In vitro shear bond strength of 2 resin cements to zirconia and lithium disilicate: An in vitro study

Statement of problem: There is little evidence on how the multiple layers of zirconia (ZrO₂) or glazed material will affect the shear bond strength (SBS) of different resin cements. Purpose: The purpose of this in vitro study was to compare the SBS of 2 resin cements with the different layers of a monolithic polychromatic ZrO₂ ceramic, both glazed and nonglazed, and a lithium disilicate (LDS) ceramic. Material and methods: One hundred and sixty-eight composite resin cylinders and 48 monolithic polychromic ZrO₂ plates were prepared. Twenty-four were milled and sintered, and 24 were milled and sintered and had a glaze cycle applied with no liquid glaze. These plates and 12 LDS plates were mounted in autopolymerized acrylic resin. Bonding surfaces were polished, airborne-particle abraded, and cleaned ultrasonically. The different layers (cubic, hybrid, and tetragonal) of the ZrO₂ plates were identified and marked. The plates were assigned to 2 cement groups: a self-adhesive, autopolymerized resin cement, and a dual-polymerizing, adhesive resin cement (DPRC). Bonding surfaces were cleaned and treated according to the cement manufacturer's instructions. Three composite resin cylinders were luted to the ZrO₂ plates at the appropriate layer, and 2 cylinders were luted to each LDS plate. The specimens were stored in a moist environment for 24 hours at 37 °C. The SBS test was performed with a universal testing machine. Visual inspections of the debonded surfaces were compared under magnification. The data were analyzed with a 2-way ANOVA and a subsequent Student t test (α=.05). Results: The 2-way ANOVA found no difference among luting agent and LDS and ZrO₂. The SBSs of the nonglazed tetragonal and cubic layer to the ZrO₂ were higher than to the surface exposed to a glazing cycle (P=.001). The bonded surfaces were examined tactilely and under ×3.5 magnification, followed by light and scanning electron microscopy and recorded as either adhesive, cohesive, or mixed. Almost all failures in the glazed ZrO₂ were mixed and cohesive. However, more adhesive failures were observed in the DPRC group of nonglazed ZrO₂. Conclusions: No differences were found between the 2 luting agents for the LDS. For the ZrO₂ cubic and tetragonal layers, the DPRC had higher bond strengths to the nonglazed surfaces.