Effect of ovariectomy and alendronate on implant osseointegration in rat maxillary bone

Bisphosphonates such as alendronate (ALD), although controversial, are worthy of investigation for the enhancement of implant osseointegration in patients with low bone mass who are already taking bisphosphonates for osteoporosis. These patients may receive additional benefits and be acceptable candidates for dental implants without needing to change their medication regimen and possibly as a result of their medication regimen. The purpose of this study was to compare implant osseointegration in maxillary bone of normal rats with a rat model of postmenopausal estrogen deficiency (ovariectomized [OVX]), with and without ALD. An experimental group of 32 rats was divided in 4 groups: ALD-OVX (n=8 OVX with ALD), OVX (n=8 OVX without ALD), ALD (n=8 normal rats with ALD), and control (n=8 normal rats). All rats received one titanium microscrew implant in the left edentulous region of the maxillary arch. The ALD-OVX and ALD groups received subcutaneous injections of ALD 3 times a week. On the fourth week after ALD administration, an implant was placed in all 32 rats. The maxilla of each rat was radiographed 4 times: at 0, 7, 14, and 28 days. On day 28 after implant placement, all rats were killed, and the peri-implant tissue was embedded in plastic or paraffin for histological examination. The X rays were used for a chronologic calculation of the contact ratio between implant and bone surfaces. Radiographic bone density was determined at 3 points: mesial, apical, and distal. The results show that osseointegration of the implants was impaired in the estrogen-deficient OVX rats compared with the ALD-OVX rats. Fifty percent of the implants were lost at 2 weeks in the OVX group. Radiographic evidence suggested that none of the implants in the OVX group osseointegrated. In the histologic examination more bone was observed around implants from the ALD-OVX and ALD groups than around implants from the OVX group. The OVX group presented a dramatic reduction in implant bone contact at 2 weeks and a significant 13% reduction at 4 weeks vs day of implant (P = .006). The ALD-OVX group presented 50% more bone density than the OVX group (P = .0003). Both ALD groups (ALD and ALD-OVX) had significantly higher radiographic bone density than the other groups (P < .01 for each comparison). In conclusion, osseointegration of implants was enhanced by ALD. Radiographic bone density and contact ratio improved with ALD administration. Implant osseointegration was impaired by estrogen deficiency in the OVX group.