Comparative study of gene expression during tooth eruption and orthodontic tooth movement in mice

Objective: The aim of this study was to understand tooth eruption by comparing the gene expression during tooth eruption and orthodontic tooth movement (OTM). Materials and methods: Orthodontic force was applied on maxillary molars for 2, 4, 7 and 14 days to study tooth movement. Mice at PN 0, 7, 10, 15 and 21 were fixed to observe tooth eruption. Comparative study of two procedures was assessed by haematoxylin and eosin, tartrate-resistant acid phosphatase staining and in situ hybridization for matrix metalloproteinase (Mmp)2, 13, bone sialoprotein (Bsp) and osteocalcin (Ocn). Results: Tartrate-resistant acid phosphatase activity and expression of Mmp2, 13 were obviously detectable in the compression region during OTM. They were also identified in the occlusal and apical region of alveolar bone during tooth eruption. Strong expression of Bsp and Ocn was detectable at the tension side during OTM. These genes were also expressed in the inner lateral region of alveolar bone adjacent to the tooth, but absent in the inner surface of the occlusal and root apical regions during tooth eruption. Conclusion: The process of alveolar bone metabolism during developmental eruption and OTM shares the same mechanism. Internal force, as the orthodontic force for OTM, may be initiating factor for tooth eruption.