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
.