Effect of Etidronate on Bone Remodeling in Dog Mandibular Condyle

Abstract

Bisphosphonates, drugs which inhibit bone resorption and remodeling, are currently prescribed for the treatment of osteoporosis. Previous research suggests that decreased bone turnover may lead to accumulation of microdamage, possibly increasing the risk for fracture in some sites. The effects of bisphosphonate therapy on the mandibular condyle have not been quantitatively studied. The purpose of the proposed study was to histomorphometrically quantify the effects of etidronate (a bisphosphonate) on trabecular bone sites of the dog mandibular condyle and to compare this to another trabecular bone site (vertebrae) to determine whether the two sites were affected differently. Eleven mature female dogs were treated with high- (5 mg/kg/d) and low- (0.5 mg/kg/d) dose etidronate therapy for seven months. Fluorochrome labels were used to mark sites of bone mineralization for the calculation of static and dynamic histomorphometric parameters. High-dose therapy resulted in a complete inhibition of remodeling, as shown by the reduction of mineral apposition rate (MAR), bone formation rate (BFR), and mineralizing surface (MS/BS) to zero. Low-dose therapy also decreased BFR and MS/BS. Osteoid accumulation was only significant in the high-dose therapy group, but there was no evidence of osteomalacia (osteoid volume < 5%). Etidronate treatment had no significant effect on bone volume, trabecular number, trabecular thickness, or trabecular separation. Vertebral trabeculae ranged from 5.5 to 9.5 times greater in number than mandibular trabeculae, but were 45 to 60 percent thinner and closer together. The interaction between dosage and site was insignificant for all parameters studied. Further investigation is needed to determine whether these effects will prove to be harmful to the mandibular condyle, especially over a long period of time.