The present study is a double-blind randomized controlled trial evaluating the effect of 35% phosphoric etching gel (test group) compared to the effect of saline (control group) for implant surface decontamination combined with mechanical debridement during surgical peri-implantitis treatment. Patients were randomly assigned to the test or control group using a one-to-one allocation ratio. The study has been conducted in full accordance with the World Medical Association Declaration of Helsinki (version 2008) and was approved by the Institutional Review Board of the University Medical Center Groningen, the Netherlands (METc2013.005). Written informed consent was obtained from all participants before entering the trial. Clinical trial registration was done at the Netherlands National Trial Register (http://www.trialregister.nl, trial number NTR5185). The CONSORT guidelines for reporting a clinical trial were followed.

Patients participating in this study were consecutively selected from the patient populations of the Center of Dentistry and Oral Hygiene and the Department of Oral and Maxillofacial Surgery of the University Medical Center Groningen, Groningen, The Netherlands, from October 2012 to April 2014.

Adult patients with at least one endosseous implant with clinical and radiographical signs of peri-implantitis were included. Peri-implantitis was defined as a loss of marginal bone ≥2 mm in combination with bleeding and/or suppuration on probing and a peri-implant probing depth ≥5 mm [32]. Implants had to be in function for at least 2 years.

Exclusion criteria were:

Contraindications for the surgical procedures;

A history of local radiotherapy to the head and neck region;

Pregnancy and lactation;

Uncontrolled diabetes;

Systemic use of antibiotics within 3 months before inclusion;

Long-term use of anti-inflammatory drugs;

Incapability of performing basal oral hygiene measures as a result of physical or mental disorders;

Uncontrolled periodontitis (PPD >5 mm);

Implants with bone loss exceeding two thirds of the length of the implant or implants with bone loss beyond the transverse openings in hollow implants;