Role of the microgap between implant and abutment: A retrospective histologic evaluation in monkeys

Background: It has been hypothesized that a certain width of the peri-implant mucosa is required to enable a proper epithelial-connective tissue attachment and, if this soft tissue dimension is not adequate, bone resorption will occur to ensure the establishment of attachment with an appropriate biological width. The reason for the accelerated bone loss around submerged 2-piece implants in the first year after the restoration is not known, but one possibility is that the gap between components plays a role in this process. Recent studies have shown that for all 2-part implants, the bone crest level changes appeared dependent on the location of the microgap. Methods: The aim of the present study was a retrospective histologic evaluation in monkeys of the bone response to implants inserted 1 to 2 mm above the alveolar crest (group 1, 15 implants), at the level of the alveolar crest (group 2, 12 implants), or 1 to 1.5 mm below the alveolar crest (group 3, 13 implants). These implants had been early loaded, immediately loaded, and inserted immediately postextraction. Results: In group 1, a 0.13 +/- 0.12 mm bone increase in a coronal direction was seen. In group 2, a 2.1 +/- 0.29 mm vertical bone loss was present. In group 3, a mean 3.6 +/- 0.46 mm vertical bone loss extending in an apical direction was observed. Statistically significant differences were observed between all 3 groups. Conclusions: Our results confirm data published previously that if the microgap was moved coronally away from the alveolar crest, less bone loss would occur and if the microgap was moved apical to the alveolar crest, greater amounts of bone resorption were present. This remodeling is not dependent on early and immediate loading of the implants or on immediate postextraction insertion.