Objectives This in vitro study was performed to evaluate fatigue survival by shear test in the union of leucite-reinforced feldspathic ceramic using different cement thicknesses. Materials and Methods Leucite-reinforced glass ceramics blocks were sectioned in 2-mm thick slices where resin cylinders were cemented. The samples were distributed in two experimental groups (n = 20) according to the cement thickness (60 and 300 μm). The specimens of each group were submitted to the stepwise fatigue test in the mechanical cycling machine under shear stress state, with a frequency of 2 Hz, a step-size of 0.16 bar, starting with a load of 31 N (1.0 bar) and a lifetime of 20,000 cycles at each load step. Results The samples were analyzed in a stereomicroscope and scanning electron microscopy to determine the failure type. There is no significant difference between the mean values of shear bond strength according to both groups. Log-rank (p = 0.925) and Wilcoxon (p = 0.520) tests revealed a similar survival probability in both cement layer thicknesses according to the confidence interval (95%). The fracture analysis showed that the mixed failure was the most common failure type in the 300-μm thickness group (80%), while adhesive failure was predominant in the 60-μm thickness group (67%). The different cement thicknesses did not influence the leucite ceramic bonding in fatigue shear testing; however, the thicker cement layer increased the predominance of the ceramic material failure. Conclusion The resin cement thicknesses bonded to leucite ceramic did not influence the long-term interfacial shear bond strength, although thicker cement layer increased the ceramic material cohesive failure. Regardless the cement layer thickness, the shear bond strength lifetime decreases under fatigue.

Objetivo: Analisar a influência da resistência de união entre cimento resinoso e cerâmica feldspática utilizando concentrações e tempos de aplicação diferentes de acído fluorídrico (HF). Material e Métodos: Foram confeccionados 18 discos de cerâmica feldspática (Ø10mm - 2mm de espessura) através da técnica incremental, que foram incluídos em resina acrílica e regularizados com lixas de carbeto de silício com granulações de 600, 1200 e 2000 através de uma máquina de polimento com velocidade de 600 rpm para regularização. Logo após foram mergulhadas em água destilada durante 10 minutos em cuba ultrassônica. Todos corpos de prova foram condicionados com HF e silanizados. Foram confeccionados quatro cilindros de cimento sobre cada corpo de prova (n=12), feitos com cimento resinoso Relyx ARC. Logo após, dividiu-se em seis grupos de acordo com o protocolo de tratamento de superfície: G1 (5% - 40s); G2 (5% - 60s); G3 (5% - 80s); G4 (10% - 40s); G5 (10% - 60s) e G6 (10% - 80s). Os corpos de prova foram submetidos ao Teste de Microcisalhamento, com força vertical a uma velocidade de 0,5 mm/min sobre a peça. A resistência de união ao microcisalhamento foi calculada e expressa em Megapascal (MPa). Os dados foram submetidos à análise de variância (ANOVA) dois fatores e para comparações múltiplas foi utilizado o Teste de Tukey, sendo o nível de significância de 5%. Resultados: Quando analisado a concentração do HF, não houve diferenças estatísticas (p>0,05). Na comparação dos tempos de aplicação, G3 (5% - 80s) e G6 (10% - 80s) obtiveram maiores resultados de resistência ao microcisalhamento que os demais grupos. Conclusão: As diferentes concentrações de HF não influenciaram na resistência de união entre cerâmica feldspática e cimento resinoso. Já o aumento do tempo de condicionamento com HF afetou na resistência de união

To evaluate Knoop microhardness and diametral compression strength at different polymerization times. A total of 80 cylindrical samples with Filtek resin™ One Bulk Fill were made to perform the in vitro study, using half of total samples (n=40) for each test and divided equally between groups (n=10). All samples were made according to ISO 4049 using 2 mm thickness Teflon matrix and a central orifice with 4 mm diameter. Four different times of light-curing in Standard mode suggested by the light-unit manufacturer were selected, therefore, group 1 samples (G1) were light-cured for 5 seconds; group 2 (G2) for 10 seconds; group 3 (G3) for 15 seconds, and group 4 (G4) for 20 seconds. A radiant display, which means a power in mW/cm 2 by time in seconds was expressed in Joules (J). The samples were stored in a dark container with distilled water at a temperature of 37°C for 48 hours before testing. One-way analysis of variance (ANOVA) with T-Test (LSD) of multiple comparisons of the mean values of Knoop hardness and diametral compression strength was performed, with significance index α=0.05. Regarding the Knoop microhardness test, G1 (35.73 ± 6.2) presented the lowest values, followed by G2, while G3 and G4 did not present statistical differences between them. For the diametral compression test, G1 (1387.76 ± 190.51) obtained the lowest value when compared to the other groups. G2, G3, and G4 did not present significant statistical differences. The different polymerization times influenced the Knoop microhardness and the diametral compression strength of Bulk Fill resin.