The pooled results based on all included studies not showed a significant association between MMP-9 -1562C>T and periodontitis risk under all genetic models (allele model: T vs. C, OR=0.787, 95% C=0.459–1.348, P=0.383 (Fig. 2A); heterozygote model: TC vs. CC, OR=0.795, 95% CI=0.546–1.156, P=0.229; homozygote model: TT vs. CC, OR=0.600, 95% CI=0.237–1.517, P=0.280 (Fig. 2B); dominant model: TT+TC vs. CC, OR=0.767, 95% CI=0.463–1.269, P=0.301; and recessive model: TT vs. TC+CC, OR=0.691, 95% CI=0.330–1.444, P=0.326). This evidence concerns the gene MMP9 and periodontitis.