ABSTRACT
<p><b>OBJECTIVE</b>To investigate the expression and the localization of Cathepsin K and IL-6 mRNA in root-resorbing tissue and to elucidate the molecular changes and mechanism of root resorption induced by tooth movement.</p><p><b>METHODS</b>Rats were subject to experimental tooth movement to induce root resorption. In situ hybridization was performed to identify the cells in root-resorbing tissue that produced Cathepsin K or IL-6 the difference of CK mRNA or IL-6 mRNA expression between root resorption group and control group was calculated by t-test.</p><p><b>RESULTS</b>Cathepsin K mRNA was highly and selectively expressed in multinuclear odontoclast and IL-6 mRNA expressed in fibroblast, osteoblast, osteocyte and cementoblast. The expression of Cathepsin K mRNA and IL-6 mRNA in root-resorbing tissue increased evidently compared with the normal periodontium.</p><p><b>CONCLUSIONS</b>Odontoclast in the root-resorbing tissue expresses Cathepsin K mRNA that participates in proteolysis during root resorption. IL-6 plays a very important role in the root resorption as a multifunctional cytokine.</p>