Clinical outcomes following surgical treatment of peri-implantitis at grafted and non-grafted implant sites: a retrospective analysis

For this retrospective analysis, standardized clinical record forms of a total of 39 partially/fully edentulous patients (25 female and 12 male) exhibiting 57 implants were screened. All patients had attended the Department of Oral Surgery, Heinrich Heine University, Düsseldorf, Germany for the treatment of peri-implantitis between 2007 and 2010, and were under regular implant maintenance care. The mean follow-up time was 41.9 ± 34.75 months (range 6 to 126 months). Some patients were also participating in a randomized prospective clinical study, which aimed at investigating the effects of two surface decontamination methods on the clinical outcomes following combined therapy [14].

A data extraction template was generated and used for the anonymous acquisition of demographic study variables/implant site characteristics and baseline as well as follow-up clinical measurements after surgical therapy. The study was in accordance with the Helsinki Declaration, as revised in 2013 and approved by the local ethics committee.

For patient selection, the following inclusion criteria were defined:

Patients whose data files lacked information on the bone grafting procedures at the implant site or lacked information on augmentation protocols (i.e., lateral ridge augmentation or sinus floor elevation; one- or two-stage approach), and patients who did not comply with at least 6 months of follow-up were not included in the analysis.

Peri-implantitis was defined as bleeding on probing (BOP) with or without suppuration (Supp) in addition to changes in the radiographic bone level. Interproximal bone level changes were estimated on intraoral radiographs. In the absence of available baseline radiographs taken at prosthesis installation, “a threshold vertical distance of 2 mm from the expected marginal bone level” was used to assess bone loss [3].

The identified patients with a history of grafting had received the following treatment protocols:

After an initial course of non-surgical therapy, each subject had received a combined (i.e., implantoplasty + augmentative therapy) surgical treatment procedure [14] at respective implant sites (Fig. 1). This procedure included open flap debridement and a meticulous granulation tissue removal using conventional plastic curets (Straumann Dental Implant System; Institut Straumann AG, Basel, Switzerland) and an implantoplasty at both buccally (i.e., Classes Ib and Ic) and supracrestally (i.e., class II) (Fig. 1) exposed implant surfaces. This was accomplished using diamond burs (ZR Diamonds; Gebr. Brasseler GmbH & Co. KG, Lemgo, Germany) and Arkansas stones under copious irrigation with sterile saline. The remaining unmodified implant surfaces at the respective intrabony defect areas (i.e., classes Ib, Ic, and Ie) were decontaminated using either an Er:YAG laser device (energy density of 11.4 J/cm2, 10 Hz) (elexxion delos; elexxion AG, Radolfzell, Germany) or debrided using plastic curetes and cotton pellets soaked in sterile saline (Straumann Dental Implant System). Respective intrabony defect compartments were homogeneously filled using NBM (BioOss spongiosa granules, particle size 0.25–1 mm; Geistlich, Wolhusen, Switzerland) and were covered with CM (BioGide; Geistlich). Transmucosal healing was supported by a peri- and postoperative antibiotic medication for 5 days.

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].

In general, disease resolution (i.e., the absence of BOP and PD ≥ 6 mm) was achieved in 19 out of 57 (33%) implants and in 11 out of 39 (28%) patients. At the patient level, disease resolution was obtained in 4 out of 10 patients (40%) at grafted sites and in 7 out of 29 patients (24.1%) at non-grafted sites. The chi-square test (χ2) demonstrated no significant difference between the two patient groups (p = 0.579, df = 1, χ2 = 0.307) (Table 2, Fig. 3a). However, the results of the implant-level analysis revealed a significant difference between the two groups, indicating a higher disease resolution at grafted implant sites (9/16 (56%) compared to non-grafted sites (10/41 (25%)) (p = 0.048, df = 1, χ2 = 3.921) (Fig. 3b).

Mean and median BOP reduction values (%) for the 2 groups are presented in Table 3. At the patient level, mean BOP reduction amounted to 77.45% (minimum 0%; maximum 100%) and 60.64% (minimum 0%; maximum 100%) at grafted and non-grafted sites, respectively.

At the implant level, BOP reduction was noted to be 74.96% (minimum 0%; maximum 100%) at grafted implant sites and 54.88% (minimum 0%; maximum 100%) at non-grafted implant sites. According to the results of the chi-square test, the mean BOP reduction did not differ significantly between the groups at either the patient (p = 0.778, df = 1, χ2 = 0.079) or the implant (p = 0.515, df = 1, χ2 = 0.422) level (Fig. 4).

The reduction in the maximum PD (mm) values between the 2 groups is presented in Table 4. At the patient level, reduction in the maximum PD values amounted to 1.57 mm (minimum − 1.0 mm; maximum 4 mm) and 2.20 mm (minimum: − 4.0 mm; maximum 6.0 mm) at grafted and non-grafted sites, respectively. At the implant level, the corresponding reduction in the maximum PD values were calculated to be 1.31 mm (minimum − 4.0 mm; maximum 4.0 mm) at grafted implant sites and 2.10 mm (minimum − 4.0 mm; maximum 6.0 mm) at non-grafted implant sites. For the between-group comparison, no significant difference could be detected between the groups at both the patient (p = 0.968, df = 1, χ2 = 0.002, chi-square test) and implant (p = 1, df = 1, χ2 = 0.00026, chi-square test) level (Fig. 5).