MMP9 and periodontitis: Among the 23 types of MMPs identified so far, upregulation of MMP-8 and MMP-9 has been associated with periodontitis and peri-implantitis (Araújo et al., 2011; Franco et al., 2017; Al-Majid et al., 2018; Checchi et al., 2020), and other studies have reported that these two MMPs are linked to disease progression and bone loss (Arakawa et al., 2012; Al-Majid et al., 2018).