Fatigue Behavior of Monolithic Zirconia-Reinforced Lithium Silicate Ceramic Restorations: Effects of Conditionings of the Intaglio Surface and the Resin Cements

Objective: This study assessed the effect of conditioning of the intaglio surface and resin cements on the fatigue behavior of zirconia-reinforced lithium silicate ceramic (ZLS) restorations cemented to a dentin analogue. Methods: ZLS ceramic (0=10 mm, thickness=1.5 mm) and dentin analogue (0=10 mm, thickness=2.0 mm) discs were produced and allocated according to the study factors, totaling nine study groups: ceramic surface treatment (three levels: hydrofluoric acid etching [HF]; self-etching ceramic primer [EP]; tribochemical silica coating [TBS]) and resin cement (three levels: 10-methacryloyloxydecyl dihydrogen phosphate [nMDP]; MDP-containing conventional resin cement [MDP]; self-adhesive resin cement [SA]). The ceramic bonding surfaces were treated and cemented on the dentin analogue, and all the specimens were aged for 5000 thermal cycles (5 degrees C-55 degrees C) prior to fatigue testing. The stepwise fatigue test (20 Hz frequency) started with a load of 400 N (5000 cycles) followed by steps of 500, 600, and up to 1800 N (step-size: 100 N) at a maximum of 10,000 cycles each step. The specimens were loaded until failure (crack), which was detected by light transillumination and visual inspection at the end of each step. The fatigue failure load and number of cycles for failure data were analyzed by the Kaplan-Meier (log-rank test; alpha=0.05). Topographic and fractographic analyses were also performed. Results: HF- (973.33-1206.67 N) and EP- (866.67-1066.67 N) treated specimens failed at statistically similar loads and higher than TBS (546.67-733.33 N), regardless of the cement used. All the fractographical inspections demonstrated failure as radial crack. Conclusion: The HF and EP treatments promoted better mechanical fatigue behavior of the ceramic restoration, while tribochemical silica coating induced worse fatigue results and should be avoided for treating the ZLS surface prior to bonding.