS 2.GLYCOPROTEINS
- 33. COLLAGEN • The main types of collagen in the PDL are TYPE I and TYPE III. • More than 70 % of PDL is Type I . • Type I is uniformly distributed in the ligament . • Type III collagen accounts for about 20 % of collagen fibers, found in periphery of Sharpey’s fiber attachments into alveolar bone. • Type IV and VII are associated with epithelial cell rests and blood vessels. • Type XIII collagen is believed to occur within the PDL only when ligament is fully functional . 33/71
- 34. • The collagen is gathered to form bundles approximately 5 um in diameter. These bundles are termed as PRINCIPAL FIBERS. • Within each collagen bundle , subunits are present called collagen fibrils. 34/71
- 35. 35/71 Turnover Rate of the Collagen: • The rate of turnover of collagen within the PDL is faster than all other connective tissues. • Sodek (1977) found collagen synthesis in PDL of adult rat to be 2 fold greater than that of gingiva 4 fold greater than that of skin 6 fold greater than that of bone. • The rate appears to be highest towards the root apex. • The collagen on the tooth side has low turnover rate than that on the bone side where it shows high turnover rate.
- 36. PRINCIPAL PDL FIBERS 36/71 • The principle fibres of Periodontal ligament (Holmstrup 1996). • These are collagenous and follow a wavy pattern when viewed in longitudinal section . • They are thought to contribute to the regulation of mineralization and to tissue cohesion at sites of increased biomechanical strain. (Mc Kee MD, Zalzal S, Nanci A 1996) • The adult human PDL fibers : 54- 59 nm in diameter.
- 37. 37 Fibre Group Origin and insertion Supposed function 1) Alveolar crest Extend obliquely from the cementum just beneath the junctional epithelium to the alveolar crest and to the fibrous layer of the periosteum covering the alveolar bone. Retains tooth in the socket Oppose lateral forces Prevents extrusion & intrusion of tooth. Protects deeper periodontal ligament structures 2) Horizontal group They extend from cementum to alveolar bone in horizontal direction at right angles to long axis of tooth. Occupy 10-15 % of coronal root surface. Restrain lateral tooth movements. 3) Oblique group Largest group of PDL fibers. Occupy 80-85% of root surface. Extend from cementum in a coronal direction obliquely to the bone. They bear the brunt of vertical masticatory stresses and transform them into tension on alveolar bone and resist intrusive forces. 4) Apical group The apical fibres radiate in a rather irregular fashion from cementum to the apical region of the socket They donot occur in incompletely formed roots. Prevent tooth tipping Resist luxation. Protect blood, lymph and nerve supplies to tooth. 5) Inter radicular group. They fan out from the cementum to the tooth in the furcation areas of multirooted teeth. Aid in resisting tipping torquing and luxation.
- 38. SHARPEYS FIBERS 38/71 • The collagen bundles of the periodontal ligament embedded into cementum and alveolar bone – are called as Sharpey’s fibers. • Orientation is similar to that of adjacent periodontal ligament bundles. • Are more numerous but smaller at their attachment into cementum than alveolar bone. • Sharpey’s fibers in Acellular cementum- fully mineralized. Cellular cementum & AB – partially mineralized. • Few Sharpey’s fibers pass uninterruptedly through bone of alveolar process – Transalveolar fibers.
- 39. INTERMEDIATE PLEXUS Earlier it was believed that principal fibers follow a wavy course from cementum to bone and are joined in the mid region of the periodontal space giving rise to a zone of distinct appearance i.e the Intermediate plexus . Research over past yrs suggests that cemental fibers meet and fuse with osseous fibers, no such plexus remains. Secondly the entire PDL is metabolically active , not just the middle or intermediate zone (Thomas M. Hassel). The recent concept is that, fibers cross the entire width of periodontal space but branch en route and join neighboring fibers to from a complex three dimensional network . 39/71
- 40. ELASTIC FIBERS • There are three types of elastic fibers which are histochemically and ultrastructurally different. • Mature Elastic fibers , Eulanin fibers and the Oxytalan fibers . • Eulanin fibers and Oxytalan fibers have been described as immature elastic fibers. MATURE ELASTIC FIBERS • Consist of microfibrillar component surrounding an amorphous core of elastin protein . 40/71
- 41. • Restricted to walls of blood vessels in humans • PDL fibers do not contain mature elastin but two immature forms are found oxytalan and eulanin OXYTALAN FIBERS • Are micro fibrils • Run in apico-coronal direction to bend and attach at cervical third of root (Fulmer et al. 1974) • Diameter – 0.5-2.5um • Volume – 3% • Function is unknown but they may play a role in - supporting blood vessels of PDL. - tooth support (abutments/ Orthodontically moved teeth) 41/71 Oxytalan fibers. (A) Cementum, (B) Principal oxytalan fiber, (C) Oxytalan tract, and (D) Periodontal vessel.
- 42. EULANIN FIBERS • Are bundles of microfibrils embedded in a small amount of amorphous elastin. • An elastic meshwork has been described in the PDL as being composed of many elastin lamellae with peripheral oxytalan & eulanin fibers • Functions - Regulate vascular flow - Role in tooth support - Facilitate fibroblast attachment and migration 42/71
- 43. RETICULAR FIBERS • These are immature collagen fibers with argyrophilic staining properties and are related to basement membrane of blood vessels and epithelial cells which lie within the periodontal ligament. SECONDARY FIBERS • Represent the newly formed collagenous elements, not yet incorporated into principal fiber bundle. • Located between and among the principal fibers. • These are relatively non-directional and randomly oriented. • Appear to transverse the periodontal ligament space corono-apically and are often associated with path of vasculature and nervous elements. 43/71
- 44. INDIFFERENT FIBER PLEXUS • Described by Shackleford, 1971 • Small Collagen fibers in association with the larger principal collagen fiber • Run in all directions forming a plexus. • Once the tooth has erupted into clinical occlusion such an intermediate plexus is no longer demonstrable. • Intermediate plexus has been reinterpreted by Sloan as representing merely an optical effect explained entirely by the arrangement of middle layer collagen into sheets rather than bundles. 44/71
- 45. GROUND SUBSTANCE • The ground substance is the gel like matrix synthesized by the fibroblast family & fills the space between the fibers and cells. COMPOSITION • Consists of a biochemically complex, highly hydrated, semisolid gel. • Water content of 70% • Glycosaminoglycan's – hyaluronic acid, Proteoglycans( versican , decorin ) • Glycoproteins -fibronectin , laminin, vibronectin , tenascin 45/71
- 46. PROTEOGLYCANS • Large group of anionic macromolecules that consists of a protein core to which are attached hexose amine containing polysaccharides called GAG chains. 46/71 1. Decorin – regulates growth of collagen fibrils. 2. Versican – binds cell surface glycoproteins to ECM. 3. Prelecan - binds to fibronectin & helps anchor fibroblast to ECM. 4. Syndecan - binds to collagen & other glycoproteins. 5. CD44 – binds to glycoproteins.
- 47. • With the exception of hyluronic acid, the other glycosamino glycans are sulphated and covalently attached to the core proteins at the reducing terminus of PG. • The major GAGs are: 1. Chondroitin Sulphate 2. Dermatan Sulphate 3. Heparin Sulphate 4. Hyaluronic Acid 5. Keratan Sulphate 47/71
- 48. GLYCOPROTEINS • Three distinctly related glycoprotiens of the extra cellular matrix have been localized in the decalcified sections of human periodontal ligament, namely: • It promotes the attachment of cells to the substaratum especially to collagen. • It is expressed strongly along attachment sites of the PDL collagen fibers to cementum but not bone. • In addition to its function as an adhesion protein it is also involved in blood coagulation, wound healing and chemotaxis. 1. FIBRONECTIN 48/71
- 49. 2. TENASCIN : • Also known as cytotactin • It is the other glycoprotein identified in the PDL . • It is found mostly in healing wounds. • Unlike fibronectin it is not uniformly distributed through out the PDL. • But is concentrated in between the less densely packed collagen fibrils near cementum and alveolar bone. • Present in the glycoproteins of periodontal ligament with a smaller role in cell attachment and organization of basement membrane. 49/71
- 50. 3. LAMININ : • Major glycoprotein component of basement membrane of Epithelial cell rests of Mallassez.. • Implicated in variety of functions including. Cell adhesion Migration Differentiation • Other glycoproteins like Entactin (Nidogen ) – dumb bell shaped glycoprotiens Vitronectin Thrombospondin May also be present in the glycoproteins of PDL with a smaller role in cell attachment and organization of basement membrane.50/71
- 51. BLOOD SUPPLY 51/71 Blood supply is derived mainly from : Inferior and superior alveolar arteries to mand. & max respectively from 3 sources: 1. Apical vessels (Dental artery) – supply dental pulp 2. Transalveolar vessels (rami perforantes-penetrating vessels from alveolar bone) 3. Intraseptal vessels (anastomosing vessels from the gingiva) • Ramify and form a rich network of arcades more evident adjacent to bone than cementum.. • Blood Supply: Posterior teeth > Anterior teeth • Gingival third > Apical third > Middle third
- 52. Nerve sUPPLY 52/71 The nerve fibres supplying the PDL – 2 types sensory autonomic. • The nerve follow almost the same course as the blood vessels. • Nerve bundle divide → myelinated fibers → lose their myelin sheath → end in one of the 4 types of neural terminations : Free endings with treelike ramifications : • terminal branching of myelinated fibers • 0.2-1 um in diameter • fine, non myelinated fibers only type of ending in tooth pulp → classic model of pure nociception. •Located at regular intervals along the length of the root.
- 53. 53/71 Ruffini’s endings : • Found around the root apex. • Appear dendritic and end in terminal expansions among the PDL fiber bundles. • Are mechanoreceptors. Meissner's corpuscles : mid-root, for tactile perception Encapsulated spindle type : temperature receptor, associated with root apex.
- 54. Lymphatic drainage 54/71 • Lymph vessels - Follow the course of blood vessels. • Course apically - pass through the fundus of the socket or they may pass through the cribriform plate to empty into larger channels pursuing intraosseous paths.
- 55. Functions of pdl 55/71 I. PHYSICAL FUNCTION : 1) Provision of a soft tissue ‘casing’ to protect the vessels and nerves from injury by mechanical forces. 2) Transmission of occlusal forces to the bone. 3) Attachment of the teeth to the bone. 4) Maintainence of the gingival tissues in their proper relationship to the teeth. 5) Resistance to the impact of occlusal forces (Shock absorption).
- 56. 56/71 When a force is applied to the crown Principal fibers first unfold and straighten Transmit forces to the alveolar bone Causes elastic deformation of the bony socket. Finally, when the alveolar bone has reached its limit The load is transmitted to the basal bone. TENSIONAL THEORY States that the principal fibers of PDL are the major factors in supporting the tooth and transmitting the forces to the bone. Many investigators find this theory insufficient to explain available experimental evidence.
- 57. Force applied on tooth Extra-cellular fluid from PDL escapes to marrow spaces Depletion of fluid, Fibers absorb slack and tighten Blood vessels stenosis Arterial back pressure created Ballooning of vessels Passage of blood ultra filtrates into the tissues Lost fluid replenished VISCOELASTIC THEORY According to this, the displacement of tooth is largely controlled by fluid movement, with fibers having only secondary role (Bien SM, 1966 and Birn H, 1966) 57/71
- 58. 58/71 THE THIXOTROPIC THEORY However the presence of organized collagen fibers make this theory unacceptable. Claims that the PDL has the rheologic behaviour of a thixotropic gel (i.e. the property of becoming gel when shaken or stirred and then becoming semisolid again).
- 59. 59/71 II. FORMATIVE AND REMODELING FUNCTION : • Cells of the PDL participate in the formation and resorption of cementum and bone, which occur in - physiologic tooth movement, - accommodation of the periodontium to occlusal forces - in the repair of injures. • Remodeling : The 3-D organization of the fiber meshwork is adapted to accommodate for positional changes of the tooth in its socket or changes in functional state (such as hypofunction). • It relates to adaptability of PDL tissues. • Both these processes can occur simultaneously and may therefore be indistinguishable.
- 60. • The PDL is constantly undergoing remodeling. Old cells & fibers are broken down & replaced by new ones, & mitotic activity can be observed in the fibroblasts & endothelial cells (Muhlemann; 1954) • Sodek (1977) has demonstrated that the periodontal ligament incorporates proline at least 5 times faster than gingiva or alveolar bone and that the biological half-life of mature collagen was 20% and 17% less than found in gingiva and alveolar bone, respectively. 60/71
- 61. 61/71 III. NUTRITIONAL: • PDL supplies nutrients to the cementum , bone, and gingiva by way of blood vessels and provides lymphatic drainage. • The PDL contains blood vessels, which provide anabolites and other substance to the cementum, bone and gingiva. & removes catabolites. IV. HOMEOSTATIC: • Adaptability to rapidly changing applied forces and its capacity to maintain its width at constant diameter throughout life. • Its is evident that the cells of PDL have the ability to resorb and synthesize the extracellular substance of the connective tissue of the ligament , alveolar bone and cementum
- 62. V. SENSORY FUNCTION • The PDL is abundantly supplied with sensory nerve fibers capable of the repair of transmitting tactile, pressure and pain sensations by the trigeminal pathway. • The PDL provides a most efficient proprioceptive mechanism. • 4 types of neural terminations are seen 1. Free nerve endings –pain(at regular intervals along the length of the root. 2. Ruffini like mechanoreceptors (apical area) 3. Meissner’s corpuscles - mechanoreceptors (middle 3rd) 4. Spindle like pressure and vibration endings (apex) 62/71
- 63. aGE CHANGES IN PDL 63/71 • Increase in the collagen fibrosis & decrease in cellularity (Grant & Bernick 1972). • Areas of hyalinization are present. • Sporadic mineralization of the fibers also occurs. • Decrease in the no of periodontal fibers (Grant et al 1973). • Decrease in the cellularity & the formation of multinucleated fibroblasts. • Decrease in collagen synthesis (Johnson et al 1986). • The surfaces of the periodontal alveolar bone are jagged & uneven & an irregular insertion of fibers is seen. • Replacement of some of the PDL space by interstitial areas & fat cells. • Structural organization of the ligament degenerates with age.
- 64. WIDTH OF THE PERIODONTAL LIGAMENT SPACE • The width of the periodontal ligament space of nonfunctioning teeth is narrower than that of functioning teeth (Klein 1928, Kronfeld 1931). • If, with increasing age, less teeth are present, the force acting on the remaining teeth may increase and an increasing width of the periodontal ligament space with age. • On the other hand, it has also been noted that the masticatory forces decrease with age (Helkins et al 1977, Herring 1977). This could explain decrease in the periodontal ligament space with age. 64/71
- 65. REGULATION OF PDL WIDTH • An important measure of periodontal ligament homeostasis. • The ability of periodontal ligament cells to synthesize and secrete a wide range of regulatory molecules is essential in accurately maintaining the width of the periodontal ligament in spite of high-amplitude physical forces during mastication and despite the presence of osteogenic cells within the whole width of the periodontal ligament. (McCulloch, 1983) 65/71
- 66. • Transforming growth factor-β isoforms -synthesized by periodontal ligament cells can dose-dependently down- regulate osteoblastic differentiation of periodontal ligament cells (Brady TA et al. 1998) • Prostaglandins - also produced by periodontal ligament cells, can inhibit mineralized bone nodule formation and prevent mineralization by periodontal ligament cells in vitro (Ogiso B, Hughes FJ, et al. 1991,1992) • Paracrine factors - inhibit bone resorption (Ginger MS, et al 1991) 66/71
- 67. • Pro-inflammatory cytokine interleukin-1 (Shimizu N et al 1995) and one of the isoenzymes responsible for prostaglandin synthesis - cyclooxygenase 2 ( Shimizu N et al 1998) are induced by applied mechanical force on periodontal ligament cells in vitro. • As prostaglandins and interleukin-1 can strongly induce matrix degradation, there is evidently an important relationship between mechanical forces, cytokine production and regulation of the periodontal ligament space. 67/71
- 68. PDL RELATIONSHIP WITH IMPLANTS • Implants do not employ a gomphosis to provide support and attachment to the jaw bones as does the PDL , but still it serves as a replacement for natural teeth. • The absence of PDL around implants – absence of resilient connection between teeth and jaw bone thus any occlusal disharmony will have repercussions at bone to implant interface. • No intrusion or migration can compensate for the eventful presence of a premature contact. • Absence of PDL leads to : reduced tactile sensitivity & reduced reflex function. • Even if certain degree of perception is present – Osseoperception. 68/71
- 69. CONCLUSION • The periodontal ligament is a fibrous connective tissue forming important part of the Periodontium. • The PDL is a physically small, but functionally important tissue in tooth support, proprioception and regulation of alveolar bone volume. • The PDL is an absolute requirement for rapid remodeling of alveolar bone when forces are applied to teeth. • Cell of the periodontal ligament are Pluri-potent and helps in the regeneration of all the components of Periodontium lost in the periodontal disease process. 69/71
- 70. • A better understanding of cell and molecular biology of developing and regenerating periodontium offers newer avenues to regenerate the PDL. • Yet safeguarding the integrity of the PDL and alveolar bone is still one of the most important challenge . 70/71
- 71. REFERENCES 1) Clinical Periodontology 10th edition. F.A. Carranza, M.G. Newman . 2) Clinical Periodontology and Implant Dentistry, 4th edition. Jan Lindhe, Thorkild Karring, Niklaus P. Lang. 3) Tencate’s Oral histology, Development, Structure and function. 4th edition. 4) Orbans Oral Histology And Embryology. 12th Edition 5) Dental embrology, histology and anatomy. Mary Bath- Balogh, Margret J Ferhrenbach. 2nd edition. 6) Development and general structures of the periodontium. Periodontol 2000;24,2000;9-22. 71/71
- 72. Perfection is not attainable But If we chase Perfection we can achieve Excellence 72