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.

Phosphoric acid gel as agent for implant surface decontamination has only been investigated in two other clinical studies. Strooker et al. used phosphoric acid 35% for peri-implant supportive therapy and found greater reductions in bacterial load, but no significant clinical differences compared to conventional mechanical supportive therapy. They concluded that local application of 35% phosphoric acid gel can be as effective as conventional mechanical therapy in the professional supportive care of oral implants. In the study of Wiltfang et al., 20% etching gel was used for implant surface decontamination in a combined surgical protocol for treatment of peri-implantitis. Thirty-six implants with peri-implantitis in 22 patients were followed for 1 year. The implants were decontaminated with etching gel, and the defects were filled with autologous bone mixed with an osteoinductive material for regenerative treatment of bone defects. In their study, previous microbiological tests (not published) of implants in situ had revealed complete elimination of the bacterial microflora after decontamination with etching gel, which is close to our results of “complete” elimination (reduction below detection level) in 20 out of 23 implants. They concluded that their surgical protocol in combination with phosphoric etching gel provides a reliable method to treat peri-implant bone defects.

Phosphoric acid used in an in vitro setting has only been described in a study by Tastepe et al.. The use of an air abrasive device with four different powders was compared to phosphoric acid. In contrast to our study and the previous described clinical studies, the use of phosphoric acid was not efficient in removing biofilm.