Histological study of the effects of bisphosphonate adminstration on tooth movements in rats

ABSTRACT

This study was designed to clarify the effects of systemic administration of bisphosphonate, pamidronate, on the bone resorbing activity of osteoclasts during relapse of rat molars, after experimental movement. The Waldo method was used on 24 rats to induce mesial movement of the maxillary first molars. An elastic band was inserted between the upper first and second molars of 7-week-old rats and removed 21 days later. At 1 day before elastic band removal, bisphosphonate . was administered via a tail vein. After elastic band removal, the rats were further maintained for 0, 5, or 10 days. The relapse of the first molars was studied by means of light and scanning-electron and transmission-electron microscopy. Administration of bisphosphonate significantly decreases the relapse of moved teeth to their original positions. In bisphosphonate-treated rats, osteoclasts aggregated in a fewer and smaller number along the alveolar bone surfaces facing the periodontal ligament and also induced structural changes in osteoclasts, such as disappearance of ruffled borders and cytoplasmic polarity These results suggest that a single systemic administration of bisphosphonate decreases the extent of initial relapse in experimentally moved rat molars via a mechanism involving impairment of the structure and resorptive functions of osteoclasts