The Effect of Alendronate and Risedronate on Bone Remodeling in the Canine Maxilla

Abstract

Bisphosphonates, effective inhibitors of bone resorption, are used in the treatment of postmenopausal osteoporosis. At present, the effects of bisphosphonate therapy on the maxilla have not been quantitatively studied. As part of the masticatory system, dentate alveolar bone is exposed to a unique pattern of loading. As such, data obtained from bisphosphonate studies of other bones may not be applicable to the cortical bone of the dentate maxilla. The objective of this study is to histomorphometrically quantify the effects of alendronate and risedronate therapy on alveolar bone of the dog maxilla (MX) and to determine if this site is affected differently than the cortical bone in the rib (R) from these same animals. Twenty-two female dogs were divided into three treatment groups of 1 mg/kg/day alendronate, 0.5 mg/kg/day risedronate, and a saline vehicle control. Fluorochrome labels were used to mark sites of bone formation. Maxillary and rib specimens from each dog were prepared for analysis of static and dynamic histomorphometric parameters. MX cortical bone surrounding the third premolar was further analyzed by side (buccal vs. lingual) and region (coronal vs. apical). Mineralizing surface (MS/BS) and bone formation rate (BFR) in the coronal maxilla of the control group is significantly (p < 0.05) higher than that of the bisphosphonate groups. In bisphosphonate treated animals, MS/BS, BFR, and activation frequency (AcF) were significantly (p < 0.05) higher in the R than in the MX. In all treatment groups, very little osteoid was detected, and no significant difference in the mineral apposition rate (MAR) was noted. These results indicate that: (1) bisphosphonate dosages used in this study effectively inhibited remodeling within the dog maxilla; (2) alveolar bone remodeling was decreased more than remodeling in rib cortical bone; (3) within the dentate maxilla, alveolar bone remodeling was decreased more in the coronal than in the apical region, and (4) none of the groups appears to show inhibition of mineralization.