Randomised study for the 1-year crestal bone maintenance around modified diameter implants with different loading protocols: a radiographic evaluation.

This study evaluated by standardised digitised periapical radiography the crestal bone maintenance around modified diameter internal hex implants with variable thread design and narrow neck loaded with different procedures. Forty implants were placed in 25 patients. Twenty implants were conventionally loaded, 20 ones immediately loaded. Radiographs were taken with a customised bite record and processed with software. Measurements of bone from the fixture-abutment junction to mesial and distal marginal bone levels were made. Student's t test statistical analysis was adopted. Baseline data were variable; at 1-year follow-up, there were no significant differences for marginal bone loss between immediately and conventionally loaded maxillary implants (p = 0.1031), whilst there were slight significant differences between immediately and conventionally loaded implants in the mandible (p = 0.0141). Crestal bone maintenance around conventionally and immediately loaded modified diameter implants was similar, with slight significant differences in mandible where a lower marginal bone loss was observed.

A 16-year study of the microgap between 272 human titanium implants and their abutments.

A microgap has been described at the level of the implant-abutment connection. 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. The authors report on 272 implants with screw- or cement-retained abutments retrieved from humans for different causes during a 16-year period. In the implants with screw-retained abutments, a 60-microm microgap was present at the level of implant-abutment connection. In some areas the titanium had sheared off from the surface and from the internal threads. The contact between the threads of the implant and those of the abutment was limited to a few areas. Bacteria were often present in the microgaps between implant and abutment and in the internal portion of the implants. In implants with cement-retained abutments, a 40-microm microgap was found at the level of the implant-abutment connection. No mechanical damage was observed at the level of the implant or of the abutment. All the internal voids were always completely filled by the cement. No bacteria were observed in the internal portion of the implants or at the level of the microgap. The differences in the size of the microgap between the two groups were statistically significant (P < .05). 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. In these retrieved implants, the size of the microgap was markedly variable and much larger than that observed in vitro.