A double-blind, placebo-controlled, prospective cross-over study was made. All the patients were edentulous and were divided into two groups: A) with no peri-implant disease; B) with peri-implant mucositis affecting one or more implants. Patients with peri-implantitis were excluded. All patients in both groups initially received the oral probiotic Lactobacillus reuteri Prodentis, followed by placebo. Only the supervisor of the study knew this information; clinical examiner and patients were blind. Were studied: crevicular fluid volume, modified plaque index, probing depth, modified gingival index, and concentrations of interleukin 1β, interleukin 6 and interleukin 8, and Bacterial load.