Previous studies have demonstrated an increase in bone mass and density with the use of bisphosphonate in osteoporosis. This agent acts as an inhibitor of osteoclastic activity, and results in increase of net osteoblastic activity. Currently, it has been reported that bisphosphonate has direct effect on osteoblast.

This study was designed to evaluate the effect of alendronate on bone regeneration in defect of rat calvaria. The animals used for these experiments were 48 male rats, over 6-8 weeks old. They were divided into three groups according to the dose of alendronate(MK-217®, Merck, USA) administered. After the calvarial defects were surgically created, the rats received a peritoneal alendronate(0.25mg/kg) in group I, a peritoneal alendronate(1.25mg/kg) in group II, and a peritoneal normal saline injection in the control group. Three and six weeks later, blood was sampled and evaluated for alkaline phosphatase activity. The animals were sacrificed for histological observation and histometric analysis of the level of bone formation.

The alkaline phosphatase activity was similar in three groups at 3 weeks of experiment. The activity at 6 weeks increased more than twice, compared to 3 weeks, and was slightly higher in group I than the other two groups.

In histological observation, all the groups at 3 weeks, osteoblast rimming and new bone formation were observed along the defect margin. At 6 weeks, the defect was almost closed with new and more mature bone, but new bone is thinner than original bone in the central portion of defect.

In histometric analysis, group I and II at 3 weeks showed significantly greater new bone formation than the control, and all the groups at 6 weeks showed similar amount of bone formation.

These result suggest that alendronate administration in the dose of 0.25mg/kg and 1.25mg/kg promote osseous regeneration.