Analysis of Dimensional Changes in the Screw and the Surface Topography at the Interface of a Titanium Screw and a Zirconia Abutment Under Cyclic Loading: An In Vitro Study

Purpose: The purpose of this experiment was to analyze the mechanics of the ceramic abutment-implant joint and the dimensional changes in the abutment screws from cyclic loading. Materials and Methods: Two groups of experimental assemblies were used, one with zirconia abutments and the other with titanium abutments (n = 10). Each specimen consisted of an implant, an abutment, and a metal crown affixed in an acrylic resin base. The specimens were subjected to cyclic loading of 200 N for 1 million cycles at 10 Hz. After loading, a torque-angle signature analysis was done, the dimensions of the screws were measured, and the implant-abutment interfaces were examined with scanning electron microscopy. Results: There was a statistically significant increase in the total length of the screws: 121 µm in the titanium group versus 88 µm in the zirconia group (P .004). Microscopic analysis showed collected debris on the zirconia abutment undersurface and the screws. A statistically similar decrease in torque was observed: 18% for zirconia versus 13.5% for titanium. Radiographic microanalysis revealed that the debris collected in the zirconia assemblies was essentially a collection of titanium, vanadium, and aluminum, with traces of zirconium. Conclusions: While there was a loss of torque in both types of abutments, the stability of the zirconia abutment-implant joint was not affected by the loading. The study provides a better understanding of zirconia abutments, screw designs, and the mechanism holding together the implant-abutment assembly.