Alveolar bone

Alveolar bone

1. ALVEOLAR BONE

2. Contents Introduction Bone Histology Cells and Intercellular Matrix Bone Development Remodelling Age Changes Clinical Considerations Conclusion References

3. Introduction

4. Bone - used to designate both an organ and a tissue Specialized mineralized connective tissue

5. Functions:

6. CLASSIFICATION (Ten Cate ) DEVELOPMENTALLY, Endochondral bone Intramembranous bone HISTOLOGICALLY, according to its density, mature bone can be divided into; Compact (cortical) bone Cancellous (spongy) bone

7. MICROSCOPICALLY: Lamellar bone Fibrous bone LAMELLAR BONE: Most of the bones, whether compact or cancellous , are composed of thin plates of bony tissues called lamellae. These are arranged in piles in a cancellous bone, but in concentric cylinders ( Haversian system or secondary osteon ) in a compact bone.

8. FIBROUS BONE (WOVEN BONE): It is found in young fetal bone. Collagen fibers - more variable diameter Irregular orientation giving it matted appearance

9. DEVELOPMENT OF ALVEOLAR PROCESS Alveolar process is dependent on the presence of teeth for its development and maintenance. At the late bell stage, bony septa and bony bridge start to form, and separate the individual tooth germs from another, keeping individual tooth germs in clearly outlined bony compartment. (BERKOVITZ)

10. Initially, this bone forms a thin egg shell of support, termed as the ‘tooth crypt’, around each tooth germ.

11. FIG. 9-5 A developing root shown by a divergent apex around the dental papilla (arrow), which is enclosed by an opaque bony crypt.

12. Relationship between a deciduous tooth & its accompanying succedaneous tooth detailing the formation of the alveolar bone - Scoh , Symonds 1974 12 /85 AT BIRTH AT 7MONTHS AT 2½ YRS 7 YRS

13. Bone 67 % Inorganic Hydroxyapatite 33 % (organic) 28% 5 % Collagen type Ӏ Non coll. proteins (ca 10 {po 4 } 6 {oh} 2 )

14. Osteocalcin , Osteonectin , Bone morphogenic proteins, Phosphoproteins and Proteoglycans Ground substance- Glycosaminoglycans , proteoglycans and water Osteopontin , Bone Sialoprotein - cell adhesion proteins (Mackie et al, 2003)

15. Osteocalcin (bone GLA protein) Found in bone matrix Expressed only by fully differentiated cells Specifically localized to developing bone Produced by osteoblasts and odontoblasts Role in bone formation

16. Osteopontin Glycosylated phosphoprotein Role in bone formation and resorption Synthetized by osteoblasts , osteoclasts , osteocytes , smooth muscles and epithelial cells Role in cell adhesion Significant amounts at mineralizing front

17. Bone sialoprotein Structural protein of bone Restricted to mineralized tissues Secreted by osteoblasts

18. Osteonectin Glycoprotein bound to HA Calcium binding glycoprotein Synthesized by fibroblasts and role in wound healing

19. Inorganic material- calcium, phosphate ,hydroxyl, carbonate, citrate Trace amounts of sodium, magnesium and fluorine ( Glimcher 1990) Hydroxyapetite crystals of ultramicroscopic size Enzymes like alkaline phosphatase , ATP and pyrophosphatase Parallel to collagen fibres and contribute to lamellar appearance of bone

20. Alveolar bone Portion of maxilla and mandible that forms and supports the tooth sockets (alveoli) Forms when tooth erupts to provide osseous attachment to PDL Disappears gradually after tooth loss ‘ Tooth dependent bony structure’ (Schroeder et al, 1991)

21. Transverse section Longitudinal section

22. Morphology determined by size, shape, function and location of teeth Formed during fetal growth by intramembraneous ossification

23. Cancellous Bone Compact Bone Shelf like bone

24. Holds the tooth firmly in position during mastication Aids in movement Adapts to occlusal loads Helps to move the teeth for better occlusion. Functions of alveolar bone

25. Supplies vessels to the PDL. Houses & protects developing permanent teeth while supporting primary teeth . Organizes successive eruptions of primary & secondary teeth.

26. Bone Histology

27. Three parts 1) External plate of cortical bone 2) Inner socket wall 3) Cancellous trabeculae (between two compact layers)- function of support

28. Cortical bone 1) Circumferential lamellae (encloses entire adult bone and forms the outer perimeter

29. 2) Concentric lamellae (make up bulk of compact bone and forms the basic metabolic unit of bone, the osteon ) 3) Interstitial lamellae (inter-spread between adjacent concentric lamellae and fill the spaces between them..actually fragments of pre-existing concentric lamellae and can be of many shapes)

30. Osteon –cylinder of bone parallel to long axis of bone (structural and metabolic units) Haversian canal –in centre of osteon , lined by single layer of bone cells Each canal has a capillary

31. Haversian canals interconnected by Volkmann canals System for dense bones like cortical plates and alveolar bone proper, where surface vessels are unable to supply blood

32. Socket wall Dense , lamellated bone – alveolar bone proper (contains sharpeys fibers and circumferential lamellae)

33. Cribriform plate (anatomic term) Lamina dura (radiographic term) Bundle bone ( histologic term)

34. Bundle bone Bone adjacent to PDL that contain sharpeys fibers Contains higher calcium than other areas Many features in common with cementum layer on root surface Collagen fibers larger in diameter, less numerous , less mature

35. Localized within alveolar bone proper Sharpeys fibers completely calcified or partially calcified with uncalcified core Not unique to jaw -occurs wherever ligaments and muscles are attached Thickness of 100-200 microns High turnover rate

36. FIBER ARRANGEMENT IN ABP DOUBLE FIBRILLAR ORIENTATION: Extrinsic fibers - Sharpey’s fibers run perpendicular to bone surface produced by PDL fibroblast At their insertion in bone, they become mineralized, with their periphery being hypermineralized than cores. Intrinsic fibers Laid down by osteoblasts between Sharpey’s fibers Irregularly arranged & less dense.

37. Cancellous bone Presence of trabeculae enclosing irregular marrow spaces lined with a layer of thin, flattened endosteal cells Variation in trabeculae pattern depending upon occlusal forces and genetically Matrix consists of irregularly arranged lamellae separated by incremental and resorption lines

38. Found in inter- radicular and inter-dental spaces Maxilla>mandible Trabeculae alligned in path of tensile and compressive stresses to provide maximal resistance to occlusal forces with minimum bone substance (Glickman et al 1970) in thickness and number with force

39. Spongy bone (anatomic term) Trabecular bone (radiographic term) Cancellous bone ( histologic term)

40. CANCELLOUS BONE: Type 1: The interdental and interradicular trabeculae are regular and horizontal in a ladder like arrangement. Type 2: Shows irregularly arranged numerous delicate interdental and interradicular trabeculae

41. CORTICAL BONE SPONGY BONE About 85% of bone About 15% of bone Lesser turnover than spongy Higher turnover Remodel about 3% of its mass each year remodel about 25% of its mass each year Mechanical/protective role More metabolic function

42. Interdental septum Consists of cancellous bone bordered by alveolar bone proper of approximating teeth and facial and lingual cortical plates Narrow septa- only cribriform plate Irregular window

43. Study by Heins et al 1986 Area Cribriform plate+cancellous bone Only cribriform plate Irregular window Maxillary molars 66.6% 20.8% 12.5% Mandibular premolar and molar 85% 15% 0%

44. Mesiodistal angulation of IDS is parallel to line drawn between CEJ of approximating teeth (Ritchey et al, 1953) Shape and size of IDS depends on 1) Size and convexity of crowns of approximating teeth 2) Position of teeth 3) Degree of eruption

45. Crest of IDS located 1-2 mm apical to CEJ of adjacent teeth

46. Diagram of relation between CE junction of adjacent teeth shape of crest of alveolar septa

47. Bone marrow

48. Cells

49. CELL TYPES IN BONE

50. Determined osteogenic precursor cells Inducible osteogenic precursor cells Muscles. Friedenstein (1973) divided osteoprogenitor cells into:

51. Osteoblast Produce organic matrix of bone Differentiated from pluripotent follicle cells No decrease with age Uninuclear cells Secrets collagen as well as non collagenous proteins Present on outer bone surface

52. Have high levels of alkaline phosphatase (this feature distinguishes it from fibroblasts) Alkaline phosphatase believed to cleave organically bound phosphate and help in bone growth Active -plump, cuboidal Inactive -flattened

53. Secrete type Ӏ and V collagen, variety of cytokines and several members of BMP such as BMP-2, BMP-7, TGF- ß , IGF-1, IGF-2 BMP family helps in bone formation and repair Under physiologic condition which support resorption - release of IL-6 and hydrolytic enzymes

54. Osteocyte Enclosed within spaces called lacunae within calcified matrix Entrapped Osteoblasts Reduction in size and loss of matrix synthesizing ability after being entrapped Excess space- lacunae

55. Extend processes into canaliculi that radiate from lacunae Anastomosing system Bring O 2 and nutrients to osteocytes through blood and remove metabolic waste products

56. More rapid the bone formation-more osteoblasts get entrapped – more osteocytes ( eg - bone formed during repair) Osteolytic osteolysis - osteocytes capable of resorption

57. Three functional states of osteocytes Quiescent osteocytes : paucity of rER , diminished golgi apparatus An osmiophilic lamina representing mature calcified matrix is seen in close apposition to cell membrane. Formative osteocyte : abundant rER & golgi apparatus evidence of osteoid in pericellular space within the lacuna. Resorptive osteocyte : Numerous ER & well developed golgi apparatus. The pericellular space is devoid of collagen fibrils & may contain a flocculent material suggestive of breakdown product. ‘ Osteocytic osteolysis ’.

58. Osteoclast Originate from hematopoietic tissue Fusion of mononuclear cells (blood derived monocytes ) to form a multinucleated cell Very large, 5-50 nuclei Active on less than 1% of bone surface Mobile and capable of migrating

59. Lie in Howships lacunae Acidophilic cytoplasm Active osteoclasts - ruffled border facing bone (hydrolytic enzymes are secreted) Increases surface area

60. Clear zone devoid of organelles but rich in actin filament, vinculin , talin (site of adhesion of osteoclast to bone) Sealing zone Ruffled border- enzymes like tartarate resistant acid phosphatase , carbonic anhydrase , proton pump ATP’s Cathepsin containing cytoplasmic vesicles near ruffled border

61. OSTEOCLASTIC FUNCTION IN BONE RESORPTION

62. Attachment of the osteoclast to mineralized bone surface Creation of sealed acidic environment through action of proton pump which demineralizes bone & exposes the organic matrix Degradation of the exposed organic matrix to its constituent amino acids by the action of released enzymes like acid phosphatase & cathepsin Sequestering of the mineral ions & amino acids within the osteoclasts . Tencate 1994- Described sequence of events of resorptive process:

63. Bone Lining Cells - When bone is no longer forming…..surface osteoblasts become inactive ….. Lining cells . - Thin flat nucleus, few cytoplasmic organelles - Retain gap junctions with osteocytes ….functions to control mineral homeostasis & endure bone vitality.

64. Periosteum and endosteum Both are layers of differentiated osteogenic connective tissue Periosteum covers outer surface of bone and endosteum lines the internal bone cavities Bundles of collagen fibres from outer layer penetrate bone and bind periosteum to bone Endosteum composed of a single layer of osteoblasts with some connective tissue

65. Periosteum

66. Functions of periosteum Medium through which muscles, tendons and ligaments are attached to bone Nutritive function to the bone Osteoprogenitor cells – Important role during development and repair after fracture Fibrous layer- acts as limiting membrane ( exostoses in cases of periosteal tear)

67. Bone Development

68. 1) Endochondral bone formation 2) Intramembranous bone formation 3) Sutural bone formation

69. Endochondral bone formation Cartilage replaced by bone Shape of cartilage resembles miniature version of bone to be formed At end of long bones, vertebrae, ribs, head of mandible and base of skull Condensation of mesenchymal cells

70. Perichondrium at the periphery Rapid growth of cartilage Cartilage replaced by bone gradually by osteoblasts at periphery

71. Intramembranous bone formation Occurs directly within mesenchyme Bone develops directly within the soft connective tissue Vascularity increases and osteoblasts differentiate and lay down bone Occurs at multiple sites (primary ossification center)

72. Ossification centers grow radially Cranial vault, maxilla, body of mandible and mid shafts of long bones Proceeds at extremely rapid rate Woven bone formed first in form of radiating spikules which ultimately fuse to form plates Transition of woven bone to lamellar bone

73. Mesenchymal condensation followed by increase in vascularity Some mesenchymal cells lay down collagen fibre bundles forming a membrane

74. Some differentiate into osteoblasts and lay down osteoid Which then gets calcified Mineralization always lags behind the production of bone matrix

75. Sutural bone growth Bone forms along suture margins Found in skull Fibrous joints between bones Allow only limited movement Helps skull and face to accommodate growing organs like eyes and brain

76. Vascular supply Derived from inferior and superior alveolar arteries of maxilla and mandible Lymphatic drainage Submandibular lymph nodes Nerve supply Branches from anterior, middle and posterior superior alveolar nerves for maxilla and branches from inferior alveolar nerve for mandible

77. Osseous topography Bone contour follows root prominence Intervening vertical depressions that taper towards margin Height of facial/lingual plates affected by 1) Allignment of teeth 2) Angulation of root to bone 3) Occlusal force

78. Osseus topography: Normally: prominence of the roots with the intervening vertical depressions that taper toward the margin. On the labial version: the margins of the labial bone is thinned to a knife edge & presents an accentuated arc in the direction of the apex. On the lingual version: the margins of the labial bone is blunt & rounded & horizontal rather than arcuate .

79. Buttressing bone- adaptive mechanism against occlusal force (thickened cervical portion of alveolar plate)

80. Fenestration and Dehiscence Fenestration - Isolated areas in which root is denuded of bone and root surface covered only by periosteum and overlying gingiva Dehiscence - Denuded area extends through marginal bone

81. Facial > lingual Anteriors > posteriors Frequently bilateral 20% of all teeth affected Caused due to malposition , root prominence , labial protrusion and a thin cortical plate Can complicate procedure and outcome of periodontal surgery

82. Remodelling

83. Remodeling of alveolar bone Least stable of periodontal tissues Structure in a constant state of flux

84. Remodeling is the major pathway of bone changes in shape , resistance to forces , repair of wounds, and calcium and phosphate homeostasis in the body . REMODELING

85. Regulation of bone remodelling is a complex process involving hormones and local factors acting in a autocrine and paracrine manner on the generation and activity of differentiated bone cells – Sodek et al 2000 Bone- 99% of body calcium ions Major source of calcium release when blood Ca Monitored by parathyroid gland

86. Bone coupling Decrease in blood Ca Detected by receptors on chief cells of parathyroid gland Release of PTH Stimulate osteoblasts to release IL-1 and IL-6 Stimulates monocytes to migrate to area Monocytes coalesces to form multinucleated osteoclasts in presence of LIF- Leukemia inhibiting factor released by osteoblasts Bone resorption Release of Ca ions from hydroxyapetite crystals Normal blood calcium levels PTH secretion stopped by feedback mechanism Organic matrix resorbed with hydroxyapetite Collagen breakdown Release of organic substrate which are covalently bound to collagen Stimulates differentiation of osteoblasts Bone deposition

87. ‘COUPLING’ refers to interdependency of osteoclasts and osteoblasts in remodelling Bone multicellular unit (BMU ) Reversal line

88. MEDIATORS OF BONE RESORPTION

89. STIMULI FACTORS REGULATING OSTEOCLAST FORMATION & FUNCTION

90. POTENTIAL THERAPEUTIC STRATEGIES TO TREAT BONE RESORPTION

91. Age changes Similar to those occurring in remainder of skeletal system Osteoporosis with ageing Decreased vascularity Reduction in metabolic rate and healing capacity (implants, extraction sockets, bone grafts) Bone resorption may be increased or decreased More irregular periodontal surface

92. Thinning of cortical plates Rarification of bone Reduction in no of trabeculae Lacunar resorption more prominent Susceptibility to fracture Thickening of collagen fibers Decrease in water content

93. Clinical and implant considerations

94. - Gingival margins …follows the contour of alveolar process . Abnormalities such as ledges, exostosis & tori …reflect on gingiva . - Areas of fenestrations & dehiscence - partial thickness flap. Clinical Considerations

95. - Process of bone remodeling - in orthodontic treatment. - Knowledge of the various factors regulating bone formation has resulted in their use for regeneration of bone.

96. Buccal -lingual/palatal ridge resorption during first 3 months after extraction about 30%... Reaching 50% at the end of 1 year ( Schropp et al , 2003) Resorption more pronounced at buccal than lingual/palatal aspect of ridge leading to shift of center of ridge towards lingual/palatal side

97. Socket preservation

98. Classification ( Lekhom and Zarb - 1985) 4 bone qualities for the anterior regions of the jaw bone: Quality1, Quality 2, Quality 3, Quality 4

99. Misch Bone Density Classification D1-dense cortical D2-porus cortical and coarse trabecular D3-porus cortical and fine trabecular D4-fine trabecular

100. Regional Acceleratory Phenomena Local response to a noxious stimulus. A process by which tissue forms faster than the normal regional regeneration process. - Frost et al, 1983 By enhancing the various healing stages, this phenomena makes the healing process occur 2 – 10 times faster than normal physiologic healing. RAP begins within a few days of injury, typically peaks at 1 - 2 months , usually lasts 4 months in bone, & may take 6 - >24 months to subside.

101. Duration & intensity of RAP α type & amount of stimulus & the site where it was produced. Noxious stimuli of sufficient magnitude: can evoke RAP . Fractures Mechanical abuses Noninfectious inflammatory injuries: dental implant procedures Bone grafting surgeries Internal fixation procedures Mucoperiosteal surgery

102. Injury to bone: Pathologic process Arthrofibrosis Neuropathic soft tissue problems Rheumatoid phenomena Secondary osteoporosis Excessice heat RAP is delayed / not initiated. Formation of biologically delayed union / nonunion .

103. RAP does not result in a change in bone volume. Restricted to bone remodelling . More evident in cortical bone . Usually accompanied by a systemic response: S ystemic A cceleratory P henomena Biochemical agents also appear to facilitate the RAP. PG E 1 Bisphosphonate

104. Inadequate RAP is associated with: DM Peripheral neuropathies Regional sensory denervation Severe radiation damage Severe malnutrition

105. Conclusion Thus a sound knowledge of bone anatomy, histology and physiology, will help the clinician in diagnosing and treatment planning, and lead to a favorable outcome of surgical procedures performed

106. References Carranza’s Clinical Periodontology - 10 th edition Clinical Periodontology and Implant Dentistry- Jan Lindhe - 5 th edition Contemporary Implant Dentistry- Carl Misch - 3 rd edition Orban’s Oral Histology and Embryology- 11 th edition Structure of Periodontal Tissues in Health and Disease- Periodontology 2000, vol 40, 2006, 11-28

107. Thank you