Abstract
Objective: The objective was to in-vitro evaluate the mode of failure of abutments supporting fixed partial dentures (FPDs) via different retention techniques. Materials and Methods: Thirty-six implants with diameter and length of 4.5 and 13 mm, respectively, were used to prepare 18 samples of FPDs. Based on the variations on abutment's design, the FPDs were divided into three groups: Group A is cement-based retention; Group B is screw-based retention; and Group C is multiunit screw-based retention. Using a chewing simulator, cyclic loads of 1,250,000 load cycles with the load of 70N were applied on all samples to simulate 5 years of human functional chewing. The samples were loaded until failure using an electromechanical test machine. Sample-size estimation was done and fracture-load values were recorded as means and corresponding standard deviations; and group comparisons were done using one-way analysis of variance and Tukey's post hoc tests. A P value below 0.01 was nominated as an indicator of statistical significance. Results: In total, 36 samples (12 implant-abutment connections per group) were assessed. Abutment bending was observed in 6 (50%), 6 (50%) and 6 (50%) samples in groups A, B and C, respectively. De-attachment of the FPD form the abutment occurred in 5 (41.7%) and 5 (41.7%) samples in groups A and C, respectively. Screw fracture and fracture of FPD at the connector side occurred in 1 (8.3%) and 1 (8.3%) sample in groups A and C, correspondingly. Failure of the FPD was more often encountered in groups A (100%) and C (100%), compared to group B (50%). Conclusion: All abutments underwent failures under cyclic loading with abutment bending being the most common failure mode. Cement- and multi-screw-supported abutments fail more often than screw-supported abutments.