**2.8 Matrix metalloproteinase and tissue inhibitor of matrix metalloproteinase**

Matrix metalloproteinases (MMPs) are the key enzymes, which play a major role in the destruction of the collagenous and non-collagenous proteins of the connective tissue component. This is essential for maintaining the normal tissue homeostasis. To date, at least 26 members of MMPs have been identified. In periodontitis, this tissue homeostasis is altered with more destruction of connective tissue components and less inhibition by the TIMPs. Elevated levels of MMP-1, MMP-2, MMP-3, MMP-8, and MMP-9 have been detected in gingival crevicular fluid, peri-implant sulcular fluid, and gingival tissue of periodontitis patients. Thus, the genetic changes of the MMPs and TIMPs might play a role in the etiopathogenesis of periodontitis. According to Li et al., there was no significant association of MMP1, 8, 9, 12, 2, or 13 polymorphism with periodontitis. They did a meta-analysis of 17 studies [21]. Thus, the role of MMPs and TIMPs gene polymorphism with periodontitis has to be explored with further refined studies.
