María del Mar Pérez

Optical behavior of dental zirconia and dentin analyzed by Kubelka–Munk theory

OBJECTIVES To use the Kubelka-Munk theory to evaluate the scattering (S), absorption (K) and transmittance (T) of non-colored and colored dental zirconia systems and human (HD) and bovine (BD) dentins. METHODS Two zirconia systems were used: ZC- ZirCAD (Ivoclar Vivadent) and LV-LAVA (3M ESPE). Specimens from each ceramic system were divided into 3 groups (n=5): ZC1 and LV1 (non-colored); ZC2 and LV2 colored to shade A1, and ZC3 and LV3 colored to shade A3. Five human and bovine anterior teeth were flattened and polished through 1200 grit SiC paper to expose the superficial buccal dentin. All samples were prepared to a final thickness of 0.5 mm. Diffuse reflectance was measured against white and black backgrounds, using a spectroradiometer in a viewing booth with D65 illuminant and d/0° geometry. S and K coefficients and T were calculated using Kubelka-Munks equations. Data was statistically analyzed using Kruskal-Wallis, Mann-Whitney tests, and VAF coefficient. RESULTS Spectral distributions of S, K and T were wavelength dependent. The spectral behavior of S and T was similar to HD (VAF≥96.80), even though they were statistically different (p≤0.05). The spectral behavior of K was also similar to HD, except for LV1 (VAF=38.62), yet all ceramics were statistically different from HD (p≤0.05). HD and BD showed similar values of S and T (p>0.05). SIGNIFICANCE The dental professional should consider the optical behavior differences between the zirconia systems evaluated and the human dentin to achieve optimal esthetics in restorative dentistry.

Colour parameters and shade correspondence of CAD–CAM ceramic systems

OBJECTIVES To evaluate colour differences between (1) CAD-CAM ceramic systems considering shades A1, A2 and A3 and the corresponding nominal shade of VC (Vita Classical shade guide) and (2) shades A1-A2, A2-A3 and A1, A2 and A3 within the same ceramic system. METHODS Samples of shades A1, A2 and A3 were fabricated (n=5) from CAD-CAM ceramic blocks (IPS e.max(®) CAD LT and HT, IPS Empress(®) CAD LT and HT, Paradigm™ C, and VITABLOCS(®) Mark II) and polished to 1.0±0.01mm in thickness. Spectral reflectance and colour coordinates were measured using a spectroradiometer inside a viewing booth using the CIE D65 illuminant and the d/0° geometry. Spectral reflectance curves were compared using VAF coefficient and were statistically analyzed using Kruskal-Wallis and the Mann-Whitney U test (α=0.05). Colour coordinates were statistically analyzed using one-way ANOVA, Tukeys test with Bonferroni correction (α=0.001). All colour differences (ΔEab(*) and ΔE00) were analyzed through comparisons with the PT - perceptibility and AT - acceptability thresholds for dental ceramics. RESULTS ΔE between ceramic systems and its corresponding shade ranged from 6.32 to 13.42 (ΔEab(*)) and 4.48 to 9.30 (ΔE00). ΔE between shades A1-A2, A2-A3 and A1, A2 and A3 ranged, respectively, 1.93-4.82, 1.22-5.59 and 3.63-8.84 (ΔEab(*)); 1.54-3.87, 1.03-3.90 and 2.95-6.51 (ΔE00). CONCLUSIONS Considering the corresponding nominal shade from VC, none of the ceramic systems showed colour differences below the AT. In addition, some ceramic systems showed colour differences below AT (shades A1-A2 and A2-A3) and below PT (shades A2-A3). CLINICAL SIGNIFICANCE Careful adjustments should be made to the final shade of CAD-CAM ceramic restorations to reach a clinically acceptable shade match.

Predictive algorithms for determination of reflectance data from quantity of pigments within experimental dental resin composites

BackgroundBeing able to estimate (predict) the final spectrum of reflectance of a biomaterial, especially when the final color and appearance are fundamental for their clinical success (as is the case of dental resin composites), could be a very useful tool for the industrial development of these type of materials. The main objective of this study was the development of predictive models which enable the determination of the reflectance spectrum of experimental dental resin composites based on type and quantity of pigments used in their chemical formulation.Methods49 types of experimental dental resin composites were formulated as a mixture of organic matrix, inorganic filler, photo activator and other components in minor quantities (accelerator, inhibitor, fluorescent agent and 4 types of pigments). Spectral reflectance of all samples were measured, before and after artificial chromatic aging, using a spectroradiometer. A Multiple Nonlinear Regression Model (MNLR) was used to predict the values of the Reflectance Factors values in the visible range (380 nm-780 nm), before and after aging, from % Pigment (%P1, %P2, %P3 and %P4) within the formulation.ResultsThe average value of the prediction error of the model was 3.46% (SD: 1.82) across all wavelengths for samples before aging and 3.54% (SD: 1.17) for samples after aging. The differences found between the predicted and measured values of the chromatic coordinates are smaller than the acceptability threshold and, in some cases, are even below the perceptibility threshold.ConclusionsWithin the framework of this pilot study, the nonlinear predictive models developed allow the prediction, with a high degree of accuracy, of the reflectance spectrum of the experimental dental resin composites.

Optical properties of supra-nano spherical filled resin composites compared to nanofilled, nano-hybrid and micro-hybrid composites.

This study aimed to evaluate and compare the optical properties of supra-nano spherical filled resin composites and the nanofilled, nano-hybrid and microhybrid composites using the Kubelka-Munk Theory. Diffuse reflectance of samples (Shade A2) was measured against white and black backgrounds, using a spectroradiometer, using a viewing booth with D65 illuminant and d/0º geometry. S and K coefficients and T were calculated using Kubelka-Munks equations. The spectral behavior of S, K and T was similar for all dental resin composites analyzed (VAF close to 100%), even though they were, generally, statistically different (p≤0.05). The K-M T values overestimate the real value of Transmittance of the resin composites. Supra-nano spherical filled resin composites show the highest scattering and Transmittance when compared with the others materials, probably due to the shape and size of the filler. Such difference should be taken into consideration in a clinical situation to reproduce natural esthetic restorations.

Color difference thresholds for computer-simulated human Gingiva

OBJECTIVE To determine 50:50% perceptibility threshold (PT) and 50:50% acceptability threshold (AT) for computer-simulated samples of human gingiva using CIEDE2000 and CIELAB color difference formulas. MATERIALS AND METHODS Each of the 60 pairs of simulated human gingiva was displayed on a calibrated monitor, together with three pairs of upper central incisors of different lightness. The color of gingiva left and right from the midline was compared. A total of 30 observers (15 dentists, 15 laypersons) participated in the study. CIEDE2000 and CIELAB formulas were used to calculate the thresholds and a Takagi-Sugeno-Kang Fuzzy Approximation model was used as fitting procedure. Paired t-test (α = 0.05) was used in evaluation of statistical significance of differences. RESULTS The PT and AT for CIEDE2000 and 95% confidence intervals were 1.1 [0.4, 1.7] and 2.8 [1.8, 4.0], respectively. Corresponding CIELAB values were 1.7 [0.2, 2.6] and 3.7 [2.1, 5.7]. Significant differences (P < .01) were recorded between PT and AT, between the corresponding threshold values in CIEDE2000 and CIELAB formulas as well as between dentists and laypersons. CONCLUSIONS The difference between the perceptibility and acceptability threshold for gingiva was statistically significant in both CIEDE2000 and CIELAB. The same was true for differences between the corresponding thresholds using two color difference formulas, and between dentists and laypersons. Visual thresholds of human gingiva were not dependent upon lightness of adjacent teeth. Overall, CIEDE2000 color difference formula provided better fit than CIELAB formula in the evaluation of color difference thresholds of human gingiva. CLINICAL SIGNIFICANCE The data on visual thresholds for healthy human gingiva can be used as quality control tool/guide for selection and evaluation of dental materials, interpretation of color-related findings in clinical dentistry and research, and for standardization in dentistry. It is of particular value that this study was designed based on in-vivo color evaluation of healthy keratinized gingiva of subjects of different ethnicities, age groups, and gender.

Gingival shade guides: Colorimetric and spectral modeling

OBJECTIVE To design colorimetric and spectral models of gingival shade guides that adequately represent the color of human gingiva. MATERIALS AND METHODS A previously compiled database on the spectral reflectance of healthy keratinized gingiva was used for optimization. Coverage Error (CE) and Maximal Error (ME) were optimized using CIELAB and CIEDE2000 color difference formulas. A two-phase process included an FCM algorithm and a nonlinear optimization. A t test was used to compare the performance of the different numbers of clusters/tabs in gingival shade guide models (α = .05). RESULTS CIELAB CE and ME for shade guide models with 3 to 6 clusters ranged from 3.1 to 3.9 (P = .028 for 3 vs. 4; and P = .033 for 5 vs. 6 cluster/tab comparison), while the corresponding CIEDE2000 range was from 2.1 to 2.8 (P < .001 for 3 vs. 4 tabs; P < .025 for 4 vs. 5; and P = 0.029 for 5 vs. 6 tab comparisons). The percentage of data points exhibiting a CIELAB color difference lower than the acceptability threshold ranged from 48.7% to 71.4%, and from 52.9% to 82.4%. for CIEDE2000. CONCLUSIONS An increase in the number of clusters in the gingival shade guide models was associated with a decrease in coverage error (better match) to human gingiva. Gingival shade guide models with only 4 tabs provided a CIELAB and CIEDE2000 coverage error lower than the acceptability threshold for gingival color. Spectral clustering of human gingiva was determined to be valid. CIEDE2000 color difference formula outperformed the CIELAB formula in the optimization process. CLINICAL SIGNIFICANCE Providing a shade guide model with a small number of tabs and a coverage error lower than the 50:50% acceptability threshold would be an optimal solution for shade matching in dentistry. However, no actual gingival or tooth shade guide complies with this. The clustering method, with optimization of both Coverage Error and Maximal Error and spectral clustering that enables more reliable color formulation of cluster representatives of shade guide models, represents an advance when it comes to computer modeling in dentistry.

Colorimetric study of Transitions Look lenses

Spectral transmittances of three new photochromatic lenses have been measured at different activation states produced by the four luminous sources of a VeriVide CAC 120 cabinet. The greatest transmittance changes were found for the UV and D65 sources. These transmittances changes lead to average CIELAB color differences lower than 6 CIELAB units for the 24 chips of a GretagMacbeth color chart.