MMP9 and periodontitis: Finally, 17 case-control studies, investigating the association of MMP-1 (−1607 1G/2G, −519 A/G, and −422 A/T), MMP-2 (−1575 G/A, −1306 C/T, −790 T/G, and −735 C/T), MMP-3 (−1171 5A/6A), MMP-8 (−799 C/T, −381 A/G, and +17 C/G), MMP-9 (−1562 C/T and +279 R/Q), MMP-12 (−357 Asn/Ser), and MMP-13 (−77 A/G and 11A/12A) with periodontitis risk, were included in this meta-analysis [8, 11–14, 16, 22–32].