MMP8 and periodontitis: Neutrophil collagenase, also called matrix metalloproteinase (MMP)-8, polymorphonuclear (PMN) leukocyte collagenase, or collagenase-2, has been identified and characterized as a major collagenolytic enzyme that causes active periodontal and peri-implant degeneration (APD) in periodontitis and peri-implantitis [3–7].