In this study, we reviewed the clinical parameters of 130 implants in 55 patients during ongoing long-term maintenance. We focused on the history of periodontitis and compared the parameters in two groups classified according to a history of periodontitis. A previous study on the prevalence of periodontitis revealed that moderate or severe periodontitis was observed in 64% of people over 65 years of age [19], and that the number of remaining teeth also decreased after the age of 60 [20]. Consistent with these findings, our study suggests that periodontal treatment was started at an older age in the HP group. Previous reports recommended that the follow-up period evaluating the peri-implant tissue should be 5 years or longer. The mean maintenance period of this survey was 6 years and 6 months in total. Therefore, we consider that the observation period of this study was sufficiently long-term and reasonable, resulting in a potentially predictive result [3]. The implant maintenance period of the HP group was longer than that of H group, possibly because the HP group consisted of patients with a history of good compliance who had visited the university hospital for long-term periodontal treatment and understood the importance of periodontal treatment and were likely to continue with maintenance visits after the implant treatment. However, it was expected that patients in the H group are often only partially treated and they had less experienced to receive comprehensive or long-term treatment. We hypothesized that the patients of H group might have felt less necessity of receiving maintenance because they were healthy.

A history of periodontitis has been recognized as an important risk indicator for peri-implantitis [2, 3, 21] and is known to lower the success rate during maintenance. Thus, for long-term implant stability, it is important to perform appropriate periodontal treatment [22,23,24].

The difference between the number of natural teeth at the first visit and at the beginning of implant treatment indicates that many teeth were extracted in the HP group compared with the H group during the active treatment period. One limitation of this study is that we did not investigate the reasons for tooth extraction. We inferred that in the HP group, many teeth were removed because of periodontitis, whereas a smaller number were extracted in the H group because of root fracture or apical periodontitis. There was no significant difference in the number of implants between the groups. However, the number of natural teeth before implant treatment was smaller in the HP group than in the H group. It is possible that the implants in these patients were used as bridge abutments for wide defects and that the size of the defect was not necessarily reflected in the number of implants.