RESUMEN
OBJECTIVES: In this study, the authors attempted to develop a photoconductive method for measuring light transmission through a crown restoration to the root dentin; metal-ceramic crowns with four coping designs (metal collar, and metal framework ending 0, 1, and 2mm coronal to the axiogingival line angle) and two all-ceramic crowns (Empress II and In-Ceram Alumina) were compared. METHODS: According to pre-registered templates, 36 crowns were fabricated for an extracted central incisor. A cadmium sulfide (CdS) photoconductive cell was secured onto the root of a tooth, which was fixed in a light box. The validity and reliability of the experimental design were verified, and the impedance of the cell was recorded when the crowns were placed on the prepared tooth with or without try-in pastes under a constant luminance. RESULTS: A significant correlation (r= -0.99, p<0.001) was found between the light intensity and impedance of the CdS cell, and a 1.15% coefficient of variation between repeated measurements was observed. In this study, Empress II crowns had the smallest impedance, indicating that they provided the best light transmission. Conventional metal-ceramic crowns had the least light transmission, which was significantly improved by reducing the metal collar (p<0.05). The framework of metal-ceramic crowns which ended 2mm coronal to the axiogingival line angle showed as much light transmission as the In-Ceram crowns. The impedance increased when try-in pastes were employed in all test groups. SIGNIFICANCE: The photoconductive method was proven to be a reliable technique for measuring the light transmitted through restorations into the adjacent tissue.
Asunto(s)
Coronas , Porcelana Dental/química , Diseño de Prótesis Dental , Aleaciones de Cerámica y Metal/química , Raíz del Diente/anatomía & histología , Silicatos de Aluminio/química , Compuestos de Cadmio , Aleaciones de Cromo/química , Cementos Dentales/química , Dentina/anatomía & histología , Humanos , Incisivo , Luz , Compuestos de Litio/química , Ensayo de Materiales , Óptica y Fotónica/instrumentación , Compuestos de Potasio/química , Radiometría/instrumentación , Reproducibilidad de los Resultados , Sulfuros , Propiedades de Superficie , Preparación Protodóncica del Diente/clasificaciónRESUMEN
Grinding intaglio surfaces of ceramic restorations with diamond burs is a common procedure to improve fit. This study evaluated the effects of simulated diamond bur grinding and subsequent veneer firing and glazing on a lithium disilicate glass-ceramic. The results revealed a significant reduction in the roughness and strength of the material after diamond bur grinding, whereas the strength was restored through crack healing and formation of a glass layer after heat treatment. The finding indicates that grinding of lithium disilicate ceramics with diamond burs may introduce flaws and cracks, and therefore subsequent heat treatments, veneer firing, or glazing, are suggested.