Color acceptance of direct dental restorative materials by human observers

The purposes of this study were to evaluate the CIELAB, CMC (2:1), and CMC (1:1) formulas to identify which provides the best indicator for acceptability of small color differences in the esthetic dental restorative materials, to determine if different groups of observers have different levels of acceptability, and to estimate the color difference that would indicate acceptability between a restoration and an adjacent tooth. The subject population of human observers was divided into four groups, each containing 12 subjects. The composition of the groups were: Group 1, dental auxiliaries and hygienists; Group 2, dentists; Group 3, dental materials scientists; and Group 4, patients. A color vision screening test was administered to each subject to ensure that only observers with normal color vision were evaluated. A composite resin color discrimination test was developed specifically for this study. This test was composed of six sets of discs fabricated from dental composite resin restorative materials. Each set consisted of one standard disc representing tooth color. In each set, six discs representing composite resin restorations were matched to the standard disc for a total of 36 pairings in the test. Color differences between the standard discs and the restoration discs were calculated in CIELAB, CMC (1:1), and CMC (2:1) color units. The subjects were asked to evaluate the composite resin materials as to acceptability of color differences between the disc pairs. The data were analyzed by logistic regression analysis for each observer and by each ΔE formula to generate receiver operating characteristics (ROC) curves. The areas under these ROC curves were calculated and ranked. ANOVA and Tukey's Studentized Range (HSD) Test were applied to the ranks. In regard to the acceptance of dental restorations based solely on color difference, the CMC (1:1) color difference formula gave better correlation than the CIELAB formula for small color differences in the esthetic dental restorative materials. There were significant differences found between the experiment groups in regard to acceptability of color differences using the CMC (1:1) and CIELAB formulas. The dental hygienist/auxiliaries group proved to be more discriminating in accepting differences between tooth and composite resin restorative material color than patients. The mean 50:50 ΔE replacement points for all subjects were 2.29 and 2.72 color units for the CMC (1:1) and CIELAB formulas, respectively. © 2000 John Wiley & Sons, Inc. Col Res Appl, 25, 278–285, 2000     

Color specification of two new resin composites and influence of stratification on their chromatic perception

Accurate color reproduction in conservative dentistry is fundamental to the aesthetic success of the restorations. The need to specify the color objectively has been known for some years, and this article aims to make a contribution to this field. This work is part of a multidisciplinary research project, and it has a double aim. The first purpose was to measure the color differences between the two new composite resin restorative materials and the most used dental color scale. Measurements show some differences from color shades indicated by the manufacturers and those obtained from experimental data. The influence of different order of enamel and dentin layers on color perception was also investigated to evaluate clinical strategies useful to obtain desired result. Relevant differences are observed in the stratification of dentin and enamel discs especially for one of the two studied composites.     

Comparison of the translucency of two multishaded composite resins polymerized with direct or indirect method

The aim of this study was to measure the translucency of one indirect and direct resin composite after polymerization and to examine the effect of color parameters on this property. Tescera and Filtek Ultimate, each containing three shade groups (Enamel, Dentin and Body for Filtek Ultimate; and Incisal, Opaceous Dentin and Body for Tescera), were investigated. The translucency parameter (TP) was measured as the color difference between a specimen over a white and black background. Significant differences were observed in TP values between shade groups. Tukey’s multiple comparison test revealed TP values among the groups of Filtek Ultimate-Enamel > Tescera-Incisal > Filtek Ultimate-Body > Tescera-Body = Filtek Ultimate-Dentin > Tescera-Opaceous Dentin. In conclusion, it is concluded that the translucency of resin composite was affected by polymerization and color parameters.     

Color stability of bulk‐fill composites immersed in different drinks

Bulk‐fill composites show structural differences compared to those of conventional resin composites. Their more reactive photoinitiators, monomer compositions, and increased filler content may result in higher color stability than for conventional ones. Therefore, this study aimed to assess the color stability of three different bulk‐fill composites and one conventional resin composite with a higher filler load after 1 week and 1 month of immersion in different drinks. The resin composite materials that were tested demonstrated significantly different color changes after immersion in the four solutions during both evaluation periods. Immersion in coffee and red wine showed noticeable staining of all the materials. The discoloration effect of staining solutions on the resin composites depends both on the material composition and on the pigment types found in the solutions.     

塑料色母粒色差原因和改进

色差是塑料色母粒制造过程中重要的质量控制指标。本文就色差产生的原因,从原材料、设备、操作工艺、环境、人为差错等方面着手,考虑到树脂和着色剂加工的性能,进行分析探讨,并提出改进措施。     

The Perception of a Colored Translucent Sheet on a Background

Metelli's theory of the perception of translucency models the effective reflectance of a translucent sheet on a background as a partitive mixture of the color of the sheet and the color of the background. In the achromatic case, the usable (that is, scale-invariant) rules governing the apparent reflectances are the same as those that would emerge from the Kubelka-Munk theory. For chromatic translucency, the relationships are more complex, but a set of rules still emerge from the partitive-mixture theory that are invariant to tradeoffs between illuminant and reflectances. This column sets forth the rules in the hopes that they will have graphical applications, both on computer VDUs and in hardcopy.     

Comparison of the metrics between the CIELAB and the DIN99 uniform color spaces using dental resin composite material values

The sizes for the perceptible or acceptable color difference measured with instruments vary by factors such as instrument, material, and color‐difference formula. To compensate for disagreement of the CIELAB color difference (ΔE^*_ab) with the human observer, the CIEDE2000 formula was developed. However, since this formula has no uniform color space (UCS), DIN99 UCS may be an alternative UCS at present. The purpose of this study was to determine the correlation between the CIELAB UCS and DIN99 UCS using dental resin composites. Changes and correlations in color coordinates (CIE L*,a*, and b* versus L₉₉, a₉₉, and b₉₉ from DIN99) and color differences (ΔE^*_ab and ΔE₉₉) of dental resin composites after polymerization and thermocycling were determined. After transformation into DIN99 formula, the a value (red–green parameter) shifted to higher values, and the span of distribution was maintained after transformation. However, the span of distribution of b values (yellow–blue parameter) was reduced. Although color differences with the two formulas were correlated after polymerization and thermocycling (r = 0.77 and 0.68, respectively), the color coordinates and color differences with DIN99 were significantly different from those with CIELAB. New UCS (DIN99) was different from the present CIELAB UCS with respect to color coordinates (a and b) and color difference. Adaptation of a more observer‐response relevant uniform color space should be considered after visual confirmation with dental esthetic materials. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 168–173, 2006     

Gloss and goniocolorimetry of printed materials

Angular distribution of reflectance spectra and of colorimetric parameters for printed papers (varnished and not) and foils, clear and metallized, were measured by goniospectrophotometry, with a photomultiplier for visible region, or a spectrocolorimeter as a detector, keeping the light source in a fixed position, ?45° anormally. All reflectance spectra were related to near‐Lambertian BaSO₄ powder white standard, relative to which the color coordinates were calculated. The photometric cosine law holds for an ideal diffuser; consequently, all color parameters are significantly perturbed by gloss in a large region, several 10's of degrees around the specular angle. The reflectance peak in the specular angle region of glossy material can be well approximated by the Lorentz function, especially in the vicinity of the specular angle. Lightness, chroma, and hue angle in the gloss angle region suffer as a result of high changes and extremes depending on the gloss of the material tested. This is what complicates color measurements and full determination or definition of the complex appearance of printed materials. The change of chroma with varnishing of glossless materials was clearly elucidated. It was found that “bottom color gloss” considerably influences the appearance of printed metallized foils or other prints on high glossy substrates. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 335–342, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10177     

Illuminant invariance from a single reflected light

This article presents an algorithm for computing an illuminant‐invariant quantity inherent in a single pixel of an imaged object color. The invariance pertains for two different assumptions about the illuminant spectrum: the photoreceptor sensitivities and the reflectance spectrum of the object. For one regime the illuminant spectrum is exponential, the photoreceptor sensitivities are equal‐width Gaussians, and the reflectance is also Gaussian. For the other regime the illuminant is a Wien approximation to a blackbody radiator, the photoreceptor sensitivities are narrow band in wavelength, and the reflectance is unconstrained. The existence of two regimes for the invariant testifies to its robustness. Computing this invariant over all pixels in an image will assist object‐color recognition (machine‐vision color constancy) without resorting to the usual assumption that illuminant variation over a scene is gradual compared to reflectance variation over that scene. © 2002 John Wiley & Sons, Inc. Col Res Appl, 27, 45–48, 2002     

Wear of zirconia/leucite glass-ceramics composites: A chewing simulator study

Leucite and zirconia are commonly used in the production of prosthetic dental materials. Leucite presents attractive optical properties but low toughness and wear resistance, which limits its use. Zirconia has much higher toughness, but due to aesthetic reasons and ageing issues, needs to be glass veneered. Chipping of such veneer is usually responsible for the abnormal wear induced on the antagonist teeth. Leucite reinforced with 25% of nano-zirconia is a promising alternative to overcome these issues, allowing the production of dental restorations without veneer. This study aims to investigate if leucite-zirconia composites have suitable optical, mechanical and tribological properties to be used in dental restoration. Samples with different compositions of leucite and/or nano-zirconia were produced by unidirectional compression and characterized concerning density, surface morphology, roughness, hardness, toughness, and translucency. Wear tests were performed in a chewing simulator using human cusps as counterbodies. Tests were also performed in glazed zirconia for comparison. 25% ZrO₂ leads to the lowest wear of the tribological pair among the studied systems, except 100% ZrO₂. This can be attributed to the toughening effect of zirconia and reduced size of third body particles. Abrasion was the main wear mechanism observed in this pair. In addition, this was the composite that presented the highest translucency.     

Effect of thermal aging on the mechanical and optical properties of a polyester resin

Thermal aging of an unsaturated polyester resin at 150°C was followed for a period of 960 h. The mechanical properties of cured polyester resin were enhanced at the start of aging, followed by slight deterioration. However, some improvement in the tensile strength and modulus were observed at the end of aging. The optical properties, viz., absorbance, transmittance, and reflectance, exhibited the usual change in polymer degradation; the absorbance showed an increase as a function of aging time, whereas the transmittance and reflectance decreased.     

Influence of surface roughness on the diffuse to near‐normal viewing reflectance factor of coatings and its consequences on color measurements

In this work, we discuss the effect of surface roughness on the measurement of the diffuse to near‐normal viewing reflectance factor of coatings and evaluate its impact on the corresponding color coordinates. We compare specular component included (SCI) and excluded measurements. We introduce a gloss‐factor to account for surface roughness in specular component excluded measurements. We present experimental results on samples with different degrees of surface roughness. Samples in this study were chosen to expose the contribution of the surface in the reflectance factor. For slightly rough surfaces, the influence on the measured reflectance factor depends on whether the specular‐component is included or excluded. As the surface roughness increases, the specular‐excluded reflectance factor increases approaching its value with the SCI further roughness lead to similar measurement results in both configurations. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 177–187, 2013.     

No measured effect of a familiar contextual object on color constancy

Some familiar objects have a typical color, such as the yellow of a banana. The presence of such objects in a scene is a potential cue to the scene illumination, since the light reflected from them should on average be consistent with their typical surface reflectance. Although there are many studies on how the identity of an object affects how its color is perceived, little is known about whether the presence of a familiar object in a scene helps the visual system stabilize the color appearance of other objects with respect to changes in illumination. We used a successive color matching procedure in three experiments designed to address this question. Across the experiments we studied a total of six subjects (two in Experiment 1, three in Experiment 2, and four in Experiment 3) with partial overlap of subjects between experiments. We compared measured color constancy across conditions in which a familiar object cue to the illuminant was available with conditions in which such a cue was not present. Overall, our results do not reveal a reliable improvement in color constancy with the addition of a familiar object to a scene. An analysis of the experimental power of our data suggests that if there is such an effect, it is small: less than approximately a change of 0.09 in a constancy index where an absence of constancy corresponds to an index value of 0 and perfect constancy corresponds to an index value of 1. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 347–359, 2014     

Color appearance modeling of bicolor striped woven fabrics considering neighboring color effects

In this article, the effect of the spatial and colorimetric attributes of neighboring color on color appearance shift in bicolor striped woven fabrics is investigated. A total of 240 test/neighboring woven color combinations were constructed in four different striped paradigms. Each test color in the combinations was visually assessed by 12 observer panels with the use of the magnitude estimation method estimating the magnitude of perceptual color attributes lightness, colorfulness, and hue. The visual estimates obtained were analyzed statistically by employing correlation and simple regression methods, and, as a result, the following significant neighboring color effects were detected and individually defined: (1) neighboring color's size, lightness, colorfulness, and hue on test color's lightness, (2) neighboring color's colorfulness and hue on test color's colorfulness, and (3) neighboring color's hue on test color's hue. Furthermore, through multiple regression analysis, color appearance models by which the lightness, colorfulness, and hue of bicolor woven fabrics can be predicted were derived. The predictive performance of the models was evaluated by calculating the difference between the visually estimated and the predicted color appearances, using ΔL*, ΔC*, Δh°, and ΔE_CMC(2:1). Among all the derived models, the model producing the smallest mean error was chosen as a final model, and its great accuracy in color appearance predictions was verified through further statistical evaluation. It is envisaged that the findings of this research are of benefit to design textile products with bicolor striped woven fabrics to have desired color appearances. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 512–521, 2017     

A new approach to appearance characterization

A proposal to characterize appearance in three different categories—color, cesia, and spatial properties or spatiality—is made. Color will include whiteness and yellowing and is related to optical power spectral properties of the stimulus detected by observers. Cesia will include transparency, translucence, gloss, luster, haze, lightness, opacity, matt, etc., and is related to the properties of reflecting, transmitting, or diffusing light by objects or materials evaluated by human observation. Spatial properties are divided in two main groups: (1) modes of appearance in which color is modified depending on the angle of observation related to the light incidence angle, such as metallic, pearlescent, or iridescent materials, and (2) modes of appearance related to optical properties of surfaces or objects in which effects of ordered patterns (textures) or finishing characteristics can be described by spatial filtering (roughness, polish, distinctness of image, orange peel, etc.). © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 164–167, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20205     

Digital color reconstructions of cultural heritage using color‐managed imaging and small‐aperture spectrophotometry

There are many examples of cultural heritage having optical properties that have changed with the passage of time. Examples include the yellowing, darkening, and fading of paints and varnishes caused by light exposure and atmospheric pollution. When it is infeasible to treat an object, an image simulation can provide a view to the past, known as a color reconstruction. A technique is described that relies on a color‐managed image, spectral reflectance factor measurements of the object, an optical model of colorant mixing, an optical database of artist materials, spreadsheet software, and image editing software. Spectral calculations are used to create adjustment curves where segmented portions of an object's image are translated in color. This approach has been used to produce color reconstructions of paintings by Vincent van Gogh and Georges Seurat. This colorimetric translation methodology is described and an example shown for the Chicago version of Vincent van Gogh's Bedroom. The methodology is compared with pixel‐based processing.     

Using discrete optimization for designing dental shade guides

A key criterion in the design of dental shade guides used for matching tooth color is that the shade tabs cover the natural tooth color space as completely as possible with a manageable number of tabs. Earlier studies have designed hypothetical shade guides from a given population of tooth colors described in the CIELAB system using the goal of minimizing the mean coverage error. In this study, we investigate this topic using the goal of maximizing coverage, meaning that as many measured colors as possible were within a given color difference from the nearest shade tab of the guide. We use techniques of linear discrete optimization to determine the positions of the shade tabs and consider both color difference formulas, CIELAB and CIEDE2000, in an exemplary tooth color population. We obtain coverage error and coverage figures for hypothetical shade guides of various numbers of tabs designed with the goal of either minimizing coverage error or maximizing coverage. Results show that discrete optimization and the goal of maximizing coverage could be used to improve shade guide development. The described technique could be used not only for dental shade guides development, but also for any purpose requiring coverage of as many colors as possible while keeping the number of reference colors manageable. © 2009 Wiley Periodicals, Inc. Col Res Appl, 2010     

Spectral analysis of blacks

The spectral behavior of different black surfaces including papers and fabrics are investigated in this study. Several colored pigments are mixed with the blacks in different concentrations to prepare black surfaces with different shades while a series of black dyestuffs are applied on textile materials to increase the ranges of black objects. The principal component analysis technique is applied to determine the actual spectral size of the reflectance dataset. The technique simply extracts the principal directions of spectral data and organizes them in restricted spectral spaces. Three different spectral spaces, i.e., the reflectance spectra, the Kubelka‐Munk function of reflectance as well as the inverse of reflectance factor are selected to present the samples in the restricted spaces. Based on the results, it is found that, there are no significant differences between the employed spaces and far from the employed spectral domains, black surfaces could be adequately described in a three‐dimensional space. The three extracted statistical colorants are used for reconstruction of reflectance spectra of samples while the root mean square error percentage and the color difference values under the standard observing condition confirm the suitability of such virtual primaries. The work is extended to reconstruction of spectral data from colorimetric information and the adequacy of such three‐dimensional space is reconfirmed. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2012     

Analysis of the spectral reflectance and color of mineral pigments affected by their particle size

The color of mineral pigments changes obviously with their particle size. However, how the particle size of these mineral pigments affects the color of the mineral pigment color block remains unclear. Based on optical principles and the physical properties of mineral pigment particles, our analysis found that changes in the particle size not only nonlinearly affect the behavior of light at the first surface of the mineral pigment color block, but also affect the interaction of light with the particles within the body of the mineral pigment color block, ultimately changing the spectral reflectance and color of the mineral pigment color block. Finally, we derived a nonlinear monotonically decreasing relationship between the particle size and the spectral reflectance. The experiment conducted in this article selected six kinds of mineral pigments as color block samples and observed the changes in the spectral reflectance and color value with the particle size. These studies are beneficial for color researchers conducting scientific research related to mineral pigments.