Objective: to evaluate early osseointegration of dental implants installed with two different drilling protocols.
Material and methods: thirty-six cylindrical shape Mozo Grau implants, with a diameter of 3.75 and 11 mm long, were placed into the distal condyle (submerged) of each femur of 18 New Zealand rabbits. In the control group, a 3.3 mm diameter drill was used as the last one prior implant installation (standard protocol). In the test group, the same procedure was carried out but an additional 3.5 mm drill was used as the final one (oversized protocol) Thus, we could obtain different primary stability at day 0 between groups. Sacrifice of the animals was after 2, 4 and 8 weeks. Histomorphometric analysis (bone-to-implant contact ratio [BIC%]) and implant stability quotient (ISQ) values (Ostell ) were registered at each sacrifice time.
Results: the ISQ values were statistically significant different between groups at day 0 (control: 69.65; test: 64.81); and after 2 weeks (control: 77.93; test: 74). However, after 4 and 8 weeks the results were similar. BIC% showed a similar tendency, with 58.69% for the control group and 40.94% for the test group after 2 weeks, this difference being statistically significant. At 4- and 8-week interval, BIC% was similar.
Conclusion: at 2-week interval (early healing), osseointegration had been influenced by different primary stability at implant installation, being slower in the oversized protocol (lower primary stability), which could be especially risky in challenging clinical situations, such as soft bone (class 3 and 4) and early/immediate loading. However, from 4 week on, these differences disappeared. Nevertheless, we have to consider that a direct transfer of the results of this animal study (time bone repair mechanisms) into clinic has to be done with caution.