Lightness, chroma and hue differences on visual shade matching

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.

In-vivo repeatability of three intra-oral spectrophotometers

OBJECTIVE

The objective was to assess the repeatability of three spectrophotometers, based on the CIELCh factors and shadeguide reference measurements.

MATERIALS AND METHODS

Color analysis was performed using three devices: Rayplicker, Easyshade 4, and Easyshade V. Five repeated measures were performed by the same operator, on the right central maxillary incisor of 30 patients. The CIELCh factors were retrieved and the intra-class correlation was calculated. The Vita Classical and Vita 3D Master shadeguides were used to evaluate the respective Fleiss' Kappa factors.

RESULTS

Rayplicker and Easyshade V demonstrated strong intra-class correlation based on the CIELCh factors: 0.98, 0.99, and 0.91 for Rayplicker, and 0.95, 0.99, and 0.93 for Easyshade V, for the L*, C*, and h* parameters, respectively. Regarding the repeatability of the shadeguide data, while Easyshade 4 had the best repeatability when using the Vita Classical as a reference, Rayplicker and Easyshade V showed better repeatability when using the Vita 3D Master.

CONCLUSION

These findings suggest that both Rayplicker and Easyshade V are reliable devices for measuring CIELCh parameters. In terms of shadeguide references, the reliability of spectrophotometers is generally lower compared to the CIELCh measurements.

CLINICAL SIGNIFICANCE

Given their good repeatability, both the Rayplicker and the Easyshade V spectrophotometers are reliable tools for prosthetic dental practices.

Effect of an Effervescent Multivitamin on Color and Surface Roughness of Micro-Hybrid Dental Resin Composites

The use of multivitamins has become widespread globally, yet there is a scarcity of studies investigating their impact on resin composite restorations. This study aimed to evaluate the effect of an effervescent multivitamin tablet on micro-hybrid dental resin composites' surface roughness and color. Fifty disc-shaped samples (8 × 2 mm, shade A2; n = 10) were prepared and polished using five different micro-hybrid resin composites (Pergamon, Dentac, Turkey; Estelite Posterior, Tokuyama, Japan; Geanial Anterior, GC, Japan; Charisma Opal, Kulzer, Germany; Beautifil II, Shofu, USA). Samples were immersed in 200 mL water to one effervescent multivitamin tablet (Redoxon Triple Action, Bayer) at 24 °C for 2 min a day in 24 h intervals for 30 days. All samples' surface roughness (Ra) and ΔE(L*a*b) measurements were recorded at the beginning and end of the 30 days. The Wald chi-square and a two-way ANOVA were used for statistical analysis (significance level p < 0.05). The resin composite type and exposure to the multivitamin had a statistically significant effect on Ra values (p < 0.05). The resin composite type had a statistically significant effect on ΔE values, likely due to the higher mean value of BII (p = 0.040). The surface roughness and color of resin composites can be affected by multivitamins with a pH value of 3.0. Therefore, it is important to consider the patient's routine vitamin intake during resin composite selection. Additional research is required to explore the properties of different dental restorative materials.

Fusion machine learning model predicts CAD-CAM ceramic colors and the corresponding minimal thicknesses over various clinical backgrounds

OBJECTIVES

This study has developed and optimized a machine learning model to accurately predict the final colors of CAD-CAM ceramics and determine their required minimum thicknesses to cover different clinical backgrounds.

METHODS

A total of 120 ceramic specimens (2 mm, 1 mm and 0.5 mm thickness; n = 10) of four CAD-CAM ceramics - IPS e.max, IPS ZirCAD, Upcera Li CAD and Upcera TT CAD - were studied. The CIELab coordinates (L*, a* and b*) of each specimen were obtained over seven different clinical backgrounds (A1, A2, A3.5, ND2, ND7, cobalt-chromium alloy (CC) and medium precious alloy (MPA)) using a digital spectrophotometer. The color difference (ΔE) and lightness difference (ΔL) results were submitted to 39 different models. The prediction results from the top-performing models were used to develop a fusion model via the Stacking integrated learning method for best-fitting prediction. The SHapley Additive exPlanation (SHAP) was performed to interpret the feature importance.

RESULTS

The fusion model, which combined the ExtraTreesRegressor (ET) and XGBRegressor (XGB) models, demonstrated minimal prediction errors (R2 = 0.9) in the external testing sets. Among the investigated variables, thickness and background colors (CC and MPA) majorly influenced the final color of restoration. To achieve perfect aesthetic restoration (ΔE<2.6), at least 1.9 mm IPS ZirCAD or 1.6 mm Upcera TT CAD were required to cover the CC background, while two tested glass-ceramics did not meet the requirements even with thicknesses over 2 mm.

SIGNIFICANCE

The fusion model provided a promising tool for automate decision-making in material selection with minimal thickness over various clinical background.

Evaluation of the Color Stability of Three Resin-Ceramic Materials Using a Spectrophotometer and a Digital Photography Software

Background

Computer-aided design/computer-aided manufacturing (CAD/CAM) resin ceramics allow easier milling than glass ceramics but are suspected to be more stainable. Although Photoshop® is widely used for picture analysis, its potential for shade selection has not been properly assessed.

Aim

Purpose primary: To evaluate the color stability of three CAD/CAM resin ceramics and Lithium Disilicate. Secondary: to compare the color evaluation between a spectrophotometer (Vita Easyshade compact) and Photoshop software.

Materials and Methods

Three CAD/CAM resin ceramic materials (n = 10) and a fourth group of lithium disilicate were used. Half of each group were thermocycled (5°C and 55°C; 3000 cycles). All samples were immersed in colored beverages (coffee, tea and red wine) for 30 days. Values were obtained by spectrophotometry and photographs analyzed using Photoshop software. The parameters measured were CIEL*a*b, and the color difference (ΔE) was analyzed. A mixed model test was used to compare the results through time and materials (α = 0.05). The comparison between the spectrophotometer and Photoshop results was performed using the bivariate Pearson's correlation test.

Results

Lithium disilicate glass ceramic exhibited less color change (ΔE = 14) than resin ceramics (15.7 < ΔE < 18.7). The least change was noted with GC Cerasmart (ΔE = 15.7) followed by Vita Enamic (ΔE = 17*) and Brilliant Crios (ΔE = 18.7*). Spectrophotometer and Photoshop values showed low correlations.

Conclusions

Resin ceramics may suffer from color change in clinical use. Photoshop is technique sensitive; pictures are easily affected by the light conditions and camera settings.

A Comprehensive Quality Analysis of Different Colors of Medicinal and Edible Honeysuckle

Honeysuckle (the dried flower bud or opening flower of Lonicera japonica Thunb.), a medicinal and edible substance, has is greatly popular among consumers for its remarkable health effects, such as antioxidant, antibacterial, and anti-inflammatory effects. However, due to the influences of processing methods, storage conditions, and other factors, honeysuckles show different colors which can directly reflect the quality and the price on the market. In order to comprehensively compare the quality of different colors, 55 batches of honeysuckle samples were collected and analyzed. Their color parameters, chlorophyll content (chl), total phenol content (TPC), total flavonoid content (TFC), antioxidant activity (AA), main active compounds, and metabolites were measured. As a result, the initial green-white (GW) samples, a kind of highest-quality honeysuckle, had the smallest a* value, largest h*, chl, TPC, TFC, and AA values, and highest content of chlorogenic acid and cynaroside. There was a significant difference between GW samples and a series of discolored samples. As the color darkened or lightened, the quality gradually decreased. The yellow-brown (YB) samples were of the worst quality and were no longer available for clinical and health purposes. A series of differential metabolites, such as quercetin-7-O-glucoside and secologanoside, could be used as important references to evaluate the quality of differently colored samples. The metabolic profile of honeysuckle provided new insights into the process of color change and laid a foundation for further honeysuckle quality control. The correlation results showed that the a* and h* values significantly affect the abovementioned quality indicators and the 10 main active compounds. In other words, the color difference could directly reflect the quality and clinical efficacy. Multiple regression analysis was carried out using combined L*, a*, and b* values to predict the quality of honeysuckle. This is the first time the quality of different color honeysuckle samples on the post-harvest link has been systematically compared and a demonstration of medicinal and edible substances with different colors has been provided.

The accuracies of three intraoral scanners with regards to shade determination: An in vitro study

PURPOSE

To compare the accuracy of three intraoral scanners for shade determination function in vitro, and to preliminarily investigate the shade-matching characteristics of the three intraoral scanners.

MATERIALS & METHODS

The shade of the middle third region of each shade tab on the Vita Classical A1-D4 shade guide (VC) was measured by a spectrophotometer (Vita Easyshade V, VE) and three intraoral scanners, including CEREC Omnicam (OM), 3Shape TRIOS 3 (T3), and TRIOS 4 (T4). A conversion table between VC values and CIELAB values was established from the database of VE to analyze the trueness. The reproducibility of the instruments was then compared by repeating the measurements five times.

RESULTS

The mean color difference for each instrument was highest in the OM, followed by the T4, and lowest in the T3 and VE, repectively. The L^* and a^* value for OM, and the b^* value for T4, were significantly different from those for VE (p <0.05). The reproducibility of the instrument was highest in the VE (Fleiss' kappa: 0.95), followed by the T3 (Fleiss' kappa: 0.89), T4 (Fleiss' kappa: 0.87), and OM (Fleiss' kappa: 0.78).

CONCLUSIONS

Of the three intraoral scanners, the trueness was best on the T3. The reproducibility of all the instruments was excellent. This article is protected by copyright. All rights reserved.

Evaluation of Color and Spectral Behavior of a Novel Flowable Resin Composite after Water Aging: An In Vitro Study

Background: This study aimed to evaluate the color matching, light transmittance, and reflectance characteristics of the novel flowable resin composite OCF-001 (OCF). Methods: Fifty-four resin composite molds were made with simulated class I cavities of A2, A3, and A4 shades by filling the rubber mold interspace with Estelite Sigma Quick (ESQ), Gracefil Putty (GP) and Filtek Supremme Ultra (FSU). After applying the adhesive, three different flowable resin composites (n = 6), OCF, Gracefil LoFlo (GLF), and Supreme Ultra Flowable (SUF), were used to fill the cavities. A colorimeter was used to measure the color parameters (CIEDE2000). The color measurements were taken immediately and after 28 days. Data were analyzed using the nonparametric Kruskal–Wallis (α = 0.05) and Wilcoxon tests. The light transmittance and reflection characteristics were measured with a black background using a spectrophotometer under D65 illumination. Results: The ΔE₀₀, and ΔC of OCF was lower than other tested materials in A2 and A3 shades both immediately and after 28 days. OCF showed the highest transmittance characteristic, and a relatively stable reflectance curve in all the wavelengths. Conclusions: OCF showed better shade matching with the surrounding shades of A2 and A3, a relative uniform reflectance and higher light transmission properties.

Color and optical properties of 3D printing restorative polymer‐based materials: A scoping review

Objective

Color and optical properties are particularly crucial to mimic natural tooth. This scoping review aimed to present an overview of the literature published on color and optical properties of 3D printing restorative polymer‐based materials. The literature search was performed in MED‐LINE/Pubmed, Scopus and Web of Science.

Materials and methods

The literature search was conducted in the three databases based on the question: “Are the optical properties and color adequately reported on polymer‐based 3D printing dental restorative materials studies?” with no restriction on year of publication. Data were reported and synthesized following PRISMA‐ScR statement.

Results

Nine studies fit the inclusion criteria. Five studies focused on evaluating only color stability; three articles assessed the color stability along with mechanical and morphological properties and only one study compared color parameters of 3D printed to conventional polymers. Two studies evaluated translucency parameter and no study was found evaluating scattering, absorption, and transmittance.

Conclusions

Color and optical properties of 3D printed polymers that can be used in restorative dentistry are not adequately evaluated and characterized. Future studies on the influence of experimental printing conditions should include these physical properties to assist on improving esthetics.

Clinical significance

This review shows the scarce literature existing on color and optical properties of 3D printing restorative polymer‐based materials. These properties and their study are of outmost importance to create materials that mimic natural tooth to allow clinicians to obtain esthetically pleasant restorations.

Masking Ability of Monolithic and Layered Zirconia Crowns on Discolored Substrates

There is scarce information on the colorimetric behavior of monolithic and layered zirconia crowns in combination with various abutment colors. This study evaluated the masking ability on discolored substrates of monolithic and layered zirconia crowns. Anterior crowns were fabricated using 3Y-TZP zirconia and layering ceramic and divided into three groups: monolithic (ML), bi-layer (BL), and tri-layer (TL). The crowns were placed over eleven substrates (ND1-ND9, zirconia, metal), and CIE L*, a*, b*, C*, and h° color coordinates were measured in the cervical, middle, and incisal areas with a spectrophotometer. Masking ability was calculated using the color difference formula, and values were interpreted according to the perceptibility and acceptability thresholds. Data were analyzed statistically (α = 0.001). The L* coordinate was not significantly different between BL and TL crowns, regardless of the measurement area or substrate (p ≥ 0.001). In the middle area, the L* coordinate of the ML group was statistically different from the BL and TL groups only for zirconia and metal substrates, while in the incisal area, only for ND7 and metal substrates. The a* coordinate was significantly different between the ML and layered crowns for all measurement areas and substrates (except zirconia). The b* and C* coordinates differed significantly between the groups only in the cervical area (p < 0.001). The ML crown had better masking ability than the BL and TL crowns. However, the color differences for ML crowns were below the acceptability threshold for ND2, ND3, and ND7 substrates in the cervical and middle areas and below perceptibility threshold only for the incisal area. The lowest masking ability of the crowns was found for ND9 and metal substrates in all measurement areas.

Evaluation of accuracy and characteristics of tooth-color matching by intraoral scanners based on Munsell color system: an in vivo study

To compare the accuracy of visual and instrumental methods for tooth-color matching based on three attributes in the Munsell color system and to investigate the characteristics of intraoral scanners for tooth-color matching. Shades of the cervical, middle, and incisal third region of 130 maxillary anterior teeth were matched visually by an experienced prosthodontist (EP) using Vita classical A1-D4 (VC) and Vita System 3D-Master (V3D) shade guides, and digitally by a spectrophotometer (Vita Easyshade V, VE) and two intraoral scanners (3Shape TRIOS 3, T3; TRIOS 4, T4). VE was used as a reference. The reproducibility of the three test groups was examined by repeating the measurements in triplicate. The overall trueness of the three test groups (from high to low) was T3 > EP > T4 for VC values (p < 0.01), and T3, EP > T4 (p < 0.01) for V3D. The trueness of T3 in incisal regions was lower than cervical and middle regions. When hue or lightness was correct, the mismatched chroma in test groups was smaller than VE (p < 0.01). The repeatability of EP was the poorest (p < 0.01). The color-matching trueness of T3 was higher than EP and T4. The reproducibility of intraoral scanners was better than visual methodology.

Comparison of visual shade matching and photographic shade analysis

OBJECTIVE

To compare the performance of a standardized photographic shade analysis (PSA) and visual shade matching (VSM) using two color difference formulas.

MATERIALS AND METHODS

Fifty observers (35 undergraduate and 15 graduate students) evaluated the color of two upper left central incisors (LT-light tooth, and DT-dark tooth). VSM was performed using the VITA 3D Master (3D) shade guide in a controlled clinical environment. For PSA, a cross-polarized filter and a gray card (Whibal) were used to standardize the photographs taken (target teeth and shade tabs from 3D). From the pictures obtained, the CIELAB coordinates, and color differences ( Δ E ab * and ΔE₀₀ ) were obtained. The shade tabs selected by two experienced researchers were conducted as part of the pilot study, and finally used as a standard for the analysis. Data were analyzed using descriptive statistics and the chi-square test (p ≤ 0.05).

RESULTS

Shade tabs selections of VSM and PSA agreed only for LT. The best "Match" selected by the researchers agreed with data from PSA using ΔE₀₀ . PSA using ΔE₀₀ showed higher total percentages of "Match" and higher percentage of agreement among observers. A relationship was found for LT performing the PSA (p < 0.05).

CONCLUSIONS

The performance of the PSA was better than the VSM, but only when the CIEDE2000 color difference formula was used. Therefore, the color difference formulas influenced on the performance of PSA. Finally, the PSA improved the precision of the VSM.

CLINICAL SIGNIFICANCE

To use a standardized PSA to improve the VSM and shade communication in clinical esthetic dentistry.

[Modern aspects of determining dental color in aesthetic dentistry]

One of the important factors for creating a beautiful smile is the color of the teeth, which for most people has a more important role than anatomical characteristics. The exact reproduction of the color of the tooth affects the appearance and psycho-emotional state of the patient. The purpose of this work is to review domestic and foreign literature on methods for determining the color of teeth. Methods for determining color are divided into visual, spectrophotometric, colorimetric, digital photo analysis and computer method. The most common in the practice of a dentist is visual, which is based on comparing the examined tooth with color templates. Determination of the color of teeth using scales does not give a reliable result, which is due to the small number of shades in the colors, the phenomenon of metamerism, the impossibility of converting the obtained data into digital values, etc. The hardware method for determining the color of teeth compensates for the disadvantages of the visual and has a high adaptability, which requires many interrelated factors. Due to the complexity and high cost, the devices are used mainly for research purposes. Currently, innovative methods for determining the color of teeth, based on digital and computer analysis, are being actively developed. Thus, hardware methods for determining the color of teeth significantly increase the accuracy of choosing the shade of a future aesthetic restoration or orthopedic construction, excluding subjective factors, however, they require mandatory certification. Correct color assessment and identification helps to reduce costly re-treatments and reduce warranty costs. Despite this, visual methods using scales remain in demand among practicing doctors, due to their low cost and ease of use. The accuracy of determining the color of teeth in this case depends on the professionalism of the dentist, as well as on the correctness of the photo protocol.

Experimental methodologies to evaluate the masking ability of dental materials: A systematic review

OBJECTIVE

To conduct a systematic review on the masking ability of discolored substrates, analyzing the capacity and quality of the response produced by the different methodologies and techniques applied to overcome this clinical challenge.

MATERIALS AND METHODS

The study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The electronic search was conducted in MEDLINE/PubMed, Scopus and Web of Science databases, without date restriction. In vitro studies, written in English, applying different methodologies to evaluate masking ability were included. The variables of interest were: type, color and thickness of the restorative and/or cement material; use of pigments in the restorative material and/or cement; color of the substrate; and background color used for the evaluations.

RESULTS

Database search retrieved 307 eligible papers with a final inclusion of 47 published papers. Approximately 98% of the studies used ΔE, 36% used TP, and only 6% used CR to evaluate the masking ability of restorative materials.

CONCLUSIONS

The most appropriate methodology to evaluate the masking ability is using color difference equations (ΔE) associated with the perceptibility and acceptability thresholds.

CLINICAL SIGNIFICANCE

As different methodologies have been used to evaluate the masking ability of esthetic restorative materials on colored substrates, there is an urgent need to reach a consensus and propose a method, which is suggested by the present systematic review.

Impact of short-term dental dehydration on in-vivo dental color and whiteness

OBJECTIVE

To determine in-vivo chromatic and whiteness changes produced by short-term dental dehydration.

METHODS

Spectral reflectance of 452 upper incisors (226 centrals and 226 laterals) of 113 participants were measured using a spectroradiometer at baseline and after short-term dehydration (minutes 2, 4, 6, 8 and 10). CIE L*a*b* color coordinates (L*, a*, b*, C*_ab and h_ab) and whiteness index for dentistry (WI_D) were calculated. Color differences (ΔE₀₀, ΔE_ab^*) and whiteness differences (ΔWI_D) were computed and interpreted based on their respective 50:50% perceptibility (PT) and acceptability thresholds (AT). Statistical analysis was performed using the related samples Wilcoxon signed-rank test.

RESULTS

L* showed an increasing trend with dehydration, while a*, b*, C*_ab and h_ab have a decreasing tendency. All chromatic coordinates showed statistically significant differences (p < 0.003) at each interval of dehydration compared with baseline, except a* for all teeth. For ΔE₀₀ and ΔE_ab^* values were higher than PT after 2 min of teeth dehydration and higher than AT after 6 and 8 min, respectively. The percentage of teeth exceeding corresponding PT was higher than 50% after 2 min. WI_D index increased with dehydration time, while whiteness differences were clinically perceptible after 4 min. Statistically significant differences were found for WI_D between all dehydration intervals (except 8-10 min). The percentage of teeth exceeding whiteness PT was higher than 50% after 6 min of teeth dehydration.

CONCLUSIONS

Short-term dental dehydration produces clinically unacceptable changes in tooth color and clinically perceptible increase in tooth whiteness level.

CLINICAL SIGNIFICANCE

Clinical shade matching must be done within the first two minutes of any clinical procedure that requires precise chromatic determination but implies a risk of tooth dehydration.

Clinical threshold of the translucency parameter of maxillary central incisors

The aim of this in vivo study is to describe the clinical threshold and relative factors associated with the translucency of maxillary central incisors. Bilateral maxillary central incisors were measured in 106 individuals using a digital colorimeter against black and white backings. The translucency parameters (TP) of incisors and the difference in TP (ΔTP) between the left and right maxillary central incisors of the same individual was calculated. The mean TP value of the maxillary incisors was 8.22. There was a significant effect of age on the translucency of the maxillary central incisors (p<0.05). The TP of females was higher than that of males (p<0.05). The absolute mean value of ΔTP was 1.33. The ΔTP of the two maxillary central incisors in the same individual can be used as a reference for the threshold value of translucency.

Accuracy and repeatability of different intraoral scanners on shade determination

OBJECTIVE

To evaluate the accuracy and repeatability of different intraoral scanners on shade determination.

MATERIALS AND METHODS

Ten different shades of Vita Mark II blocks were used. A disc-shape specimen (10 mm in diameter and 1 mm thick) per ceramic block was fabricated. Ten color measurements per specimen were performed by each instrument (Vita Easyshade V [control], 3shape Trios, Cerec Omnicam, Cerec Primescan) and recorded in Vita Classic color system. The number of correct shade match per instrument for each shade was recorded. Instrumental accuracy was compared using Cochran Q test and repeatability was analyzed using Cronbach's alpha.

RESULTS

There was a significant difference in the instrumental accuracy for shade determination (p < 0.001). There was no statistical difference between the Easyshade V (78%) and the 3Shape Trios (66%) (p > 0.05), with the latter being similar to the other scanners Primescan(63%) and Omnicam (57%) (p > 0.05). No significant difference was found (p > 0.05) when different shades were evaluated by the same instrument. Similar repeatability was found for the different devices, ranging from 44.3% for Easyshade to 51.9% for Omnicam.

CONCLUSION

The evaluated instruments showed less than expected repeatability and accuracy on measuring different dental shades. Therefore, caution should be exercised when using instrumental shade determination, which should be accompanied by experienced human visual assessment.

CLINICAL SIGNIFICANCE

The outcome of this study might help clinicians evaluate the performance of intraoral scanners as a shade matching tool.

Colour thresholds of the gingival chromatic space

OBJECTIVE

To establish the thresholds of chromatic perception and clinical acceptability of gingival colour according to professional category and in accordance with the perceptibility/acceptability threshold of 50:50 (colour differences that can be perceived/accepted by 50 % of the observers).

METHODS

A total of 21 different coloured samples made of pink gingiva Heraceram porcelain were used. Dentists (n = 54), dental assistants (n = 56), dental students (n = 126) and participants unrelated to dentistry (n = 116) were asked to identify pairs of samples that appeared identical. In addition, they were asked to indicate the pairs of samples whose colour they considered to be acceptable for use in a dental rehabilitation. A least squares regression was adjusted using an S-shaped curve of the equation y = exp (B0 + B1/x). The adjusted model was used to predict a colour difference value for an acceptability percentage of 50 %.

RESULTS

The threshold value for the perception of colour changes in human gingiva varies from ΔEab* 2.3 ± 0.38 units and CIEDE2000 (ΔE00) 1.5 ± 0.28units (dental students) to ΔEab* 2.7 ± 0.43 units and ΔE00 1.8 ± 0.30 units (participants unrelated to dentistry). The threshold of gingival acceptability varies from ΔEab* 2.9 ± 0.43 units and ΔE00 2.0 ± 0.31 units (dental assistants) to ΔEab* 3.6 ± 0.54 units and ΔE00 2.5 ± 0.41 units (dental students).

CONCLUSION

From the total number of samples, the average threshold of perception for the gingival chromatic space is 3.1 units for ΔEab* and 2.1 units for ΔE00. Moreover, the mean gingival acceptance threshold is 4.1 units for ΔEab* and 2.9 units for ΔE00. These thresholds are similar for all professional categories studied.

CLINICAL SIGNIFICANCE

The determination of the perception and acceptability thresholds in the gingival chromatic space are of special relevance for designing the physical shade tabs used in gingival colour guides. The results from this work will aid in selecting optimal gingival colour for patients.

Analysis of color differences in stained contemporary esthetic dental materials

STATEMENT OF PROBLEM

Although contemporary analytical methods are available for application to data which exhibit a lack of equality of variances or a lack of normality in the error distribution, little guidance is provided for selecting the methods of data handling and analysis which best fit color difference data for stained esthetic materials.

PURPOSE

The purposes of this in vitro study were to apply information criteria of analysis of variance (ANOVA) methods of differing error distributions and covariance structures when analyzing color differences to determine the degree of alienation among 3 Commission Internationale de l'Eclairage (CIE) color difference formulae to assess the linearity of relationships among these formulae and to independently assess differences among various computer-aided design and computer-aided manufacture (CAD-CAM) materials in any color change after common forms of staining over time.

MATERIAL AND METHODS

Hybrid ceramic, resin nanoceramic, feldspathic-ceramic, and lithium-disilicate ceramic specimens (N=128) were subjected to staining from water, tea, coffee, and red wine over 1, 7, and 30 days, with color differences calculated from baseline. Akaike information criteria (AIC) and Bayesian information criteria (BIC) values were determined for Gaussian and lognormal error distributions at covariance structures of standard variance components and compound-symmetry. The analysis of variance used to analyze any significant effects on these color differences was the one with the lowest AIC and BIC values. Then, for each solution, day, and CIE color difference formula, any significant difference in the color differences between all pairs of materials was found by Bonferroni-corrected Student t tests. Those statistically significant pairwise comparisons where the larger of the color differences met or exceeded the acceptability threshold were labeled as statistically and visually noteworthy.

RESULTS

For this color difference data set, the lognormal error distribution and the covariance structure of compound symmetry provided the best AIC and BIC. Because the interaction between material, solution, and day was statistically significant (P<.001), pairwise comparisons were made between all pairs of materials for each level of solution and day studied. Noteworthy differences were identified, where hybrid ceramic and resin nanoceramic each had color changes after staining in coffee and red wine that were greater than each of feldspathic-ceramic and lithium-disilicate ceramic.

CONCLUSIONS

AIC and BIC values evaluate distinctively the Gaussian and lognormal error distributions when analyzing highly varying color differences. Although there is a high linear correlation between the 3 color difference formulae studied, each formula is unique, and each represents a different assessment of the perceived color difference. CAD-CAM materials, staining liquids, and time points affected the notable color changes.

Effect of substrate and cement on the final color of zirconia-based all-ceramic crowns

OBJECTIVE

To evaluate the influence of the substrate and the cement on the final color of ceramic crowns.

METHODS

Prosthetic crowns (framework + porcelain) were fabricated using two all-ceramic systems (YZ, 3 mol% yttria-stabilized tetragonal zirconia; IZ, alumina-based zirconia-reinforced glass-infiltrated ceramic) and a metal-ceramic system (MC; n = 8). Metal (M) and resin (R) were used as substrate abutments. For R substrate, crowns were evaluated as seated (R) and after cementation (R-C). CIELAB color coordinates were obtained using a dental spectrophotometer with D65 light illumination. CIELAB, CIEDE2000 (1:1:1) and CIEDE2000 (2:1:1) color difference metrics were used. Data were analyzed using 95% confidence intervals and compared to perceptibility (PT) and acceptability (AT) thresholds.

RESULTS

The ∆ E ab * , ∆E₀₀ (1 : 1 : 1), and ∆E₀₀ (2 : 1 : 1) values of the restorative systems evaluated using different substrates (M.R) were similar to the AT values of each metric. When non-cemented and cemented crowns were evaluated (R.R-C), MC had color difference values at PT and below AT; while YZ and IZ showed similar values to AT, for ∆ E ab * and ∆E₀₀ (1 : 1 : 1) metrics.

CONCLUSION

The substrate and cement affected the final color of zirconia-based all-ceramic crowns, but the color differences corresponded to an acceptable match.

CLINICAL SIGNIFICANCE

As both substrate and cement influence the final color of multi-layered ceramic prosthesis, dentists and dental technicians should understand the optical properties of dental ceramics to reproduce the natural appearance of dental structures and maximize the chance for excellent color matches.

Color matching of full ceramic versus metal-ceramic crowns - a spectrophotometric study

Background and aims

To verify the color match of metal-ceramic and full ceramic crowns, using instrumental methods.

Methods

A number of 153 teeth (anterior and posterior teeth), in 62 patients, were restored with metal ceramic (MC, n=119), pressed-ceramic (PC, n=28), and zirconia-ceramic (ZC, n=6) full coverage crowns. The shade of a reference natural tooth was recorded instrumentally with a dental spectrophotometer (Vitaeasyshade Advance 4.0) in “single tooth measurement”, which provided the base color in Vita Classic (VC) and Vita 3D Master shades (3D).

For verifying the outcome of the restoration “verify restoration” mode was used, and ΔE values were recorded for both VC and 3D Master shade guides. Moreover, matching symbols were also recorded (***=good, **=fair, *=poor). Descriptive statistics was performed and data were analyzed (One-sample z-Test, α=0.05) for comparison with visual thresholds in dentistry (Perceptibility Threshold – PT=1.2 and Acceptability Threshold – AT=2.7).

Results

The data did not follow a normal distribution (Kolmogorov-Smirnov test, p<0.05). Recorded color difference was significantly higher than PT and AT, for all types of restorations, regardless of the coding system (p<0.05). For MC crowns in 2.52% (4.20% for 3D) of the cases the color difference was smaller than PT, in 19.32% (the same for 3D) of cases was between PT and AT, and in 78.15% (76.47% for 3D) of cases was higher than the AT. For PC crowns in 3.57% (0% for 3D) of the cases the color difference was smaller than PT, in 25% (32.14% for 3D) of cases was between PT and AT, and in 71.42% (67.85% for 3D) of cases was higher than the AT. In the case of ZC crowns none of the restorations had color difference smaller than PT, but in 16.66% of cases was between PT and AT, and in 83.33% of cases was higher than the AT, for both VC and 3D.

Conclusion

Within the limitations of the study, a better color match was achieved in the case of pressed ceramic crowns, made of lithium disilicate. In most of the situations the color difference between the restoration and the reference tooth exceeded the perceptibility thresholds, but the matching was recorded as “fair” by the spectrophotometer.

Proposal for a gingival shade guide based on in vivo spectrophotometric measurements

PURPOSE

The purpose of this study was to propose and assess a shade guide for pink gingival aesthetics using a Spanish population sample.

MATERIALS AND METHODS

The L^*, C^*, h, a^* and b^* coordinates of 259 participants were measured using a spectrophotometer in 3 standardized points along the attached gingiva of the maxillary central incisors. A hierarchical clustering analysis was applied to obtain separate solutions regarding the number of shade tabs. For each of the solutions obtained, color differences (ΔE^*) were calculated using the CIELab and CIEDE2000 formulas, and the proposed shade guide was selected considering (1) the color differences between tabs and (2) the coverage error of each of the solutions.

RESULTS

The proposed shade guide consisted of 8 gingival shade tabs and achieved CIELab and CIEDE2000 coverage errors of less than the respective 50:50% acceptability thresholds (ΔE^*=4.6 units and ΔE₀₀=4.1). The coordinates for the various gingival shade tabs were as follows: Tab 1: L^*43.3, a^*21.9, b^*12.3 (1.6); Tab 2: L^*42.9, a^*34.1, b^*19.1; Tab 3: L^*46.5, a^*25.8, b^*10.9; Tab 4: L^*46.5, a^*27.3, b^*15.1; Tab 5: L^*49.6, a^*23.5, b^*16.8; Tab 6: L^*51.5, a^*19.7, b^*13.6; Tab 7: L^*55.9, a^*22.0, b^* 15.0; and Tab 8: L^*56.0, a^*19.9, b^*18.8.

CONCLUSION

The CIELab and CIEDE2000 coverage errors for the 8 shade tabs of the proposed gingival shade guide were significantly lower than those of other guides. Therefore, despite the limitations of this study, the proposed guide is more appropriate for matching gingival shade in the Spanish general population.

Influence of Bleaching and Aging Procedures on Color and Whiteness of Dental Composites

Bleaching can cause perceptible color changes on resin-based composite (RBC) restorations that may not be stable with aging. The objective of this study was to evaluate color stability and whiteness variations of RBCs after bleaching and aging procedures. Discs (10 mm in diameter and 1 mm thick) of shades A2 and A3 were fabricated from two RBCs (Filtek Z250 and Filtek Z350 XT) and divided into three subgroups (for each composite and shade) (n=5) as follows: control (no bleaching), at-home bleaching, and in-office bleaching. All specimens underwent an accelerated artificial aging up to 450 KJ/m2 and 900 KJ/m2 in an aging chamber (Suntest XXL+). A spectroradiometer (SpectraScan PR-670) was used to obtain CIE L*a*b* coordinates. CIEDE2000 color difference (ΔE00) and whiteness index for dentistry (WID) were used to evaluate color stability. Color and whiteness differences data were analyzed considering the 50:50% visual color difference thresholds (perceptibility [PT] and acceptability [AT]) and 50:50% whiteness thresholds (whiteness perceptibility [WPT] and whiteness acceptability [WAT]). Analysis of variance and Tukey tests (α=0.05) were used to statistically analyze the data. After bleaching, all specimens showed ΔE00 and ΔWID values below their corresponding acceptability thresholds (AT and WAT, respectively). After aging, L* and WID values decreased while b* values increased (p≤0.05), resulting in ΔE00 and ΔWID values above AT and WAT, respectively. Color changes after bleaching RBCs were clinically acceptable, while aging provoked clinically perceptible color changes.

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.

Precision of a Reflectance Spectrophotometer in Measuring Anterior Tooth Color

Background:

Intraorally, a common instrumental approach for measuring tooth color is reflectance spectrophotometry.

Objective:

To evaluate the precision of a reflectance spectrophotometer in accurately measuring anterior tooth color.

Methods:

The twelve labial surfaces of the anterior teeth of sixteen patients were measured spectrophotometrically (SpectroShadeTM Micro) on three non-consecutive days (1st, 2nd, 8th). Tooth color was converted to L*, a* and b* colorimetric values; intra-examiner repeatability was assessed in ΔΕ-units between two same day repeated measurements. Intra-examiner reproducibility was measured for the effect of tooth type, time and their interaction.The linear effect of the acquisition angle on the colorimetric values of each tooth was also estimated.

Results:

The highest values of systematic or random error occurred for teeth #33, #43 and #32. There were no statistically significant differences in systematic or random errors for any tooth between the three measurement days. Statistically significant differences were found for tooth type (p=0.039), whereas time and tooth and time interaction were not statistically significant. A statistically significant linear correlation was found between the L* and a* values and the acquisition angle for teeth #12 and #31, (p<0.008).

Conclusion:

The reflectance spectrophotometer provided a precise measurement of tooth color in-vivo since the systematic and random errors generated were below the threshold for perceivable color mismatches (ΔΕ<1). In rejection of the null hypotheses, the tooth type (maxillary central incisors) and variation of the acquisition angle of image capture (L* and a* parameters in teeth #12 and #31) affected the reproducibility of intraoral spectrophotometric measurements.