Purpose: Bacterial penetration and colonization of the microgap at the implant-abutment interface have been reported in several studies. The aim of this study was to evaluate the effectiveness of placing a silicone membrane between the abutment and the implant platform in an attempt to seal the interface. Materials and Methods: A total of 15 external-hex implants were placed in 10 patients with clinically healthy peri-implant tissues, and all of the patients had ceramic prosthetic crowns. Samples were collected from the microgaps before, 30 days after, and 90 days after insertion of a silicone membrane. Bacterial DNA was extracted and submitted in triplicate to polymerase chain reaction using primers specific for four peri-implant pathogens: Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, and Tannerella forsythia. Results: In the initial samples, a positivity of 52% was found, which was different from that found in samples collected after 30 days (32%) and 90 days (27%) after insertion of the membrane. Conclusion: It was evident that the silicone membrane reduced, but did not prevent, penetration of these species into external-hex implants. Keywords: bacterial infiltration, dental implants, microbiology