Differential response in alveolar bone osteoclasts residing at two different bone sites.

Using a histochemical method for demonstrating acid phosphatase activity, we have studied osteoclasts residing at two different bone sites in rat incisor alveolar bone, one at the endosteum and the other at the tooth socket, and compared the response of these osteoclasts to systemic changes. After 12 days of calcium (0%) or phosphorus (0.2%) deprivation, the number of osteoclasts/cross section at the endosteum increased 463% (P less than 0.001) and 103% (P less than 0.002), respectively. After 10 days of calcium or phosphorus replenishment, the number of osteoclasts at this bone site decreased to levels not significantly different from those in the control. In contrast, the number of osteoclasts at the incisor socket remained insignificantly changed throughout the experimental period. A similar osteoclast differential response was also observed in the alveolar bone surrounding the first molar tooth. After 12 days of calcium deprivation, the number of osteoclasts/mm bone surface increased 371% (P less than 0.001) at the endosteum but remained insignificantly changed at the first molar socket. These results suggest that an osteoclast differential response exists in alveolar bone and that the response may be of significance inasmuch as the major function of alveolar bone is to support the teeth. The work described here supports the concept of local as well as systemic regulation of bone metabolism to simultaneously perform the dual functions of mineral homeostasis and mechanical support.