ALVEOLAR BONE

CONTENTS INTRODUCTION DEFINITION FUNCTIONS GROSS HISTOLOGY OF BONE BONE FORMATION BONE TURNOVER REMODELING PARTS OF ALVEOLAR BONE BUNDLE BONE OSSEOUS TOPOGRAPHY CLINICAL CONSIDERATIONS BONE LOSS AND PATTERNS OF BONE DESTRUCTION FACTORS AFFECTING BONE MORPHOLOGY IN PERIODONTAL DISEASES

INTRODUCTION Specialized part that forms primary support structure for teeth Constitutes alveolar process – tooth dependent Subjected to continual and rapid remodeling- for positional adaptation Similar to basal bone histologically, but differ in positional adaptation

DEFINITION Portion of maxilla and mandible that forms and supports tooth sockets

FUNCTIONS Frame work Central axis Support and transmits weight Locomotion Protection Calcium storage Form blood Of alveolar process in particular Socket formation Esthetics Distribution of occlusal forces

GROSS HISTOLOGY Outer compact bone Inner medullary bone

Components of bone

Cellular components Osteoblasts:- Uninucleated Secretory cells Produce type I collagen, non-collagenous and plasma proteins Osteocyte:- Occupy lacunae Number varies Continumm involving changes in extracellular environment and cellular changes Osteocytic osteolysis Presence of cell process within canaliculi

Bone lining cells:- Represents final phenotypes of osteoblastic lineage Transition involves a series of changes Osteoclasts:- ability to respond to biologically regulatory factors and functional forces is because of osteoclasts Large multinucleated cells Haemopoetic origin Ruffled border Causes resorption in acidic extracellular environment

Matrix Forms a scaffold of interwoven collagen fibres within and between which small uniform plate like carbonated hydroxyapatite crystals are deposited. collagen:- Type I,III,V,XII Stabilized by cross links Orientation

Non-collageous:- Proteins- osteocalcin, bone sialoprotein, osteonectin, osteopontin Proteoglycan- chondroitin sulphate, biglycan, decorin Proteins from blood and tissue fluids- albumin, immunoglobulin, matrix gla protein Inorganic:- Calcium, phosphate Hydroxyl, citrate, carbonate Sodium, magnesium, fluoride

Bone formation Endocondral Intramembraneous Sutural

Mineralization Matrix vesicles Heterogeous nucleation Two mechanisms involved- Matrix vesicles Heterogeous nucleation

Factors regulating bone formation- Harmones- parathyroid, vitamin D3, glucocorticoids, insulin, growth harmone, thyroid, estrogen. Growth factors- TGF-β, IGF-I &II, FGF, PDGF Factors regulating resorption PTH, Vit D, IL-1,6, TNF-α, TGF- α, lymphotoxin Factors that inhibit resorption Calcitonin, estrogen, TGF-β, IFN-G, PGE2.

Bone turnover Replacement of old bone by new bone is called bone turnover. - formed on periosteal surface and removed from endosteal surface. The leading edge of resorption is termed cutting cone Formation of cement/reversal line New bone deposited – filling cone

Bone remodeling Important functional charecteristic of alveolar bone is its capacity to undergo continuous remodeling in response to functional demands. Involves three phases Resorption phase Reversal phase (Baron) Formation phase Resting phase- follows until the functional condition locally activate a new cycle. Bone balance is negative.

On appositional side charecterised by the presence of continuous row of osteoblast cells that lie between sharpey’s fibers over a layer of osteoid tissue. Bone balance is positive. Changes in external architecture accompanied by changes in internal architecture. Remodeling never reach periodontal ligament space.

Cement lines Are hypomineralized lines with less calcium and phosphate content and more sulphur content Provides striking mechanical properties Cells responsible for remodeling:- In mature periodontium, the renewal of the alveolar wall is effected by the periodontal ligament cells. Fewer data exist on the origin and location of osteoclast precursor.

Parts of alveolar bone The alveolar bone is divisible into separate areas on the anatomic basis, but it functions as a unit, with all parts interrelated in the support of teeth.

Interdental septum separates two adjacent tooth sockets. may contain cancellous bone surrounded by cortical bone or may be made up of entirely of cribriform plates. mesiodistal angulation of the alveolar crest parallels the line drawn between CEJ of approximating teeth.

Bundle bone Consists of extrinsic and intrinsic components Thickness varies between 100-200µm Other names include cribriform plate, lamina dura, alveolar bone proper All forms of bone histology is observed Osseous topography:- bone contour confirms to the prominence of roots, alignment of the teeth, angulation of the root to the bone and occlusal forces.

Clinical considerations Orthodontic movement of the teeth Qualitative and quantitative adaptation Healing of fractures and extractions Harmful change associated with periodontal diseases Tooth dependent- endodontic therapy Fenestrations and dehisence ankylosis

Bone loss patterns of bone destruction By extension of gingival inflamation By TFO By systemic disorders Factors determining bone morphology in periodontal diseases Normal variations Exostoses TFO Buttressing bone formation Food impaction Juvenile periodontitis

Patterns of bone loss - horizontal bone loss - vertical defects - osseous craters - bulbous bone contours - ledges - reversed architecture -furcation involvement

Conclusion Alveolar bone is a specialized, mineralized connective tissue that supports the roots of the teeth Alveolar bone is the least stable of the periodontal tissues because the structure is in constant state of flux.

References Clinical periodontology- caranza 8th and 9th edition Clinical periodontics and implant dentistry- Jan lindhe Periodontics – Grant Oral histology and embryology –Ten cate - orbans Periodontics 2000- 1995,1997