THE EFFECT OF AGING ON MICROSHEAR BOND STRENGTH OF RESIN CEMENT TO MONOLITHIC ZIRCONIA

Purpose. Successful long-term bonding to zirconia ceramic remains a challenge, requiring special cements and treatments, which might negatively affect the ceramic.
The purpose of this study was to evaluate the durability of micro-shear bond strength between resin cement containing phosphate monomer and zirconia ceramic submitted to different surface treatments before and after aging.
Material and methods monolithic zirconia (Bruxzir Glidewell, California, USA) was selected as the substrate material. The ceramic surfaces, were either left untreated as-sintered (Group NT), silica coated with Rocatec soft system (3M/ESPE, USA) (Group CT), or treated with Alloy Primer (Kurary, Japan) (Group PR). They were bonded with a dual-cured resin cement; Panavia v5 (Kurary), using an adhesive system (Clearfil SE Bond). A micro-shear bond test was carried out to measure the bond strength of the resin cement to the zirconia surface. Samples were tested in a universal testing machine at a crosshead speed of 0.5 mm/minute before and after 90 days of water storage and 6000 thermal cycles (dwell time, 30 seconds). Statistical analysis was performed using a two-way ANOVA model, at pResults. Mean microshear bond strength ranged from 14.39 to 21.59 MPa after 3 days and from 5.64 to 20.42 MPa after aging. Water storage and thermal cycling decreased bond strength significantly for NT and PR groups, while it had no significant effect on CT group. Early bond strength was highest with CT and PR groups with no significant difference between them, and they were both statistically significantly higher than NT group. SEM analysis showed an increase in interfacial adhesive failure after aging.
Conclusions. Within the limitations of this study, it was concluded that silica coating and application of a chemical primer produced higher bond strengths to resin cement than leaving zirconia untreated. Aging significantly reduced the bond strengths for the untreated and primed zirconia, while silica coated zirconia remained stable and was not affected.