Molecular markers of early orthodontic tooth movement

Abstract

Objective: To understand the molecular basis of early orthodontic tooth movement by looking atthe expression of KI-67, runt-related transcription factor 2 (Runx2), and tumor necrosis factorligand superfamily member 11 (RANKL) proteins.Materials and Methods: We employed a rat model of early orthodontic tooth movement using asplit-mouth design (where contralateral side serves as a control) and performed immunohistochemicalstaining to map the spatial expression patterns of three proteins at 3 and 24 hours afterappliance insertion.Results: We observed increased expression of KI-67, a proliferation marker, and RANKL, a moleculeassociated with osteoclastic differentiation, in the compression sites of the periodontal ligamentsubjected to 3 hours of force. In contrast, there was increased expression of KI-67 andRunx2, a marker of osteoblast precursors, in tension areas after 24 hours of force. DecreasedKI-67 expression in the mesial and distal regions of the periodontal ligament was observed at themidpoint of the tooth root.Conclusions: The early RANKL expression indicates that at this early stage cells are involvedin osteoclast precursor signaling. Also, decreased KI-67 expression found near the midpoint ofthe tooth root is believed to represent the center of rotation, providing a molecular means ofvisualizing mechanical loading patterns. (Angle Orthod. 2009;79:1108-1113.) © 2009 by The EH Angle Education and Research Foundation, Inc.