Lack of the bone remodeling in osteopetrotic (op/op) mice associated with microdontia

Osteopetrosis is an inherited metabolic disease characterized by an excessi ve accumulation of bone. This is associated with an osteoclast deficiency. Osteopetrosis is always accompanied by the failure and/or delay of tooth er uption. The present study was conducted to examine in detail the morphologi cal and histological changes of growth of the third molars in the osteopetr osis (op/op) mouse. At the age of 10 days, normal and op/op mice showed no detectable difference in the shape of the third molar follicles. However, t he third molars in the op/op mouse became obscured by the proliferation of neighboring bone trabeculae. Moreover, no tartrate-resistant acid phosphata se-positive cells were detected on the bone surfaces of 10-day-old op/op mi ce. Ankylosis between the root dentin and proliferating bone trabeculae was a common feature in the 20- and 30-day-old op/op mice. The third molars er upted into the oral cavity before the age of 30 days in normal mice, and th e crowns, roots, and periodontal ligaments appeared well developed. Through out the experiment, it seemed that the primary cause of the microdontia and ankylosis of the developing root in the mutant mouse was a deficiency of o steoclasts, with attendant lack of bone remodeling.