Periodontal Ligament

Periodontal Ligament

1. PERIODONTAL LIGAMENT A SEMINAR Presented by: Dr. Abhishek Gakhar Department of Periodontics At I.T.S DENTAL COLLEGE,HOSPITAL &RESEARCH CENTRE,GREATER NOIDA 26th Sep 2012 Moderator - Dr. Kanwarjit Singh A si

2. Table of Contents Introduction Structure Evolution Development Constituents of the pdl Blood supply Nerve supply Functions Clinical Corelations Conclusion References

3. INTRODUCTION Soft fibrous specialised connective tissue present in periodontal space b/w cementum of root &bone forming the socket wall. (1) Other names Gomphosis Desmodent Pericementum Dental Periosteum Alveo -dental ligament Periodontal membrane

4. StrUCTurE Hour-glass shaped Widest cervically Is the dense, fibrous connective tissue Average width is 0.2mm Nonfunctional , unerupted Bears Heavy occlusal stress Thickness decreases with age

5. EVOLUTION Reptiles teeth are ankylosed to bone & growth is by sutures Teeth fixed to bone Mammals teeth are suspended by ligaments in sockets & growth is by cartilage. The teeth are independent of bone- individual tooth movement

6. DEVELOPMENT Hertwigs Epith Root Sheath Epithelial Rests of Malassez Cells of dental follicle migrate to root dentin Migrated follicular cells - cementoblast lay  cementum Other cells of dental follicle differentiate into fibroblast, synthesize fibers & extra cellularsubstance of PDL (2)

7. CONSTITUENTS OF THE PDL

8. SYNTHetIC CELLS The characteristic of synthetic cells are: Should be actively synthesizing ribosomes . Increase in rough endoplasmic reticulum and golgi apparatus. Large open faced or vesicular nucleus with prominent nucleoli. (2)

9. OSTEOBLASTS Uninucleated cells Cuboidal in shape Basophilic cytoplasm Numerous orgenelles Get incorporated as osteocytes (2)

10. Synthesize both collagenous and noncollagenous bone proteins . (3) Osteoblasts also synthesize the enzyme alkaline phosphatase, which is needed locally for the mineralization of osteoid. The precursor cell of the osteoblast is the preosteoblast . (4) Osteoblasts have all the characteristics of hard tissue-forming cells. When the bone is no longer forming, the surfaces of the osteoblasts become inactive and are called Lining cells.

11. Function: Osteoblasts help in the synthesis of alveolar bone.

12. FIBROBLASTS Constitute 65% of total cell population Remodeling of collagen Parallel to the collagen fibres Well developed cytoskeleton Interconnected by desmosomes. Appear as elongated cells with pseudopodia like process . (5)

13. Extensive cytoplasm Prominent nucleus- flat, disc shaped Occupys 30% of cell space Cell organelles-protein synthesis, Numerous Cytoplasmic processes Mitochondria numerous, Lysosomes large , membrane bound vesicles

14. The fibroblast is stellate shaped cell which produces: 1. COLLAGEN FIBERS 2. RETICULIN FIBERS 3. OXYTALAN FIBERS Various stages in the production of collagen fibers are as follows: The first molecule released by fibroblasts is tropocollagen which contains three polypeptide chains intertwined to form helix. Tropocollagen molecules are aggregated longitudinally to form protofibrils , which are subsequently laterally arranged parallel to form collagen fibrils. (6)

15. FUNCTION : PRODUCTION OF VARIOUS TYPES OF FIBERS & IS ALSO INSTRUMENTAL IN THE SYNTHESIS OF CONNECTIVE TISSUE MATRIX

16. CEMENTOBLASTS Observed during phases of active cementum deposition (7) Oval to cuboidal shape Basophilic due to high %membrane bound and free ribosomes . large nuclei Structure depends on activity After some cementum has been laid down, its mineralization begins with the help of calcium and phosphate ions.

17. FUNCTION : Cementoblasts synthesize the organic matrix of the cementum

18. OSTEOCLASTS Large & multinucleated gaint cells Located in Howships lacunae. Seen adjacent to the bone surface Irregular distribution Appear only in active resorption  / deposition Cytoplasm-vacuolated ,numerous mitochondria

19. Derived from a monocytic -macrophage system, which are responsible for bone resorbtion . ( 8 ) They are multinucleated cells with fine, fingerlike cytoplasmic processes and are rich in lysosomes that contain tartrate-resistant acid phosphatase (TRAP ). ( 9 ) Osteoclasts lie in resorbtion craters known as Howship’s lacunae on bone surfaces or in deep resorption cavities called cutting cones. These bone cells can only resorb mineralized bone matrix.

20. The surface of an osteoclasts which is in contact with bone has a ruffled border. Resorption occurs in two stages: The mineral is removed at bone margins and then exposed organic matrix disintegrates .

21. CEMENTOCLASTS Cementoclasts are found in periodontal ligament but not remodeled like alveolar bone and periodontal ligament. These are found on the surface of cementum.

22. PROGENITOR CELLS Progenitor cells are the undifferentiated mesenchymal cells , which have the capacity to undergo mitotic division and replace the differentiated cells Located in perivasular region and have a small cnucleus and little cytoplasm (5) . When cell division occurs, one of the daughter cells differentiate into functional type of connective tissue cells. The other remaining cells retain their capacity to divide.

23. EPITHELIAL CELL RESTS OF MALASSEZ These cells are the remnants of the epithelium of Hertwig’s Epithelial Root Sheath close to cementum. These cells exhibit monofilaments and are attached to each other by desmosomes. They are round to ovoid cells with central darkly stained nuclei. Can develop into pathological cysts. Normal function is unknown. The epithelia cells are isolated from connective tissue by a basal lamina.

24. Although seen in longitudinal sections as isolated cell clusters surrounded by a basement membrane, which separates them from the surrounding connective tissue, they apparently form a continuous network ensheathing the root at a certain distance. Although the number of epithelial rests of Malassez decreases with age, cell mitotic Activity has also been observed. (2,4)

25. Periodontal ligament showing epithelial cell rests of malassez , indicated by arrows

26. DEFENCE CELLS MAST CELLS Small round or oval. Numerous cytoplasmic granules, which mask its small, indistinct nucleus. The diameter of mast cells is about 12 to 15 microns. The granules contain heparin and histamine . The release of histamine into the extracellular compartment causes proliferation of the endothelial and mesenchymal cells.

27. FUNCTION: Degranulate in response to antigen- antibody formation on their surface

28. MACROPHAGES Derived from blood monocytes Present near the blood vessels. These cells have a horse-shoe shaped or kidney shaped nucleus with peripheral chromatin and cytoplasm contain phagocytosed material.

29. FUNCTION Phagocytosis of dead cells . Secretion of growth factor , which help to regulate the proliferation of adjacent fibroblasts

30. EXTRACELLULAR SUBSTANCE Extra cellular substance comprises the following: 1. Fibers a) Collagen b) Oxytalan 2. Ground Substance a) Proteoglycans b) Glycoproteins

31. PRINCIPAL FIBERS The most important element of periodontal ligament -principal fibers The principal fibers are collagenous in nature and a arranged in bundles Follow a wavy course Dia-5 µm Primarily composed of type I & III collagen fibrils.

32. COLLAGEN Collagen is a high molecular weight protein. Composed of 3 polypeptide α -chain coiled around each other- Triple helix Individual fibril diameter = 50 – 60 nm Half life : 3 - 23 day collagen imparts a unique combination of flexibility and strength to tissue. Vitamin C help in formation and repair of collagen

33. Collagen macromolecules are rod like and are arranged in form of fibrils. Fibrils are packed side by side to form fibers.

34. Principal fibers of the PDL Alveolar crest group Horizontal group Oblique group Apical group Interradicular group

35. ALVEOLAR CREst gROUP These fibers extend obliquely from the cementum over the alveolar crest to alveolar crest. The alveolar crest fibers prevent extrusion of tooth and resist lateral tooth movements. .These fibers resists vertical and intrusive forces

36. HORIZONTAL FIBRES Horizontal fibers extend at right angles to long axis of tooth from the cementum to alveolar bone. These fibers are located apical to the level of alveolar bone crest. These fibers resists horizontal and tipping forces.

37. OBLIQUE FIBRES T he main attachment of the tooth. They run obliquely in coronal direction. These fibers mainly resists the vertical and intrusive forces. They bear the brunt of vertical masticatory stresses and transfer them on to the alveolar bone

38. APICAL FIBRES The apical fibers radiate in a rather irregular manner f They do not occur on incompletely formed roots. These fibers resist vertical forceps.

39. INTER-RADICULAR FIBERS These fibers are seen mainly in multi-rooted teeth with bifurcations and trifurcations ,fanning out from cementum into bone. These fibers resists vertical and lateral movements

40. TRANSEPTAL FIBRES D o not have osseous attachment  Run from cementum to cementum Reconstructed even after destruction

41. Oxytalan fibres These are elastic fibres found in the PL Restricted to the walls of the blood vessels. They originate from cementun or bone & are embedded into walls of the blood vessels. Function- support blood vessels & regulate vascular flow These oxytalan fibers run perpendicular to the collagen fibres .

42. Elaunin fibres Represents another form of elastic tissue consisting of bundles of microfibrils embedded within a small quantity of elastin . They form a network together with oxytalan fibers, extending from cementum to bone & sheathing the collagen fibers of PDL .

43. INTERMEDIATE PLEXUS: It is a zone of loose not well oriented collagen fibers in the center of the periodontal space. In this zone the fiber radiating from bone and cementum intermingle to form lattice network. Earlier it was thought that this is zone of rapid remodeling of fibers and necessary for tooth movement. It is presently believed/ concluded that this is just an artifact arising out of plane of section. In completely erupted tooth these fibers are no longer exist.

44. SHARPEY’S FIBERS Collagen fibers bundles are anchored in cementum at one end of PDL space and alveolar bone at other end. These fibers do not run in straight line but have a wavy course.

45. Ground substance It mainly consists of- GAG’s such as hyaluronic acid Proteoglycans Glycoprotein i.e. fibronectin and tenascin . It also consists of water 70%. They are present between cells & fibers of the PDL.

46. Blood supply Main blood supply is from superior and inferior alveolar arteries . The blood vessels are derived from the following: 1. BRANCHES FROM APICAL VESSELS Vessels supplying the pulp. 2. BRANCHES FROM INTRA-ALVEOLAR VESSELS:- Vessels run horizontally and penetrate the alveolar bone to enter into the periodontal ligament.

47. 3. BRANCHES FROM GINGIVAL VESSELS :- The arterioles and capillaries ramify and form a rich network. Rich vascular plexus is found at the apex and in cervical part of ligament.

48. Nerve supply Nerves pass through apical foramen to enter the PL. Finer branches enter middle & cervical portions of the PL through openings in the alveolar bone Nerves supplying the PDL are : Superior Alveolar Nerve & Inferior Alveolar Nerve Branches of trigeminal nerve These nerve fibers provide sense of touch, pressure, pain and proprioception during mastication

49. There are four types of neural terminations in the PDL that have been described: 1- Free endings- Sensory, pain perception 2- Ruffini’s Corpuscles- knob-like, mechanoreceptors 3- Tactile ( meissner’s ) corpuscles –mid root, mechanoreceptors 4- Spindle type nerve endings -apex

50. CEMENTICLES Small calcified bodies Remain free or fused into large calcified mass. They may be joined with cementum to form excementoses . Degenerated epithelial cells form the nidus for their calcification. Old age

51. FUNCTIONS PHYSICAL FUNCTION Provision of soft tissue ‘casing” in order to protect the vessels and nerves from injury due to mechanical forces. Transmission of occlusal forces to bone. Depending on type of force applied, axial force when applied causes stretching of oblique fibers of periodontal ligament.

52. C) Attaches the teeth to the bone. D) Maintains the gingival tissues in their proper relationship to the teeth. E) “Shock absorption” resists the impact of occlusal surfaces.

53. Two theories have been explained for mechanism of tooth support. TENSIONAL THEORY VISCOELASTIC THEORY

54. A. TENSIONAL THEORY According to it, principal fibers play a major role in supporting tooth and transmitting forces to bone. When forces are applied to tooth, principal fibers unfold and straighten and then transmit the forces to alveolar bone, causing elastic deformation of socket.

55. A. Tooth in a resting state B. The periodontal ligament fibers are compressed in areas of pressure and stretched in area of tension.

56. VISCOELASTIC THEORY According to it, the fluid movement largely controls the displacement of the tooth, with fibers playing a secondary role. When forces are transmitted to the tooth, the extracellular fluid is pushed from periodontal ligament into marrow spaces through the cribriform plate. After depletion of tissue fluids, the bundle fibers absorb the shock and tighten.

57. FORMATIVE & REMODELLING FUNCTION Cells of the periodontal ligament have the capacity to control the synthesis and resorption of cementum, ligament and alveolar bone. Periodontal ligament undergoes constant remodeling, old cells and fibers are broken down and replaced by new ones.

58. Nutritive function Blood vessels of periodontal ligament provide nutrition to the cells of periodontium , because they contain various anabolites and other substances, which are required by cells of ligament. Compression of blood vessels (due to heavy forces applied on tooth) leads to necrosis of cells. Blood vessels also remove catabolites .

59. SENSORY FUNCTION The nerve bundles found in periodontal ligament, divide into single myelinated nerve, which later on lose their myelin sheath and end in one of the four types of nerve termination: 1. Free endings , carry pain sensations. 2. Ruffini like mechanoreceptors located in the apical area. 3. Meissener’s corpuscles are also mechanoreceptors located primarily in mid-root region. 4. Spindle like pressure endings, located mainly in apex. Pain sensation is transmitted by small diameter nerves, temperature by intermediate type; pressure by large myelinated fibers.

60. HOMEOSTATIC MECHANISM The resorption and synthesis are controlled procedures. If there is a long term damage of periodontal ligament, which is not repaired, the bone is deposited in the periodontal space. This results in obliteration of space and ankylosis between bone and the tooth. The quality of tissue changes if balance between synthesis and resorption is disturbed.

61. If there is deprivation of Vit . C which are essential for collagen synthesis, resorption of collagen will continue. So there is progressive destruction and loss of extra cellular substance of ligament. This occurs more on bone side of ligament. Hence, loss of attachment between bone and tooth and at last, loss of tooth.

62. CLINICAL CONSIDERATIONS The primary role of periodontal ligament is to support the tooth in the bony socket. AGE CHANGES The width of periodontal ligament varies from 0.15 to 0.38mm. The average width is: - 0.21mm at 11 to 16 years of age. - 0.18mm at 32 to 50 years of age. - 0.15mm at 51 to 67 years width of periodontal ligament decreases as age advances Aging results in more number of elastic fibers and decrease in vascularity , mitotic activity, fibroblasts and in the number of collagen fibers and mucopolysaccharides .

63. PERIAPICAL LESIONS Periapical area of the tooth is the main pathologic site. 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.

64. 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. The rate of mesial drift of tooth is related to health, dietary factor and age. It varies from 0.05 to 0.7mm per year

65. Trauma : The trauma can be result from number of ways: Abnormal occlusal function,Accidental blows. Premature contacts from high points in restoration. Excessive orthodontic forces. All of the above leads to pulpal injury result in periapical changes. Over instrumentation during RCT causes profuse periapical haemorrhage and dissemination of dentin debris beyond the apical foramina. It result in edematous PDL, intense neutrophil inflammatory infiltrate.

66. Surface resorption : When there is very less damage to PDL – Adjacent PDL is proliferates. Inflammatory resorption : When there is infection is there – inflammation of bone and PDL – which is replaced by granulation tissue. Replacement resorption : When there is severe damage to PDL, resorption of bone, cementum , PDL it is replaced by the bone. Results in ankylosis of tooth

67. Orthodontic tooth movement Depends on resorbtion and formation of bone and periodontal ligament (i.e. remodelling). when a orthodontic force is applied through PDL to the tooth there is a initial compression of PDL on pressure side followed by the bone- resorbtion , whereas in tension side there is bone apposition. Application of large amount of force result in necrosis and death of PDL

68. REVIEW OF lIteraturE Carranza FA, and Saglie , 1984 :The PDL acts as a shock absorber & a means of transmitting occlusal forces to bone GriffinCJ 1968:Presence of unnmyelinated nerve endings in the periodontal membrane Grant DA, Stern, Listgarten,1988: PDL plays an active role in the resorption and formation of collagen and cementum and the fibroblasts of the PDL may develop into cementoblasts and osteoblasts . ButlerWT,Birkedal-hansen,Beegle et al ,1975:studied the proteins in the periodontium,concluded with the identification of type I & III collagen. Genco R, Goldman, HM., and Cohen, 1990: Periodontal regeneration is defined as restoration of the periodontal attachmentapparatus , which includes periodontal ligament, cementum, and alveolar bone, and gingival

69. Nyman S, Gottlow J, Karring T, et al. 1982:cells from the periodontal ligament (PDL) are responsible for the reestablishment of periodontal attachment. A study done on Dogs by Isaka et. al. concluded that dogs periodontal ligament cells retain capability to differentiate into osteoblast lineage & may act in periodontal regeneration of periodontal ligament with new cementum formation .

70. CONCLUSION: The diseases of PDL are often irreversible once destroyed the PDL is difficult to regenerate and damage of PDL result in loss of tooth. So, all operative procedures must be performed so as to maintain and restore the PDL is optimum health and function.

71. References 1) Glossary of Periodontal Terms 2) FerminA , Carranza, Newmann , Takei; clinical periodontology ;9thedition;45–51. 3)R.Tencate,AntonioNanci;oralhistology,development,structure&function;6thedition;111–143. 4) FerminA , Carranza, Newmann , Takei; clinical periodontology ;9thedition;45–51 . 5) Junqueria LC, Carneiro J, Kelley RO: Basic Histology, ed6, Norwalk, Conn, 1989, Appleton & Lange. 6) Hagel- Bradway S, Dziak R: Regulation of bone cells metabolism, J Oral Pathol Med 18:344,1989 7 ) Sicher H, DuBrul EL: Oral Anatomy, ed6, St Louis, 1975

72. 8)Chambers TJ: The cellular basis of bone resorption , Clin J Periodontal Res 1:120, 1966. 9 )Bernard GW, Ko JS: Osteoclast formation in vitro form bone marrow, mononuclear cells in osteoclast-free bone, Am J Anat 161:415, 1981