Anatomy of Lamellar Bone and Alveolar Bone

Bone Tissue

• Definition: Rigid form of specialized connective tissue that forms the endoskeleton of vertebrates, helping with movement, support, and protection of various organs.
• Composition: 67% inorganic component (hydroxyapatite) and 33% organic matrix (28% type I collagen and 5% non-collagenous proteins).
• Functions: Dynamic tissue that is continually being formed and resorbed in response to mechanical, nutritional, and hormonal influences throughout life; serves as a source of calcium.

Types of Bone

• Lamellar Bone:
  • Compact Bone: Dense, ivory-like bone formed of regular, arranged lamellae; forms flat bones and outer coverage of long bones.
  • Cancellous Bone: Porous, sponge-like bone formed of irregular trabeculae; highly vascular.
• Non-Lamellar Bone:
  • Embryonic bone or temporary bone; present in fetus, callus of fracture, and healing sockets.
  • Characterized by irregular arrangement of collagen fibers and large number of osteocytes; resorbed and replaced by lamellar bone.
• Bundle Bone:
  • Lining of tooth socket; more radio-opaque.

Alveolar Bone

• Definition: Bone of the jaws containing the sockets (alveoli) for the teeth; functional bone.
• Structure:
  • Alveolar bone proper:
    • Bundle bone: Portion of inner alveolar wall that gives attachment to periodontal ligament fibers and into which Sharpey's fibers are inserted.
    • Lamellar bone: Bone immediately adjacent to bundle bone; contains lamellae, Haversian systems, and canaliculi.
  • Supporting alveolar bone:
    • Sporting spongiosa: Contains trabeculae that enclose irregularly shaped marrow spaces; varies widely depending on occlusal forces.
    • Cortical plates: Compact bone in nature with longitudinal lamellae and Haversian systems.

Clinical Considerations of Alveolar Bone

• Density of alveolar bone: Classified into four types (D1-D4) in an edentulous jawbone; important to identify type before implant placement.
• Physiologic remodeling of the alveolar process: Turnover rate of alveolar bone is higher compared to other parts of the skeleton; highest level of remodeling occurs in the bundle bone.
• Tooth movement:
  • Physiological tooth movement: Slight tipping of the tooth in its socket during eruption; changes in tooth position that occur during and after eruption.
  • Orthodontic tooth movement: Applies force to induce bone resorption on the pressure side and bone apposition on the tension side.
• Resorption of the alveolar bone after extraction:
  • Tooth extraction leads to reduction in the buccolingual and apico-coronal dimensions.
  • Bone resorption occurs more at the buccal aspect than at the lingual aspect, leading to greater vertical bone loss buccally than lingually.

Age Changes of Alveolar Bone

• Increase in brittleness due to decreased water content.
• Widening of marrow spaces and thinning of trabeculae of supporting spongiosa.
• Resorption after loss of teeth.
• Approximation of maxillary sinus floor after extraction of teeth.
• Mental foramen becomes closer to the upper border of the mandible.