Long-term Aging Affects Resin Bond Strength to Zirconia-Reinforced Lithium Silicate

Objectives: The objective was to evaluate the effect of aging conditions and resin cement type on the bond strength to zirconia-reinforced lithium silicate (ZLS) ceramic in vitro.
Methods: Standardized ZLS (CELTRA Duo, Dentsply Sirona) discs (n=60) were hydrofluoric acid (5%) etched for 30 seconds and bonded to resin cylinders (coreX flow, Dentsply Sirona) by use of two different dual-polymerizing resin cements (self-adhesive resin cement, Calibra Universal, Dentsply Sirona; amine-free resin cement, Variolink Esthetic, Ivovoclar Vivadent GmbH) (n=30 per cement) in combination with their corresponding silane coupling agents (Calibra silane, Dentsply Sirona; Monobond Plus, Ivoclar Vivadent GmbH). For each cement, subgroups of n=10 specimens were artificially aged by either 3 days water storage (short-term aging), 30 days water storage including 7,500 thermocycles (6.5°C/60°C) (medium-term aging), or 150 days water storage including 37,500 thermocycles (long-term aging). Surviving specimens were tested with respect to their macro-tensile bond strength in a universal testing machine (Zwick/Roell Z005) with crosshead speed of 1mm/min. The failure mode of all specimens was optically assessed and expressed as the percentage of an adhesive failure in relation to the whole bonding area. Bond strength data were statistically analyzed by use of two-way ANOVA and Tukey HSD test (all α=0.05).
Results: ANOVA revealed bond strength was statistically significantly affected only by the aging conditions (F=65.99; p<0.001). Both cements exhibited statistically significant (p<0.001) lower mean bond strength values after long-term (<10MPa) than after short (≈30MPa) and medium-term (≈20MPa) aging. Lower mean bond strength after medium than after short-term aging was detected for specimens bonded with the amine-free resin cement (p=0.03), whereas there was no difference when the self-adhesive cement was used (p=0.40). For both cements, the percentage of an adhesive failure increased with prolonged aging.
Conclusions: Short and medium-term bond strength data were of limited significance with regard to the long-term performance of the adhesives.