Histopathological study of effects of aging on bone regeneration

Comparison between growing and adult rabbits with respect to the healing process of bone cavities in the mandible

Abstract

Effects of aging on the regeneration of bone were evaluated by comparing male New Zealand White Rabbits of different ages with respect to the healing process of bony cavities in the mandible. Rabbits were divided into two groups according to age: a 14-weekold group, representing young or growing rabbits, and a 30-week-old group, representing adult or aging rabbits. A bony cavity of 12×10×4mm was prepared in the mandible of both groups; the periosteum was preserved carefully. Bone formation and cellular proliferation were examined morphologically, histomorphometically, and immunohistochemically using anti-BrdU monoclonal antibody. The results were as follows:
1) New bone formation and bone remodeling in the bony cavities of adult rabbit mandibles started later and the rate of bone formation was lower than that of the young rabbits.
2) The number of BrdU-positive cells in the bony cavities of the adult group was significantly less than that of the young group. The results suggested that aging was associated with decreased osteoblast acitivity.
3) Although adult rabbits showed significantly less new bone formation than young rabbits during the healing of bony cavities, the bony cavities in both groups were filled with new bone, and the mandibular outline was repaired by new cortical bone resulting from remodeling of newly formed bone 28 days after surgery.
4) During the healing process, the periosteum seems to play an important role in the formation of the mandibular outline, irrespective of age.