Comparison of two color-difference formulas using the Bland-Altman approach based on natural tooth color space

Chroma-dependence of CIEDE2000 acceptability thresholds for dentistry

OBJECTIVES

Determine visual 50:50% color difference acceptability thresholds (AT) for regions of the dental color space with varying chromaticity.

METHODS

A 40-observer panel belonging to two different groups (dentists and laypersons) evaluated 144 dental resin composites pairs (divided in three different sets of 48 pairs according to chroma value: Low Chroma (LC), Medium Chroma (MC) and High Chroma (HC) placed 40 cm away and inside of a viewing cabinet (D65 Standard light source; diffuse/0° geometry). A Takagi-Sugeno-Kang (TSK) fuzzy approximation was used for fitting the data points and calculate the 50:50% acceptability thresholds in CIEDE2000. A paired t-test was used to evaluate the statistical significance between thresholds differences and Bonferroni correction was applied.

RESULTS

The CIEDE2000 50:50% AT were ∆E00  = 2.84, ∆E00  = 2.31 and ∆E00  = 1.80 for LC, MC and HC sets of sample pairs, respectively. The 50:50% AT values were statistically significant between the different sets of sample pairs, as well as the 50:50% AT values obtained for different observer groups.

CONCLUSIONS

50:50% CIEDE2000 acceptability thresholds for dentistry are significantly different depending on the chromaticity of the samples. Observers show higher acceptability for more achromatic samples (low chroma value) than for more chromatic samples.

CLINICAL SIGNIFICANCE

The difference in the AT for distinct regions of the dental color space can assist professionals as a quality control tool to assess clinical performance and interpret visual and instrumental findings in clinical dentistry, dental research, and subsequent standardization processes.

An In-Vitro Study to Evaluate the Effect of Denture Cleansing Agents on Color Stability of Denture Bases Fabricated Using CAD/CAM Milling, 3D-Printing and Conventional Techniques

The current literature lacks substantial information about the effect of denture cleansers on the color stability of denture bases formed using Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) additive and CAD/CAM subtractive manufacturing techniques. This study aimed to assess the effect of two commercially available denture cleansers on the color stability of denture base resins fabricated using four different techniques. Forty-five disc-shaped specimens were fabricated using each technique. Initial color readings were recorded. Specimens were randomly divided into three subgroups (n = 15): a control group (distilled water) and two denture cleanser groups. They were immersed in these solutions, simulating 180 days of use. Final color readings were recorded. The color difference was calculated, and the data were statistically analyzed. For all the specimens, significant color changes were observed after immersion in denture cleanser solutions. The extent of color change varied according to the type of denture cleanser used. When placed in the denture cleanser solutions, the CAD/CAM subtractive group showed the maximum color change (−1.10 and −0.72), while the CAD/CAM additive (3D printing) groups showed the least color change (−0.48 and −0.54). Clinicians should choose appropriate denture cleansers for newly introduced denture base resins to minimize the changes in the color of the dentures.

Assessment of the effect of experimental bleaching agent with nano-bioactive material on postoperative sensitivity: A randomized, triple blind clinical trial

OBJECTIVES

This clinical study aimed to evaluate the effect of incorporating bioactive nanoparticles (n-Bm) inside an in-office bleaching gel on the risk and intensity of tooth sensitivity (TS) and on bleaching effectiveness.

MATERIALS AND METHODS

Sixty-six participants were selected and randomly assigned into two groups: control-only in-office gel and experimental-in-office gel with n-Bm. Teeth were bleached in two sessions (3 × 15-min). TS was recorded using a VAS and NRS. The color change was evaluated by subjective (VITA Classical and VITA Bleachedguide) and objective (Easyshade spectrophotometer) methods at baseline and 30 days after the end of treatment. The TS was evaluated by McNemar, Wilcoxon Signed Rank, and paired t test. The color changes between groups were compared using paired t test (α = 0.05).

RESULTS

No significant differences between the groups were observed in the risk (control = 27% [95%IC 18-39]; experimental = 21% [95%IC 13-32]) and intensity of TS, as well as in the color change (p >0.05) for any color measurement.

CONCLUSION

The inclusion of n-Bm into the bleaching agents did not affect the whitening effectiveness, as well as the risk and intensity of TS between groups. However, the results of the absolute risk of TS were low for both in-office gels used.

CLINICAL SIGNIFICANCE

Despite no significant differences between groups, both experimental bleaching agents present suitable results with low values for TS.

Color adjustment potential of single-shade resin composite to various-shade human teeth: Effect of structural color phenomenon

This study evaluated the effect of the structural color phenomenon in resin composites (RCs) on the color adjustment of restorations by investgating their color reproduction performance in human incisors of various shade. Cervical cavities were filled with a single-shade RC with 260 nm spherical fillers (Omnichroma (OMN)), conventional A2-shade RCs (Estelite Σ Quick or Clearfil AP-X), or experimental RCs with 5-50 nm fumed silica fillers (R1) and 100 nm spherical fillers (R2). Color parameters (L*C*h*) were measured using a CIE XYZ camera along the centerline of the restorations, and the color difference (∆E₀₀) between corresponding areas of intact and restored teeth was calculated. Additionally, the reflectance spectra of OMN, R1, and R2 were investigated. OMN exhibited significantly lower ∆E₀₀ than other tested RCs (p<0.05) and its reflection spectrum ranged from blue to red, while a blue peak was observed with R1 and R2, indicating a higher color adjustment potential of OMN.

Effect of topical application of nanoencapsulated eugenol on dental sensitivity reduction after in-office dental bleaching: a randomized, triple-blind clinical trial

PURPOSE

This randomized, split-mouth, triple-blind clinical study evaluated the effect of application of nanoencapsulated eugenol (NE) on the absolute risk and intensity of tooth sensitivity (TS) resulting from in-office bleaching.

METHODS

Fifty-six patients received a NE in one hemiarch and a placebo gel in the other hemiarch, determined by random sequence, before in-office bleaching. A visual analogue scale (VAS) (0-10) and a numeric rating scale (NRS) (0-4) were used to record TS during bleaching and 1 and 48 h after bleaching. The tooth color was performed from baseline to 2 weeks after bleaching with shade guides (ΔSGU) and a spectrophotometer (∆E_ab , ∆E_00, and WI_D ). The TS was assessed through the McNemar test (α = 0.05) and by the Wilcoxon signed-rank test (NRS) and paired t-test (VAS). The paired test-t was employed to compare the color changes (ΔSGU and ΔE_ab , ∆E_00, and WI_D ). The significance level was 5%.

RESULTS

No statistically significant difference was found in the absolute risk or intensity of TS between both groups (p > 0.05). A significant color change was observed in both groups (p > 0.05).

CONCLUSION

Administration of the gel containing NE before the in-office dental bleaching did not reduce the TS and did not interfere in the bleaching effect.

CLINICAL RELEVANCE STATEMENT

The use of desensitizing gel containing NE did not reduce in-office bleaching-induced tooth sensitivity.

New insights in the reproducibility of visual and electronic tooth color assessment for dental practice

Background

The aim of the study was to compare a 2D and 3D color system concerning a variety of statistical and graphical methods to assess validity and reliability of color measurements, and provide guidance on when to use which system and how to interpret color distance measures, including ΔE and d(0M1).

Methods

The color of teeth 14 to 24 of 35 patients undergoing regular bleaching treatment was visually assessed and electronically measured with the spectrophotometer Shade Inspector™. Tooth color was recorded before bleaching treatment, after 14 days, and again after 6 months. VITAPAN® Classical (2D) and VITA-3D-Master® (3D) served as reference systems.

Results

Concerning repeated measurements, the 2D system was superior to the 3D system, both visually and electronically in terms of ΔE and d(OM1), for statistics of agreement and reliability. All four methods showed strong patterns in Bland-Altman plots. In the 3D system, hue was less reliable than lightness and chroma, which was more pronounced visually than electronically. The smallest detectable color difference varied among the four methods used, and was most favorable in the electronic 2D system. Comparing the methods, the agreement between the 2D and 3D system in terms of ΔE was not good. The reliability of the visual and electronic method was essentially the same in the 2D and 3D systems; this comparability is fair to good.

Clinical relevance

The 3D system may confuse human raters and even electronic devices. The 2D system is the simple and best choice.

Recent Advances in Color and Whiteness Evaluations in Dentistry

Background:

The final goal of color measurement or shade specification in dentistry is the reproduction by prosthetic materials of all important appearance characteristics of natural oral structures. The application of color science in dentistry is an objective way to measure and evaluate such structures and dental materials in clinical practice and dental research.

Methods:

Literature on color science was reviewed to present new metrics to evaluate color differences of dental materials and dental structures. Visual acceptability and perceptibility values of color differences are reviewed and new whiteness indexes to describe whiteness in dentistry are presented.

Results:

In the last decade, the CIELAB 50:50% perceptibility and acceptability thresholds were set to 1.2 and 2.7, respectively, and the CIEDE2000 50:50% perceptibility and acceptability thresholds were set to 0.8 and 1.8. The CIEDE2000 color-difference formula became increasingly popular in dentistry. Developments in color science have led to the description of tooth whiteness and changes in tooth whiteness based on whiteness indexes, with the most relevant being the WID whiteness index, which is a customized index based in CIELAB color space.

Conclusion:

The application of color science in dentistry has allowed the precise description of tooth color and whiteness. The revised and new CIEDE2000 color-difference formula is expected to fully replace the outdated CIELAB formula in almost all dental applications. Recent psychophysical studies have reported values of visual thresholds and new whiteness indexes, which can serve as quality control tools to guide the selection of esthetic dental materials, evaluate clinical performance, and interpret visual and instrumental findings in clinical dentistry, dental research, and subsequent standardization.

The effect of electronic cigarettes on dental enamel color

OBJECTIVE

The use of electronic cigarettes (ECIGs) has recently increased as an alternative to conventional smoking tobacco products. The literature is scarce on the effects of ECIGs on dental and oral structures. Therefore, the objective of this study was to observe whether ECIG aerosol could alter the color of dental enamel.

MATERIALS AND METHODS

Sixty-three bovine enamel specimens were randomly separated into groups (n = 7) and treated with aerosols with different e-liquid flavors (neutral, menthol, and tobacco) and nicotine content (0, 12, and 18 mg). The initial color assessment was performed using a spectrophotometer (Easy Shade-Vita). Dental enamel was exposed to 20 cycles of ECIG aerosol in a smoking machine, and the final color was measured. The color change was evaluated using ΔEab, ΔE00, and Whiteness Index (WI_D ) formulae. Differences in L* a* b* coordinates were calculated, and data were analyzed (two-way ANOVA, uncorrected Fisher's LSD post hoc test, α = 0.05).

RESULTS

Luminosity (ΔL) was reduced by aerosols with almost all levels of nicotine content and neutral and menthol flavors. Flavored e-liquids caused more color change (P < .05) according to ΔEab and ΔE00. ΔE values from both formulae exceeded the thresholds for perceptible visual alterations of color. WI_D increased after ECIGs exposure for menthol and tobacco and decreased for neutral flavors.

CONCLUSIONS

ECIG aerosol from e-liquids with different nicotine contents and flavors altered enamel color. Menthol and tobacco e-liquids may alter the enamel color decreasing the yellowness of the enamel compared to neutral e-liquid.

CLINICAL SIGNIFICANCE

Electronic cigarettes can cause perceptible changes in tooth color, altering dental esthetics.

Comparison of two color-difference formulas using the Bland-Altman approach based on gingiva color space

The objectives of this study were to determine the relationship between the results provided by the classical CIELab (ΔE_ab*) and the CIEDE2000 (ΔE00) formulas and the gingival color space using the Bland and Altman limits of agreement, to use this relationship to establish the equivalences between the gingival color thresholds of perceptibility of both formulas, and to evaluate whether the relationship between ΔE_ab* and ΔE00 is modified depending on the axis in which the changes occur. The means of the L*, a*, and b* coordinates of the 21 gingiva porcelain samples (Heraceram, Heraeus Kulzer Mitsui Chemical Groups) were used and the differences in color were calculated in 210 pairs of samples using the CIELab (ΔE*ab) and CIEDE2000 (ΔE00) color-difference formulas. The results obtained with these formulas were compared and the limits of agreement after a logarithmic transformation of the data were obtained. The relationship between both formulas was ln ΔE₀₀ = - 0.22 + ln ΔE_ab*. The results obtained with the CIELab formula were between 1.01 (95% confidence interval 0.98-1.03) and 1.54 (95% confidence interval 1.52-1.59) times higher than those obtained with the CIEDE200 formula. In the gingiva color space, the scale factor between the CIEDE2000 and CIELab values changes from 0.63 to 1.02, such that providing an accurate scale factor between both values proves difficult. The pairs with the highest ratio were those where the difference in color was mainly due to changes in lightness, whereas the pairs with the smallest ratio were those where the difference in color was mainly due to changes in the blue-yellow or green-red axes.

Comparison of the CIELab and CIEDE 2000 Color Difference Formulas on Gingival Color Space

PURPOSE

To evaluate the CIELAB and CIEDE2000 formulas to determine which better reflects the difference in color perception, and whether there are gender differences in color perception.

MATERIALS AND METHODS

Fifty-six participants grouped 21 different-colored disks made of pink porcelain (color range: from 36.8 to 63.9 for L^* , from 16.4 to 35.2 for a^* , from 6.2 to 21.6 for b^* ), in which the only requirement was that each group be comprised of disks with chromatically indistinguishable colors. Each participant was free to choose the number and composition of the groups. Using the results obtained, a dissimilarity matrix was generated, and nonmetric multidimensional scaling (MDS) was applied to obtain the coordinates of the disks within a Euclidean space.

RESULTS

The linear correlation coefficient between the interpoint distances of the MDS configuration (MDS_total sample) and the color differences with the CIELAB formula (ΔE^* _ab ) was 0.719 (p < 0.001), whereas with the CIEDE2000 formula (ΔE00), it was 0.726 (p < 0.001). For the configuration obtained in the women's group (MDS_w), the correlations between the interpoint distances and the CIELab color difference was 0.720 (p < 0.001), and the CIEDE2000 color differences was 0.730 (p < 0.001). For the configuration obtained in the men's group (MDS_m), the perceived color differences, calculated with both formulas, were less sensitive, 0.670 for CIELab formula and 0.677 for CIEDE2000 formula.

CONCLUSIONS

Considering the limitations of this study, the data analyzed indicated that the CIEDE2000 formula reflected the color differences perceived by the human eye similar to the CIELAB formula (ΔE^* _ab ). Also, women were confirmed to be more sensitive than men to differences in color.

Relative Translucency of a Multilayered Ultratranslucent Zirconia Material

AIM

The aim of this study was to compare the translucency parameter (TP) of ultratranslucent multilayered (UTML) zirconia according to thickness and layer level.

MATERIALS AND METHODS

Rectangles of UTML zirconia with four layers [dentin layer (DEL), first transitional layer (FTL), second transitional layer (STL), and enamel layer (ENL)] and four different thicknesses (0.4, 0.6, 0.8, and 1 mm) were milled from blanks. Digital images were taken in a dark studio against white and black backgrounds under simulated daylight illumination and international commission on illumination (CIE) Lab* color values recorded using Photoshop Creative Cloud software. The TP was computed and compared according to thickness and layer level using analysis of variance (ANOVA) followed by Bonferroni post hoc analysis for multiple comparisons. Significance was set at p < 0.05.

RESULTS

In each thickness, TP values were similar between any two layers. The significant effect of thickness on the TP was observed only in the first two layers. In the DEL, translucency was significantly greater at 0.4 mm than all other thicknesses. In the FTL, differences were significant between 0.4 and 0.8 mm and between 0.4 and 1 mm.

CONCLUSION

The investigated zirconia does not seem to show gradational changes in relative translucency from dentin to enamel levels regardless of the thickness used. Thickness affected the TP only in the first two layers with better translu-cency at 0.4 mm.

CLINICAL SIGNIFICANCE

Since relative translucency does not seem to be significantly different between layers, clinicians can modify the apicocoronal positioning of the UTML layers within the restoration according to the desired Chroma without any implications on the clinically perceived translucency. While the thickness of 0.4 mm may be suggested for anterior esthetic veneers because of its higher translucency, the other thicknesses of 0.6 to 1 mm can be used to mask colored abutments in full contour restorations.

Prediction of a nail polish colour applied on a nail

OBJECTIVE

The colour of a nail polish varies according to the nail on which it is applied. The objective of this study was to predict the colour of the nail polish on a given nail and to study how the colour varies depending on the nail polish thickness.

METHODS

Six nail polishes were applied in one, two and three layers on the nails of one subject, thus forming eighteen samples. The spectral reflectances of the eighteen nail polishes applied on the nails with different thicknesses were obtained by spectrophotometry. The spectral reflectances of the nails without polish were also measured using the same technique. The thicknesses of nail polishes were measured by high-definition optical coherence tomography (HD-OCT). Then, to determine the physical parameters of the nail polish itself, we applied the six nail polishes on an opacity drawdown chart and we measured the spectral reflectance and the thickness of each patch using spectrophotometry and HD-OCT, respectively. The Kubelka-Munk theory was used to get the predicted spectral reflectance of the nail polish applied on the nail according to the polish thickness by knowing the parameter of the polish itself and the spectral reflectance of the nail. The predicted spectral reflectances were finally compared with those measured directly on the nails.

RESULTS

The predicted spectral reflectances were rather close to measured ones. Consequently, knowing the colour of the nail without polish and the optical parameters of the nail polish itself, we can estimate the colour of the nail polish applied on the nail depending on its thickness.

CONCLUSION

Our study showed that the Kubelka-Munk theory can be used to predict the nail polish colour. The ability to predict the real colour of a nail polish applied on a nail could help a nail polish manufacturer to improve his polish formulae in order to obtain a precise colour.

Tooth colour and whiteness: A review

OBJECTIVES

To review current knowledge concerning the application of colour science on tooth colour and whiteness description, measurement, distribution and its psychological impact.

DATA SOURCES

"Scopus" databases were searched electronically with the principal keywords tooth, teeth, colour, white, whiteness. Language was restricted to English and original studies and reviews were included. Conference papers and abstracts were excluded.

CONCLUSIONS

The appearance and colour of teeth are a common concern for patients across many populations and are associated with an increased desire for treatments that improve dental aesthetics, including tooth whitening. The application of colour science in dentistry has allowed the precise description of tooth colour and whiteness. Coupled with the advances in instrumental tooth colour measurement, such as spectrophotometers, colorimeters, spectroradiometers and digital imaging systems, these parameters are quantifiable in a reproducible and robust manner. These principles have been applied to the tooth colour distribution in many study populations, indicating, in general, differences in tooth colour for subject age and gender, but not for ethnicity. Psychophysical studies on tooth colour and whiteness via third party assessment of images indicate that whitened teeth lead to judgements that are more positive on personality traits such as social competence and appeal, intellectual ability and relationship satisfaction.

Effect of 2 Bleaching Agents with a Content of High Concentrated Hydrogen Peroxide on Stained 2 CAD/CAM Blocks and a Nanohybrid Composite Resin: An AFM Evaluation

The aim of this study was to evaluate color stability of 3 restorative materials, discoloration ability of different solutions, efficacy of 2 office bleaching agents, and surface roughness and topography. Sixty specimens for Clearfil Majesty Esthetic (CME), Lava Ultimate (LU), and Vita Enamic (VE) were prepared. They were immersed into 3 staining solutions for 2 weeks and then they were bleached. According to the measured L^⁎, a^⁎, and b^⁎ parameters described by CIELAB system, color changes (ΔE₀₀), translucency parameters (TP), whiteness index values (W^⁎), and changes in closeness to pure white (ΔW^⁎) were calculated. Then 3 specimens from each group were scanned with an atomic force microscope for surface analysis. After staining, CME groups and control groups of LU and VE showed clinically acceptable color changes (ΔE₀₀ < 1,8). After bleaching, while a reverse effect on color was observed, VE showed the furthest color values to pure white. There was no statistically significant difference between whiteness index values of LU and CME. LU was the most translucent material during the study and TP values of materials showed minimal differences. Most of the VE groups and a control group of LU showed surface roughness (R_a) values higher than critical value for biofilm accumulation (0,2 μm).

Influence of tongue position on the determination of tooth shade

STATEMENT OF PROBLEM

Dentists frequently use electronic devices to determine tooth color. However, neither the instructions for these devices nor the accompanying brochures refer to the environmental conditions required at the point of measurement.

PURPOSE

The purpose of this multicenter prospective clinical study was to reveal whether a change in the oral background influences tooth color determination.

MATERIAL AND METHODS

Students (N=42) at the dental clinic in Berlin, Leipzig, Greifswald and Olomouc (women n=27, men n=15) participated in this study. It was their first contact with the spectral photometer (Easyshade Advance 4.0; VITA Zahnfabrik). After a short introduction on how to use the device, the students made 1-point measurements on the same patient on the maxillary central incisor. In the first measurement, the patient's mouth was open, and the palatal surface uncovered. In the second measurement, the patient's mouth was closed slightly, and the tongue pressed on the lingual surface of the maxillary central incisor. The mean ±SD and the 95% confidence interval (95 % CI) were calculated using the Student t test for each test series (α=.05).

RESULTS

Statistical evaluation of the 2 measurements revealed changes in the L*a*b* values with a mean L*=0.204, a*=-0.351, and b*=0.02; a median of 0.4, -0.3, and -0.1, respectively; a ±SD of 2.37, 0.64, and 0.89, respectively; and 95% CIs of L*=-0.476 to 0.884, a*=-0.531 to -0.702, and b*=-0.23 to 0.52, respectively. These differences were not statistically significant (P>.05). The measurements of L*, a*, and b* with and without tongue coverage of the lingual surfaces of the maxillary teeth did not show any statistically significant differences (P=.663).

CONCLUSIONS

The results demonstrate that the position of the tongue does not influence measurement accuracy during the application of the Easyshade Advance device.