Peri-Implantitis-Associated Microbiota before and after Peri-Implantitis Treatment, the Biofilm "Competitive Balancing" Effect: A Systematic Review of Randomized Controlled Trials

This systematic review of RCTs aimed to characterize short- and long-term changes in peri-implantitis-associated microbiota (total biofilm microbial load and predominant pathogens' counts) following (any) peri-implantitis treatment in systemically healthy, non-smoking, partially/totally edentulous adults. The study protocol, compliant with the PRISMA statement, was registered on PROSPERO (CRD42024514521) before the literature search. Data from 11 RCTs, assessed through the ROBINS-2 tool, were qualitatively synthesized. No data were retrieved on total edentulism, healthy peri-implant/periodontal sites, treated mucositis, gingivitis, and periodontitis sites. Shortly after treatment, , , and prevailed, indicating early colonization, as after implant placement. After both surgical and non-surgical approaches, although not eradicated, the peri-implant total biofilm load, red- and orange-complex species, and counts generally decreased for up to about three months. However, one month after treatment, red-complex species and increased, likely due to persistent tissue-invasive bacteria, unresolved pathological conditions (high probing depth values) favoring anaerobiosis and dysbiosis, and a qualitatively and quantitatively decreased biofilm community, competing and balancing the predominant pathogens (biofilm "competitive balancing" effect), thus allowing recolonization by more virulent bacteria. Red-complex bacteria gradually leveled off to baseline at the six- and twelve-month follow-ups. remained almost unchanged after treatment.