Histomorphometric study of bone reactions during orthodontic tooth movement in rats

The biological response to orthodontic tooth movement has generally focused on reactions within the periodontal ligament (PDL), whereas less attention has been paid to the behavior of neighboring bone. The purpose of the stud y was to describe the influence of orthodontic force on bone surrounding th e displaced tooth and the adjacent, untreated teeth, Bone changes in relati on to treatment time and different sites were investigated. A mesial tippin g of the left maxillary first molar was obtained from 54 adult male Wistar rats. Oxytetracycline was injected subcutaneously 48 h before killing, whic h took place after 4, 7, or 14 days. The maxilla was fixed in paraformaldeh yde and embedded undecalcified in methylmethacrylate, A set of thick horizo ntal sections was taken from the cervical, intermediate, and apical levels of the roots. The sections were microadiographed and analyzed microscopical ly under bright-field and fluorescent illumination. Bone fraction and PDL w idth was measured using a Zeiss Videoplan device equipped with an overlay s ystem. New bone formation was detected by oxytetracycline labels. The analy sis showed a consistent, significant decrease of the alveolar bone fraction around both displaced and adjacent teeth at ail treatment times, Appositio n, indicated by the tetracycline uptake, was found on the periosteal side o f the treated hemimaxilla and, after 14 days, also on the surface toward wh ich the tooth was moving and around the adjacent teeth. These results sugge st that a time rather than a space relationship exists between bone resorpt ion and formation and that the whole hemimaxilla reacts to the mechanical c hallenge, resembling the regional acceleratory phenomenon (RAP) observed in other circumstances. (C) 1999 by Elsevier Science Inc. All rights reserved .