Gene Expression in Response to Orthodontic Tooth Movement

Orthodontic tooth movement results from bone remodeling following a force application to a tooth. Clinical and histological studies have been carried out to elucidate the biology of tooth movement; however, the molecular events leading to this process are largely unknown. Objectives: To test the hypothesis that by comparing the expression of mRNAs in the periodontium and surrounding bone subjected to optimal orthodontic forces (determined to produce tooth movement without causing root resorption), and teeth where no forces are applied, we can identify the molecules involved in the sequence of events leading to tooth movement. Methods: Animal procedures were approved by the USC Animal Ethics Review Board. 80 Wistar rats (45-50 days old) were used. A continuous force of 30 grams was applied to the left maxillary first molar using Ni-Ti closed coil springs and rats were sacrificed after 0,1,3,5,7,14,21 and 28 days. Total RNAs obtained from left and right (control) molars were converted into cDNA, labeled with P33 and hybridized to Plastic Rat Microarrays containing 3,897 genes (Clontech, CA). Analysis of gene expression was done using the AtlasImage 2.7 and Atlas Navigator 2.0 software (Clontech, CA). Results: Significant (p<0.05) tooth movement was produced (0.5mm/4weeks) as a result of the force applied and histological analysis indicated that movement was achieved without causing root resorption. Microarray analysis indicated that more than 130 genes were up- or down- regulated after 1 day of applying the orthodontic forces, amongst them several transcription and growth factors (Sp1, Growth differentiation factor 9B, Myogenic factor, etc) as well as extracellular matrix proteins like Matrix Gla protein. Conclusions: The application of Microarray technology provides a tool to understand the sequence of events, at the molecular level, associated with bone remodeling in response to orthodontic tooth movement. This study was supported by a grant from the AAOF.