Relative translucency of six all-ceramic systems. Part I: Core materials

Statement of problem. All-ceramic restorations have been advocated for superior esthetics. Various materials have been used to improve ceramic core strength, but it is unclear whether they affect the opacity of all-ceramic systems. Purpose. This study compared the translucency of 6 all-ceramic system core materials at Clinically appropriate thicknesses. Material and methods. Disc specimens 13 mm in diameter and 0.49 +/- 0.01 mm in thickness were fabricated from the following materials (n = 5 per group): IPS Empress dentin, IPS Empress 2 dentin, In-Ceram Alumina core, In-Ceram Spinell core, In-Ceram Zirconia core, and Procera AllCeram core. Empress and Empress 2 dentin specimens also were fabricated and tested at a thickness of 0.77 +/- 0.02 mm (the manufacturer's recommended core thickness is 0.8 mm). A high-noble metal-ceramic alloy (Pore. 52 SF) served as the control, and Vitadur Alpha opaque dentin was used as a standard. Sample reflectance (ratio of the intensity of reflected light to that of the incident light) was measured with an integrating sphere attached to a spectrophotometer across the visible spectrum (380 to 700 nm); 0-degree illumination and diffuse viewing geometry were used. Contrast ratios were calculated from the luminous reflectance (Y) of the specimens with a black (Yb) and a white (Yw) backing to give Yb/Yw with CIE illuminant D65 and a 2-degree observer function (0.0 = transparent, 1.0 = opaque). One-way analysis of variance and Tukey's multiple-comparison test were used to analyze the data (P<.05). Results. Contrast ratios in order of most translucent to most opaque were as follows: Vitadur Alpha 0.60 +/- 0.03, Empress (0.5 mm) 0.64 +/- 0.01, In-Ceram Spinell 0.67 +/- 0.02, Empress 2 (0.5 mm) 0.68 +/- 0.02, Empress (0.8 mm) 0.72 +/- 0.01, Procera 0.72 0.01, Empress 2 (0.8 mm) 0.74 +/- 0.01, In-Ceram Alumina 0.87 +/- 0.01, In-Ceram Zirconia 1.00 +/- 0.01, and 52 SF alloy 1.00 +/- 0.00. Conclusion. Within the limitations of this study, there was a range of ceramic core translucency at clinically relevant core thicknesses. In order of decreasing translucency, the ranges were Vitadur Alpha dentin (standard) > In-Ceram Spinell > Empress, Procera, Empress 2 > In-Ceram Alumina > In-Ceram Zirconia, 52 SF alloy.