The impact of tooth colour on the perceptions of age and social judgements.

OBJECTIVE: Psychological research has established that the presence of dental anomalies negatively impact social judgements. This study sought to determine the effects of tooth colour on the subjective ratings of social judgements in a group of Caucasian adults. METHODS: A cross sectional experimental analogue design comprised fifty Caucasian adults: 25 women and 25 men. A total of 54 digitally modified photographs of Caucasian males and females (darkened, natural, whitened teeth) were evaluated. All participants evaluated each of the images on 12 characteristics: popularity, friendliness, social life, success, graduation, happiness, intelligence, perceived age, introversion/extraversion, self-confidence, attractiveness and satisfaction with the tooth shade. Analysis of variance (ANOVA) was used to compare ratings. RESULTS: Participants associated darkened teeth with poorer subjective ratings, with the highest ratings been given to whitened teeth, and natural teeth being intermediate. These trends were similar across all participant age groups and gender. Further, the gender and age groups of the images had a significant effect on the appraisals. Faces of younger models received higher ratings than the faces of older models and female images were rated higher than the males. CONCLUSION: In the absence of other information, tooth colour exerts an influence upon the appraisals made in social situations. It appears that whitened tooth appearance is preferred to natural tooth appearance, irrespective of age and gender of the judge. The faces with more whitened dentition are perceived to be younger across all age groups and gender of the judges. Participants dissatisfied with their own tooth shade drew out more stereotypic behaviour. CLINICAL SIGNIFICANCE STATEMENT: This research used standardised tooth colour as a basis to investigate perceived age and social functioning. As clinicians face daily challenges to achieve patient satisfaction with respect to dental aesthetics, standardizing the colour may enhance the patients' satisfaction. Further, participants dissatisfied with their own tooth shade drew out more stereotypic behaviour. The whitened dentition may impair the psychological well-being of the individuals and is probably a reason for the increasing demand for cosmetic dental procedures. These results may be instructive for the development of a psycho-educational intervention to prevent any unrealistic expectations.

Color adjustment potential of resin composites.

The study objective was to explore a new method for quantifying the color adjustment potential originating from physical translucency on a set of 7 resin composites, and then for testing the hypothesis that color adjustment potential is dependent on the composites and shades studied. Two-composite specimens (an outer base shade with an inner hole filled with inner test shades) and single-composite specimens of all shades were made. A 1-mm circular area, with its center in the middle of the specimen (P0mm), was measured by means of spectroradiometry. A newly developed equation for quantification of the color adjustment potential was tested. Color adjustment potential at P0mm ranged from -0.19 (negative color adjustment/contrast) to 0.61. Within the limitations of this study, a newly developed concept and equation have proved the existence of the physical component of color adjustment of translucent dental materials. Color adjustment potential was dependent on composite and shade.

Multiple groups of orientation-selective visual mechanisms underlying rapid orientated-line detection.

Visual search for an edge or line element differing in orientation from a background of other edge or line elements can be performed rapidly and effortlessly. In this study, based on psychophysical measurements with ten human observers, threshold values of the angle between a target and background line elements were obtained as functions of background-element orientation, in brief masked displays. A repeated-loess analysis of the threshold functions suggested the existence of several groups of orientation-selective mechanisms contributing to rapid orientated-line detection; specifically, coarse, intermediate and fine mechanisms with preferred orientations spaced at angles of approximately 90 degrees, 35 degrees, and 10 degrees-25 degrees, respectively. The preferred orientations of coarse and some intermediate mechanisms coincided with the vertical or horizontal of the frontoparallel plane, but the preferred orientations of fine mechanisms varied randomly from observer to observer, possibly reflecting individual variations in neuronal sampling characteristics.

Orientation contrast vs orientation in line-target detection.

This study concerns the roles of absolute and relative orientation in determining detectability of a line-element target in a background field of uniformly oriented line elements. Target detectability was determined as a function of background-field orientation, sampled at 5 deg intervals, for three levels of orientation contrast--the difference between target and background orientations--sampled at 10, 20 and 30 deg. Stimulus displays were presented briefly and followed by a mask. There were 10 observers, whose detection performance was quantified by the discrimination index d' from signal detection theory. Target detectability was found to depend both on absolute orientation, represented by background-field orientation, and on orientation contrast. At each level of orientation contrast, performance was best when the background field, not the target element, was vertical or horizontal. These data are difficult to explain by general models of orientation discrimination based on simple orientation opponency between local line-sensitive filter units; three other models specifically concerned with target detection are briefly considered.

The spatio-chromatic sensitivity of the human visual system.

The response of the human visual system depends on a multitude of image features, such as the wavelength (colour) of the visual stimulus and its spatial frequency content. Hence we need to take into account the spatial and chromatic sensitivity as well as spatio-chromatic interactions to properly characterize visual sensitivity. In this paper we report two experiments that further characterize the spatio-chromatic sensitivity of the human visual system for stationary stimuli, namely the detection of small visual orientation differences and the detection of blur. In both cases we find that the visual system is equally sensitive to red-green and to black-white modulations for a wide range of spatial parameters. Furthermore, the contrast dependence for red green and black white modulations is identical, suggesting that the same mechanism mediates both types of stimulus. Our results are in accordance with the hypothesis that both tasks are mediated by the parvocellular as opposed to the magnocellular pathway.

Spectrophotometric analysis of all-ceramic materials and their interaction with luting agents and different backgrounds.

In this study, two All-Ceramic (AC) materials--Empress 2 (EMP) (Ivoclar Vivadent AG, Schaan, Liechtenstein) and In-Ceram ALUMINA (ICA) (Vita Zahnfabrik, Bad Säckingen, Germany)--were analyzed, along with the effects of 3 luting agents-viz. Zinc Phosphate cement (ZNPO, PhospaCEM PL, Ivoclar Vivadent AG, Schaan, Liechtenstein), Glass Ionomer Cement (GIC, Ketac-Cem Radiopaque, ESPE Dental AG, Seefeld, Germany), and Compolute (COMP, ESPE Dental AG, Seefeld, Germany)--on the final color, using the CIELab system. Color differences (DeltaL, Deltaa, Deltab, and DeltaE) were calculated for samples with luting agents and for samples without luting agents with standard white and black backgrounds, with the use of a spectrophotometer, Luci 100 (Dr. Lange, Berlin, Germany). One-way ANOVA for DeltaL, Deltaa, Deltab, and DeltaE within both the AC systems, with and without luting agents, showed significant contributions of the background (p < 0.05). EMP was seen to be more translucent than ICA. Darker ceramics showed less color variation. Luting agents altered the final color of the restoration. ZNPO was least translucent, followed by GIC and COMP. Marginal increases in thicknesses of ICA samples (0.4 mm) do not show a statistically significant color difference. No method exists to predict the outcome of an AC restoration based on consideration of the luting agent and the background color.

Macular pigment and color discrimination.

An earlier modeling study of the effect of changes in macular pigment optical density (MPOD) on a wide range of surface colors is re-examined. That study reported changes in local chromaticity variance and in color spacing, some of which were incompatible with tritan-like confusions in normals associated with high-simulated MPOD. This disagreement might have arisen through the use of the von Kries correction for adaptation. The analysis is repeated, using 1782 reflectance spectra of natural and man-made colors. These colors are segregated into an array of 25 equally populated cells in an analogue of the MacLeod-Boynton cone excitation diagram. Removing the von Kries correction restores compatibility with other experimental data. Differences between the results for normal and anomalous trichromats, noted in the earlier study, are confirmed. An analysis of local chromaticity variance across color space indicates the presence of systematic patterns. The earlier study also reported differences in results across observer types (for example, between normals and protanomals) and this is addressed here by utilizing fundamentals defined by a variable photopigment template. Chromaticities are computed for the same 1782 reflectance spectra for normals and for a set of protanomals (for whom the anomalous L pigment is shifted between the normal L and M spectral locations). Colors are segregated into an array of 100 cells in an analogue of the MacLeod-Boynton cone excitation diagram. Changes in chromaticity variance with MPOD for these cells are mapped for normals and protanomals. Variance along the L/(L + M) axis is sensitive to the number of cells used for segmentation. It also increases with MPOD for normal observers but this trend reverses as the wavelength of maximum sensitivity of the L cone shifts towards shorter wavelengths (protanomalous locations).

Invariant cone-excitation ratios may predict transparency.

Cone-excitation ratios for pairs of surfaces are almost invariant under changes in illumination and offer a possible basis for color constancy [Proc. R. Soc. London Ser. B 257, 115 (1994)]. We extend this idea to the perception of transparency on the basis of the close analogy between the changes in color signals that occur for surfaces when the illumination changes and the changes in color signals when the surfaces are covered by a filter. This study presents measurements and simulations to investigate the conditions under which cone-excitation ratios are statistically invariant for physically transparent systems. The invariance breaks down when the spectral transmission of the filters is low at some or all wavelengths. We suggest that cone-excitation ratios might be useful to define the stimulus conditions necessary for the perception of transparency.

Optimized model of oriented-line-target detection using vertical and horizontal filters.

A line-element target differing sufficiently in orientation from a background of line elements can be visually detected easily and quickly; orientation thresholds for such detection are lowest when the background elements are all vertical or all horizontal. A simple quantitative model of this performance was constructed from three processing stages: (1) linear filtering by two classes of anisotropic filters, (2) nonlinear point transformation, and (3) estimation of a signal-to-noise ratio based on responses to images with and without a target. A Monte Carlo optimization procedure (simulated annealing) was used to determine the model parameter values required for providing an accurate description of psychophysical data on orientation increment thresholds.

Blur tolerance for luminance and chromatic stimuli.

We investigated the blur tolerance of human observers for stimuli modulated along the isoluminant red-green, the isoluminant yellow-blue, and the luminance (black-white) direction in color space. We report the following results: (i) Blur difference thresholds for red-green and luminance stimuli (of equal cone contrast) are very similar and as low as 0.5 min of visual angle; for yellow-blue the lowest blur thresholds are much higher (1.5 min of visual angle). (ii) The smallest blur thresholds are found for slightly blurred square waves (reference blur of 1 arc min) and not for sharp edges. (iii) Blur thresholds for red-green and black-white follow a Weber law for reference (pedestal) blurs greater than the optimum blur. (iv) Using the model proposed by Watt and Morgan [Vision Res. 24, 1387 (1984)] we estimated the internal blur of the visual system for the black-white and the red-green color directions and arrived at the following estimates: 1.2 arc min for black-white stimuli at 10% contrast and 0.9 arc min for red-green stimuli at 10% cone contrast. Blur tolerance for yellow-blue is independent of external blur and cannot be predicted by the model. (v) The contrast dependence of blur sensitivity is similar for red-green and luminance modulations (slopes of -0.15 and -0.16 in log-log coordinates, respectively) and slightly stronger for yellow-blue (slope = -0.75). Blur discrimination thresholds are not predicted by the contrast sensitivity function of the visual system. Our findings are useful for predicting blur tolerance for complex images and provide a spatial frequency cutoff point when Gaussian low-pass filters are used for noise removal in colored images. They are also useful as a baseline for the study of visual disorders such as amblyopia.