BoP has been used to evaluate inflammatory conditions of periodontal tissue [33] and can also be an important evaluation item for peri-implant tissues. To avoid diagnosing bleeding resulting from strong probing as a false positive, we set the probing pressure to 0.15 N [34]. BoP values were low, with no significant difference between the groups (H group, 0.30; HP group, 0.28). This result was similar to that of a previous study that reported a low bleeding index in the implant group with a low plaque index [35].

There was no significant difference between mPI and BoP when clinical parameters were compared, and there was a significant difference for PPD only in the HP group. For this reason, we analyzed the correlation of the characteristics of patients with significant differences only for PPD. In the H group, a significant correlation with PPD was found only for the number of extracted teeth, suggesting that PPD was correlated with the number of teeth extracted due to reason that it was not periodontitis.

However, in the HP group, age, number of teeth, extracted teeth, and maintenance period all correlated with PPD. This finding suggests that the implant PPD reflects the period required for periodontitis treatment and complexity of treatment before implant placement. Although the number of teeth at the beginning of implant treatment showed only a negative correlation, the small number of teeth present indicates that a large number of teeth were extracted as a result of periodontitis, suggesting that the implant PPD is affected by this. From these results, it can be speculated that the severity of periodontitis before the implant treatment is also reflected in the PPD.

Correlations between PPD and the two other clinical parameters, mPI and BoP, were examined in each group. Because this study targeted all patients who received maintenance, it was predicted that the hygiene around the implants in both groups would be good. However, there was a significant difference between PPD and mPI only in the HP group. It was assumed that the probing depth and oral hygiene around implant appeared to be affected each other in the HP group. In contrast with the target group of our study, there may have been a significant correlation between PPD and mPI in a patient group that had not received maintenance and that had poor oral hygiene.