Of the 55 subjects, 25 were male and 30 were female (H group: 8/10, HP group: 17/20, respectively). A total of 130 implants (H group 39, HP group 91) were included in the analysis (Table 2). The mean maintenance period was 6 years and 6 months. The average number of natural teeth at the first visit and at the beginning of implant treatment were 25.3 ± 2.9 and 22.4 ± 4.5, respectively. Comparison between the H and HP groups revealed a significant difference in patient age at the time of maintenance, number of natural teeth at the beginning of implant treatment, total number of extracted teeth, and time since implant placement.

Among all the subjects, 14 implants (10.8%) had peri-implantitis, all belonging to the HP group (6 patients). Details of periodontitis diagnosis in the HP group were generalized moderate periodontitis (22 patients, 53 implants), generalized moderate periodontitis + localized severe periodontitis (11 patients, 23 implants), and generalized severe periodontitis (4 patients, 15 implants) (Table 3). The proportion of peri-implantitis for each diagnosis were 5.7% (3/53) for generalized moderate periodontitis, 13.0% (3/23) for generalized moderate periodontitis + localized severe periodontitis, and 53.3% (8/15) for generalized severe periodontitis at the implant level. The prevalence of peri-implantitis in the HP group was 15.4% (14/91 at the implant level) and 16.2% (3/37 at the patient level).

The data from each subgroup are shown in Table 4.

The mPI score for the total study population was 0.21 ± 0.30 (mean ± SD). The mean scores of the H and HP groups were 0.18 (median, 0.25) and 0.23 (median, 0.25), respectively.

The PPD of the total study population was 3.19 ± 0.96 mm (mean ± SD). The mean PPDs of the H and HP groups were 2.87 mm (median, 2.83 mm) and 3.33 mm (median, 3.00 mm), respectively.

The BoP score of the total study population was 0.28 ± 0.29 (mean ± SD). The mean scores of the H and HP groups were 0.30 (median, 0.17) and 0.28 (median, 0.17), respectively.