For all patients, the following clinical parameters were available: BOP (as measured within 60 s after probing) and PD (as measured in millimeters from the mucosal margin to the bottom of the probeable pocket). BOP and PD were assessed at six aspects around the implant: mesio-buccal, mid-buccal, disto-buccal, mesio-oral, mid-oral, and disto-oral. Maximum PD values (max PD) and mean BOP scores were evaluated before the surgical intervention and at the final follow-up.

The primary outcome variable was disease resolution (i.e., the composite outcome of the absence of BOP and probing pocket depths (PD ≥ 6 mm). Reduction of mean BOP and maximum PD values were defined as secondary outcome variables.

Commercially available and open source software programs (SPSS Statistics 23.0: IBM Corp., Ehningen, Germany and R Development Core Team) were used. Mean values, standard deviations (SD), medians, minimums, and maximums were calculated for mean BOP and maximum PD scores.

The analyses were performed at both patient and implant levels. Prior to this analysis, clinical parameters were pooled according to the grafting procedure (grafted or non-grafted), considering the patient as statistical unit. The differences in the baseline maximum PD values between the grafted and non-grafted implant sites were assessed using Wilcoxon rank-sum test. To evaluate disease resolution, changes in mean BOP and maximum PD between the groups (i.e., non-grafted vs. grafted) chi-square test (χ²) were applied. For the evaluation of disease resolution, if patients exhibited multiple implants with different treatment outcomes, they were assigned to a group according to the worst one. Based on the sample size calculation, for a large effect size (w = 0.5, df = 1, alpha = 0.05, power = 0.8), a minimum of 32 patients were needed [15].

The results were considered statistically significant at p < 0.05.