This randomized controlled trial aimed to determine the effect of 35% phosphoric etching gel on decontamination of the implant surface during resective surgical treatment of peri-implantitis. Both decontamination procedures (mechanical debridement with curettes and gauzes combined with phosphoric acid 35% and mechanical debridement combined with sterile saline) resulted in a significant immediate reduction in counts of anaerobic bacteria on the implant surface. This immediate reduction was greater when phosphoric acid was used. Although the difference in log-transformed mean anaerobic counts between both decontaminating procedures did not reach the level of statistical significance (p = 0.108), there were significantly less culture-positive implants after the decontamination procedure in the phosphoric acid group (p = 0.042). As our study focused on the decontaminating effect of phosphoric acid on implant surfaces, we used the microbiological parameter as primary outcome variable. To evaluate the effect of the intervention on this microbiological parameter, an in vivo situation was chosen to benefit the influence of a clinical situation. In addition, we evaluated secondary outcome parameters indicating the clinical effect of the treatment procedure, i.e., disease resolution 3 months after active treatment.

At 3 months post-surgery, disease resolution was more frequently observed in the control group (75% of implants) than in the test group (63.3% of implants). However, no significant differences in clinical and microbiological outcomes between control and test group were found. Although the study was “a priori” not powered to detect clinical differences, no trend was observed for superior results of one decontamination procedure over the other.

To our knowledge, this is the first randomized controlled clinical trial reporting on the effect of phosphoric acid in relation to peri-implantitis treatment. The reason for choosing phosphoric acid as decontaminating agent was that acids with low pH exert a strong bactericidal effect [22, 36], and phosphoric acid does not seem to chemically damage titanium implant surface [37]. A gel as application mode has the great advantage of being precisely applicable with minimal touching of the surrounding bone or connective tissue. A disadvantage of a gel might be the limited flow in deeper areas of the rough implant surface. To overcome this problem, it was decided to continuously rub the etching gel onto the implant surface with a small brush during the decontamination period.