Implant mobility;

Implants at which no position could be identified where proper probing measurements could be performed;

Previous surgical treatment of the peri-implantitis lesions.

The study protocol was based on the study protocols of two previous studies evaluating the decontaminating effect of chlorhexidine during surgical peri-implantitis treatment [10, 32] and is briefly described below.

Within 1 month before surgical treatment, all patients received extensive oral hygiene instructions and mechanical non-surgical debridement of implants and remaining dentition using hand instrumentation and/or an ultrasonic device. Immediately before surgical treatment screw-retained suprastructures were removed. In order to obtain an optimal overview of the peri-implant area during surgery, prior to the procedure, only screw-retained suprastructures were removed. Cemented single crowns or bridges on mesostructures were left in place to prevent any damage to these structures. Directly after surgery, the screw-retained suprastructures were placed back. Cemented single crowns or bridges on mesostructures were left in place to prevent any damage to these structures. Vertical releasing incisions extending into the alveolar mucosa were placed using a surgical blade (no. 15), and full thickness mucoperiosteal flaps were raised buccally and lingually. Flaps were designed to allow optimal access to the peri-implant bone defect. Granulation tissue was removed using titanium curettes (Gracey; Hu-Friedy®, Chicago, IL, USA). The implant surfaces were mechanically cleaned using titanium curettes and gauzes and cotton pellets soaked in saline. Next, the patients were randomly allocated to either the test or control group. Subsequently, implants were cleaned with either local application of 35% phosphoric acid gel (pH 1) for 1 min (Temrex gel, Temrex, Freeport, NY, USA) (test group) or by rinsing with an abundant amount of sterile saline for 1 min (control group). Care was taken to apply the phosphoric etching gel precisely on the implant surface using a syringe with a small tip. During 1 min, the etching gel was continuously rubbed on to the implant surface with a small brush. In both groups, the intervention continued with rinsing of the implant surface with an abundant amount of sterile saline for 1 min.