Comparative Evaluation of Microgap at the Interface of Titanium and Zirconium Abutments Following Oblique Cyclic Loading: An in vitro Study

Microgap in the implant-abutment interface is one of the main challenges in the treatment of two-piece implants. This study aimed to investigate the effect of two types of abutments (zirconia and titanium) on microgap at implant-abutment interface area under oblique cyclic loading in vitro.  In this in vitro study, 12 implant-abutment assemblies were used, each containing six sets with either zirconia or titanium abutments and vertically mounted in the modified resin blocks of auto-polymerized polyester base. The specimens were then subjected to oblique cyclic loading of 75 N at a 30 ± 2 degrees angle to the longitudinal axis of the implant with a frequency of 1 Hz in 500,000 cycles, equivalent to 20 months of human mastication. For the microgap analysis, direct observation from the top was used with a scanning electron microscopy (SEM) with a magnification of 5000×. Statistical analysis was used to compare the microgap before and after the application of loading with the paired t-test.   The amount of microgap before force application in the titanium abutment group was (2.6±0.7) significantly higher than the zirconia abutments (1.9±0.5) (P = 0.033). The dimension of the microgap in the titanium abutment group significantly decreased following cyclic loading (P = 0.047), but in the zirconia group showed a significant increase (P = 0.035). Finally, the dimension of the microgap following oblique cyclic loading in the titanium abutment group (2.0±0.8) was not significantly different with the zirconia abutments (2.7±0.9) (P = 0.262). The difference of microgap after oblique cyclic loading between two types of titanium abutment and zirconium abutment is not significant, and both are clinically acceptable.