Effects of Zoledronate on Alveolar Bone and Teeth in Rats: Relationship Between Root Resorption and Occlusion

Bisphosphonates (BPs) are used to treat osteoporosis and other bone metabolic diseases. Zoledronate (ZOL), a third-generation BP, induces osteoclast apoptosis and inhibits bone resorption. Previous studies have mainly focused on limb bones, and few studies have reported the effects of ZOL administration alone in the oral region. The objective of this study was to investigate the effects of ZOL on teeth and alveolar bone.

Wistar rats were injected intraperitoneally with 40 or 400 μg/kg ZOL, and the right mandibular first molar of some rats were extracted. The rats were euthanized 3 weeks postoperatively. The tibia and maxilla were analyzed histopathologically using hematoxylin and eosin (HE) or tartrate-resistant acid phosphatase (TRAP) staining.

In the 40 and 400 μg/kg ZOL groups, dense trabecular bone tissues were observed in the tibia. Osteoclasts in the tibia and alveolar bone were enlarged and had numerous nuclei, and many osteoclasts were detached from the bone surface. These changes were more evident in the 400 μg/kg ZOL group. Root resorption in the maxillary first molar was observed in the apical dentin, and the odontoclasts within the resorption cavities were TRAP-positive. In an experiment with tooth extraction, the nonocclusal side of the maxilla exhibited significantly fewer root resorption cavities than the occlusal side in both 40 and 400 μg/kg ZOL groups.

These findings demonstrate that ZOL administration induces irregularities in the alveolar bone surface and root resorption in a dose-dependent manner. They also suggest a correlation between occlusal status and the extent of root resorption in ZOL-treated rats.