RESUMO
OBJECTIVE: To evaluate the effects of hard machining, glaze firing and hydrofluoric acid etching on the biaxial flexural strength and roughness of a CAD/CAM leucite glass-ceramic; to investigate if ceramic post-machining surface roughness is influenced by the machining order and by the pair of burs used for it. METHODS: A hundred forty four discs were machined by six nominally identical pairs of burs and divided into groups (n=24): (1) machining-M, (2) machining and glaze firing-MG, (3) machining and hydrofluoric acid etching-MA, (4) machining, glaze firing and hydrofluoric acid etching-MGA, (5) machining followed by polishing, as a control-MP, (6) machining, polishing and hydrofluoric acid etching-MPA. The roughness after each treatment (Ra and Rz) was measured. The discs were submitted to a piston-on-three ball flexure test (ISO 6872/2008) and strength data analyzed through Weibull statistics (95% CI). RESULTS: M resulted in lower characteristic strength (σ0) (128.2MPa) than MP (177.2MPa). The glaze firing reduced σ0 (109MPa), without affecting roughness. Hydrofluoric acid etching increased the roughness without affecting σ0. Spearman's coefficient (rs) indicated strong and significant correlation between machining order and roughness (rsRa=-0.66; rsRz=-0.73). The ceramic post-machining surface roughness differed significantly according to the pair of burs employed (p<0.05). SIGNIFICANCE: hard machining and glaze firing reduced the leucite ceramic strength, while hydrofluoric acid etching did not affect the strength. Variability in the roughness might be expected after machining, since it was influenced by the machining order and by the bur pairing.
Assuntos
Condicionamento Ácido do Dente , Silicatos de Alumínio/química , Cerâmica/química , Desenho Assistido por Computador , Análise do Estresse Dentário , Dureza , Temperatura Alta , Ácido Fluorídrico , Teste de Materiais , Propriedades de SuperfícieRESUMO
Introducción: Los procedimientos restauradores indirectos son comunes en la clínica diaria actual. Se debe tener cuidado especial en la cementación, pues la gran mayoría de los fracasos ocurren en la interfase diente/restauración. Por esto es indispensable un adecuado tratamiento de superficie de la restauración para lograr una adhesión óptima a la superficie dentaria. Materiales y Métodos: Treinta cilindros de porcelana VITA VM 13 con dimensiones de 5 mm de altura y 7 mm de diámetro fueron separadas aleatoriamente en 3 grupos (n=10) de acuerdo con los tratamientos recibidos. Grupo I (control) - sin acondicionamiento superficial; Grupo II - grabado con ácido fluorhídrico al 9.6 por ciento por 1 minuto; Grupo III - grabado con ácido fluorhídrico al 9.6 por ciento por 2 minutos. Estas fueron probadas en cuanto a su resistencia de unión a la tracción en una máquina universal para pruebas (INSTRON modelo 4411, 3M). Los valores, expresados en MPa, fueron analizados estadísticamente a un nivel de significación del 5 por ciento, usando el Análisis de la Varianza (ANOVA) de un factor. Resultados: En relación con la prueba de resistencia de unión a la tracción, se encontraron los siguientes valores medios para cada grupo: Grupo I (control) - x=3.35 MPa; Grupo II - x=4.64 MPa; Grupo III - x=3.80 MPa. Conclusiones: Según los resultados obtenidos, se puede concluir que el tratamiento de superficie con ácido fluorhídrico durante 1 minuto, promueve microrretenciones que aumentan significativamente los valores de resistencia a la tracción, que puede traducirse en un beneficio clínico mayor.
Aim: Indirect restorative procedures are common in the current daily practice. Special care must be taken in the cement, as the vast majority of failures occurs at the interface tooth /restoration. Therefore a proper surface treatment of the restoration is essential to achieve optimum adhesion to the tooth surface. Materials and Methods: Thirty porcelain cylinders VITA VM 13 with dimensions of 5 mm in height and 7 mm in diameter were randomly divided into 3 groups (n=10) according to the treatments received. Group I (control) - no surface conditioning; Group II- recorded with 9.6 percent hydrofluoric acid for 1 minute; Group III - recorded with 9.6 percent hydrofluoric acid for 2 minutes. Their tensile bond strength was tested in a universal testing machine (Instron Model 4411, 3M). The values, expressed in MPa, were statistically analyzed at a level of significance of 5 percent, using Analysis of Variance (ANOVA) of a factor. Results: In relation to the bond strength test, tensile strength, revealed the following values for each group: Group I (control) - x=3.35 MPa, Group II - x=4.64 MPa, Group III - x=3.80 MPa. Conclusions: According to the results, it can be concluded that the surface treatment with hydrofluoric acid for 1 minute promotes microretentions, which significantly increase the values of bond strength, tensile strength. This can result in a higher clinical benefit.