We examined clinical parameters in patients receiving long-term implant maintenance. There were significant differences between the H and HP groups in age at the time of maintenance, number of natural teeth at the beginning of implant treatment, total number of extracted teeth, and maintenance. The prevalence of implant-based peri-implantitis was 10.8% of all the implants. All implants with peri-implantitis came from the HP group, and many belonged to patients with a history of severe periodontitis. The PPD around implants was significantly greater in the HP group than in the H group. We found weak positive correlations between PPD and BoP (r _s  = 0.401, p < 0.05) in the H group and between PPD and BoP (r _s  = 0.241, p < 0.05) and PPD and mPI (r _s  = 0.228, p < 0.05) in the HP group. Our findings suggest that the clinical parameter of probing pocket depth is a critical index for the diagnosis of peri-implant disease during the maintenance period among healthy and history-of-periodontitis groups.