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Implants and surrounding tissues were washed in saline solution and immediately fixed in 4% paraformaldehyde and 0.1% glutaraldehyde in 0.15 M cacodylate buffer at 4☌ and pH 7.4 to be processed for histology. In these retrieved implants, the size of the microgap was markedly variable and much larger than that observed in vitro. In conclusion, in screw-retained abutments the microgap can be a critical factor for colonization of bacteria, whereas in cement-retained abutments all the internal spaces were filled by cement. The differences in the size of the microgap between the two groups were statistically significant ( P <. No bacteria were observed in the internal portion of the implants or at the level of the microgap. All the internal voids were always completely filled by the cement. No mechanical damage was observed at the level of the implant or of the abutment. In implants with cement-retained abutments, a 40-μm microgap was found at the level of the implant-abutment connection. Bacteria were often present in the microgaps between implant and abutment and in the internal portion of the implants. The contact between the threads of the implant and those of the abutment was limited to a few areas. In some areas the titanium had sheared off from the surface and from the internal threads. In the implants with screw-retained abutments, a 60-μm microgap was present at the level of implant-abutment connection. The authors report on 272 implants with screw- or cement-retained abutments retrieved from humans for different causes during a 16-year period. This microgap can be colonized by bacteria, and this fact could have relevance on the remodeling of the peri-implant crestal bone and on the long-term health of the peri-implant tissues. A microgap has been described at the level of the implant-abutment connection.