Kensara et al. (2020) [39] also evaluated the existing evidence on the immune response associated with peri-implantitis in comparison to healthy implants; according to the results, the pro-inflammatory cytokines and MMPs (IL-1β, IL-6, IL-17, TNF-α, MMP-2, and MMP-9) are expressed at a higher level in peri-implantitis sites compared to in the control group. This evidence concerns the gene MMP9 and Peri-Implantitis.