1. INTRODUCTIONThe term periodontium arises from greek words peri meaning around and odont meaning tooth. Tissues that invest and support the teeth are collectively termed PERIODONTIUM.

2. DEFINITION Periodontal ligament is an unique multifunctional soft specialized , vascular and highly cellular connective tissue that surrounds the tooth root and connects it to the inner wall of the alveolar bone. (1)It is continuous with the connective tissue of the gingiva and communicates with marrow spaces through vascular channels in the bone. OTHER NAMES: 1. Periodontal membrane 2. Alveolo-dental ligament 3. Desmodont 4. Pericementum 5. Dental periosteum 6. Gomphosis(2) 3. DEVELOPMENT OF PERIODONTAL LIGAMENT Enamel organ is surrounded by a condensation of ecto mesenchymal cells calleddental sac. The part of the dental sac immediately close to the enamel organ is called dental follicle. (3) Once the Hertwig Epithelial root sheath disintegrates leaving behind the Epithelialrests of Malassez, cells of the dental follicle come close to the surface of newly formed dentin. The dental follicle cells then differentiate into cementoblasts & lay downcementum on dentin on the developing root. The other cells of the dental follicle differentiate into fibroblast & lay down fibers & ground substance of the periodontal ligament. 4. As the crown approaches the oral mucosa during tooth eruption, thesefibroblast become active & start producing collagen fibrils. They initially lack orientation, but they soon acquire an orientation oblique to the tooth.(4) The first collagen bundles appear in the region immediately apical to thecemento enamel junction & give rise to gingivodental fiber groups. As tooth eruption progresses, additional oblique fibers appear & become attached to the newly formed cementum & bone. 5. DEVELOPMENT OF PERIODONTAL LIGAMENTJan Lindhe, Niklaus P. Lang, Thorkild Karring Clinical Periodontology and Implant Dentistry 5TH EDITION 6. The transseptal & alveolar crest fibers develop when the tooth merges intothe oral cavity. Alveolar bone deposition occurs simultaneously with periodontal ligament organization. Sharpeys fibers are fewer in number & more widely spaced than thoseemerging from the cementum.(5) At the later stage, alveolar fibers extend into the middle zone to join thelengthening cemental fibers ,attain their classic orientation, thickness & strength when occlusal function is established. 7. DEVELOPMENT OF PERIODONTIUMJan Lindhe, Niklaus P. Lang, Thorkild Karring Clinical Periodontology and Implant Dentistry 5TH EDITION 8. Rearrangement of the fiber ends in the plexus, is supposed toaccommodate tooth eruption without necessitating the embedding of new fibers into the tooth & the bone. As the tooth eruption proceeds, the obliquity of the fibersgradually decreases and the position of the Cememtoenamel junction , which is originally apical to the crest of the crypt, comes to the level of the crest and then coronal to the alveolar crest. 9. PERIODONTAL LIGAMENT SIZE & SHAPE The Average width -> 0.2mm. It ranges in width from 0.15 to 0.38 ,thinnest portion aroundthe middle third of the root.At age of 11 - 16 years - width is 0.21 mm -> 32 - 52 years - width is 0.18 mm -> 51 - 67 years - width is 0.18 mm(6) Progressive decrease of width occurs with increase of age. The periodontal space is often Hour glass shaped , with narrowest portion in the midroot region near the fulcrum about which the tooth moves. 10. PRINCIPAL FIBERS These are the important elements of the Periodontal ligament which are collagenous , arranged in bundles and follow a wavy course when viewed in longitudinal sections.The principal fibers bundles consist of individual fibers forming a continuous anastomosing network between tooth and bone. 11. Transseptal group : These fibers extend inter proximally over the alveolar crest and are embedded inthe cementum of adjacent teeth. They are reconstructed even after destruction of the alveolar bone has occurred in periodontal disease. Resist tooth separation, mesial or distal. Alveolar crest group: Alveolar crest fibers extend obliquely from the cementum just beneath thejunctional epithelium to the alveolar crest. Fibres also run from the cementum over alveolar crest and to the fibrous layer of the periosteum covering alveolar bone They prevent the extrusion of teeth and resist lateral movements of tooth.(7) Their incision does not significantly increase tooth mobility. 12. PRINCIPAL FIBRES Jan Lindhe, Niklaus P. Lang, Thorkild Karring Clinical Periodontology and Implant Dentistry 5TH EDITION 13. PRINCIPAL FIBRES Horizontal group These group of fibers extend at right angles to the long axis of the tooth from -> the cementum to the alveolar bone. Resist horizontal and tipping forces. Oblique Group Oblique fibers, the largest group in the periodontal ligament, extend from the cementum in a coronal direction obliquely to the bone. They bear the brunt of vertical masticatory stress and transform them into tension on to the alveolar bone. It is the largest prinicpal fibre group They resist apically directed masticatory forces 14. Mosby's Dental Dictionary, 2nd edition. 2008 Elsevier, 15. Apical group The apical group radiate from the cementum to the bone at the fundus ofthe socket. They do not occur on incompletely formed roots. Functions- They prevent tooth tipping,resist forces of luxation .Inter radicular fibers These fibers fan out, from the cementum to the teeth on the furcationareas of multirooted teeth. They resist forces of luxation and roatation. 16. RELATED STUDIES Study conducted by EINAR KVAM To study TOPOGRAPHY OF PRINICPAL FIBRES(1973) Untreated human premolars were fixed in 4 % buffered Formaldehyde, The fibrous tissue of root surfaces were studied in SEM. RESULTS1.They occur in smaller bundles 2.fibre bundles appear to increase by additional layer of peripheral bundles 3.On root surface->outer portion of fibre bundles interlaced with fibrous coating(3) 17. RESULTS In demineralized sections Principal fibres bundles transversed the cementum. Principal fibres connecting the periodontal ligament werearranged in ladder like fashion. At Cemento Dentinal junction, fibres ended as finger like projections,rendering an irregular borders between dentin and cementum 18. SHARPEYS FIBRES The collagen bundles of the periodontal ligament are embedded into cementum and alveolar bone similar to that of tendon inserting into bone. These fibers are called as Sharpeys fibers.These fibers level to concentrate on the crestal region. Orientation is similar to that of adjacent periodontal ligament bundles. The Bone adjacent to the periodontal ligament that contains a great number of sharpeys fibers are called as Bundle bone. Some sharpeys fibers are completely calcified but most contain an uncalcifiedcentral core within a calcified outer layer.(9) 19. INTERMEDIARY PLEXUS OF PERIODONTAL LIGAMENT The principal fibers frequently run a wavy course from cementum tobone. It may appear as fibers arising from cementum & bone are joined in the midregion of the periodontal ligament space, giving rise to a zone of distinct appearance, called Intermediate plexus. INDIFFERENT FIBER PLEXUSIn addition to these fiber types, shakle ford has described small collagen fibers in association with larger collagen fibers. These fibers run in all directions forming a plexus that has been termed the indifferent fiber plexus.(10) 20. CELLS OF THE PERIODONTAL LIGAMENT 1) CONNECTIVE TISSUE CELLS A. SYNTHETIC CELLSB. RESORPTIVE CELLS2). EPITHELIAL REST CELLS -Fibroblasts Cementoblasts Osteoblasts Osteoclasts Odontoclasts CementoblastsEpithelial rests of malassez3). DEFENSE CELLS1. Macrophages 2. Mast cells 3. Eosinophils 21. CONNECTIVE TISSUE CELLS FIBROBLASTS: Most predominant cell type of periodontal ligament. -> found between the fibers of the periodontal ligament, where they are surrounded by fibers & ground substance. STRUCTURE: Ovoid or elongated cells oriented along the principal fibres. Large cells with an extensive cytoplasm Associated with protein synthesis & secretion (e.g. RER, several Golgicomplex, & many secretary vesicles) (11) 22. PERIODONTAL FIBROBLASTS Periodontal ligament fibroblasts are large cells with an extensive cytoplasm They have a well-developed cytoskeleton . Adherens and gap junctions, reflecting the functional demands placed on the cells. Aligned along the general direction of the fiber Extend cytoplasmic processes that wrap around them. The collagen fibrils of the bundles are continuously being remodeled by the fibroblasts. The remodeling of collagen in the ligament is not confined to any intermediate zone, but occurs across the entire width of the ligament. Because of exceptionally high rate of turnover of collagen in the ligament, any interference in the fibroblast function by disease rapidly produces a loss of the tooths supporting tissue.(12) 23. OSTEOBLASTS Found on the surface of the alveolar bone . Ultrastrucutre is same as that osteoblasts anywhere in the body. Bone forming cells derived from osteoprogenitor cells. Seen on surfaces of bone giving an epithelium like appearance. Shape varies(seen as oral, triangular, cuboidal) etc. Nucleus is ovoid and euchromatic Cytoplasm is basophilic ( because of abundant rough endoplasmic reticulum) Responsible for laying down the organic matrix of bone including thecollagen fibers. Alkaline phosphatase present in osteoblasts is responsible for its mineralization(13) 24. ELECTRON MICROGRAPH OSTEOBLAST CROSS SECTIONOrban's Oral Histology and Embryology 25. FUNCTIONS Maintain the integrity of the lacunae and canaliculi. Open the channels for diffusion of nutrition through the bone. Play a role in removal or deposition of matrix and of calcium when required. Osteoblasts first migrate away from the bone surface into the body ofperiodontal ligament before eventually taking up their functional position. Osteoblasts form a cell layer over forming bone surface and act as barrierthat control ion flux into out bone(14) 26. CEMENTOBLASTS These are the cells responsible for secreting the organic matrix (mainlycollagen) of cementum. As distinct layer of cells on the root surface, similar to osteoblastic layer butnot regular in arrangement. Differs from periodontal ligament fibroblasts in-> Appear near the cementum. Less rough Endoplasmic Recticulum More Mitochondria(15) 27. CEMENTOBLASTS CEMENTOBLASTDENTINPERIODONTAL LIGAMENTCEMENTUMCEMENTOI D TISSUE CEMENTOBLATOrbans Oral Histology and Embryology,Surinder Nath page -155 28. RESORPTIVE CELLS OSTEOCLASTS Bone resorbing cells. Present on the surface of bone where it is removed. At such locations the cells occupy pits called Resorption bays or lacunae of howship. Large cells : 20 100 m diameters. Numerous nucleus : upto 20 or more Cytoplasm : Numerous mitochondria lysosomes Osteoclasts are formed by fusion of mononuclear cells arising frombone marrow. They do not cover the whole of resorbing surface at any one time, rather they service a much larger area by demonstrating considerable motility. Inhibitor->Osteoprotegrin(16) 29. CEMENTOCLASTS Resemble Osteoclasts. Located in howships lacunae. Origin unknown but believed to be same as that ofOsteoclasts. Since constant deposition of cementum occurs, these cells are not seen during normal functioning of cementum. 30. CEMENTOCLASTS STRUCTURE:1.Cytoplasma exhibit numerous lysozomes and mitochondria 2.Ruffled border->part of plasma memberane lying adjacent to bone. 3.Few ribosomes. 4.Less rough endoplasmic retiuculum. 31. EPITHELIAL CELL RESTS OF MALASSEZ Form a latticework in the periodontal ligament and appear as either isolated clusters of cells or interlacing strands. Represent the remnants of developmental Hertwig epithelial root sheath which is involved in differentiation of root odontoblasts and also secrete enamel like proteins on the root surface. Arranged in close packing of cuboidal cells,completely surrounded by connective tissue cells. Located closer to cementum than to alveolar bone. Situated in the periodontal ligament at a distance of 1575 m from thecementum on the root surface.(17) As age increases the epithelial cell rest move vertically and are located mostly inthe vertical region in the gingiva. 32. EPITHELIAL RESTSOrban's Oral Histology and Embryology PAGE -186 33. RELATED STUDIES Loe and waerhaug (1960)(18) After reimplantation studies observed that -> Ankylosis and subsequent root resorption never occurred when a periodontalligament that contained epithelial cell rest was retained. These authors suggest that epithelial cell rest may be the factor in limiting theresorption and play a role in maintenance of periodontal space.(18) 34. DEFENSE CELLS Macrophage cells Have the ability to phagocytose unwanted material. Macrophages are usually described as fixed when they are attached to fibers or as motile (free).(19) Fixed macrophages resembles fibroblasts but free macrophages are rounded. Nuclei smaller and stain intensely than fibroblasts. (kidney shaped). Cytoplasm contain numerous lysosomes which help in digesting material phagocytosed by macrophages. Macrophages may fuse together to form multinucleated giant cells. 35. MULTIVESICULATED BODY OF MACROPHAGENon Myelinated Nerve fibersOrban's Oral Histology and Embryology,Page 129 36. MAST CELLS These are round or oval cells. Nucleus small centrally placed Microvilli (filopodia) present on cell surface. Presence of numerous granules in the cytoplasm. Granules are known tocontain acid mono polysacharrides. The cell membrane of mast cells contain antibodies which react with theantigen.(20) This leads to rupture of the cells which discharge histamine and serotonin.The discharge in turn lead to local reactions like utricaria or severe general reactions like Anaphylactic shock. 37. PERIODONTAL LIGAMENT IN HEALTHA SEMINAR SUBMITTED BYDR JOHNN KAZIMM DEPARTMENT OF PERIODONTICS AT I.T.S DENTAL COLLEGE, HOSPITAL & RESEARCH CENTRE, GREATER NOIDA 8 th November 2013 PART -2MODERATOR: Dr Annapurna Ahuja 38. EXTRA CELLULAR SUBSTANCES 1) Connective tissue fibers.Collagen fibers Oxytalan fibres Reticular fibers Elastic fibres 2) Ground SubstanceProteoglycans Glycoprotein. 39. COLLAGEN FIBRES Formed by fibroblasts. The predominant collagens of the periodontal ligament are type I, III, andXII, within individual fibrils having a relatively smaller average diameter than tendon collagen fibrils. Collagen type IV found in basement membrane of Junctional epithelium and epithelial rests of PDL. These fibers of the periodontal ligament have a structural requirement towithstand intensive forces from mastication and to accommodate tooth eruption. The collagen fibril diameters of the periodontal ligament are relatively small,with mean diameter of order 45 55 m which is much less compared to other connective tissues e.g. Tendon fibril >250 m. 40. COLLAGEN FIBRESCOLLAGEN FIBRESSURFACE OF CEMENTUM COLLAGEN FIBRES EMBEDDED IN CEMENTUMOrban's Oral Histology and Embryology,Page , Page 156 41. FUNCTIONAL ADAPTATIONS OF THE COLLAGEN FIBRES OF THE PERIODONTAL LIGAMENT The internal orientation of collagen fibres in connective tissues suggested thatcollagenous bundles could resist axially directed forces. The arrangement of majority of periodontal ligament collagen fibres into horizontal and obliquely directed groups may therefore be adapted to resist axial forces. (21) Such an arrangement has mechanical advantages over a simple radial arrangement. The overlapping arrangement of the bundles may also be advantageous inresisting intrusive forces, as axial displacement of the tooth would tend to straighten out the fibre bundles and compress the blood vessels. 42. IMMATURE FORMS OF ELASTIN OXYTALAN ELUANIN Oxytalan Run parallel to the root surface via vertical direction and bend to attach to cementum in the cervical third of the root. Restricted to the walls of the blood vessels. Regulate vascular flow and play a part in supporting the blood vessels of the periodontal ligament. Form a three dimensional meshwork that extends from cementum to peripheral blood vessels. Important for fibroblast adhesion and migration. Eluanin Elastic meshwork in periodontal ligament is composed of elaunin fibres andoxytalan fibres. 43. Tranmission Electron Microgrpah of Oxytalan Fibre in Cross Section Oxytalan Fibre Surroundedby Collagen FiberSpaces represent Ground SubstanceOrban's Oral Histology and Embryology,Page Page-192 44. GROUND SUBSTANCE OF THE PERIODONTAL LIGAMENT The ground substance is the gel like matrix which is synthesized by the cellsof the fibroblast family. Two types of glyco conjugates to form the major constituents of the groundsubstance. Proteoglycans Glyco proteins 45. PROTEOGLYCANS Composed of specific core of proteins to which one or more glycosaminoglycans (GAG) chains are covalently attached through a sequence, usually the trisaccharide galactose xylose. Glycosomino glycans.(22) Linear polymers of dissacharide which contain a hexosamine (usually D- Nacetyl glucosamine or D-N- acetyl galactosomine) and a hexuronic and either D- glucuronic acid. Chondroitin Sulphate Dermatan Sulphate Heparin Sulphate Hyaluronic Acid Currently termed as hyaluronan. Is a non- sulphated glycosaminoglycans. Keratan SulphateNot seen in periodontal ligament but unique among glycosoaminoglycans, as it does not contain hexuronic acid. 46. GLYCOPROTEINS Three distinctly related glycoprotiens of the extra cellular matrix have beenlocalized in the decalcified sections of human periodontal ligament, namely: Fibronectin-> Present in loose connective tissues and in embroyonicbasement membrane (not in adults) Laminin-> Major glycoprotein component of basement membranes. Tenascin-> Present in the glycoproteins of periodontal ligament with asmaller role in cell attachment and organization of basement membrane. 47. PERIODONTAL LIGAMENT VASCULATURE The blood supply to the supporting structures of the tooth is derived fromthe inferior & superior alveolar arteries to the mandible & maxilla, & it reaches the periodontal ligament from three sources: Apical Vessels. Penetrating vessels from the alveolar bone Anastomosing vessels from the gingiva.(23) The branches of the apical vessels supply the apical region of theperiodontal ligament before the vessels enter the dental pulp. The trans-alveolar vessels are branches of the intraseptal vessels that perforate the lamina dura & enter the ligament. The intraseptal vessels continue to vascularize the gingiva. Vessels within the periodontal ligament are contained in interstitial spaces of loose connective tissue between the principal fibers & are connected in a netlike plexus that runs longitudinally & closer to the bone than the cementum. 48. PDL VASCULATURE1.THROUGH PERIODONTAL LIGAMENT2.THROUGH ALVEOLAR BONE 3.SURFACE OF PERIOSTEUMLouis F rose,Brian,Cohen.Periodontics,Surgery Page 23 49. VASCULAR SUPPLY Numerous branches arise from the intraalveolar vessels to run horizontally,penetrate the alveolar bone & enter the ligament, they are called perforating arteries. The blood supply increases from the > 1.Incisors to the molars, 2.Greatest in the gingival third of single rooted teeth, in the apical third 3.Least in the middle third 4.Equal in the apical & middle third of the multi rooted teeth, 5.Greater on the mesial & distal surfaces than on the facial & lingual surfaces 6.Greater on the mesial surfaces of mandibular molars than on the distal surfaces.(24) 50. CLINICAL IMPORTANCE This pattern of distribution has a clinical importance. In the healing of the extraction wounds, new tissues invader fromperforations & formation of blood clot occupying the socket is more rapid in its gingival & apical areas. Within the ligament, the arteries occupy the areas of loose connective tissuecalled as interstitial areas between the principal fiber bundles. Vessels course in a apico-occlusal direction with numerous transverse connections. 51. INNERVATION OF PERIODONTAL LIGAMENT Small fibers in the periodontal ligament, particularly the A and C fibers. The trigeminal nerve innervates the periodontal ligament through maxillarynerve or inferior alveolar branches. The majority of the nerves supplying the periodontal ligament pass throughforamina on the alveolar bone to enter the periodontal ligament space close to the tooth apex, while others enter via the lateral aspect of the alveolar wall. 52. INNERVATION OF PERIODONTAL LIGAMENT These nerve bundles terminates as mentioned into four types : FREE NERVE ENDING Located at regular intervals along the length of the root. RUFFINIS CORPUCLESAppear dendrite and end in terminal expansions among the periodontal ligament fiber bundles. Subdivided into simple & compound forms.(25) THIRD TYPEIs coiled form found in midregion of periodontal ligament whose function & structure have not been determined. FOURTH TYPE Lowest frequency Consists of spindle like endings surrounded by fibrous capsule. 53. CEMENTICLES These are calcified masses found in the periodontal ligament. These bodies found in the older individuals and they remain free, they mayfuse into large calcified masses or they may be joined with the cementum. As the cementum thickens with age , it may envelope the bodies and will beadherent to the cementum , they form excementosis. Their origin is unknown. It was thought that degenerated epithelial cells form the nidus for theircalcification. 54. FUNCTIONS OF PERIODONTAL LIGAMENT Physical -> Provision of a soft tissue "casing" to protect the vessels and nerves from injuryby mechanical force Transmission of occlusal forces to the bone. Attachment of the teeth to the bone. Maintenance of the gingival tissues in their proper relationship to the teeth. Resistance to the impact of occlusal forces (shock absorption) . 55. SHOCK ABSORPTION THREE THEORIES ARE PROPOSED TENSIONAL THEORY:Force is applied to the crown,fibres first unfold,straighten and then transmits forces to the alveolar bone causing an elastic deformation of socket, when the alveolar bone has reached its limit, the load is transmitted to the basal bone. VISCOELASTIC THEORY:Displacement of tooth to be primarily controlled by the fluid movements.When forces are transmitted to the tooth, the extracellular fluid passes from the periodontal ligament into the marrow spaces of the bone through the foramina in the cortical layer. Perforations in the lamina dura link the periodontal ligament with the cancellous portion of the alveolar bone.After depletion of the tissue fluids , the fibre bundles absorb and tighten, this leads to blood vessel stenosis , arterial back pressure and passage of blood ultra filtrates into the tissues there by replenishing the fluids. THIXOTROPIC GEL THEORY:Periodontal ligament has behaviour of thixotropic gel(property of becoming fluid when shaken or stirred and then becoming semisolid again). The physiologic response of the periodontal ligament may be explained by changes in the viscosity of the biologic system.(26) 56. FORMATIVE AND REMODELING The periodontal ligament is constantly undergoing remodeling. Old cells andfibres are broken down and replaced by new ones. The rate of formation and differentiation of the fibroblasts affects the rate of formation of collagen, cementum and bone. 3) Nutritional:The periodontal ligament supplies nutrients to the cementum, bone, and gingiva by way of the blood vessels and provides lymphatic drainage. 57. FUNCTIONS Sensory: The periodontal ligament is abundantly supplied with sensory nervefibers capable of transmitting tactile, pressure, and pain sensations by the trigeminal pathways. Nerve bundles pass into the periodontal ligament from the periapical areaand through channels from the alveolar bone that follow the course of the blood vessels. They divide into single myelinated fibers, which ultimately lose their myelinsheaths . 58. EXTERNAL FORCES & PERIODONTIUM The periodontium exists for the purpose of supporting teeth during function& depends on the stimulation it receives from function for the presentation of its structure. Therefore, a constant & sensitive balance is present between external forces & the periodontal structures. The periodontal ligament also depends on stimulation provided by function to preserve its structure. Within physiologic limits, the periodontal ligament can accommodate & function with an increase in diameter & number of Sharpeys fibers. Forces that exceed the adaptive capacity of the periodontium produce injurycalled Trauma from occlusion. The periodontal ligament also atrophies, appearing thinned, & the fibers arereduced in no. & density, disoriented, & ultimately arranged parallel to root surface. This phenomenon is called disuse atrophy or a functional atrophy.(27) 59. CLINICAL CONSIDERATIONS Trauma to the ligament due to mechanical separation can producepathological changes such as fracture or resorption of the cementum, tears of fiber bundles, hemorrhage and necrosis. This result in resorption of bone and periodontal ligament is widened, so the teeth become loose. Orthodontic tooth movement depends on resorption and formation of both bone and periodontal ligament ->stimulated by both tension and pressure Application of large forces->necrosis of periodontal ligament(28) 60. CLINICAL CONSIDERATIONS In SCLERODERMA, the periodontal ligament is uniformly widened at theexpense of surrounding alveolar bone. Malignancy, both primary and metastatic, can affect the alveolar ridge and oftenpresents as periodontal disease. A uniform widening of the periodontal ligament can be an early sign ofosteosarcoma. Irregular destruction of the periodontal bone without tooth displacement is frequently the result of squamous cell carcinoma or metastatic carcinoma. 61. EFFECTS OF AGING ON THE PERIODONTAL LIGAMENT Reduction in vascularity, elasticity & reparative capacity are some of thecommon manifestations of ageing, generally noticed in all tissues. Gottlieb & Orban believed that with age , gingival recession & alveolar bone resorption occur & termed it as senile atrophy.(29) Decreased number of fibroblasts with more irregular structure is seen. Decreased Collagen synthesis with increasing age. Decrease in no. of periodontal fibers. The fiber bundles were thicker, broader and more highly organized. Areas of hyalinization were present. Decreased organic matrix production & epithelial cell rests. Increased amount of elastic fibers. The surfaces of the periodontal alveolar bone were jagged & uneven & an irregular insertion of fibers were seen. 62. EFFECTS OF AGING In children, periodontal ligament space is wider in children partly because ofthinner cementum & alveolar cortical plates.(30) It contains less fibers & more blood vessels. Alveolar bone has largermarrow spaces & fewer trabeculae than in adults. Marrow is also more vascular. Radiographically, distance from the Cementoenamel junction to thealveolar bone crest of primary canines & molars in the range of 0 to 2 mm. The susceptibility to periodontal disease is more significant for the rateof periodontal destruction than the length of time plaque is present (the age effect)(31) 63. Thank You 64. Refrences 1. Michael G. Newman, DDS, Henry Takei, DDS, PerryR. Klokkevold Carranzas Clinical Periodontology: Elsevier 2. Shantipriya Reddy, Reddy e,ssentials of Clinical Periodontology and Periodontics (492) 3. Antonio Nanci Ten Cate's Oral Histology: Development, Structure, and Function Elsevier Health Sciences 2008 65. Refrences 4. Periodontics Revisited,(pg 16) Shalu Bath 5. Michael G. Newman, DDS, Henry Takei, DDS, Perry R.Klokkevold Carranzas Clinical Periodontology:Elsevier 6. Md. Abdul Kadir Intentional Replantation of Molar Tooth City Dental College J. Volume-9, Number-1, January2012 7. Essentials of Oral Histology By K. Chatterje 01-Dec2006 - Medical 106 pg 8. EINAR KVAM,Topography of principal fibers European Journal of Oral Sciences;81:(7)pages 553557,1973 66. Refrences 9.Krishna kumar Review of Clinical,Periodontology 2007 pg 46 10. Shackleford JM: The indifferent fiber plexus and its relationship to principal fibers of the periodontium. Am J Anat 1971; 131:427. 11.Surindar Nath Bhaskar Orban's Oral Histology and Embryology pg 180 12.Antonio Nanci Structure of periodontal tissues in health and disease Periodontology 2000, Vol. 40, 2006, 1128 67. Refrences 13V Dhakray, M Mittal, P Khanna, M Jain, B Yadav Evolution AndHistory Of The Periodontal Ligament - A Review Internet Journal of Medical Technology:6,1 14. Antonio Nanci Ten Cate's Oral Histology: Development, Structure, and Function Elsevier Health Sciences 2008 15. Ultrastructural and morphometric analyses of human cementoblasts and periodontal fibroblasts.A Yamasaki, G G Rose, G J Pinero, C J Mahan,Journal of Periodontology, 04/1987; 58(3):192-201. 16. Textbook of Human Histology,By Inderbir Singh pg 104 17. Jan Lindhe, Niklaus P. Lang, Thorkild Karring Clinical Periodontology and Implant Dentistry Page 30, 5 th edition 2009 68. Refrences 18.Loe Waerhuaug j Experimental Reimplantaion ofteeth.Archives of oral biology 3; 176- 183 19.E Robert burns A human cell biology.Mosby 2007 20.Stanley Leonard Robbins Pathology Volume 2 Saunders 1967 21. B. K. B. Berkovitz, B. J. Moxham, Hubert N. Newman,The periodontal ligament in health and disease pg 446 69. Refrences 22. Ajit Varki and Nathan Sharon Essentials ofGlycobiolgy 2nd edition 23. Cohen L.Vascular Literature of mandible. J dent res 39:396,1960 24. Michael G. Newman, DDS, Henry Takei, DDS, Perry R. Klokkevold Carranzas Clinical Periodontology:Elsevier 25. Antonio Nanci Ten Cate's Oral Histology:Development, Structure, and Function Elsevier Health Sciences 2008 26. Periodontics Revisited,(pg 19) Shalu Bathia 70. 27. Michael G. Newman, DDS, Henry Takei, DDS,Perry R. Klokkevold Carranzas Clinical Periodontology:Elsevier pg 44 28.Surnder nath bhaskar,Orbans oral histology & emryology pg 200 29.Gottlieb b,Orba b,Active and passive continous eruption of teeth,J dent res 13:214,1933 30. Richard Welbury, Monty S. Duggal, Marie Thrse Hosey,Paediatric Dentistry ,Oxford pg 416 31. Van der Velden U,Effect of age on the periodontium J Clin Periodontol 1984 May;11(5):281-94.