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Biopolymers are biodegradable and renewable and can significantly reduce environmental impacts. For this reason, biocomposites based on a plasticized starch and cross-linker matrix and with a microfibrillated OCC cardboard cellulose reinforcement were developed. Biocomposites were prepared by suspension casting with varied amounts of microfibrillated cellulose: 0, 4, 8, and 12 wt%. Polyethylene glycol diglycidyl ether (PEGDE) was used as a cross-linking, water-soluble, and non-toxic agent. Microfibrillated cellulose (MFC) from OCC cardboard showed appropriate properties and potential for good performance as a reinforcement. In general, microfiber incorporation and matrix cross-linking increased crystallization, reduced water adsorption, and improved the physical and tensile properties of the plasticized starch. Biocomposites cross-linked with PEGDE and reinforced with 12 wt% MFC showed the best properties. The chemical and structural changes induced by the cross-linking of starch chains and MFC reinforcement were confirmed by FTIR, NMR, and XRD. Biodegradation higher than 80% was achieved for most biocomposites in 15 days of laboratory compost. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the optical properties and the relative translucency parameter of Ceramill ZI White (3Y‐TZP) and Ceramill Zolid FX White (5Y‐PSZ) zirconia ceramic systems and compare them with those of the bovine dentin and enamel/dentin structures. Materials and Methods: 3Y‐TZP and 5Y‐PSZ zirconia ceramic systems were evaluated. A 0.5‐mm‐thick 3Y‐TZP (3Y‐NC.5), 0.5‐mm‐thick (5Y‐NC.5), and 1.4‐mm‐thick (5Y‐C.14) were used. A 0.5‐mm‐thick dentin specimens and 1.4‐mm‐thick enamel/dentin specimens (n = 5) were obtained from anterior bovine maxillary teeth. Scattering, absorption, transmittance, and albedo coefficient were calculated using Kubelka–Munk's model. Data were statistically analyzed using Kruskal–Wallis and Mann–Whitney tests (p < 0.001), and goodness‐of‐fit coefficient (GFC). Relative translucency parameter differences were evaluated using translucency thresholds. Results: Reflectance, scattering, absorption, and transmittance properties were wavelength dependent. Good matches (GFC ≥ 0.999) in spectral reflectance were observed between 0.5‐mm‐thick dentin and 1.4‐mm‐thick enamel/dentin, and 3Y‐NC.5 and 5Y‐NC.5. Scattering was the main optical extinction process during light interaction with zirconia and dental structures, as indicated by albedo coefficient. Translucency differences were acceptable only for 3Y‐NC.5 and the dentin structure, and 5Y‐C.14 and the enamel/dentin structure. Conclusions: Optical properties of 3Y‐TZP and 5Y‐PSZ dental zirconia differed from each other and from bovine dental structures. Nevertheless, 3Y‐TZP showed similar relative translucency parameter to bovine dentin. Clinical Significance: To achieve the best esthetic results in restorative dentistry, it is crucial for clinicians to know about the optical properties of 3Y‐TZP and 5Y‐PSZ and to be able to compare these properties with those of dental structures. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate gingiva‐colored resin‐based composites' (GCRBC) color stability and degree of conversion (DC%). Methods: Eight discs (8 × 1 mm) of 20 shades of GCRBC were prepared. Color coordinates were measured against a gray background with a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry at baseline and after 30 days of storage in distilled water, coffee, and red wine. Color differences (∆E00) between final and baseline conditions were calculated. An ATR‐FTIR spectrometer with a diamond tip was used to calculate DC%. The results were analyzed statistically using ANOVA and Tukey post‐hoc test. The level of significance was p < 0.05. Results: DC% and color stability correlated with each other and with the GCRBC brand. DC% ranged between 43% and 96%, highest values correspond to flowable composites. All composites have experienced color changes after immersion in water, wine and coffee. However, the magnitude of the color change has varied widely depending on the immersion medium and the GCRBC. Color changes generated by the wine were, globally, greater than those induced by coffee (p < 0.001) and above the acceptability thresholds. Conclusions: The DC% of GCRBCs is sufficient to achieve adequate biocompatibility and physicomechanical properties, but the high susceptibility to staining could compromise aesthetic long‐term results. Clinical Significance: The degree of conversion and the color stability of gingiva‐colored resin‐based composites correlated with each other. All composites have experienced color changes after immersion in water, wine and coffee. Color changes generated by wine were, globally, greater than those induced by coffee and above the acceptability thresholds that could compromise aesthetic long‐term results. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate the effect of thickness on color and translucency of a multi‐color polymer‐infiltrated ceramic‐network (PICN) material. Methods: Specimens of 0.5, 1.0, 1.5 mm thicknesses were obtained by sectioning VITA ENAMIC® multiColor (E‐MC) High Translucent CAD‐CAM blocks (1M1‐HT, 1M2‐HT, 2M2‐HT, 3M2‐HT, and 4M2‐HT). Spectral reflectance and color coordinates were measured on white and black backgrounds using a spectroradiometer, CIE D65 illuminant and CIE 45°/0° geometry. CIEDE2000 color and translucency differences (ΔE00 and ΔTP00) between thicknesses and adjacent layers were evaluated using their respective 50:50% perceptibility and acceptability thresholds (PT00 and AT00). Results: In general, ΔE00 between thicknesses for all shades and layers were above AT00 in general. Chroma decreased from cervical to incisal layers with statistically significant differences (p < 0.05), and ΔE00 between sequential layers were above PT00, for all shades and thicknesses. TP00 decreased from 0.5 to 1.5 mm and increased from cervical to incisal layers for all shades with statically significant translucency differences (p < 0.05). In general, for all thicknesses, TPT00 < ΔTP00 < TAT00 for sequential layers. Conclusions: The gradient in color and translucency of E‐MC PICN material was influenced by the thickness of the CAD‐CAM block. In addition, color and TP transition values between the layers depends on the thickness and shade. Clinical significance: The effect of thickness must be taken into account by dental technicians and dentists when CAD‐CAM multicolor PICN materials are used. [ABSTRACT FROM AUTHOR]

Transparent conductive electrodes have become essential components of numerous optoelectronic devices. However, their optical properties are typically characterized by the direct transmittance achieved by making use of spectrophotometers, avoiding an in-depth knowledge of the processes involved in radiation attenuation. A different procedure based on the Double Integration Sphere combined with the numerical Inverse Adding-Doubling (IAD) method is employed in this work to provide a comprehensive description of the physical processes limiting the light transmittance in commercial indium tin oxide (ITO) deposited on flexible PET samples, highlighting the noticeable contribution of light scattering on the total extinction of radiation. Moreover, harnessing their flexibility, the samples were subjected to different mechanical stresses to assess their impact on the material's optical and electrical properties. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate color inconstancy of dental ceramics under the white light-emitting diode illuminants recently proposed by the CIE. From spectral reflectance factors of 18 dental ceramics (VST, NSP, and IEC; shades A1, A2, A3, A3.5, B2, and C2), the corresponding colors under illuminant D65 and CIE 1931 Standard Colorimetric Observer were computed for all samples, using the chromatic adaptation transform CIECAT16. CIEDE2000 color differences between dental ceramics illuminated by CIE D65 standard illuminant and different white LED illuminants were calculated. Perceptibility and acceptability thresholds (PT00 and AP00) in dental ceramics were used to analyze color changes. Color gamut size was within the same range for all illuminants and for all ceramics, since MCDM computed values were 4.1–4.4 for VST, 4.0–4.2 for NSP, and 4.3–4.6 for IEC. For all ceramics and shades, the color inconstancies were higher than 50:50% PT00 and, in general, lower than 50:50% AT00. The effect of CIE-proposed LED illuminants on dental ceramic is perceptible and slightly lower than on natural teeth. Dental clinicians should consider these lighting effects on the visual appearance of dental ceramics. [ABSTRACT FROM AUTHOR]

Usually, dentin and enamel shades are layered in dental restorations with the purpose of mimicking the natural appearance of teeth. The main objective of this study was to develop and assess accuracy of a color-prediction method for both monolithic and layered dental resin-based composites with varying shades and under different illuminants. A total of 15 different shades of VITAPAN Excell, VITAPAN Dentine and VITA Physiodens as well as VITA Enamel of five different thicknesses (0.5–2.5 mm range) were used to manufacture monolithic and layered samples. A non-contact spectroradiometer with CIE 45 ∘ / 0 ∘ geometry was used to measure the color of all samples over a standard ceramic black background. Second-degree polynomial regression was used as predictive method for CIE-L*a*b* color coordinates. Performance of predictive models was tested using the CIEDE2000 total color difference formula ( Δ E 00 ), while accuracy was evaluated by comparative assessment of Δ E 00 with corresponding 50:50% acceptability ( A T 00 ) and perceptibly ( P T 00 ) thresholds for dentistry. A mean color difference between measured (real) and predicted color of Δ E 00 = 1.71 , with 62.86% of the color differences below A T 00 and 28.57% below P T 00 , was registered for monolithic samples. For bi-layered samples, the mean color difference was roughly Δ E 00 = 0.50 , with generally 100% and more than 85% of the estimations below A T 00 and P T 00 , respectively. The predictive method allowed highly accurate color estimations for both monolithic and layered dental resin-based composites with varying thicknesses and under different illuminations. These results could be useful to maximize the clinical success of dental restorations. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effect of layering strategy and substrate color on the masking ability of resin composites. Materials and Methods: A1‐shaded specimens from Charisma Diamond and Filtek Z350XT were produced using different layering strategies. Color measurements were made by a reflectance spectrophotometer over A2, C2, A3.5, C3, C4 substrates. Color differences were calculated and interpreted by the 50%:50% perceptibility and acceptability visual thresholds. Data was analyzed by Kruskal–Wallis and Dunn post hoc test. Chi‐square test was used to determine the association between masking ability, and independent variables. Results: Color differences were significantly lower on A2 and C2 in comparison with C4 for the majority of the layering strategies. Acceptable matches were observed on most of the combinations over A2. Moderately unacceptable mismatches were observed in most of the combinations over C2 and A3.5. Clearly unacceptable mismatches were observed on the C3 and C4. The ΔE00 color shifts were predominantly influenced by ΔL00 for all layering strategies and substrate colors. Conclusion: Masking ability was affected by the layering strategy and substrate color. Acceptable masking was associated with A2 and C2, and with layering strategy composed of 0.5 mm enamel opacity and 1.0 mm dentin opacity thicknesses, using the Filtek Z350XT. Clinical Significance: Resin composites—shade A1—applied by different layering strategies with a final thickness of 1.5 mm were able to mask mild and moderately discolored substrates. Severely discolored substrates were not masked effectively. [ABSTRACT FROM AUTHOR]

A full comprehension of colorimetric relationships within and between teeth is key for aesthetic success of a dental restoration. In this sense, hyperspectral imaging can provide point-wise reliable measurements of the tooth surface, which can serve for this purpose. The aim of this study was to use a hyperspectral imaging system for the colorimetric characterization of 4 in-vivo maxillary anterior teeth and to cross-check the results with similar studies carried out with other measuring systems in order to validate the proposed capturing protocol. Hyperspectral reflectance images (Specim IQ), of the upper central (UCI) and lateral incisors (ULI), were captured on 30 participants. CIE-L*a*b* values were calculated for the incisal (I), middle (M) and cervical (C) third of each target tooth. Δ E a b * and Δ E 00 total color differences were computed between different tooth areas and adjacent teeth, and evaluated according to the perceptibility (PT) and acceptability (AT) thresholds for dentistry. Non-perceptible color differences were found between UCIs and ULIs. Mean color differences between UCI and ULI exceeded AT ( Δ E a b * = 7.39–7.42; Δ E 00 = 5.71–5.74) in all cases. Large chromatic variations between I, M and C areas of the same tooth were registered ( Δ E a b * = 5.01–6.07 and Δ E 00 = 4.07–5.03; Δ E a b * = 5.80–8.16 and Δ E 00 = 4.37–5.15; and Δ E a b * = 5.42–5.92 and Δ E 00 = 3.87–4.16 between C and M, C and I and M and I, respectively). The use of a hyperspectral camera has proven to be a reliable and effective method for color evaluation of in-vivo natural teeth. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The most recent generation of bioengineered human skin allows for the efficient treatment of patients with severe skin defects. Despite UV sunlight can seriously affect human skin, the optical behavior in the UV range of skin models is still unexplored. In the present study, absorbance and transmittance of the UGRSKIN bioartificial skin substitute generated with human skin cells combined with fibrin-agarose biomaterials were evaluated for: UV-C (200–280 nm), -B (280–315 nm), and -A (315–400 nm) spectral range after 7, 14, 21 and 28 days of ex vivo development. The epidermis of the bioartificial skin substitute was able to mature and differentiate in a time-dependent manner, expressing relevant molecules able to absorb most of the incoming UV radiation. Absorbance spectral behavior of the skin substitutes showed similar patterns to control native skin (VAF > 99.4%), with values 0.85–0.90 times lower than control values at 7 and 14- days and 1.05–1.10 times the control values at 21- and 28-days. UV absorbance increased, and UV transmission decreased with culture time, and comparable results to the control were found at 21 and 28 days. These findings support the use of samples corresponding to 21 or 28 days of development for clinical purposes due to their higher histological similarities with native skin, but also because of their absorbance of UV radiation. [ABSTRACT FROM AUTHOR]

Dental materials are mainly tested in vitro, so laboratory conditions must reproduce the oral environment to ensure the validity of their results. This study aimed to evaluate the influence of backgrounds on the color of gingiva-colored resin-based composites (GCRBC). Three discs of each of 20 shades of GCRBCs and each thickness (1 and 2 mm) were prepared. Diffuse reflectance was measured on-air and over three natural teeth (0M3/B1, 3M3/B3, and 5M3/B4 shades of Vita 3D Master/Vita Classical guides, respectively) using a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry. CIEDE2000 color difference formula and its 50:50% perceptibility and acceptability thresholds have been used to calculate and interpret the results. It can be stated that the background influences the color of all GCRBCs tested, although the effect is more pronounced for 1 mm thick samples. L*, a* and b* coordinates values of GCRBCs on air were significantly different from those obtained on natural teeth backgrounds, and the total color differences were greater than the acceptability thresholds. Since GCRBCs are placed on a dental substrate in clinical conditions, it is not advisable to perform color measurements of GCRBCs on-air because of the high color differences found. This recommendation is especially relevant for thin specimens. [ABSTRACT FROM AUTHOR]

Objective: Evaluate the effectiveness and color stability of bleaching techniques on blood‐stained teeth. Material and Methods: The teeth were stained by blood and allocated to groups: walking bleach, inside/outside, and in‐office bleaching. L*, a*, b*, C*, h° color coordinates were measured using a clinical spectrophotometer at baseline, weekly (T1‐T2‐T3), and at 1‐week (T4), 6‐months (T5), and 1‐year (T6) follow‐up evaluations. ΔEab*, ΔE00, and ΔWID were calculated between sequential evaluation timepoints and between baseline and each evaluation timepoint. Color coordinates and WID differences in each timepoint and technique were analyzed by Wilcoxon Signed Rank, Kruskal‐Wallis and Mann–Whitney U test, respectively. ΔEab*, ΔE00, and ΔWID were interpreted by color visual thresholds. Results: The techniques presented a significant increase in L* and WID and, a significant decrease in a* and b* until the completion of treatments. Statistical differences between the techniques for a*, b* and WID were observed from T1 until T3. All techniques demonstrated excellent effectiveness for ΔEab*, ΔE00, and ΔWID between baseline and each evaluation and follow‐up timepoints. However, at T6, it was possible to identify a rebound effect for all techniques. Conclusions: All bleaching techniques presented excellent effectiveness. The stability of the whitening produced was maintained for 6 months. Clinical Significance: Effective whitening of blood‐stained teeth was achieved using walking bleach (sodium perborate), inside/outside (hydrogen peroxide ‐ 7.5%) and in‐office techniques (hydrogen peroxide ‐ 35%). The bleaching techniques were effective after the completion of the treatments. A slight rebound was observed at 1 year follow‐up. [ABSTRACT FROM AUTHOR]

Objective: To evaluate color, lightness, chroma, hue, and translucency adjustment potential of resin composites using CIEDE2000 color difference formula. Methods: Three resin composites (Filtek Universal, Harmonize, and Omnichroma) were tested. Two types of specimens were prepared: an outer base shade with an inner hole filled with test shades and single‐composite specimens of all shades. Spectrorradiometric reflectances measurements and subsequent CIELAB color coordinates and translucency parameter (TP) were performed. Color (CAP00), lightness, chroma, hue, and translucency (TAP00) adjustment potential using CIEDE2000 color difference were computed. Color and transparency differences among composite materials and shades were statistically tested (P < 0.05). Results: Positive CAP00 and TAP00 values were found for majority of tested materials. CAP00 values ranged from −0.14 to 0.89, with the highest values found for Omnichroma (>0.75 in all cases). TAP00 values ranged from −0.06 to 0.86 with significant translucency differences among dual and single specimens. Omnichroma exhibited the highest adjustment potential for all color dimensions studied. Conclusions: Lightness, hue, chroma, and translucency adjustment potential have been introduced using CIEDE2000 color difference formula, and have shown their usefulness to evaluate blending effect in dentistry. Color coordinates and translucency adjustment potential were dependent on dental material. Omnichroma exhibited the most pronounced blending effect. Clinical significance: Resin composites with increased color and translucency adjustment may simplify shade selection, making this process easier and less time consuming. Furthermore, these materials might facilitate challenging and complex color matching situations. [ABSTRACT FROM AUTHOR]

Objective: Evaluate the masking ability of bleach‐shade resin composites applied by multilayering techniques over colored substrates. Materials and methods: Disc‐shaped specimens were fabricated from bleach‐shade resin composites using different multilayering techniques. Substrates were produced in opaque ceramic discs simulating colored substrates (A2, A3, A3.5, C2, C3, C4) and a bleached tooth (0M1). Color coordinates were obtained using a reflectance spectrophotometer. Color difference was calculated by CIEDE2000 using coordinates of 0 M1 ceramic as standard reference. Data were analyzed by one‐way ANOVA and Tukey's post‐hoc test (p ≤ 0.05). Masking ability interpretation was based on perceptibility and acceptability thresholds. Results: All combinations presented ΔE00 above the acceptable threshold (ΔE00>1.8), ranging from 2.49 to 7.42, regardless of the restorative system, multilayering strategy or substrate color. Multilayering combinations placed over A2, A3 and A3.5 were moderately (1.8<ΔE00≤3.6) and clearly unacceptable (3.6<ΔE00≤5.4), combinations associated with C2, C3 and C4 were clearly unacceptable and, extremely unacceptable (ΔE00>5.4). Lower ΔE00 was observed for combinations with 0.5 mm extra white enamel layer (2.49), or 1.0 mm white dentin layer (2.69), over A2 and A3.5 substrates. Lightness difference showed the greatest contribution to ΔE00. Conclusions: Bleach‐shade resin composite systems applied by the multilayering technique were not able to ensure effective masking ability. Clinical significance: Bleach‐shade resin composites applied with different combinations of the multilayering technique were not effective in masking colored substrates. Alternative strategies, techniques and dental materials should be explored to obtain acceptable masking. [ABSTRACT FROM AUTHOR]

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Abstract Objective To determine the visual whiteness thresholds for esthetic dentistry using the whiteness index for dentistry based on CIELAB color space (WI D). Methods A total of 60 observers (Dentists and Laypersons; n = 30) from three research sites participated in the study. A psychophysical experiment based on visual assessments of simulated images of teeth on a calibrated display was performed. Images of simulated upper central incisors (SUCI) were consecutively displayed in pairs (60) and the whiteness of each SUCI pair was compared. WI D was used to calculate the visual thresholds (WPT- perceptibility threshold; and WAT- acceptability threshold) with 95% confidence intervals (CI) and a Takagi-Sugeno-Kang (TSK) Fuzzy Approximation model was used as fitting procedure. Data was statistical analyzed using paired t -test (α = 0.05). Results WPT and WAT were 0.72 (CI: 0.0–2.69; r2 = 0.52) and 2.62 (CI: 0.2-7+; r2 = 0.57) WI D units, respectively. Significant differences (p < 0.05) were found between WPT and WAT, and between dentist (WPT = 0.46WI D units; WAT = 2.20 WI D units) and layperson (WPT = 0.94 WI D units; WAT = 2.95 WI D units). Significance The visual whiteness difference thresholds determined with WI D index can serve as reference values for research and manufacturing of dental materials, and for clinical practice situations such as assessing the effectiveness of bleaching treatments. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

To evaluate the influence of printing orientation on color and translucency of 3D printing restorative resins. Four 3D printing resin systems in the available shades (DFT-Detax Freeprint Temp- A1, A2,A3; FP-Formlabs Permanent Crown- A2,A3,B1,C2; FT- Formlabs Temporary CB- A2,A3,B1,C2; GCT-GC Temporary- Light, Medium) were evaluated. Three samples (10×10×1.2 mm) from each material were printed at two different printing orientations (0° and 90°) and polished to 1.00 ± 0,01 mm of thickness. Spectral reflectance was measured against black background using a calibrated spectroradiometer, CIE D65 standard illuminant and the 45°/0°geometry. Color and translucency differences were evaluated using CIEDE2000 metric (ΔE 00) and 50:50% perceptibility (PT 00 and TPT 00) and acceptability (AT 00 and TAT 00) thresholds. In general, color changes due to printing orientation at (0° and 90°) were mainly produced by ΔL* or ΔC*. ΔE 00 were above PT 00 for all DFT shades, FP-B1, FP-C2, FT-A2 and FT-B1. Only for DFT-1, ΔE 00 was above AT 00. ΔRTP 00 values were above TPT 00 for DFT-A1, DFT-A3, FP-B1 and FT-B1, but lower than TAT 00. The direction of the changes in translucency (ΔRTP 00) depends on the material and shade. The selection of building orientation (0° and 90°) for the 3D printed resins influence the visual color and translucency and therefore their esthetic appearance. These aspects should be considered when printing dental restorations using the evaluated materials. • Color and translucency of 3D printing resins is affected by printing orientation. • Differences in color (ΔE 00) and translucency (ΔRTP 00) may result visually perceptible. • Color differences are manly determined by lightness and chroma differences. • The direction of translucency differences depends on the material and shade. [ABSTRACT FROM AUTHOR]

• One-shaded resin-based composites show lower spectral scattering and absorbance than the group-shaded resin-based composite. • One-shaded resin-based composites present higher spectral transmittance than the group-shaded resin-based composite. • One-shaded resin-based composites are more translucent than the group-shaded resin-based composite. • Value of opalescence parameter and the effect of thickness on opalescence are material-dependents. To evaluate optical properties, and translucency and opalescence parameters of one-shaded resin-based composites. Three one-shaded resin composites (OM — Omnichroma; VP — Venus Pearl; and VD — Venus Diamond) and a group-shaded resin composite (FU- Filtek Universal A2) were used. Three composite discs from each material were fabricated for each of the following thickness: 0.5, 1.0 and 2.0 mm. Diffuse reflectance was measured against white and black backgrounds using a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry. Translucency parameter (TP) was calculated using Δ E a b * and Δ E 00. Scattering (S) and absorption (K) coefficients and transmittance (T%) were calculated using Kubelka–Munk's equations, and a reflection spectrophotometer was used to measure the opalescence parameter (OP). Data was statistically analyzed using Kruskal–Wallis, Mann–Whitney tests, and VAF coefficient. Spectral distributions of S, K and T were wavelength dependent, showing significant differences between materials of the same thickness and for different thicknesses of the same material (p < 0.001). OM showed the greatest translucency values for all thicknesses. Translucency decreased as thickness increased with statistically significant differences (p < 0.005). Values of ΔTP ab and ΔTP 00 between thicknesses were above of translucency thresholds for all materials. VP and VD showed the lowest OP values. One-shaded resin-based composites showed different optical behavior than the group-shaded resin-based composite. Understanding the optical behavior of the one-shaded resin-based composites is essential to optimize their clinical performance. [ABSTRACT FROM AUTHOR]

• Modern LED sources produce changes in color and whiteness of natural teeth. • Some LED illuminants recommended by CIE generate perceptible color shifts. • LED illuminants produce color shifts in very different directions of color space. • Color differences for pairs of teeth are almost independent of illuminants. • Whiteness differences for pairs of teeth are almost independent of illuminants. To evaluate color and whiteness changes of natural teeth under nine white LED illuminants recently proposed by CIE. From spectral reflectance factors of 36 caries-free upper central incisors, corresponding colors under illuminant D65 and CIE 1931 standard colorimetric observer were computed for all tested illuminants, using the chromatic adaptation transform CAT16. Color differences (CIELAB and CIEDE2000 units) and whiteness (W I D and W I O indices) from teeth illuminated by CIE standard illuminants (D65 and A) and white LED illuminants were calculated. The appearance of 630 pairs of teeth under all illuminants was also evaluated. Color gamuts from 36 teeth under tested illuminants showed similar volume and shape in CIELAB color space, but their centers of gravity changed in many different directions with respect to colors under D65 or A illuminants: Considering colors under D65/A, color shifts produced by white LED illuminants were in the ranges 2.0–8.6/1.1–7.0 CIELAB units (1.4–8.2/0.6–6.8 CIEDE2000 units). Average W I D and W I O values for the 36 teeth under different illuminants ranged from −5.8 to +19.3 and from −7.7 to +11.1, respectively. Considering 630 pairs of teeth, average color differences (mainly lightness differences) were below 0.5 CIELAB units (0.3 CIEDE2000 units), and average whiteness differences ranged from 8.1 to 10.7 for W I D (23.4–25.1 for W I O). Using CIE LED illuminants, most changes in color and whiteness for individual teeth were above typical threshold values of perceptibility and acceptability in dentistry. However, considering pairs of teeth, the average color and whiteness differences under all tested illuminants were very similar. [ABSTRACT FROM AUTHOR]

• Exist perceptible differences in color and translucency among layers of material. • Luminosity and saturation values decreases towards the incisal layer for all shades. • Translucency increases from cervical to incisal layers for all shades evaluated. • Shade of underlying tissues should be considered when selecting this material. To evaluate color, translucency parameter and optical properties (scattering (S), absorption (K) and transmittance (T)) of a multi-color polymer-infiltrated ceramic-network (PICN) material. Samples of shades 1M1-HT, 1M2-HT, 2M2-HT, 3M2-HT, and 4M2-HT from VITA ENAMIC® multiColor (E-MC) High Translucent were fabricated (n = 3). CAD-CAM blocks were cut and polished to 1.00 ± 0.01 mm of thickness. Diffuse reflectance and color coordinates were measured against white and black backgrounds, using a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry. Color and translucency differences were evaluated using 50:50% perceptibility (PT and TPT) and 50:50% acceptability (AT and TAT) thresholds. S and K coefficients and T were calculated using Kubelka–Munk's equations. Data was statistically analyzed using Kruskal–Wallis, Mann–Whitney tests, and VAF coefficient. Mean C* and b* values increased from incisal to cervical layers with statistically significant differences (p < 0.05). In general, ΔE 00 between sequential layers were above PT for all shades. In addition, translucency parameter (TP) increased from cervical to incisal and ΔTP 00 values were greater than TPT 00 and lower than TAT 00 between all sequential layers. Layers from all shades showed similar spectral behavior for S (97.4% ≤ VAF), K (85.0% ≤ VAF) coefficients and T (95.3% ≤ VAF). However, these values presented significant differences (p < 0.05) from cervical to incisal layers. The gradient in color and translucency of this novel CAD-CAM multi-color PICN material can assist dental technicians and dentists to reach greater esthetics than the pre-existing CAD-CAM monolithicmaterials. [ABSTRACT FROM AUTHOR]

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, ParadigmTM C, and VITABLOCS® Mark II) and polished to 1.0 ± 0.01 mm 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, Tukey's test with Bonferroni correction (α = 0.001). All colour differences (ΔE* ab and ΔE00) were analyzed through comparisons with the PT - perceptibility and AT - acceptability thresholds for dental ceramics. Results: DE between ceramic systems and its corresponding shade ranged from 6.32 to 13.42 (ΔE* ab) and 4.48 to 9.30 (ΔE00). DE 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 (ΔE* ab); 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. [ABSTRACT FROM AUTHOR]

Objective: To determine the visual 50:50% perceptibility and acceptability CIEDE2000 lightness, chroma and hue human gingiva thresholds., Methods: A psychophysical experiment based on visual assessments of simulated images of human gingiva on a calibrated display was performed. A 20-obsever panel (dentists and laypersons; n=10) evaluated three subsets of simulated human gingiva: lightness subset (|ΔL ' /ΔE 00 |≥ 0.98); chroma subset (|ΔC ' /ΔE 00 |≥ 0.98) and hue subset (|ΔH ' /ΔE 00 |≥ 0.96) using ΔE 00 < 5 units. A Takagi-Sugeno-Kang (TSK) Fuzzy Approximation model was used as fitting procedure, and 50:50% perceptibility threshold (PT) and acceptability threshold (AT) were calculated. Data was statistically analyzed using t-test (p ≤ 0.05)., Results: The 50:50% PT were ΔL' = 0.74 (95% confidence interval (CI) 0.39-1.09); ΔC' = 1.10 (95% CI 0.57-1.46); ΔH' = 2.40 (95% CI 1.66->3.85). The 50:50% AT were ΔL' = 2.57 (95% CI 2.00-3.06); ΔC' = 2.70 (95% CI 2.19-3.38). AT ΔH' may be considered no computable. PT values were statistically significant among the three metric differences (p ≤ 0.05). No difference was found between observers for PT values., Conclusions: Statistically differences in perceptual limit were found among hue, lightness and chroma for human gingiva. Thus, the observers seem to show lower sensitivity for changes in hue (ΔH ' ) than in chroma (ΔC ' ) and in lightness (ΔL ' ) in the gingiva color space., Clinical Significance: PT and AT for lightness, chroma and hue specific for human gingiva should be used when evaluating natural gingiva, pink gingival shade guides or pink materials, since the thresholds of perception and acceptability for teeth are not suitable., (Copyright © 2022. Published by Elsevier Ltd.)

Objective: To evaluate the influence of neutral color backgrounds on the perception of color differences in dentistry., Methods: A software was developed for this study that calculated the perceptibility (PT) and acceptability (AT) thresholds of color differences between a pair of computer-simulated incisor samples (n = 60 pairs) over three neutral color (white, gray and black) backgrounds. CIELAB and CIEDE2000 color difference formulas were used. Five groups of volunteer observers (N = 100) participated in the psychophysical experiment (n = 20): Dentists; Dental students; Dental auxiliaries; Dental technicians; and Laypersons. The psychophysical experiment was performed in a dark environment on a calibrated high-resolution screen. To determine PT and AT values, the 60 pairs of samples were randomly presented to each observer over the different backgrounds. The data were adjusted (TSK Fuzzy) and analyzed statistically using Student t-test and ANOVA (α = 0.05)., Results: Regardless of the metric and the background used, the PT values showed no difference among different observers (p > 0.05). Dentists showed the lowest PT values. Dental technicians showed the lowest AT (p ≤ 0.05) and similar values for the three backgrounds (p > 0.05), regardless of the metric used. The other groups of observers showed the lowest and the highest AT values when using black and white backgrounds, respectively (p ≤ 0.05)., Conclusions: The lowest AT values using a black background indicates that the use of this background allows for the evaluation of slight color differences, and should be used for challenging color differences in esthetic dentistry. This study showed the influence of the observer experience on color evaluation in dentistry., Clinical Significance: There was no influence of the background color on the perceptibility threshold. However, dentists and dental technicians showed greater ability to perceive slight color differences compared to other groups of observers., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Objective: To evaluate the influence of neutral color backgrounds on visual thresholds using three color difference metrics: CIELAB, CIEDE2000(1:1:1) and CIEDE2000(2:1:1)., Methods: Sixty observers (dentists and laypersons; n = 30) from three countries participated in the study. A psychophysical experiment based on visual assessments of simulated images of teeth on a calibrated display was performed. Images of simulated upper central incisors (SUCI) were consecutively displayed in pairs (60) on 3 neutral color backgrounds (black, grey and white). Three color difference metrics (CIELAB, CIEDE2000(1:1:1), and CIEDE2000(2:1:1)) were used to calculate the visual thresholds (PT- perceptibility threshold; and AT- acceptability threshold) with 95 % confidence intervals (CI) and a Takagi-Sugeno-Kang (TSK) Fuzzy Approximation model was used as fitting procedure. Data was statistically analyzed using paired t-test (p = 0.05)., Results: The50:50 % PT values were significantly lower over white background than over black background. The 50:50 % AT values were significantly greater over white background than over grey and black backgrounds. In most cases, the thresholds (PT and AT) values were significantly different for each color different metric over each background color (p ≤ 0.05). No difference was found between observers for PT and AT values., Conclusions: The perceptibility and acceptability thresholds in dentistry are affected by the color difference metrics and by the background color., Significance: Dental color mismatches are more difficult to be accepted over a white background., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Objective: To determine the translucency acceptability and perceptibility thresholds for dental resin composites using CIEDE2000 and CIELAB color difference formulas., Methods: A 30-observer panel performed perceptibility and acceptability judgments on 50 pairs of resin composites discs (diameter: 10mm; thickness: 1mm). Disc pair differences for the Translucency Parameter (ΔTP) were calculated using both color difference formulas (ΔTP 00 ranged from 0.11 to 7.98, and ΔTP ab ranged from 0.01 to 12.79). A Takagi-Sugeno-Kang (TSK) Fuzzy Approximation was used as fitting procedure. From the resultant fitting curves, the 95% confidence intervals were estimated and the 50:50% translucency perceptibility and acceptability thresholds (TPT and TAT) were calculated. Differences between thresholds were statistically analyzed using Student t tests (α=0.05)., Results: CIEDE2000 50:50% TPT was 0.62 and TAT was 2.62. Corresponding CIELAB values were 1.33 and 4.43, respectively. Translucency perceptibility and acceptability thresholds were significantly different using both color difference formulas (p=0.01 for TPT and p=0.005 for TAT). CIEDE2000 color difference formula provided a better data fit than CIELAB formula., Significance: The visual translucency difference thresholds determined with CIEDE2000 color difference formula can serve as reference values in the selection of resin composites and evaluation of its clinical performance., (Copyright © 2018 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.)

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, Tukey's 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., (Copyright © 2015 Elsevier Ltd. All rights reserved.)