A strict maintenance program every 3–6 months followed by a high standard of oral hygiene may hold a stable peri-implant condition after peri-implantitis surgery [16].

In the present study, access to perform sufficient plaque control at the treated implants was considered acceptable due to previous corrections of the prostheses. The frequency of supportive periodontal care (SPT) was reported to be between 6 and 12 months. Based on BoP recordings, this may not have been a sufficient regime for many of the patients in this cohort.

The patients’ general health, oral hygiene habits and compliance to the maintenance program may also affect the treatment outcome. Smoking may be a negative factor regarding complications following implant therapy [7]. In the present study, most participants were smokers or former smokers and had a history of periodontitis. No difference was noted in the number of implants with progressive bone loss versus stable conditions or between smokers and former smoker/non-smokers. This may be due to the small sample size.

In a study by Leonhardt et al. [7], nine subjects with a history of periodontitis had 26 implants diagnosed with peri-implantitis. During the 5-year follow-up after treatment, smokers with severe peri-implantitis had a less favourable treatment outcome. Another study [16] reported no difference in result between smokers and non-smokers after 2 years of follow-up.

Radiographic bone level changes for assessing the implant’s stability or progression of disease following treatment is used in several studies [7, 25]. A composite outcome regarding resolution of peri-implantitis was recommended [26].

The limitations regarding the non-standardized radiographs at the final examinations in the present study imply that results must be interpreted with care. Also, the radiopaque PTG granules were easily seen, and thereby, the cases were easily distinguished from the controls.

It has been stated that regenerative procedures do not address disease resolution but aim to fill the osseous defect [2]. Bone grafts of various materials have been used. This has classically been divided into autogenous, allogenic, xenogenic and synthetic or alloplastic materials [27].