Role of the Microgap between Implant and Abutment: a Retrospective Histologic Evaluation in Monkeys

Objective: 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. Aim of the present study was a retrospective histologic evaluation in monkeys of the bone response to implants inserted in different anatomic situations. Methods: The protocol was approved by the Ethical Committee of Buenos Aires University. Plasma-sprayed titanium implants (P.H.I., S. Vittore Olona, MI, Italy) were inserted 1-2 mm above the alveolar crest (Group 1 – 15 implants), at the level of the alveolar crest (Group 2 – 12 implants), or 1-1.5 mm below the alveolar crest (Group 3 – 13 implants). Results: In Group 1, a 0.13 mm (+/- 0.12 mm) bone increase in a coronal direction was seen. In Group 2, a 2.1 mm (+/- 0.29) vertical bone loss was present. In Group 3, a mean 3.6 mm (+/- 0.46) vertical bone loss extending in an apical direction was observed. Statistically significant differences were observed between Group 1 and Group 3, and between Group 1 and Group 2. No statistically significant differences were found between Group 2 and Group 3. Conclusion: Our results confirm the data previously published that if the microgap was moved coronally away from the alveolar crest, less bone loss would take place, and, if, on the contrary, the microgap was moved apical to the alveolar crest, greater amounts of bone resorption were present.