Protein Expression Patterns during Orthodontic Tooth Movement

Background: Orthodontic tooth movement (OTM) is produced upon the application of a controlled mechanical force that results in remodelling of the surrounding tissues, particularly the periodontal ligament (PDL). Upon force application there is an initial stage of displacement of the tooth in the periodontal space, followed by a lag phase. Force on a tooth is transduced to the PDL cells resulting in changes in osteoclastic and osteoblastic activities. The extent of the remodeling that occurs in the PDL is partly dependent on stresses and strains in the tooth-PDL-bone interface, position along the apical-coronal length of the root, axis of rotation and centre of resistance with respect to the tooth shape, and the force. Objectives:i)To determine the expression patterns of Ki67, a proliferation marker, Runx2, an osteoblastic differentiation marker, and RANKL, an osteoclastic differentiation marker, in the PDL of rat molar teeth subject to orthodontic force for 3 and 24 hours. ii)To determine the expression profile of Ki67 on the apical-coronal length of the OTM treated molars. Methods: Immunohistochemistry with antibodies against Runx2, RANKL, and Ki67 proteins was performed on horizontal sections of maxillary molars subjected to 3 and 24 hours of OTM. The PDL of the disto-palatal root of the first molars was analyzed for expression of these proteins. Results: Increased expression of Ki67 and RANKL was observed in the compression sides of the PDL of teeth subjected to 3 hours of force, contrasted with an increased expression of Ki67 and Runx2 in the tension areas of teeth moved for 24 hours. Expression of Ki67 along the length of the PDL of orthodontically moved teeth was present except ~600 µm from the furcation, a region believed to represent the tooth-tipping axis. Conclusion: Our OTM rat model provides a model that replicates the early stages of OTM. Grants: AAOF