[Show abstract][Hide abstract] ABSTRACT: To investigate the applicability of color-difference formula (CIELAB or CIEDE2000) in visual color assessments of metal-ceramic specimens in small color-difference ranges.
Metal-ceramic specimens using mixture of gradient ratio porcelain powders were fabricated to create a color pool. Color differences of specimen pairs were calculated using the CIELAB (ΔE(ab)(∗)) and CIEDE2000 (ΔE(00)). A questionnaire, composed of 1 target and 3 enactment specimens, was designed. For formula-determination, the enactment specimen with the minimum ΔE to the target specimen was registered as FS. For visual-assessment, twenty participants were asked to finish the questionnaire by choosing the most color-matched enactment specimen to the target. The percentage of the FS been selected (P(FS)) was calculated, which was used to represent the consistence of formula-determination and visual-assessment. Binomial Tests were used to compare the differences between P(FS) values and 33% (the randomized probability of the FS been selected was one out of three, approximate 33%). Regression analysis was used to determine the correlation between ΔE(ab)(∗) and ΔE(00) values.
A linear regression equation was drawn as ΔE(00)=-0.049+0.619×ΔE(ab)(∗). There were no significant differences between P(FS) values and 33% within the range of ΔE(ab)(∗)<2.0, whereas P(FS) values were significantly higher than 33% when ΔE(ab)(∗)>2.0 (P<0.001). There was a tendency of selecting the enactment specimens with lower L* values and higher b* or C' values, within the range of 1.0<ΔE(ab)(∗)<2.0.
CIE color-difference formulas were not applicable for visual color assessments of metal-ceramic specimens within the color-difference range of ΔE(ab)(∗)<2.0.
Full-text · Article · Apr 2012 · Journal of dentistry
[Show abstract][Hide abstract] ABSTRACT: To compare the optical characters of four translucent composites and natural enamel.
Thirty natural enamel slabs and 120 composite replicas (n=30) using four brands of translucent composites (Polofil Supra, Brilliant Esthetic, Gradia Direct, and Vit-l-escence) were evaluated at the thicknesses of 1.0mm and 0.8mm. The colors of the enamel slabs or corresponding composite specimens placed on an A3 shade, white and black backgrounds were measured using a spectrophotometer. Color differences (ΔE*) of the enamel-composite pairs and translucency parameter (TP) of each specimen were calculated. Reflection spectrums were recorded in the wavelength from 380nm to 780nm. Paired-t tests were performed to evaluate the differences of color coordinates (L*, a*, and b*) and TP values between the translucent composites and natural enamel.
There were significant differences of color coordinates (L*, a*, and b*) between the enamel and translucent composites (P<0.05). Although no statistical difference of TP values were found in the enamel-composite pairs with Polofil Supra and Brilliant Esthetic composites. The main peaks of the reflectance spectrums of the enamel are different from the four brands of the translucent composites. A reddish shifting of the main reflection peaks was observed, while the thickness of the composite specimens decreasing from 1.0mm to 0.8mm. Whereas, the main reflection peak was not changed in the teeth enamel.
The color and the translucency of translucent composites are different from the teeth enamel.
No preview · Article · Mar 2010 · Journal of dentistry
[Show abstract][Hide abstract] ABSTRACT: To evaluate the colour regression of bleached teeth in four experimental environments, and to explore the relationship between colour change and bulk miners loss.
Forty freshly extracted sound human incisors were in vitro treated using an in-office bleaching gel containing 38% hydroxide carbamide. The bleached teeth were subsequently divided into four groups and stored in four different environments: purified water, artificial saliva, a commercial remineralisation gel, and a desiccator. A spectrophotometer and a mu-CT were used to investigate the colour parameters (L*, a*, and b*) and the mineral content of the teeth pre- and post-bleaching. ANOVA and Tukey's post hoc analysis were performed to investigate the effect of time on the colour coordinates. Paired t-tests were used to compare the mineral content changes. Linear regression test was performed to explore the relationship of the colour coordinates and mineral content change in the colour regression process.
Colour regression occurred in the mineral containing environment accompanying with the mineral content remarkable increase in the outer layers of teeth tissue (P<0.05). No colour regression and mineral content change were found in the anhydrous environment (P>0.05). The regression of lightness is significantly correlated with the density change of teeth hard-tissue (P<0.001, r=0.611).
In this in-office bleaching system, the colour regression is mainly resulted by the reversal of lightness, and is correlated with the presence of the remineralisation processes within the teeth tissue.
No preview · Article · Nov 2009 · Journal of dentistry