Effectiveness and one-year whiteness stability of different in-office bleaching agents and alternative protocols.

STATEMENT OF PROBLEM: In-office bleaching has been widely researched. However, few studies have evaluated alternative protocols for this procedure. Moreover, information on the long-term stability of in-office whitening is limited. PURPOSE: The purpose of this in vitro study was to evaluate the effectiveness and 1-year stability of in-office bleaching with 35% hydrogen peroxide (35%HP) and 37% carbamide peroxide (37%CP) using traditional and alternative protocols. MATERIAL AND METHODS: Forty human third molars were stained with tea and allocated to groups (n=10). Traditional protocols consisted of 3 applications of 35%HP for 15 minutes and 1 application of 37%CP for 45 minutes. Alternative protocols consisted of 1 application of 35%HP for 45 minutes and 3 applications of 37%CP for 45 minutes. Protocols were applied for 3 weeks. CIELab color coordinates were measured at baseline and weekly during treatment and at 1-week, 6-month, and 1-year follow-ups. Effectiveness and stability of the bleaching treatments were interpreted using 50:50% perceptibility and acceptability thresholds. CIELab, chroma, hue angle, and whiteness index were analyzed using the Wilcoxon signed-rank test (α=.05). RESULTS: All protocols showed improvement in bleaching after the first week (P≤.005). All bleaching procedures presented excellent whitening outcomes. Alternative protocols showed a larger rebound effect after 1 year, indicating less stability. For the whiteness index, no differences between the completion of the treatments and 1-year follow-up was found for the bleaching treatments and protocols (P>.05), except for the 37%CP alternative protocol (P=.005). CONCLUSIONS: All tested protocols presented excellent effectiveness in bleaching. Traditional protocols exhibited a greater whiteness stability, while the alternative protocols showed a greater rebound effect after 1 year.

Optical properties of dental zirconia, bovine dentin, and enamel-dentin structures.

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.

Effect of layering strategy and prolonged water aging on masking ability of composite resins.

STATEMENT OF PROBLEM: Layered composite resins may adequately mask discolored substrates. However, whether color changes that occur over time affect masking ability is unclear. PURPOSE: The purpose of this in vitro study was to investigate the effect of layering and water aging on the masking ability of 2 composite resins. MATERIAL AND METHODS: Disk specimens (1.5 mm-thick and shade A1) from Charisma Diamond (CD) and Filtek Z350XT (Z350) were made according to the composite resin shade combination used in the layering strategies: bilayer for CD (enamel/dentin) and for Z350 (enamel/body and enamel/dentin) and trilayer for Z350 (enamel/body/dentin) (n=5). Color measurements were obtained with a spectrophotometer over an A3.5 ceramic substrate, and the whiteness index for dentistry (WID) was calculated. The specimens were aged in water at 37 °C and evaluated at different times: 24 hours, 1 week, 1 month, 2 months, 6 months, 12 months, 18 months, and 24 months. CIEDE2000 color differences (ΔE00) and WID differences (ΔWID) were calculated and interpreted by 50:50% color and whiteness perceptibility and acceptability thresholds. Changes among strategies and aging times were analyzed using the Kruskal-Wallis test (α=.05). Contrasts were made using the Mann-Whitney U test with Bonferroni correction (α=.001). RESULTS: ΔE00 decreased from 24 hours to 2 months of aging. From 2 months onwards, ΔE00 increased for all layering strategies and times, without significant changes in lightness for CD (P>.004). Overall, for the CD restorative system, an increase in ΔWID was observed after 1 month of aging (P<.001), while for the Z350 restorative system, ΔWID decreased after aging (P<.001), except for the Z350 bilayer strategy (enamel + dentin) at 1 week and 2 months (P>.004). For all layering strategies and aging times, color differences were higher than the 50:50% perceptibility threshold for ΔE00 and, after 6 months, higher than the 50:50% acceptability threshold for ΔE00 and the 50:50% whiteness acceptability threshold. CONCLUSIONS: The ability of the tested composite resins to mask a discolored substrate was affected by the layering approach applied and by prolonged water aging.

Color stability and degree of conversion of gingiva-colored resin-based composites.

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 ( ∆ E 00 ) 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.

Color and Translucency Variation of a One-Shaded Resin-Based Composite after Repeated Heating Cycles and Staining.

(1) Background: This study aimed to determine the effect of repeated pre-polymerization heating on the color and translucency of a one-shaded resin-based composite and to evaluate whether the heating cycles affect its color stability. (2) Methods: Fifty-six samples of 1-mm thickness were fabricated from Omnichroma (OM) after applying different heating cycles (for one, five, and ten times at 45 °C) before polymerization (n = 14/group) and afterwards were stained with a yellow dye solution. CIE L*, a*, b*, C*, h° coordinates were recorded, and color differences, whiteness, and translucency were calculated, before and after staining. (3) Results: Heating cycles significantly influenced the color coordinates, WID00, and TP00 of OM being higher after one heating cycle and decreasing as the number of heating cycles increased. The color coordinates, WID, and TP00 after staining significantly differed for each group. The color and whiteness differences calculated after staining exceeded the acceptability thresholds for all groups. The color and whiteness variations after staining were clinically unacceptable. (4) Conclusions: Repeated pre-polymerization heating induces a clinically acceptable color and translucency change to OM. Although the color changes resulting after staining are clinically unacceptable, increasing the number of heating cycles up to ten times slightly reduces the color differences.

Development of Thickness-Dependent Predictive Methods for the Estimation of the CIEL*a*b* Color Coordinates of Monolithic and Layered Dental Resin Composites.

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 (ΔE00), while accuracy was evaluated by comparative assessment of ΔE00 with corresponding 50:50% acceptability (AT00) and perceptibly (PT00) thresholds for dentistry. A mean color difference between measured (real) and predicted color of ΔE00=1.71, with 62.86% of the color differences below AT00 and 28.57% below PT00, was registered for monolithic samples. For bi-layered samples, the mean color difference was roughly ΔE00=0.50, with generally 100% and more than 85% of the estimations below AT00 and PT00, 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.

Effect of thickness on color and translucency of a multi-color polymer-infiltrated ceramic-network material.

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.

Validation of a Hyperspectral Imaging System for Color Measurement of In-Vivo Dental Structures.

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. ΔEab* and ΔE00 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 (ΔEab* = 7.39-7.42; ΔE00 = 5.71-5.74) in all cases. Large chromatic variations between I, M and C areas of the same tooth were registered (ΔEab* = 5.01-6.07 and ΔE00 = 4.07-5.03; ΔEab* = 5.80-8.16 and ΔE00 = 4.37-5.15; and ΔEab* = 5.42-5.92 and ΔE00 = 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.

Relevant optical properties for gingiva-colored resin-based composites.

OBJECTIVES: To evaluate the optical properties of gingiva-colored resin-based composites (GCRBCs). METHODS: Five discs (8 mm diameter x 1mm height) of 17 shades of GCRBCs were prepared. Diffuse reflectance was measured against white and black backgrounds using a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry. Relative translucency parameter was calculated using ΔE00 (RTP00). Translucency differences were evaluated using published data of 50:50% translucency perceptibility (TPT00) and acceptability (TAT00) thresholds. Scattering (S) and absorption (K) coefficients and transmittance (T%) were calculated using Kubelka-Munk's equations. Data were statistically analyzed using Kruskal-Wallis, Mann-Whitney tests, and VAF coefficient. RESULTS: The RTP00 values of the 17 evaluated shades ranged from 8.69 to 21.34. There were perceptible translucency differences (TPT00=0.62) between different shades of the same brand and between composites designated with the same shade of different brands. Spectral distributions of S, K and T were wavelength-dependent. Although the spectral behavior of the S and K coefficients and T% were similar for all the gingival composites evaluated, the values of these parameters presented statistically significant differences between shades, which would justify the differences found in the relative translucency parameter. CONCLUSIONS: The optical properties S, K and T% of GCRBCs were significantly different, resulting in perceptible translucency differences between the same shade of different commercial brands and between different shades of the same brand. CLINICAL SIGNIFICANCE: Translucency differences of gingiva-colored composites may significantly influence their masking ability affecting the clinician's choice of restorative material.

Optical Behavior of Human Skin Substitutes: Absorbance in the 200-400 nm UV Range.

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.

CIEDE2000 lightness, chroma and hue human gingiva thresholds.

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'/ΔE00|≥ 0.98); chroma subset (|ΔC'/ΔE00|≥ 0.98) and hue subset (|ΔH'/ΔE00|≥ 0.96) using ΔE00< 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.

Masking ability of resin composites: Effect of the layering strategy and substrate color.

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.

Does Backgrounds Color Influence the Appearance of Gingiva-Colored Resin-Based Composites?

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.

Visual and instrumental coverage error of two dental shade guides: an in vivo study.

OBJECTIVES: This study aims to evaluate in vivo the color agreement between natural teeth and dental shade guides by means of visual and instrumental coverage error ([Formula: see text]) index. MATERIALS AND METHODS: The color of the middle third of 735 incisors was visually determined by two evaluators using the Vita Classical (VC) and Vita 3D Master (V3DM) shade guides. The color match between the natural tooth and the shade tab was rated as poor (P), good (G), or optimum (O) by each observer. CIE color coordinates of the target teeth and shade tabs of VC and V3DM were instrumentally measured using a clinical spectrophotometer. Visual ([Formula: see text]) and instrumental ([Formula: see text]) coverage error indexes were computed using CIELAB and CIEDE2000 metrics for both shade guides. For [Formula: see text] calculation, only the concordant inter-observer determination on tooth shade rated as O-O or O-G was used. The results were evaluated using perceptibility (PT, [Formula: see text]= 1.2, [Formula: see text]= 0.8) and acceptability (AT, [Formula: see text]= 2.7, [Formula: see text]= 1.8) color thresholds for dentistry. RESULTS: VC and V3DM exhibited [Formula: see text] (2.5, 3.2, and 3.2, 2.7 CIELAB units; 1.9, 2.3, and 2.8, 2.4 CIEDE2000 units, respectively, for O-O and O-G match) and [Formula: see text] (4.7, 4.8, and 4.1, 4.6 CIELAB units; 3.3, 3.4, and 3.4, 3.6 CIEDE2000 units, respectively, for O-O and O-G match) values greater than 50:50% AT for both color difference formulas. [Formula: see text] contributes more than 50% (53.2-82.4% range) to the [Formula: see text] value. This contribution depends on the shade guide used and the quality of the visual rating. CONCLUSIONS: The evaluated shade guides exhibited visual coverage errors above acceptability thresholds, largely due to the contribution of the instrumental coverage error to the visual coverage error. CLINICAL RELEVANCE: It necessary to further improve commercially available dental shade guides to facilitate achievement of satisfactory esthetics results in clinical practice.

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.

Influence of manufacturing technique on the color of zirconia restorations: Monolithic versus layered crowns.

OBJECTIVES: The study aimed to compare the color of monolithic and layered zirconia crowns fabricated using different brands in the cervical, middle, and incisal areas. MATERIALS AND METHODS: A total of 45 crowns were fabricated from three brands (Katana, Nacera, Cercon) using three methods (monolithic = ML (n=5), cut-back + enamel = BL (n=5), cut-back + dentin + enamel = TL (n=5)). CIE L*, a* b*, C*, h° color coordinates were recorded with a dental spectrophotometer in cervical, middle, and incisal areas. Color differences between manufacturing techniques, tooth areas, and brands were calculated using the CIEDE2000(1:1:1) formula, and the values were compared to the perceptibility (PT00 ) and acceptability thresholds (AT00 ). Comparisons between color coordinates were analyzed statistically (Kruskal-Wallis and Mann-Whitney U tests, p < 0.001). RESULTS: Significant differences were found between CIE L*, a*, b*, C*, h° coordinates of the zirconia crowns (p < 0.001), generally. The lowest color differences were obtained between BL and TL crowns in cervical and middle areas. Color differences between cervical and middle areas were mostly below PT00 . An acceptable color difference was found between Katana and Cercon crowns. CONCLUSIONS: The manufacturing technique and the brand influenced the color of zirconia crowns. Also, the color of the crowns varied from cervical to incisal. CLINICAL SIGNIFICANCE: Reproducing the optical properties of teeth with ceramic crowns might be challenging, given the differences in the internal configuration of the enamel and dentine, as well as their complex behavior when interacting with light. When deciding whether to fabricate a monolithic crown in translucent zirconia or improve its appearance by layering with more translucent glass-ceramic, the clinicians and dental technicians must be aware of these procedures' effect on the final color of the restorations.

Reflectance and color prediction of dental material monolithic samples with varying thickness.

OBJECTIVE: To assess accuracy of reflectance reconstruction and color estimation of different dental materials with varying thicknesses using Principal Component Analysis (PCA). METHOD: A1, A2, A3, A3.5, B2, C2 and D2 shades and 5 thicknesses (within 0.5-2.5 mm range) of Vita Suprinity (VS-PC) and Vitapan Dentine (VD), were used. Reflectance measurements were performed over black background using a non-contact spectroradiometer with CIE 45∘∕0∘ geometry. A PCA based algorithm was proposed to reconstruct spectral data and color of samples, using both extrapolation and interpolation approaches. Root Mean Square Error (RMSE), Goodness of Fit (GFC), correlation coefficient (R2) as well as ΔE00 with corresponding 50:50% acceptability and perceptibly thresholds (AT and PT) were used as performance assessment. RESULTS: The interpolation approach provided an average RMSE = 0.01 and GFC > 0.999 when comparing predicted and measured spectral reflectances for both materials, while for the extrapolation approach RMSE = 0.02 and GFC > 0.999. Interpolation approach also resulted in lower overall mean color difference ΔE00 = 0.8 (ΔE00 = 0.9 for VS-PC and ΔE00 = 0.7 for VD), while using extrapolation approach resulted in higher overall mean color difference ΔE00 = 1.6, although below the AT (ΔE00 = 1.8 for VS-PC and ΔE00 = 1.5 for VD). Correlation values between predicted and measured spectral reflectances of R2 = 0.987 and R2 = 0.993 were globally obtained for VS-PC and VD, respectively. SIGNIFICANCE: The proposed PCA-based algorithm is able to efficiently predict reflectance spectrum and color of monolithic samples of different dental materials with varying thickness. It can be used to optimize dental materials manufacturing processes and to improve chromatic accuracy of clinical dental restorations.

Effectiveness and color stability of bleaching techniques on blood-stained teeth: An in vitro study.

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.

Masking ability of bleach-shade resin composites using the multilayering technique.

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.

The effects of thickness and shade on translucency parameters of contemporary, esthetic dental ceramics.

OBJECTIVE: To analyze translucency variations among four different contemporary esthetic ceramic systems having different shades and thicknesses. MATERIAL AND METHODS: Ceramic specimens having different shades and translucencies were tested: leucite reinforced glass-ceramic (ECAD), conventional feldspathic ceramic (Noritake), zirconia reinforced lithium silicate glass-ceramic (Suprinity) and hybrid ceramic (Enamic). Specimens of 0.6, 0.9, 1.2, 1.5 and 2.0-mm thickness (n = 3/group, 615 total) were prepared. Translucency (TP) and Relative Translucency (RTP) Parameters were calculated from spectroradiometric color readings. Effects of shade and thickness for a given system were statistically analyzed using MANOVA and Tukey post-hoc multiple comparisons tests. Translucency variations were assessed comparatively with literature-based perceptibility and acceptability thresholds. RESULTS: TP/RTP values of all ceramic materials decreased with increasing thickness. The most translucent specimens were 0.6-mm thick ECAD HT-A3.5 (TP = 31.99) and ECAD HT-C2 (RTP = 23.75), while the least translucent was 2-mm thick Enamic T-3 M2 (TP = 7.27; RTP = 4.79). Thickness and material type significantly influenced translucency (p < 0.001). Noritake and ECAD LT showed similar translucency values, as well as Suprinity HT and ECAD LT. CONCLUSIONS: For ceramic restorations thicker than 0.9-mm, any thickness increase of 0.3-0.5 mm produces a perceptible but clinically acceptable translucency variation. Increases in thickness larger than 0.6-mm will result in an unacceptable translucency shift. Dental practitioners need to recognize key factors that influence translucency of ceramic restorations in order to choose the optimal material, shade, translucency, and thickness suitable for different clinical scenarios. While shade plays a minor role in translucency variation, ceramic type and restoration thickness significantly affect overall translucency.