MMP9 and periodontitis: Recently, two meta-analyses estimated the association between MMP-2 -753C>T and MMP-9 -1562C>T polymorphisms and periodontitis risk, which was basically in accordance with our results that MMP-2 -753C>T and MMP-9 -1562C>T polymorphisms may not contribute to the susceptibility of periodontitis in overall analysis (8,11).