Adhesion to a Zirconia-reinforced Lithium Silicate Ceramic: Effects of Ceramic Surface Treatments and Resin Cements.

OBJECTIVE: This study had the objective to test the effect of ceramic surface treatments on the microshear bond strength (µSBS) of different resin cements to a zirconia-reinforced lithium silicate (ZLS). METHODS AND MATERIALS: ZLS blocks were sectioned, embedded in acrylic resin, and then allocated into nine groups considering two study factors: "ceramic surface treatment" (HF - hydrofluoric acid; EP - self-etching primer; TBS - tribochemical silica coating) and "resin cements" (nMDP - without MDP monomer; MDP - with MDP monomer; SA - self-adhesive). Starch tubes (n=36) were placed on the treated ceramic surface and the cement was applied. Starch tubes were removed after 24 hours of storage, and the specimens were thermocycled (5,000×; 5°C-55°C). Next, the µSBS test was performed using the wire-loop technique, and topographic and failure analyses were performed. RESULTS: The factors "ceramic surface treatment" and "resin cement" statistically influenced the µSBS results. Considering the surface treatment factor, the TBS produced statistically lower values when the MDP resin cement was applied, being only similar to the MDP plus EP group. For the resin cement factor, no difference was found for nMDP and SA groups, apart from the surface treatments. Failure analysis showed that the groups treated with EP had a greater number of pre-test failures. The surface treatments induced noteworthy topographic alterations when compared to control (no treatment). CONCLUSION: The ZLS ceramic surface treatment with tribochemical silica coating associated with the MDP-containing resin cement resulted in lower bond strength values.

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 (Ø=10 mm, thickness=1.5 mm) and dentin analogue (Ø=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°C-55°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; α=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.

CAD/CAM machining Vs pre-sintering in-lab fabrication techniques of Y-TZP ceramic specimens: Effects on their mechanical fatigue behavior.

This study evaluated the effects of different pre-sintering fabrication processing techniques of Y-TZP ceramic (CAD/CAM Vs. in-lab), considering surface characteristics and mechanical performance outcomes. Pre-sintered discs of Y-TZP ceramic (IPS e.max ZirCAD, Ivoclar Vivadent) were produced using different pre-sintering fabrication processing techniques: Machined- milling with a CAD/CAM system; Polished- fabrication using a cutting device followed by polishing (600 and 1200 SiC papers); Xfine- fabrication using a cutting machine followed by grinding with extra-fine diamond bur (grit size 30 µm); Fine- fabrication using a cutting machine followed by grinding with fine diamond bur (grit size 46 µm); SiC- fabrication using a cutting machine followed by grinding with 220 SiC paper. Afterwards, the discs were sintered and submitted to roughness (n=35), surface topography (n=2), phase transformation (n=2), biaxial flexural strength (n=20), and biaxial flexural fatigue strength (fatigue limit) (n=15) analyses. No monoclinic-phase content was observed in all processing techniques. It can be observed that obtaining a surface with similar characteristics to CAD/CAM milling is essential for the observation of similar mechanical performance. On this sense, grinding with fine diamond bur before sintering (Fine group) was the best mimic protocol in comparison to the CAD/CAM milling.