Effects of different abutment material and surgical insertion torque on the marginal adaptation of an internal conical interface: An in vitro study

Purpose: To evaluate the marginal adaptation at implant-abutment connection of an implant featuring a conical (45 degrees taper) internal hexagonal abutment with a connection depth of 2.5 mm, comparing the performance of two identical abutments of different material (titanium grade-4 and Co-Cr-alloy). Methods: Twenty implants (3.75 mm x 15 mm) were connected to non-matching abutments (5.5 mm x 10 mm) of two different materials (titanium grade-4: n = 10; Co-Cr-alloy: n = 10). The specimens were separately embedded in epoxylite resin, inside copper cylinders, and submerged without covering the most coronal portion (5 mm) of the fixture. Five specimens per group were stressed simulating a surgical 100 Ncm insertion torque, while the others had no torque simulation. All specimens were subjected to a non-axial static load (100 N) in a universal testing machine, under an angle of 30 degrees with respect to the implant axis. Once 100 N load was reached, low shrinkage self-curing resin was injected inside the cylinders, and load was maintained until complete resin polymerization. Specimens were cut and analyzed with optical and scanning-electron-microscope (SEM) to evaluate the marginal adaptation at the implant-abutment connection. Statistical analysis was performed using one-way ANOVA (p = 0.02). Results: None of the 20 samples failed. The implant-abutment connection was able to guarantee a good optical seal; SEM analysis confirmed the absence of microgaps. Conclusions: Within the limits of this study (small sample size, limited time) the marginal adaptation of the implant-abutment connection was not affected by the abutment material nor by the application of surgical insertion torque.