Periodontal ligament homeostasis

contents
Introduction
Development
Homeostasis
Contents of PDL
Functions
Age changes
Clinical considerations
Conclusion
References

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2. Periodontal ligament and Its homeostasis M. RAVINDRA I MDS Dept of Oral Pathology & Microbiology 2

3. contents Introduction Development Homeostasis Contents of PDL Functions Age changes Clinical considerations Conclusion Refferences 3

4. IntroductIon PDL is an connective tissue organ, covered by epithelium which attaches the teeth to the bones of jaw. And it provides continuously adapting apparatus for support of the teeth during function . 4

5. The term ligament is used because of it is a complex soft connective tissue, connecting two mineralized tissues . Definition: According to Caranza & Bernard: “ The periodontal ligament is the connective tissue that surrounds the root & connects it to the bone. it is continuous with the connective tissue of 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 continuous with the connective tissues of gingiva ; at the apical foramen it is continuous with the dental pulp. 5

6. SYNONYMS: Desmodont Gomphosis Pericementum Dental periosteum Alvelodental ligament Periodontal membrane 6

7. Thickness of the PDL 0.15 to 0.38mm Radiographically 0.4 to 1.5 mm It is thinnest around the middle third of the root, with an hour glass appearance. Thickness of the PDL decreases with age . Young adult - 0.21mm Mature adult - 0.18mm Old adult - 0.15mm 7

8. development Develops from Dental Follicle. Development of PDL begins with root formation. Developing Hertwig`s epithelial root sheath separates Dental papilla & dental follicle. 8

9. Dental follicle has 2 types of cells. Dental follicle proper Perifollicularmesenchyme 9

10. 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 glycoprotiens in developing PDL Type I collagen is secreted Assembles as collagen bundles on the bone and cememtum surface Establish continuity across the ligament space 10

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12. Development of Principal Fibers: Periodontal fibers develop from mesenchymal cells of the PDL. First formed fibers are Alveolar crest fibers. Fibroblast in the coronal third, align in oblique direction to the tooth long axis and start secreting alveolar crest group of fibers. 12

13. Microfibrils from cementum & alveolar bone grow towards center to meet, intertwine and fuse to form remaining groups of fibers . At the time of occulusal contact alveolar crest group and horizontal group fibers are fully developed. Oblique & Apilcal groups are under developing state . 13

14. Homeostasis of periodontal ligament 14

15. Periodontal ligament maintains its width more or less overtime. This is because of molecules secreted by different cells in the PDL. These molecules can regulate the extent of mineralization of the surrounding hard tissues like bone and cementum. These factors can prevent the fusion of the root and bone by preventing excess mineralization. 15

16. Some Factors maintaining homeostasis of PDL: Prostaglandins : Inhibit mineralized bone nodule formation by bone stromal cells. Msx2 : Prevents Osteogenic differentiation of fibroblasts by suppressing Cbfa1 (also known as Runx2 ) transcriptional activity. Bone sialoprotien : Balance between these contributes to & Osteopontin the unmineralized PDL. Matrix ‘GLA’ protein : Inhibitor of the mineralization. Glycosaminoglycans or RGD- cementum attachment protein 16

17. PDL has capacity to adapt to functional changes: Functional demand increases Width of PDL increases by as much as 50% Fiber bundle increases in thickness Functional demand decreases Narrowing of PDL Decrease in number and thickness of fiber bundle 17

18. Contents of Pdl PDL consists of Cellular components Extracellular matrix 18

19. CELLS IN PDL Mainly 5 types. Synthetic cells Resorptive cells Progenitor cells Epithelial cell rests of Malassez Defense cells. 19

20. Synthetic cells: Cells that are synthesizing proteins for secretion. Microscopically they appear as comparatively large cells with large vesicular nucleus with prominent nucleoli due to increased transcription of RNA & production of ribosomes . And cytoplasm is also abundant, due to increased activity of mitochondria, golgi membrane and RER. 20

21. Three types Osteoblasts Fibroblasts Cementoblasts 21

22. Osteoblasts : Secrete bone components. Cover the surface of the bone Microscopic features: Cuboidal in shape Prominent round nucleus at the basal end. Abundant RER, mitochondria and vesicles. Basophilic due to RER Pale juxtanuclear layer of golgi membrane. Microfilaments are present beneath the cell membrane, at the secretary surface. 22

23. Fibroblasts: Predominant cells in PDL Secret Fiber Components. Mainly secret Collagen Elastin Glycoprotien Glycosaminoglycans Matrixmetalloprotinesases (MMP`s) Responsible for the formation and remodeling of PDL fibers & signaling system to maintain the width and thickness of the PDL. 23

24. Microscopic features Fusiform in shape. Large cells with large nucleus and one or more prominent nucleoli. Extensive RER Well developed golgi Complex Abundant secretory granules containing type-1 collagen. Cytoplasmic extensions in secretory end that form 3 dimensional veils which compartmentalize collagen fibrils to fibers. 24

25. Cementoblasts : Secrete cementum. Arranged on the cementum. Microscopic features: Often indistinguishable from PDL fibroblasts. Cuboidal in shape. Large nucleus with One or more nucleoli. Abundant mitochondria & less RER. Cellular cementum secreting cells have cytoplasmic processes and the nucleoli are folded and irregularly shaped. Acellular cementum secreting cells don’t have these cytoplasmic processes. 25

26. Resorptive cells: Three types Osteoclasts Fibroblasts Cementoblasts 26

27. Osteoclasts : Responsible for bone resorption . Microscopic features: Large multinucleated but sometimes small and mono nucleated. Have eosinophilic cytoplasm. Abundant cytoplasam , mitochondria,golgicomplex , free ribosmomes , little RER. Plasma membrane is folded in the resorbing side- Ruffled boarder or Striated boarder. Under the ruffled boarder – Clear zone. Resorb bone by producing highly acidic P H . 27

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29. Fibroblasts: Show rapid degeneration of collagen by Phagocytosis , which results in fast turnover of collagen. Collagen degradation is both Extracellular Intracellular Normally intracellular in healthy tissues, where there is a controlled turnover& remodeling. Extracellular is seen in pathological conditions where degeneration is rapid and involves whole tissue, simultaneously. 29

30. Extracellular: Matrix metalloprotiens (MMP`s) secreted by fibroblasts play an important role in extracellular collagen degradation. Removal of fibronectin & proteoglycans on fibril surface by Stromelysin (MMP-III) Collagenase (MMP-I)binding Cleavage of triple helix portion of molecules with in the fibril Denaturation of collagen by MMP-IV Prteolysis of the rest of the molecule by MMP-II ( Gelatinase ) & MMP-V 30

31. Intracellular: Through Phagocytosis Intracellulrar collagen profiles – Special cell organells for collagen degradation Collagenase is not involved Lysosomal cysterine protinesases are involved. 31

32. Phagocytosis of collagen fibrils Banded fibril is surrounded by Electron- lucent zone Phagosome + lysosome  Phagolysosome Enzymic degradation of fibrils Electronlucent zone Electon dense zone Fibrils loss their characeristic structure 32

33. Cementoclasts : They resembles osteoclasts and are located in depressions in cementum resembling Howship`s lacuna. As cementum does not remodel, Cementoclasts are not usually found in the ligament . These cells only occur in some pathological conditions, during resorption of deciduous teeth and when regressive forces are applied on a tooth such as orthodontic therapy . These cells not only resorb cementum, they can destroy dentin and enamel as well thus they are called Odontoclasts . 33

34. Progenitor cells: All connective tissues including PDL contain progenitor cells that have the capacity to undergo mitotic division.  When stimulated appropriately, these cells undergo mitotic division and can differentiate into fibroblast, osteoblast or cementoblast . 34

35. Epithelial cell rests of Malassez :   These were first described by Malassez in 1884 and are the remnants of the epithelium of Hertwig’s epithelial root sheath. They persist as networks, strands, islands or tubule-like structures near and parallel to the surface of the root.  35

36. Their function is not yet clear but they could be involved in periodontal repair and regeneration. These cells may proliferate to form cysts and tumors. These cells may undergo calcification to become CEMENTICLES. 36

37. Defence cells: Mast cells Eosinophills Macrophages   MAST CELLS – These are relatively small round or oval cell having a diameter of about 12 to 15 um Mast cells are often associated with blood vessels . These cells are characterized by numerous cytoplasmic granules which frequently obscure the small , round nucleus .  37

38. MACROPHAGES- These are found in the ligament and are predominantly located adjacent to blood vessels . The wandering type are derived from blood monocytes has a characteristic ultrastructure that permits it to be readily distinguished from fibroblasts .  38

39. EOSINOPHILLS – These are seen in the periodontal ligament . They posses granules that consist of one or more crystalloid structures . These are capable of phagocytosis  . 39

40. EXTRACELLULAR SUBSTANCES FIBERS GROUND SUBSTANCE 1.Collagen 2. Elastin 3. Reticular 4. Secondary 5. Indifferent fiberplexus 6. Oxytalan Proteoglycans Glycoprotiens 40

41. FIBERS 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 .  Within each collagen bundle , subunits are present called collagen fibrils . 41

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43. PRINCIPAL PDL FIBERS : The collagen is gathered to form bundles approximately 5 um in diameter. These bundles are termed as PRINCIPAL FIBERS. 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. 43

44. Types of Principal fibers Alveolar crest Horizontal group Oblique group Apical group Inter radicular group 44

45. Fiber group Origin & insertion 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 They extend from cementum to alveolar bone in horizontal direction at right angles to long axis of tooth. Restrain lateral tooth movements . 3.Oblique Largest group of PDL fibers. Occupy 80-85% of root surface. Extend from cementum in a coronal direction obliquely to the bone. They bear vertical masticatory stresses and transform them into tension on alveolar bone and resist intrusive forces. 4. Apical The apical fibres radiate in a rather irregular fashion from cementum to the apical region of the socket Prevent tooth tipping Resist luxation . Protect blood, lymph and nerve supplies to tooth. 5. Interradicular They fan out from the cementum to the tooth in the furcation areas of multirooted teeth. Aid in resisting tipping torquing and luxation . 45

46. SHARPEYS FIBERS: 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. Sharpey’s fibers in Acellular cementum- fully mineralized. Cellular cementum & Alveolar Bone – partially mineralized. Few Sharpey’s fibers pass uninterruptedly through bone of alveolar process – Transalveolar fibers. 46

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48. ELASTIN FIBERS : There are three types of elastic fibers which are histochemically and ultrastructurally different. Mature Elastic fibers Eulanin fibers 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 .  48

49. 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 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) 49

50. 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. 50

51. 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.  51

52. INDIFFERENT FIBER PLEXUS: 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. 52

53. 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   53

54. Glycosaminoglycans :   PROTEOGLYCANS Large group of anionic macromolecules that consists of a protein core to which are attached hexose amine containing polysaccharides called GAG chains. 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 . 54

55. Glycoprotiens : Three distinctly related glycoprotiens of the extra cellular matrix have been localized in the decalcified sections of human periodontal ligament, namely Fibronectin Tenascin Laminin Other glycoproteins like Entactin , Vitronectin , Thrombospondin may also be present in the glycoprotiens of PDL with a smaller role in cell attachment and organization of basement membrane. 55

56. FUNCTIONS OF PDL Physical function Formative & Remodeling Nutritional Homeostatic Sensory function. 56

57. I.PHYSICAL FUNCTION : Provision of a soft tissue ‘casing’ to protect the vessels and nerves from injury by mechanical forces. Transmission of occlusal forces to the bone. Attachment of the teeth to the bone. Maintainence of the gingival tissues in their proper relationship to the teeth. Resistance to the impact of occlusal forces (Shock absorption). 57

58. 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. 58

59. 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. 59

60. 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 60

61. 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) 61

62. Age changes in pdl Increase in the collagen fibrosis & decrease in cellularity . Areas of hyalinization are present. Sporadic mineralization of the fibers also occurs. Decrease in the no. of periodontal fibers Decrease in the cellularity & the formation of multinucleated fibroblasts. Decrease in collagen synthesis. 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. 62

63. Clinical considerations  If gingivitis is not cured and supporting structure become involved, the disease is termed as periodontitis . There are few coccal cells and more motile rods and spirochetes in the diseased site than in the healthy site. The bacteria consists of gram-positive facultative rods and cocci in healthy site while in diseased site , gram-negative rods and anaerobes are more in number.    Resorption and formation of both bone and periodontal ligament play an important role in orthodontic tooth movement . If tooth movement takes place, the compression of PDL is compensated by bone resorption whereas on tension side, apposition takes place. 63

64.  Inflammation of the pulp reached to the apical periodontal ligament and replaces its fiber bundles with granulation tissue called as granuloma , which then progresses into apical cyst. Chronic periodontal disease can lead to infusion of microorganisms into the blood stream. The pressure receptors in ligament have a protective role. Apical blood vessels are protected from excessive compression by sensory apparatus of the teeth. 64

65. NEOPLASTIC INVOLVEMENT OF PDL: Mostly reactive rather than neoplastic. Oxytalan fibers are found in peripheral odontogenic fibromas & Adenomatoid odontogenic tumors Epithelial rests of malassez --- neoplastic change Infiltration of PDL by primary or secondary malignant tumors --- widening of PDL space--- mobility –malignant loosening of teeth.  65

66. PERIODONTAL CYSTS : Inflammatory ---- Radicular cyst Developmental ---- Lateral periodontal cyst PDL space Radiographic appearance : Thin radiolucent line interposed between the root & lamina dura . Occlusal Trauma → widened PDL space or funneling of coronal aspect of PDL space. It can also widened in case of vertical fractures & progressive systemic sclerosis (Scleroderma).  66

67. 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.  67

68. rEFFERNCES  Carranza’s Clinical Periodontology , 10th Edition Clinical Periodontology and Implantology by Jan Lindhe , 5th edition Oral Histology and Embryology by Orban , 13th edition Tencate oral histology, 5th edition  68

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