Oral Pathology: Alveolar Bone and Process

Bone Development and Remodeling

• Bone growth is rapid during childhood, slow in young adulthood, and continuous throughout life
• Influencing factors: local functional requirements, age-related changes in bone cells, systemic factors (parathyroid hormone, calcitonin, vitamin D3)

Bone Turnover (Remodeling)

• Process of replacing old bone with new bone
• Involves sequences of resorptive events:
  • Attachment of osteoclasts to mineralized surface of bone
  • Creation of acidic microenvironment, demineralization, and degradation of organic matrix
  • Secretion of new osteoid layer and calcification
• Results in formation of resting lines (hypocalcified lines representing phasic formation of bone) and reversal lines (hypocalcified lines marking change from bone resorption to deposition)

Endochondral Bone Formation

• Type of bone formation involving cartilaginous model replacement
• Mesenchymal cells condense, differentiate into chondroblasts, and lay down hyaline cartilage
• Cartilage is surrounded by perichondrium (highly vascular and containing osteogenic cells)
• Cartilage calcification, death of cartilage cells, and invasion by blood vessels and osteogenic cells
• Formation of primary and secondary areolae

Osteoclasts

• Found against the surface of calcified matrix in shallow depressions called Howship's lacunae
• Function: degradation of bone causing resorption
• Secrete enzymes (e.g., tartrate-resistant acid phosphatase) against mineral substrate

Bone Composition

• 67% inorganic hydroxyapatite crystals, calcium phosphate, and other minerals
• 33% organic components (non-collagenous proteins, osteocalcin, osteonectin, phosphoproteins, and collagen type I)

Fenestrations and Dehiscences

• Isolated areas where root is denuded of bone and covered only by periosteum and overlying gingiva (fenestrations)
• Defect extending through marginal bone (dehiscence)
• Etiology unknown; predisposing factors: prominent root contour, malposition, labial portion of root, and thin bony plate

Alveolar Process

• Defined as parts of maxilla and mandible that form and support tooth sockets
• Forms when tooth erupts, providing osseous attachment to periodontal ligament; disappears after tooth loss

Alveolar Bone Proper

• Surrounded by roots of tooth, giving attachment to principal fibers of periodontal ligament
• Histologically composed of bundle bone and lamellar bone
• Bundle bone: bone lining socket with Sharpey's fibers embedded; also called cribriform plate
• Lamellated bone: compact, with haversian system

Supporting Alveolar Bone

• Surrounds alveolar bone proper, providing support to socket
• Consists of cortical plates and spongy bone (cancellous bone)

Microscopic Structure of Bone

• Periosteum: thin connective tissue membrane covering compact bone, rich in blood vessels and nerves
• Osteon: structural and metabolic unit of lamellar bone, consisting of haversian canal and concentric, mineralized lamellae
• Haversian system: haversian canal and Volkmann's canal, providing nutrition to bone
• Lamellae: made up of osteocytes within lacunae; types include circumferential, concentric, and interstitial lamellae