MMP8 and Peri-Implantitis: Ritzer et al. [49] demonstrated by the 24/7-chewing-gum MMP-8 assay that elevated levels of MMP-8 could be detected in peri-implantitis oral fluids confirming and further extending the findings of Teronon et al., Kivelä-Rajamäki et al., Xu et al., and Kivelä-Rajamäki et al. [21–23, 30, 82].