Calculation of colour resulting from composite/compomer layering techniques

This study determined the influence of optical properties of constituent layers on the colour of double-layer aesthetic filling materials. Multiple regression equations for the Commission Internationale de I'Eclairage (CIE) L*, a* and b* of layered materials were calculated from the optical values of the covering and underlying layers. Specimens (10 mm diameter, 1 mm thickness) of two light-cured resin composites and one compomer of seven to 11 shades were used. CIE L*, a* and b* values of each specimen were measured with a colour spectrophotometer backed by a standard white background. The scattering coefficient (S), absorption coefficient (K), contrast ratio (C) and translucency parameter (T) were calculated. Double-layered specimens were formed in optical contact by joining two different shades from the same material, or resin composite as covering with a compomer underlying layer. Each of the L*, a* and b* of layered material was used as a dependent variable, and 14 optical values of underlying and covering layers were used as independent variables in forward regression analysis (P = 0.01). CIE L* after layering had a positive correlation with S of covering layer (correlation coefficient; beta = 0.79-0.91, P < 0.01) and a correlation with L* of underlying layer (beta = 0.14-0.16). CIE a* after layering had a correlation with a* of covering layer (beta = 0.83-0.94) and a correlation with a* of underlying layer (beta = 0.30-0.56). CIE b* after layering had a correlation with b* of covering layer (beta = 0.77-0.90) and a correlation with T of covering layer (beta = 0.40-0.59). The layered colour of these materials can be predicted by the derived regression equations within the limitations of this study. CIE L*, a* and b* values of double-layer material are mainly influenced by S, CIE a* and b* of covering layer, respectively.     

Difference in the colour and colour change of dental resin composites by the background

The objective of this study was to evaluate the difference in the colour and colour change of dental resin composites over commonly used two backgrounds. Colour of five uncured and cured resin composites before and after polishing with 600-, 1000- or 1500-grit SiC paper was measured according to the CIELAB colour scale relative to the illuminant D65 over a white background (WB; reflectance = 91.57%) and a light trap (LT; reflectance = 0.01%) on a reflection spectrophotometer with the SCE geometry. Colour difference (DeltaE*ab) by the background, and by the specimen conditions over each of two backgrounds was calculated. DeltaE*ab values between the same specimen by the background were 2.38-11.60. DeltaE*ab values by the specimen condition were varied by the background, and DeltaE*ab between cured/polished specimens over WB were significantly higher than those over LT (P < 0.05) except a few cases. Background influenced three-colour coordinates of CIE L*, a*, and b* values differently depending on the material and the specimen condition. Background significantly influenced the colour coordinates and colour difference by the specimen conditions. As the light trap can eliminate the influence of variations at the background, measured colour over the light trap can be the colour of material itself. Correlation between the measured colour and varied shades of background should be further studied.     

Comparison of the color of natural teeth measured by a colorimeter and Shade Vision System.

OBJECTIVES: The objectives were to measure the difference in the color and color parameters of natural teeth measured by a tristimulus colorimeter (CM, used as a reference) and Shade Vision System (SV), and to determine the influence of color parameters on the color difference between the values measured by two instruments. METHOD: Color of 12 maxillary and mandibular anterior teeth was measured by CM and SV for 47 volunteers (number of teeth=564). Color parameters such as CIE L*, a* and b* values, chroma and hue angle measured by two instruments were compared. Chroma was calculated as C*ab=(a*2 = b*2)1/2, and hue angle was calculated as h degrees =arctan(b*/a*). The influence of color parameters measured by CM on the color difference (DeltaE*(ab)) between the values measured by two instruments was analyzed with multiple regression analysis (alpha=0.01). RESULTS: Mean DeltaE*(ab) value between the values measured by two instruments was 21.7 (+/-3.7), and the mean difference in lightness (CIE L*) and chroma was 16.2 (+/-3.9) and 13.2 (+/-3.0), respectively. Difference in hue angle was high as 132.7 (+/-53.3) degrees . Except for the hue angle, all the color parameters showed significant correlations and the coefficient of determination (r(2)) was in the range of 0.089-0.478. Based on multiple regression analysis, the standardized partial correlation coefficient (beta) of the included predictors for the color difference was -0.710 for CIE L* and -0.300 for C*(ab) (p<0.01). CONCLUSION: All the color parameters showed significant but weak correlations except for hue angle. When lightness and chroma of teeth were high, color difference between the values measured by two instruments was small. Clinical accuracy of two instruments should be investigated further.     

Colour and translucency of tooth-coloured orthodontic brackets

The objective of this study was to determine the reflected and transmitted colours and the diffuse light transmittance of tooth-coloured brackets. Four ceramic and four plastic brands were evaluated and five brackets of each brand were tested. Reflected colour and spectral reflectance of the labial surface of the brackets were measured according to the Commission Internationale de l'Eclairage (CIE) colour scale and transmitted colour and diffuse spectral transmittance measured with a spectrophotometer. One-way analyses of variance were performed for the reflected and transmitted colour co-ordinates (CIE L*, a*, and b*) and for light transmittance according to bracket brand. The range for CIE L* (lightness) was 36.2-50.3, for a* (red-green parameter) -1.3-3.8 and for b* (yellow-blue parameter) -2.9-11.2. All these colour co-ordinates were influenced by bracket brand (P < 0.05). Diffuse light transmittance was also influenced by bracket brand and ranged from 44.9 to 75.9 per cent (P < 0.05). Colour and transmittance varied by bracket brand. Variations in optical properties influenced the aesthetic performance of the brackets and the degree of cure of the adhesive that is possible through the brackets. Further studies on the clinical implications of colour matching of tooth-coloured brackets with teeth should now be performed.     

应用牙科分光光度比色仪对钴铬合金基底表面4种全瓷冠色度学特征的研究

目的 采用牙科分光光度比色仪评估钴铬合金基底表面4种全瓷冠各部位的色度学参数及与目标色片的色差。方法制作钴铬合金基牙预备体（钴铬合金基底）,分别戴入Procera氧化铝（Pro-Alu）、Procera氧化锆（Pro-Zir）、Lava氧化锆（Lava-Zir）、二矽酸锂增强压铸玻璃陶瓷IPS E.max Press（E.max-HO）4种材料的底冠,并烧结与底冠相同材料的体瓷,制作成全瓷冠。采用牙科分光光度比色仪对钴铬合金基底及底冠、体瓷戴入后样本的颈1/3、体1/3、切1/3区域进行测色。以Vitapan Classical比色板A2色体瓷片为对照,比较各组样本与目标色片A2的色差。结果4种底冠均提高基牙的L*和b*值,a*值下降（除Lava-zir底冠颈部外）;4种底冠L*（除Pro-Zir与Lava-Zir切端、Lava-Zir与E.max-HO颈部外）、a*、b*值均有统计学差异。戴入体瓷后,4种全瓷冠L*值略下降（除Pro-Alu体瓷外）,a*、b*值明显上升。4种体瓷与A2体瓷色差ΔΕ均小于4。结论4种全瓷冠对金属基底都有良好遮色性,虽然明度、彩度有差别,但颜色一致性在临床可接受范围。     

Optical properties of four esthetic restorative materials after accelerated aging

PURPOSE: To determine the differences in CIE L*, a*, and b* values, translucency parameter (TP), opalescence parameter (deltaO*ab), and color difference caused by the fluorescence (deltaE*ab-FL) of resin composite, glass-ionomer, resin-modified glass-ionomer, and compomer of A2 shade before and after accelerated aging. METHODS: Color and spectral distribution of the materials were measured according to the CIELAB color scale relative to the standard illuminant D65 in the transmittance and reflectance modes. Aging was performed in an accelerated aging chamber with an energy exposure of 150 kJ/m2. The translucency parameter (TP) was calculated as the color difference (deltaE*ab) of the specimen over white and black backgrounds. Opalescence parameter (deltaO*ab) was calculated as the difference in blue-yellow coordinate (deltab*) and red-green coordinate (deltaa*) between the transmitted and reflected colors of a 1 mm-thick specimen. Color difference by the fluorescence (deltaE*ab-FL) in reflectance mode was calculated as an index of fluorescence. Differences and changes in optical properties were analyzed by the repeated-measures ANOVA. RESULTS: Type of material and the mode of measurement (transmittance and reflectance) influenced CIE L*, a* and b* values significantly (P< 0.05) before aging. Accelerated aging influenced CIE L*, a* and b* values. Aging and the type of material influenced TP, deltaO*ab and deltaE*ab-FL values significantly (P< 0.05).     

Association between masticatory performance using a colour-changeable chewing gum and jaw movement

The purpose of this study was to investigate the relationship between masticatory performance as determined using a colour-changeable chewing gum and mandibular movements. Subjects comprised 45 fully dentate adults (23 men, 22 women; mean age, 28·1 years). The gum was chewed for a specified number of chewing strokes (20, 40, 60, 80, 120 or 160 strokes) without any instructions as to chewing side. A colourimeter was used to measure L*, a* and b* values (CIE-L*a*b* colour system) for the chewed gum, then the difference between two colours in the CIE-L*a*b* colour space (ΔE) for each number of chewing strokes was calculated according to a formula. Index of masticatory performance (ΔE60) for each subject was obtained using ΔE for 20, 40, 60, 80, 120 and 160 strokes. Mandibular movements were recorded using an opto-electric system with six degrees of freedom. Twelve parameters of mandibular movements relating to amplitude, duration, velocity and angle were computed for each cycle, and mean values for 10 cycles (from cycle 11 to 20) were calculated separately. Stepwise multiple regression analysis identified maximum closing velocity and closing angle as predictors accounting for 18% of the variation in ΔE60. These results suggest that lower angles of approach to intercuspation and faster speed during closing duration are associated with colour changes in the colour-changeable chewing gum.     

Color stability of a resin-modified glass ionomer cement.

The color stability of a resin-modified glass ionomer cement (Fuji II LC) was investigated over six months using colorimetry. Five shades (A2, A3, A4, B3 and C4) were selected and 10 square specimens (7 mm wide and long, and 1.5 mm deep) were made for each shade using special grit molds. CIE L*, a*, b* color parameters of the specimens were taken at one day, one week, one month, three months and six months. Results were subjected to MANOVA and ANOVA/Scheffe's test at significance level 0.05. The effects of time on color parameters (L*, a*, b* values) were found to be shade dependent. All shades exhibited a decrease in L* values over time. With the exception of shade B3, significant differences in L* values were observed at six months. A general decrease in b* values was also observed but differences among the various time intervals were not significant except for shades A3 and C4. No apparent trends were observed for changes in a* values. For all shades, the largest color change (delta E) was observed between one day and one week. The color stability of the resin-modified glass ionomer investigated was shade dependent. A general decrease in lightness and yellow chroma was observed.     

Optical phenomenon of peri-implant soft tissue. Part I. Spectrophotometric assessment of natural tooth gingiva and peri-implant mucosa

OBJECTIVES: The purpose of this study was to investigate the difference in optical appearance of the soft tissues labial to dental implants and to analyze the effects of titanium implant neck colors transmitted through the marginal mucosa. MATERIALS AND METHODS: Fourteen patients with 15 Straumann single implant replacements in the maxillary anterior region were recruited. Color measurements of the peri-implant mucosa of test sites and the gingivae of contralateral or adjacent natural teeth as controls were made at the facial aspect of the teeth using a spectrophotometer. The color data (CIELAB color coordinates; L*, a*, b* and C*) in five incremental areas of 1 x 2 mm from the gingival margin toward the apical direction were obtained. RESULTS: A significant difference existed (P<0.01) between the test site and the control site on the mean L* and b* values in all five incremental areas (area 1-5). In contrast, there was no significant difference in the mean a* values. Discrepancies between color distributions of soft tissues were stronger in areas close to the gingival margin and decreased toward the apical direction. The mean color difference DeltaE between the test site and the control site was 7.7 in area 1 and decreased toward area 5 with a value of 6.5. However, there was no statistical difference in each of the mean values of differences in optical data, DeltaL*, Deltaa* and Deltab*, when five incremental areas of the control and the test sites were compared. CONCLUSION: It was observed that the color of soft tissue around the titanium implant was significantly different compared with the gingiva of natural teeth. Significantly lower values of CIELAB color coordinates, L* and b* were found in the peri-implant soft tissue.     

Color formulation and reproduction of opaque dental ceramic.

OBJECTIVES: The purpose of this study was to determine the validity and accuracy of mixing opaque feldspathic dental ceramic to obtain specific shades using two methods: (1) Concentration Additivity of Optical Parameters (CALAB) and (2) Concentration Additivity of Kubelka-Munk Optical Coefficients (CAK/S). METHODS: A total of 25 opaque feldspathic dental ceramic specimens were fabricated by mixing six different pure shades in different concentrations. The reflectance spectra were measured and the actual CIELAB L*, a* and b* coordinates were obtained for the 25 specimens. The CALAB and CAK/S methods were used to predict the L*, a* and b* values with reference to the concentrations of the pure shades. Correlation analysis was carried out between the actual and predicted L*, a* and b* values for both methods. The color differences (DeltaE*) between actual and predicted L*, a* and b* values were also calculated and analyzed using repeated measures ANOVA. RESULTS: Pearson's correlation coefficients between predicted and actual values for both methods were greater than 0.98. The mean DeltaE*s were 0.24 (0.11) for CALAB method and 0.21 (0.11) for the CAK/S method. The repeated measures ANOVA revealed a statistically significant difference (P=0.0213) between the mean DeltaE*s from the two methods. SIGNIFICANCE: Both methods produced mean DeltaE*s between the actual and predicted methods that were below the threshold of human perceptibility. The simpler CALAB method can be used to determine the opaque ceramic mixture for specific shades with accuracy.     

Tooth whitening with hydrogen/carbamide peroxides in association with a CPP-ACP paste at different proportions

Background: Different enhanced peroxide formulations have been developed to overcome mineral loss during tooth whitening. This study investigated the impact on tooth whitening from combining a CPP‐ACP paste with home peroxide agents at several proportions. Methods: Ninety bovine incisors were randomly allocated into nine groups (n = 10) and exposed to 7.5% hydrogen peroxide (HP), 16% carbamide peroxide (CP), a CPP‐ACP paste (Tooth Mousse/MI Paste, GC Corporation, Tokyo, Japan) and blends of HP/CP:MI at three proportions (1:1, 2:1 and 1:2). Tooth whitening was performed for 14 days and its effectiveness was measured by a spectrophotometer utilizing the CIE L*a*b* system (ΔE, ΔL*, Δa* and Δb*). Colour readings were measured at baseline (T0), 7 days of bleaching (T7), 14 days of bleaching (T14) and 7 days after the end of bleaching (T21). Data were analysed by two‐way ANOVA for paired averages followed by the Tukey’s test and Pearson’s correlation at 5%. Results: Although CP produced the greatest colour change (ΔE), all whitening protocols were considered to be effective regardless of the CPP‐ACP presence. In general, greater changes in ΔE, ΔL*, Δa*  and Δb* were detected at T14, with T21 exhibiting similar results to those at T7. A greater number of strong correlations with ΔE values was found for a* (11/15). Conclusions: Within the limitations of this study, the results indicate that the CPP‐ACP paste did not affect tooth whitening efficacy.     

Spectral reflectance and color of dentin ceramics for all-ceramic restorations

OBJECTIVE: The study was conducted to observe the spectral reflectance curves, and evaluate the color coordinates (CIELAB) of VM7 dentin ceramics (VITA, Germany) across the whole 3D-MASTER shade system. METHODS: Three disc samples, 13 mm in diameter and 1.4mm in thickness, were produced for each shade by firing following the manufacturer's instructions. Each fired disc was ground to a thickness of 1.0 mm and both faces were polished. Spectral reflectance data in the visible spectrum under the standard illuminant D65 were collected at 1 nm intervals by using a computer-controlled spectrophotometer. Color coordinates, L*, a*, b*, C*, h, in the three-dimensional CIELAB color space were obtained. RESULTS: (1) Spectral reflectance in the short-wavelength range systematically decreased with increasing chroma number (M1, M2, and M3) when compared within the same value (lightness) group (1M, 2M, 3M, 4M, and 5M). (2) Spectral reflectance decreased systematically across the whole visible spectrum with increasing value group when compared within the same chroma group. (3) A negative relationship was recognized between lightness (L*) and chromaticity index a* (red-green direction). That is, a* coordinate increases from approximately 1 for the 1M1 sample to approximately 13 for the 5M3 sample, the corresponding lightness systematically decreased from 87 to 69. (4) With increasing a* coordinate, hue angle (h) significantly decreased from 85 degrees for the 1M1 sample to 69 degrees for the 5M3 sample. (5) Lightness apparently increased with increasing hue angle (h) throughout the whole range of the 3D-MASTER shade system. (6) A strong positive relationship between chroma (C*) and chromaticity index b* (yellow-blue direction) was found, demonstrating that the chroma of the present ceramic is mainly controlled by the b* coordinate. SIGNIFICANCE: Systematic variations in spectral reflectance and color coordinates of VM7 dentin were observed throughout the 3D-MASTER shade system and were suggested to be caused by the fine structure of the sample which can interfere with shorter wavelengths in the visible spectrum.     

Effects of colour measuring mode and light source on the colour of shade guides

The objectives of this paper were to evaluate the effects of colour measuring modes [specular component excluded (SCE) versus specular component included (SCI)] and the standard light source (C, A or D65) on the colour of shade guides. After the labial part of shade tabs of two shade guides (Vita and Chromascop) was polished flat up to no. 2400 silicone carbide paper, the colour was measured according to the International Commission on Illumination (CIE)L*a*b* colour scale on a spectrophotometer. In both shade guides, all the average CIE L* values of each shade series, and most of CIE b* values were different depending on the measuring mode (P < 0.01). However, there was no difference in CIE a* values depending on the measuring mode. Colour difference (deltaE*) between the values measured with SCE mode and with SCI mode was 3.21-6.50 in Vita shade guide, 3.22-5.47 in Chromascop shade guide. DeltaE* caused by the difference in light source was very small in Vita shade guide regardless of the measuring mode. In the Vita shade guide, the shade series (A-D) was negatively correlated with CIE L* and CIE a* values measured with SCE mode. In the Chromascop shade guide, the shade series (100-500) was negatively correlated with CIE L* value measured with SCI mode.     

Camouflage effects following resin infiltration of postorthodontic white-spot lesions in vivo: One-year follow-up

Objective:To assess camouflage effects by concealment of postorthodontic white-spot lesions (WSLs) to sound adjacent enamel (SAE) achieved over 12 months with resin infiltration (Icon, DMG, Hamburg, Germany).Methods: Twenty subjects (trial teeth n_teeth = 111) who had received resin infiltration treatment of noncavitated postorthodontic WSLs were contacted for a 1-year follow-up assessment of CIE-L*a*b* colors (T12). Color and lightness (CIE-L*a*b*) data for WSLs and SAE were compared to baseline data assessed before infiltration (T0) and those assessed after 6 months (T6), using a spectrophotometer. The target parameter was the difference between the summarized color and lightness values (ΔE_WSL/SAE). Intergroup (WSL, SAE) and intertime comparisons (T0 vs T6, T12) were performed using paired t-tests at a significance level of α = 5%.Results:Nine subjects (trial teeth n_teeth = 49; male/female ratio 5/4; age range 13–19 years) were available at T12. After the highly significant reduction of ΔE_WSL/SAE discrepancies between T0 and T6, analysis of 12-month records revealed color and lightness discrepancy of WSL vs SAE that was significantly decreased compared with baseline, indicating an assimilation of WSL color to SAE appearance after infiltration, while an additional reduction of discrepancies between T6 and T12 was not significant.Conclusion:As color and lightness characteristics of the Icon infiltrant as well as the esthetic camouflage effects achieved by WSL infiltration were not altered significantly or clinically relevant after 12 months, the method of resin infiltration can be recommended for an enduring esthetic improvement of postorthodontic WSL. (Angle Orthod. 2015;85:374–380.)     

Detecting silver-containing metal ceramic alloys that discolor porcelain

Dental laboratories need an internal method to detect silver-containing metal ceramic alloys that stain porcelain. A fiberoptic colorimeter, calculations, and data describe Ag-vapor staining in standard CIE (1976) L*a*b* color space. The color difference value (CDV) of delta L*, delta a*, delta b*, and delta E* for porcelain before and after firing with Pd-Ag alloy, Au-Pt-Pd alloy, and control groups were calculated from L*, a*, and b* values. The CDV for all groups showed a more translucent (-delta L*) porcelain after the second firing. The CDV of porcelain disks exposed to Pd-Ag alloy showed an intense yellow (+ delta b*) stain with slight "greening" (-delta a*). The disks exposed to the Au-Pt-Pd group showed a slight yellow (-delta b*) stain. The delta b* values for the Pd-Ag group were significantly different from the other groups. This color shift (+ delta b) was clearly observed with the unaided eye.     

Colour and translucency of opaque-shades and body-shades of resin composites

The purpose of this study was to evaluate the optical properties--not only the translucency but also the colours--of opaque-shade resin composites. The CIELAB parameters (L*, a* and b*) of disks of A2 and opaque A2 (OA2) shades of Charisma (Heraeus-Kulzer), Solare (GC) and Filtek Supreme (3M) were evaluated on backings of black, white and the material itself to calculate the translucency parameter (TP) and the colour differences (delta E*) between A2 and OA2. A two-way analysis of variance (anova) for the TP indicated a less statistically significant TP value in the OA2 shade than the A2 shade for all products. As for the products, Charisma showed a statistically greater TP value than the other two products. Regarding the delta E* between A2 and OA2, all the products revealed clinically perceptible colour differences (delta E* > 3.3). Hence, we must take the colour differences of opaque-shade resin composites into consideration, as well as the translucency of the materials, for a clinically acceptable colour match of the restoration.     

Efficacy of a novel at-home bleaching technique with carbamide peroxides modified by CPP-ACP and its effect on the microhardness of bleached enamel

This study was designed to evaluate in vitro the efficacy of a novel at-home bleaching technique using 10% or 16% carbamide peroxide modified by casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and its influence on the microhardness of bleached enamel. A total of 40 bovine incisors were divided into four groups (n=10) according to the bleaching agent used: 10% carbamide peroxide only; a blend of 10% carbamide peroxide and a CPP-ACP paste; 16% carbamide peroxide only; and a blend of 16% carbamide peroxide and a CPP-ACP paste. During the 14-day bleaching regimen, the samples were stored in artificial saliva. The Vickers microhardness and color of the teeth were assessed at baseline (T0) and immediately after the bleaching regimen (T14) using a microhardness tester and a spectrophotometer, respectively. The degree of color change was determined by the Commission Internationale de l'Eclariage (CIE) L*a*b* system (ΔE, ΔL*, Δa*, and Δb*) and Vita shade guide parameters. The data were analyzed by analysis of variance and the Tukey test (p<0.05). The teeth that were bleached with a blend of peroxide (10% or 16%) and the CPP-ACP paste presented increased microhardness values at T14 compared with T0, whereas the samples that were bleached with peroxide only did not show any differences in their microhardness values. All of the bleaching agents were effective at whitening the teeth and did not show a statistically significant difference using the CIEL*a*b* system (ΔE, ΔL*, Δa*, and Δb*) or the Vita shade guide parameters. The use of a CPP-ACP paste with carbamide peroxide bleaching agents increased the bleached enamel's microhardness and did not have an influence on whitening efficacy.     

The use of digital imaging for colour matching and communication in restorative dentistry

OBJECTIVE: To develop a shade matching method based on digital imaging and to compare observers' ability using this method with the conventional one set against a spectrophotometric 'gold standard'. METHODS: Two Vita Lumin shade guides were used in this study, nine shades being selected from the first Vita Lumin shade guide, A2, A3, A3.5, B2, B3, B4, C1, C2 and C3. A second shade guide was used to match the selected shades. A Nikon Coolpix 990 digital camera with Nikon SB21B ring flash was used to record the digital images of the shade tabs of the two shade guides and the images were processed using Adobe Photoshop software. A total of 27 samples (three replicates of each shade of the nine tabs selected) were matched with a digital shade guide prepared from the digital images of the second shade guide by 10 observers on a computer screen (computerised matching method). The 10 observers also matched the same shade tabs using the conventional matching method simulated in a phantom head. In addition, colour values were obtained from the digital images using Adobe Photoshop and quantified according to an internationally recognised scale as CIELAB colour values, L*,a*,b*. The relationship of the digitally derived CIELAB values to the CIELAB values obtained using a reflectance spectrophotometer was investigated. RESULTS: The cross tabulation statistical analysis showed a statistically significant difference (p<0.001) between the conventional method and the computer method with a 43% and 61.1% correct match respectively. There was also a statistically significant difference between observers in both methods (p<0.001 and p<0.04 for the conventional and computer methods respectively). A statistically significant high correlation of the CIELAB colour values were found between both colour measurement methods (p<0.001). CONCLUSION: The observers' shade matching performance was significantly better with the computer method compared with the conventional one. There was a large variation in the observers' matching ability. The digital camera can be used as a means of colour measurements in the dental clinic.     

Effect of core and veneer thicknesses on the color parameters of two all-ceramic systems

STATEMENT OF PROBLEM: Specific contributions of the core and the veneer thickness on the appearance of layered disk specimens are not well characterized. PURPOSE: This study examined the effect of varying core and veneer thickness on the color parameters of layered disk specimens made of 2 ceramic systems. MATERIAL AND METHODS: Disk specimens 16 mm in diameter with core/veneer thickness (mm) of 0.8/0.2 (baseline), 0.8/0.7, 0.8/1.2, 1.0/0.5, 1.3/0.2, and 1.8/0.2 were made from a leucite-reinforced ceramic (IPS Empress; 2B shade), and thickness (mm) of 0.5/0.5 (baseline), 0.5/1.0, 0.5/1.5, 0.8/0.7, 1.0/0.5, and 1.5/0.5 were made from a glass-infiltrated spinell ceramic (In-Ceram Spinell; A2 shade). Color parameters L*, a*, and b* of CIELAB color space were measured against a neutral gray background with a tri-stimulus colorimeter, and deltaE between disk group and its respective baseline group was calculated. Analysis of variance was used to determine the effect of material and core and veneer thickness on the color parameters (alpha = .05). RESULTS: Increasing the total disk thickness resulted in decrease of L* (P < .001) and an increase of a* (P < .001), b* (P < .001), and deltaE (P = .0236). For leucite-reinforced ceramic, the core thickness, veneer thickness, and their interaction exhibited significant influence on the mean values of a* and b* (P < .0028) but not on the mean values of L*. For spinell ceramic, the core thickness and veneer thickness exhibited significant influence on the mean values of L* and b* (P < .0272) but not on a*; the interaction demonstrated significant influence on b* (P = .0003) but not on L* and a*. CONCLUSION: The color appearance of the layered ceramic disk specimens is strongly influenced not only by the core thickness and veneer thickness, but also by their interaction.     

Influence of filler distribution on the color parameters of experimental resin composites.

OBJECTIVES: Simulating the optical properties of natural tooth would be the final goal for esthetic restorative materials. Filler distribution in resin composites determines the scattering in composite materials, which in turn would influence the color parameters such as lightness, chroma and hue. The objective of this study was to determine the influence of filler size and amount on the color parameters of experimental resin composites. METHOD: Color of 11 experimental resin composites with two different sized fillers (LG: 0.77 microm and SG: 0.50 microm) in 10-70 wt% was measured by a spectrophotometer. Color coordinates (CIE L*, a* and b*), chroma and hue angle were determined. Optical constants including scattering coefficient (S), absorption coefficient (K) and light reflectivity (RI) were calculated. To determine the influence of the amount of filler on the optical parameters, Pearson correlations between the amount of filler (%) and color parameters and optical constants were calculated. Correlations between the optical constants (S, K and RI) and color parameters were calculated (p<0.05). RESULTS: S value increased as the amount of filler increased. RI value generally increased as the amount of filler increased for LG filler group, and increased up to 40% filler for SG filler group. CIE L* value increased as the amount of filler increased in both of LG and SG filler groups. CIE L* value was highly correlated with S and RI values for both filler groups (r=0.961-0.974). CONCLUSION: Lightness was highly correlated with the amount of filler, S and RI values (r=0.932-0.974). But the correlation coefficients between the amount of filler and chroma/hue were moderate (r=0.406-0.827); therefore, pigmentation would be tried to simulate the color of resin composites to those of natural tooth. Optical properties of resin composites could be partly simulated to those of teeth by controlling the filler distribution.