The purpose of this study was to evaluate the effect of design and surface finishing on fracture strength of yttria-tetragonal zirconia polycrystal (Y-TZP) crowns in monolithic (1.5 mm thickness) and bilayer (0.8 mm zirconia coping and 0.7 mm porcelain veneer) configuration after artificial aging. Bovine incisors received crown preparation and Y-TZP crowns were manufactured using CAD/CAM technique, according to the following groups (n = 10): Polished monolithic zirconia crowns (PM); Glazed monolithic zirconia crowns (GM); Bi-layer crowns (BL). Crowns were cemented with resin cement, submitted to artificial aging in a chewing simulator (2.5 million cycles/80 N/artificial saliva/37°C), and tested for fracture strength. Two remaining crowns referring to PM and GM groups were submitted to a chemical composition analysis to measure the level of yttrium after aging. One-way ANOVA and Tukey's test (P = .05) indicated that monolithic zirconia crowns presented similar fracture strength (PM = 3476.2 N ± 791.7; GM = 3561.5 N ± 991.6), which was higher than bilayer crowns (2060.4 N ± 810.6). There was no difference in the yttrium content among the three surfaces evaluated in the monolithic crowns. Thus, monolithic zirconia crowns present higher fracture strength than bilayer veneered zirconia after artificial aging and surface finishing does not affect their fracture strength.
The purpose of this study was to evaluate the fracture strength and failure mode of zirconia crowns in monolithic or bi-layer configuration after artificial aging. Thirtytwo bovine incisors received crown preparation and were scanned for the manufacturing of Y-TZP crowns using CAD/CAM technique. Crowns were fabricated according to the following groups (n=10/group): PM polished monolithic zirconia crowns of 1.5mm uniform thickness; GM glazed monolithic zirconia crowns of 1.5mm uniform thickness; BL bi-layer crowns with 0.8mm zirconia core and 0.7mm of veneered porcelain. All crowns were cemented on each respective tooth with resin cement (RelyX Unicem-2, 3M-ESPE). After the cementation, specimens were submitted to artificial aging in a chewing simulator (2.5 million cycles/ 3Hz frequency/8kg) in artificial saliva at 37°C, then the samples were submitted to fracture strength test (Instron) at a crosshead speed of 0.5mm/min. Two remaining crowns referring to PM and GM were submitted to Electron probe microanalysis (EPMA), to measure the yttrium levels after aging. One-way ANOVA and Tukey's test (p=0.05) were employed for analysis of the results. The fracture mode was evaluated with Scanning Electron Microscope (SEM). Monolithic zirconia crowns presented similar fracture strength results (PM= 3476.2N ± 791.7; GM= 3561.5N ± 991.6), which were higher (p=0.02) than the results for the bi-layer crowns (BL= 2060.4N ± 810.6). There was no significant difference in the yttrium content among worn occlusal surfaces (PM, GM) and undamaged surface in PM. Thus, the fracture strength of monolithic zirconia crowns was higher than bi-layer configuration.
Ao meu pai Aladim e minha mãe Vera, pelos ensinamentos durante toda minha vida e pelo apoio incondicional para realizar todos meus projetos.Ao meu irmão Júnior, meu grande amigo e companheiro de todas as horas.Ao meu noivo Leonardo, que participou diretamente na realização deste projeto. Pelo incentivo e dedicação durante a realização deste trabalho.
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