Use of a tetragonal structure composed of yttrium-stabilized zirconium oxide in dentistry: a study of the ceramic-zirconia interface.

Objective The introduction of yttrium-stabilized zirconia (Y-TZP) has opened new frontiers in the fields of dental-material esthetics and biocompatibility. In a previous report, we analyzed the capacity of Y-TZP to withstand maximum loading (static resistance) and the repeated application of loads lesser than those that provoke fracture (fatigue resistance). The aim of this study was to evaluate the adhesion between Y-TZP and its ceramic support (shear resistance). Materials and methods To assess this characteristic, we developed a new testing protocol to be used with specially designed cylindrical samples with ceramic covering on a zirconia base. The research was carried out in two phases: the aim of the first was to identify the approach that produced the best adhesion; the second phase aimed at identifying the mechanical and/or physical mechanisms responsible for the zirconia/ceramic adhesion. Results In the first phase, we found that the surface finish of the zirconia was the sole factor that influenced final adhesion. In the second phase, our findings showed that this adhesion is essentially due to micromechanical and physical interactions, which were not dependent on the contact pressure between the two materials or on the geometric characteristics of the ceramic covering. Conclusions On the whole, the best final result was obtained when the zirconia was subjected to surface finishing with a diamond rotary instrument, but even in this case adhesion was inferior to that achieved with a gold-alloy base.