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Alveolar bone

  1.  Introduction  Bone Histology  Cells and Intercellular Matrix  Bone Development  Remodelling  Age Changes  Clinical Considerations  Conclusion  References
  2.  Bone- used to designate both an organ and a tissue  Specialized mineralized connective tissue
  3. mineralised supporting tissue act as a reservoir for ions (especially calcium). provide a framework for bone marrow gives attachment to muscles its "plasticity', allows it to remodel according to the functional demand placed upon it.
  4.  DEVELOPMENTALLY,  Endochondral bone  Intramembranous bone  HISTOLOGICALLY, according to its density, mature bone can be divided into;  Compact (cortical) bone  Cancellous (spongy) bone
  5.  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.
  6. FIBROUS BONE (WOVEN BONE):  It is found in young fetal bone.  Collagen fibers - more variable diameter  Irregular orientation giving it matted appearance
  7.  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)
  8.  Initially, this bone forms a thin egg shell of support, termed as the ‘tooth crypt’, around each tooth germ.
  9. FIG. 9-5 A developing root shown by a divergent apex around the dental papilla (arrow), which is enclosed by an opaque bony crypt.
  10.  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 2½YRS 7YRS
  11. 67 % Inorganic Hydroxyapatite 33% (organic) 28% 5 % Collagen type Ӏ Non coll. proteins (ca10{po4}6{oh}2)
  12.  Osteocalcin, Osteonectin, Bone morphogenic proteins, Phosphoproteins and Proteoglycans  Ground substance- Glycosaminoglycans, proteoglycans and water  Osteopontin, Bone Sialoprotein- cell adhesion proteins (Mackie et al, 2003)
  13. 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
  14. 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
  15. Bone sialoprotein  Structural protein of bone  Restricted to mineralized tissues  Secreted by osteoblasts
  16. Osteonectin  Glycoprotein bound to HA  Calcium binding glycoprotein  Synthesized by fibroblasts and role in wound healing
  17.  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
  18.  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)
  19. Transverse section Longitudinal section
  20.  Morphology determined by size, shape, function and location of teeth  Formed during fetal growth by intramembraneous ossification
  21. Cancellous Bone Compact Bone Shelf like bone
  22. 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
  23. Supplies vessels to the PDL. Houses & protects developing permanent teeth while supporting primary teeth. Organizes successive eruptions of primary & secondary teeth.
  24. Three parts 1) External plate of cortical bone 2) Inner socket wall 3) Cancellous trabeculae (between two compact layers)- function of support
  25.  1) Circumferential lamellae (encloses entire adult bone and forms the outer perimeter
  26.  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)
  27.  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
  28.  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
  29.  Dense , lamellated bone – alveolar bone proper (contains sharpeys fibers and circumferential lamellae)
  30.  Cribriform plate (anatomic term)  Lamina dura (radiographic term)  Bundle bone (histologic term)
  31.  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
  32.  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
  33. 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.
  34.  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
  35.  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
  36.  Spongy bone (anatomic term)  Trabecular bone (radiographic term)  Cancellous bone (histologic term)
  37.  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
  38. 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
  39.  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
  40.  Study by Heins et al 1986 Area Cribriform plate+cancell ous bone Only cribriform plate Irregular window Maxillary molars 66.6% 20.8% 12.5% Mandibular premolar and molar 85% 15% 0%
  41.  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
  42. Crest of IDS located 1-2 mm apical to CEJ of adjacent teeth
  43. Diagram of relation between CE junction of adjacent teeth shape of crest of alveolar septa
  44. • Embryo and newborn, • Ribs, sternum, vertebrae, skull, humerus • Hemopoiesis Red hematopoietic marrow • Adult • Red marrow foci found sometimes in maxillary tuberosity, symphysis and angle of ramus • Storage of energy Yellow fatty marrow
  45.  Determined osteogenic precursor cells  Inducible osteogenic precursor cells  Muscles. Friedenstein (1973) divided osteoprogenitor cells into:
  46.  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
  47.  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
  48.  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
  49.  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
  50.  Extend processes into canaliculi that radiate from lacunae  Anastomosing system  Bring O2 and nutrients to osteocytes through blood and remove metabolic waste products
  51.  More rapid the bone formation-more osteoblasts get entrapped – more osteocytes (eg- bone formed during repair)  Osteolytic osteolysis- osteocytes capable of resorption
  52.  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’.
  53.  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
  54.  Lie in Howships lacunae  Acidophilic cytoplasm  Active osteoclasts- ruffled border facing bone (hydrolytic enzymes are secreted)  Increases surface area
  55.  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
  56. 1. Attachment of the osteoclast to mineralized bone surface 2. Creation of sealed acidic environment through action of proton pump which demineralizes bone & exposes the organic matrix 3. Degradation of the exposed organic matrix to its constituent amino acids by the action of released enzymes like acid phosphatase & cathepsin 4. Sequestering of the mineral ions & amino acids within the osteoclasts. Tencate 1994- Described sequence of events of resorptive process:
  57. - 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.
  58.  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
  59. • Rich in blood vessels, nerves • Contains collagen fibres and fibroblasts • Fibrous periosteum Outer layer(fibrous) • Composed of osteoblasts and osteoprogenitor cells • Cellular periosteum Inner layer (osteogenic)
  60.  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)
  61. 1) Endochondral bone formation 2) Intramembranous bone formation 3) Sutural bone formation
  62.  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
  63.  Perichondrium at the periphery  Rapid growth of cartilage  Cartilage replaced by bone gradually by osteoblasts at periphery
  64.  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)
  65.  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
  66.  Mesenchymal condensation followed by increase in vascularity  Some mesenchymal cells lay down collagen fibre bundles forming a membrane
  67.  Some differentiate into osteoblasts and lay down osteoid Which then gets calcified Mineralization always lags behind the production of bone matrix
  68.  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
  69. 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
  70.  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
  71. 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.
  72.  Buttressing bone- adaptive mechanism against occlusal force (thickened cervical portion of alveolar plate)
  73.  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
  74.  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
  75.  Least stable of periodontal tissues  Structure in a constant state of flux • Functional requirements • Age related changes in bone cells Local influences • Hormones (PTH, vit D, calcitonin)Systemic influences
  76.  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
  77.  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
  78. 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 Bone deposition
  79.  ‘COUPLING’ refers to interdependency of osteoclasts and osteoblasts in remodelling Bone multicellular unit (BMU) Reversal line
  81.  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
  82.  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
  83. - Gingival margins …follows the contour of alveolar process. Abnormalities such as ledges, exostosis & tori…reflect on gingiva. - Areas of fenestrations & dehiscence - partial thickness flap.
  84. - Process of bone remodeling - in orthodontic treatment. - Knowledge of the various factors regulating bone formation has resulted in their use for regeneration of bone.
  85.  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
  86.  Socket preservation
  87. Classification (Lekhom and Zarb- 1985)  4 bone qualities for the anterior regions of the jaw bone:  Quality1, Quality 2, Quality 3, Quality 4
  88. Misch Bone Density Classification  D1-dense cortical  D2-porus cortical and coarse trabecular  D3-porus cortical and fine trabecular  D4-fine trabecular
  89.  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.
  90.  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
  91.  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.
  92.  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: Systemic Acceleratory Phenomena  Biochemical agents also appear to facilitate the RAP.  PG E1  Bisphosphonate
  93.  Inadequate RAP is associated with:  DM  Peripheral neuropathies  Regional sensory denervation  Severe radiation damage  Severe malnutrition
  94. 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
  95.  Carranza’s Clinical Periodontology- 10th edition  Clinical Periodontology and Implant Dentistry- Jan Lindhe- 5th edition  Contemporary Implant Dentistry- Carl Misch- 3rd edition  Orban’s Oral Histology and Embryology- 11th edition  Structure of Periodontal Tissues in Health and Disease- Periodontology 2000, vol 40, 2006, 11-28
  96. Thank you

Editor's Notes

  1. Compact Bone: It is dense in texture like ivory, but is extremely porous. It is best developed in the cortex of long bones. This is an adaptation to bending & twisting forces. Cancellous Bone (Trabecular Bone):It is made up of a meshwork of trabeculae (rods & plates) between which are marrow containing spaces. This is an adaptation to compressive forces.
  2. Determined osteogenic precursor cells are present in bone marrow, in the endosteum and in the periosteum that cover the surfaces of the bone. These cells possess an intrinsic capacity to proliferate and differentiate into osteoblasts. Inducible osteogenic precursor cells represent mesenchymal cells present in the other organs and tissues (eg; muscles) that may become bone forming cells when exposed to specific stimuli.
  3. 5-29