Kim HK, et al. J Adv Prosthodont. 2016 Feb;8(1):37-42. http://dx.doi.org/10.4047/jap.2016.8.1.37

This study evaluated the effect of several airborne-particle abrasion protocols on the surface characteristics of monolithic zirconia and of protocol choice on the shear bond strength of resin cement. 375 bar-shaped (45×4×3mm3) and 500 disk-shaped (Ø9×1mm2) monolithic zirconia specimens were divided into 25 groups. All specimens were abraded with one of three different sizes of alumina particles (25, 50 or 125μm), two different pressures (2 or 4bar), two distinct application times (10 or 20s) and two distinct incidence angles (45° or 90°). The bar-shaped specimens were used for 3-point bending test; Weibull parameters were calculated and transformed monoclinic phase (XM), surface characteristics were examined. The disk-shaped specimens were used to determine the shear bond strength of resin cement before and after thermocycling. All data were analyzed using 4-way ANOVA and a multiple comparison Scheffé test (α=.05). The particle size, pressure and time significantly affected the flexural strength, while the incidence angle was insignificant. The XM and surface roughness were proportional to the size, pressure, time and incidence angle. The Raman spectrum analysis showed a higher proportion of the monoclinic phase as the depth of the specimen was closer to the abraded surface. In bonding with resin cement, the highest shear bond strength after thermocycling was obtained by the abrasion with 50μm particles at 4bar for 20s, regardless of incidence angle. Surface treatment of monolithic zirconia with 50μm particle at 4bar for 20s at either 45° or 90° incidence angles is recommended

Ha SR. J Adv Prosthodont. 2015 Dec;7(6):475-483. http://dx.doi.org/10.4047/jap.2015.7.6.475

Ha SR, et al. J Adv Prosthodont. 2018 Dec;10(6):395-400. https://doi.org/10.4047/jap.2018.10.6.395

The purpose of this study was to evaluate the effects of coping designs on the stress distributions in posterior zirconia crowns by non-linear three-dimensional finite element analysis. Three-dimensional finite element models of a mandibular right first molar with layers of veneering porcelain, zirconia coping, cement, and abutment tooth were designed by computer software (HyperWorks 10.0). Ten zirconia crowns with different designs were produced according to various shoulder positions and heights. The shoulders (1-mm width) exhibited incremental height increases of 1mm, 2mm, and 3mm on the buccal, lingual, and proximal sides, respectively. An axial compressive dynamic load simulating the progressive load was applied until a stainless steel ball model (7mm in diameter) deepened the veneer surface to 0.7mm in depth. Loads were placed on the inner inclines of the mesiobuccal, distobuccal, and mesiolingual cusps. Residual maximum principal stresses (MPSs) at the veneer and coping under progressive loading were determined for each zirconia crown. Reinforcements with the shoulders on the buccal, lingual, and proximal axial walls resulted in lower MPSs in the veneering porcelain but higher MPSs in the zirconia coping. As the shoulder height increased, the tensile stresses decreased, while the compressive stresses increased in the veneering porcelains. It can be concluded that the shoulder height and position in the zirconia coping will affect the MPSs of the crown. Our findings conclusively reveal the critical role of the shoulder design of the coping in preventing veneer fracture on posterior zirconia restorations by reducing tensile stresses in veneering porcelain