development of periodontium.ppt
- 2. 2/85 DEVELOPMENT OF GINGIVAL TISSUES • Gingival tissues are composed of a Superficial epithelium An underlying of ectodermal origin connective tissue of mesodermal origin • Both these tissues have components which derive from both the oral mucosa & the developing tooth germ. - Listgarten 1972,Mc Kenzie 1988
- 3. 3/85 • The epithelium of gingival tissues is composed of: - non keratinized junctional epithelium - non keratinized sulcular epithelium - keratinized oral epithelium
- 4. 4/85 • Gingival connective tissue is largely a fibrous connective tissue that has elements originating from the oral mucosa connective tissue & dentogingival fibers originate from developing dental follicle. • The gingival tissues associate with tooth via separate mechanisms. • The epithelial tissues interface with the tooth via an epithelial attachment known as Junctional Epithelium which in health, is usually located at, or coronal to the CEJ.
- 5. 5/85 • The gingival tissues attach to the root surface at or below the CEJ via fiber insertion into the cementum.
- 6. 6/85 • It follows a well defined series of events. • Prior to eruption of the tooth, Enamel of formed crown is covered with a few layers of flattened cuboidal cells called Reduced Enamel Epithelium (REE). • The basal lamina (EAL) lies in direct contact with Enamel. • REE completely encapsulates the newly formed crown & terminates at CEJ. Development of Junctional Epithelium
- 7. 7/85 • As tooth erupts ,the REE covering the tip of the crown fuses with the oral epithelium. • The migrating epithelium produces an epithelial mass between the oral epithelium & REE so that the tooth can erupt without bleeding. • Former ameloblasts do not divide.
- 8. 8/85 • Shortly, afterwards it degenerates to result in first exposure of the crown to the oral cavity. • First evidence of Junctional Epithelium is seen upon crown exposure. • As the tooth continues to erupt, the conversion of REE into to Junctional Epithelium continues.
- 9. 9/85 • Once, Enamel formation is complete, reduced ameloblasts attach via hemidesmosomes to a basal lamina that covers the crown surface referred to as internal basal lamina of REE. • This basal lamina extends apically to CEJ where it loops back to form an interface between REE & connective tissue of the mucosa that surrounds the entire crown.
- 10. 10/85 Development of Gingival Sulcus • The gingival sulcus is a shallow, V-shaped space or groove between the tooth and gingiva. • It begins to form as the tooth erupts & a separation occurs between the attached epithelium & tooth surface. • Simultaneously, epithelial cells derived from stratum intermedium also begin to transform into cells with the appearance of Junctional Epithelium.
- 11. 11/85 • Cells from stratum intermedium continue their mitotic activity. • Newly formed daughter cells migrate coronally toward the base of the gingival sulcus exfoliate allowing JE to maintain its structure via constant renewal process.
- 12. 12/85 • Gingival sulcus is formed when the tooth erupts into the oral cavity. • At that time , JE and REE form a broad band attached to tooth surface from near the tip of the crown to the CEJ. • Gingival sulcus is a shallow V- shaped groove between the tooth & gingiva that encircles the newly erupted tip of the crown. • In newly erupted tooth only Junctional epithelium persists.
- 13. 13/85 • Sulcus consists of a shallow space that is coronal to the attachment of the Junctional epithelium and bounded by tooth on one side and sulcular epithelium on the other. • The coronal extent of gingival sulcus is the gingival margin.
- 14. 14/85 • Junctional epithelium has a free surface at the bottom of the gingival sulcus. • Like oral sulcular epithelium and oral epithelium, Junctional epithelium is continuously renewed through cell division at the basal layer. • The cells migrate to base of gingival sulcus where they are shed.
- 16. 16/85 DEVELOPMENT OF CEMENTUM • It is a hard, avascular connective tissue that covers the anatomic roots of the human teeth. • It was first described microscopically in 1835 by two pupils of purkinje. • It begins at the cervical portion of the tooth at the CEJ and continues to the apex.
- 17. 17/85 DEVELOPMENT OF CEMENTUM • Formation can be divided into Prefunctional stage Functional stage
- 18. 18/85 Prefunctional stage : • Cementum is formed during the root development • Human roots form over an extended period of time ranging between 3.75 – 7.75 yrs for the permanent tooth. • Hence, Prefunctional development of Cementum is a long lasting procedure.
- 19. 19/85 Functional stage : • Commences when tooth reaches the occlusal level & continues throughout life.
- 20. 20/85 • Adaptive & reparative processes are carried out by the biological responsiveness of Cementum influences the alterations in the distribution & appearance of Cementum varieties on the root surface with time.
- 21. 21/85 CEMENTOGENESIS • After completion of crown formation the cells of the inner and outer enamel epithelium form the bilayer of cells known as Hertwig’s Epithelial Root Sheath.
- 22. 22/85
- 23. 23/85 • Continuous cell mitotic activity at the apical termination of HERS coronoapical growth of this bilayer
- 24. 24/85 • Its most apical portion, which forms a diaphragm separates the dental papilla from the dental follicle. • The inner & outer cell layer of HERS is surrounded by basement membrane.
- 25. 25/85 • The epithelial mesenchymal interactions occurring between the internal basement membrane & the cells of peripheral dental papilla differentiate into odontoblasts. • Once the first matrix of radicular dentin is formed by the maturing odontoblats & before it mineralizes, HERS becomes discontinuous.
- 26. 26/85 • Epithelial remnants of HERS persist in the developing & aging PDL, at an approximate distance of 30 – 60 µm far from the root surface, where they are referred to as Epithelial Rests of Malassez. - Malassez M L 1884
- 27. 27/85 • ERM forms a continuous network ensheathing the root at a certain distance. • Cell clusters are surrounded by a basement membrane which separates them from the surrounding connective tissues. • Function presently unknown.
- 28. 28/85 DEVELOPMENT OF DENTINO CEMENTAL JUNCTION • Differentiation of cementoblasts occurs on mantle dentin. Maturing cementoblasts extend cytoplasmic process positioning of the cemental collagen fibers interdigitation of two fibril population (Cementum & dentin) calcification starts in dentin, spreads across Cementum formation of DCJ
- 29. 29/85 DEVELOPMENT OF DENTINO CEMENTAL JUNCTION
- 30. 30/85 DEVELOPMENT OF CEMENTO ENAMEL JUNCTION • In 60% of teeth – Cementum overlaps the cervical end of enamel for a short distance. • Occurs when enamel epithelium degenerates at its cervical termination permitting connective tissue to come in direct contact with the enamel surface.
- 31. 31/85 DEVELOPMENT OF CEMENTO ENAMEL JUNCTION • In 30% of teeth – Cementum meets cervical end of enamel in a relatively sharp line.
- 32. 32/85 DEVELOPMENT OF CEMENTO ENAMEL JUNCTION • In 10% - Enamel & Cementum do not meet. • Occurs when enamel epithelium in the cervical portion of the root is delayed in its separation from dentin. • In such cases no CEJ • Zone of the root is devoid of Cementum & is, for time covered by REE.
- 33. 33/85 DEVELOPMENT OF INTERMEDIATE CEMENTUM • Just before the degeneration of the epithelial root sheath, root dentin is deposited adjacent to it as a thin, amorphous, structureless, highly mineralized secretion which appears on the surface of root dentin. • Devoid of collagen but contains tryptophan. • More evident in apical region. • Thickness : 10 – 20 µm
- 34. 34/85 DEVELOPMENT OF INTERMEDIATE CEMENTUM • This Cementum is deposited on the root surface & functions to attach secondary Cementum to its surface. • May contain epithelial cells. • Root sheath cells have an odontoblast stimulating ability as well as possible secretory functions in producing the Intermediate Cementum.
- 35. 35/85 CELLUAR AND ACELLULAR CEMENTUM • The behavior of cementoblasts during matrix formation determines the type of Cementum to be formed. • Cellular Cementum – found on apical half (thicker) • Acellular Cementum – covers the cervical half of the root dentin (thin)
- 36. 36/85 CELLULAR CEMENTUM ACELLULAR CEMENTUM
- 37. 37/85 DEVELOPMENT OF ALVEOLAR PROCESS • Alveolar bone develops as the tooth develops. • Initially, this bone forms a thin egg shell of support, termed as the ‘tooth crypt’, around each tooth germ.
- 38. 38/85 • As the root grows and lengthen alveolar bone keeps pace with the elongating and erupting tooth and maintains a relation with each tooth root.
- 39. 39/85 • Development of alveolar process begins in 8th week in utero. • At that time, within maxilla & mandible the forming alveolar bone develops a horse shoe shaped groove. • The bony groove or canal is formed by the growth of facial & lingual plates of body of maxilla or mandible & contains the developing tooth germs together with alveolar blood vessels and nerves.
- 40. 40/85 • At first developing tooth germs lie free in the groove. • Then, bony septa develops between teeth and eventually each tooth is contained in a separate crypt. • During uterine life, dental alveolus like the rest of the skeleton is formed from an embryonic type of bone composed of tiny, bony spicules.
- 41. 41/85 • Embryonic bone is of 2 types : Woven Bone Coarse Bundle Bone bundles of collagen collagen bundles run in various direction are thicker. in the matrix Follow a parallel coarse in matrix.
- 42. 42/85 • The matrix of embryonic bone consists of more glycosaminoglycans & glycoproteins than that of mature bone. • The embryonic bone, is of temporary existence and is replaced by mature or lamellar bone of the compact or spongy bone.
- 43. 43/85 MATURE BONE : • Composed of lamellae arranged in an orderly manner. • Fine fiber arrangement. • Few cells
- 44. 44/85 • The bone between the roots of the adjacent single rooted or multirooted teeth is termed as the interdental bone.
- 45. 45/85 • In its mature form, alveolar bone is composed of two parts : Alveolar Bone Proper Supporting Bone
- 46. 46/85 ALVEOLAR BONE PROPER : • It is a thin lamella of compact bone that lines the root socket & periodontal fibers are embedded in it. • Also called as Lamina Dura.
- 47. 47/85 • Alveolar bone proper is a specialized type of dense bone composed of bundle bone & haversian bone that appears radio opaque on x- ray and hence is called as Lamina Dura. • Bundle bone is named as it is penetrated by bundles of periodontal fibers. ALVEOLAR BONE PROPER :
- 48. 48/85 SUPPORTING BONE : • Consists of both spongy & compact bone • Functions in supporting the alveolar bone proper.
- 49. 49/85 • It is formed by osteogenic cells in the outermost layer of the dental follicle differentiate into osteoblasts bone matrix laid down osteocytes formed Matrix calcifies formation of mature bone DEVELOPMENT OF ALVEOLAR BONE PROPER
- 50. 50/85 • In all bony tissues a system of cell to cell communication exists between adjacent bone cells e.g. osteogenic cells, osteoblasts & osteocytes. • This takes place by 3 means : 1)Presence of junctional complex (gap) between the different cells. 2)Presence of cytoskeleton at opposing points of adjacent cells 3)Presence of small nerve fibers in the periosteum These may work together to produce effective cell communication & co-ordination of cellular activity.
- 51. 51/85 • Relationship between a deciduous tooth & its accompanying succedaneous tooth detailing the formation of the alveolar bone - Scoh,Symonds 1974 AT BIRTH AT 7MONTHS AT 2½ YRS 7 YRS
- 52. 52/85 DEVELOPMENT OF PERIODONTAL LIGAMENT • The periodontal ligament originates from the dental follicle. • It is a specialized, soft, connective tissue ligament that provides the attachment for the teeth to the adjacent alveolar bone. • Its fibers are embedded in the Cementum on the tooth’s surface & in the alveolar bone at the other end.
- 53. 53/85 DEVELOPMENT OF PERIODONTAL LIGAMENT • Delicate fiber bundles of the forming PDL fibers first appear as root formation begins. • Follicular cells show increased mitotic activity. • Inner most cells near the forming root differentiate into cementoblasts & lay down cementum. • Outer most cells osteoblasts
- 54. 54/85 • Centrally located cells in the ligament differentiate into fibroblasts. • These produce collagen fibers that becomes embedded into both cementum and bone. DEVELOPMENT OF PERIODONTAL LIGAMENT
- 55. 55/85 DEVELOPMENT OF PERIODONTAL LIGAMENT • At first, developing fibers of PDL run obliquely in a coronal direction from tooth to bone. • The apical fibroblasts are the stem cells that proliferate & migrate cervically to form the first group of collagen fibers. ACF
- 56. 56/85 DEVELOPMENT OF PERIODONTAL LIGAMENT • As tooth eruption proceeds, the obliquity of the fibers gradually decreases. ACF OF
- 57. 57/85 DEVELOPMENT OF PERIODONTAL LIGAMENT • The position of CEJ which was apical to the crest becomes level & then coronal to the alveolar crest. • This change between CEJ & alveolar crest may relate to their functional role during tooth eruption. • It also brings the final arrangement of the principal fiber groups of the mature PDL.
- 58. 58/85 DEVELOPMENT OF PRINCIPAL FIBERS A) First small brush like fibrils arise from root cementum & projects into the PDL space. - surface of bone at this stage is covered by osteoblasts. - from the surface of bone only a small number of radiating thin collagen fibrils can be seen.
- 59. 59/85 DEVELOPMENT OF PRINCIPAL FIBERS B) Number & thickness of fibers entering the bone increases & radiates towards the loose connective tissue in the mid portion of the PDL area which contains more or less randomly oriented collagen fibrils. - Fibers from cementum are still short while that of bone becomes longer. - The terminal portions of these fibers carry finger like projections.
- 60. 60/85 DEVELOPMENT OF PRINCIPAL FIBERS C) Fibers originating from cementum increase in length & thickness & fuse in the PDL space with the fibers arising from alveolar bone. - When the tooth following eruption reaches contact in occlusion & starts to function the periodontal fibers become organized in bundles & run continuously from bone to cementum.
- 61. 61/85 • Periodontal fibers run continuously from cementum to alveolar bone proper. • Periodontal fibers embedded in cementum have a smaller diameter but are more numerous in number than those embedded in alveolar bone proper.
- 62. 62/85 • Periodontal ligament is in a continuous state of remodelling, both during development & throughout life span of the tooth. • The ligament persistently maintains support of an erupting or functioning tooth.
- 63. 63/85 • Remodelling is achieved by fibroblasts that rapidly synthesize & secrete collagen. • Rapid turnover of collagen takes place throughout the whole thickness of ligament from bone to cementum. • Turnover is not restricted to the metabolically active middle zone, which is sometimes referred to as intermediate plexus. • Different rate of collagen turn over in the ligament in an apico-cervical direction.
- 64. 64/85 • Highest turn over is in apical region • Lowest in cervical region of the ligament.
- 65. 65/85 REFERENCES • Tencate’s Oral histology – Antonio Nanci • Orban’s Oral histology and embryology – S. N. Bhaskar • Biology of periodontal tissues – Bartold and Sampathnarayan • Clinical periodontology and implant dentistry – Lindhe • Oral development and histology – Avery • Clinical Periodonology – Carranza 10th edition • Biological structure of normal & diseased periodontium – Perio 2000, vol 13, 1997