| [Objective]This study compared color and translucency of lithium disilicate all-ceramic restorations with different production processes and different thicknesses. The purpose of this study was to provide referrence for dentists to design all-ceramic restorations and make choice of production processes.[Methods]30 disc-shaped IPS e.max Press specimens (10 mm in diameter), and 30 rectangle-shaped IPS e.max CAD specimens (12.6mm×10mm in sides) with different thicknesses (0.3±0.02mm,0.5±0.02mm,0.7±0.02mm,0.9±0.02mm, 1.1±0.02mm, 1.3±0.02mm) were fabricated with the heat-press technique and milling method. All specimens were wet ground with silicon carbide paper from 600-grit to 5000-grit. After ultrasonic cleaning and drying, the colors of the specimens were measured with a spectrophotometer (CM-700d) and the color parameters (L*,a*, b*) were recorded. TM-2 system was used to measure the transmittance (≌) on the wavelength range of 380-780 nm. The translucency parameter TP and color difference ΔE were calculated respectively.The specimens were veneered with IPS e.max Ceram and wet ground to obtain a total thickness of 1.5±0.02mm. After ultrasonic cleaning and drying, the value of L*、 a*、b*、TP、τ、ΔE were measured or calculated. Datas of multilayered specimens with different total thicknesses (1.3±0.02 mm,1.1±0.02 mm,0.9±0.02 mm,0.7± 0.02 mm,0.5±0.02 mm) were obtained in the same way.To make a statistical analysis, SPSS 19.0 computer program was used. ANOVA, posthoc tests (Tukey HSD) and correlational analyses were conducted, all statistical tests were performed at the 95% confidence level (a=0.05).[Results]1. The effects of the production processes on color and translucency.For lithium disilicate ceramic, the value of L*、a*、TP、τ were affected by the production processes (p<0.05), while the value of b* was not (p=0.156). IPS e.max CAD specimens had higher translucency than IPS e.max press specimens. The value of L* had no difference between different technologies when the specimens were too thin (≤0.7mm). As the specimens became thick, IPS e.max CAD specimens were more dark. IPS e.max CAD specimens gained higher a* value than IPS e.max press specimens except when the thickness is 0.5mm. Anyway, the color differences between specimens fabricated by different technologies were less than 2.6.For lithium disilicate multilayered specimens, the value of L*、a*、b* were affected by the production processes (p<0.05), while the value of TP、τ was not (p=0.210,0.739). The color differences between specimens fabricated by different technologies were not higher than 2.6.2. The effects of the ceramic thickness on color and translucency.For lithium disilicate ceramic, the value of L*、TP、τ decreased as the thickness increased. The value of a*、b* increased as the thickness increased from 0.3mm to 0.5mm, and decreased as the thickness increased from 0.7mm to 1.3mm.For lithium disilicate multilayer specimens, the value of L*、a*、b*、TP、 τ decreased as the core ceramic thickness increased. The value of L*、TP、τ decreased and the value of a*、b* increased as the veneer thickness increased.[Conclusions]1. The optical performance of lithium disilicate all-ceramic restorations were affected by production processes. The translucency of IPS e.max CAD was better than IPS e.max press. But for multilayer specimens, the translucency was not affected by production processes of core ceramic. The color differences between different production processes were hardly perceptible by observers.2. The ceramic thicknesses had effect on the optical performance of lithium disilicate all-ceramic restorations. The lightness and translucency of lithium disilicate ceramic decreased as the thickness increased. For multilayer specimens, the lightness and translucency decreased, the redness and yellowness increased when the thickness of veneer ceramic increased. The lightness and translucency decreased, the greenness and blueness increased when the thickness of core ceramic increased. |
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