Bridging instrumental and visual perception with improved color difference equations: A multi-center study.

OBJECTIVES: This multicenter study aimed to evaluate visual-instrumental agreement of six color measurement devices and optimize three color difference equations using a dataset of visual color differences (∆V) from expert observers. METHODS: A total of 154 expert observers from 16 sites across 5 countries participated, providing visual scaling on 26 sample pairs of artificial teeth using magnitude estimation. Three color difference equations (ΔE*ab, ∆E00, and CAM16-UCS) were tested. Optimization of all three equations was performed using device-specific weights, and the standardized residual sum of squares (STRESS) index was used to evaluate visual-instrumental agreement. RESULTS: The ΔE*ab formula exhibited STRESS values from 18 to 40, with visual-instrumental agreement between 60 % and 82 %. The ∆E00 formula showed STRESS values from 26 to 32, representing visual-instrumental agreement of 68 % to 74 %. CAM16-UCS demonstrated STRESS values from 32 - 39, with visual-instrumental agreement between 61-68 %. Following optimization, STRESS values decreased for all three formulas, with ΔE' demonstrating average visual-instrumental agreement of 79 % and ∆E00 of 78 %. CAM16-UCS showed average visual-instrumental agreement of 76 % post optimization. SIGNIFICANCE: Optimization of color difference equations notably improved visual-instrumental agreement, overshadowing device performance. The optimzed ΔE' formula demonstrated the best overall performance combining computational simplicty with outstanding visual-instrumental agreement.

Tooth Colour and Facial Attractiveness: Study Protocol for Self-Perception with a Gender-Based Approach.

(1) Background. The aim of the present protocol is to assess whether self-perception of tooth colour and facial attractiveness correlates with gender and mood state. (2) Study protocol. The protocol foresees a cross-sectional clinical study, developed by Sapienza University of Rome, Italy, Department of Oral and MaxilloFacial Sciences, and 15 UNID (Unione Nazionale Igienisti Dentali-National Union of Dental Hygienists)-affiliated clinical centers in Italy. The protocol consists of a clinical visit, during which photographic documentation of the face and smile is collected with spectrophotometric evaluation of tooth colour. During the visit, two validated questionnaires are filled in. The first one is filled by the operator for the collection of data on: i) patient's face and smile colorimetric characteristics; ii) patient's and operator's evaluations of the dental colour and smile attractiveness. The second one is completed by the patient for the assessment of his/her mood state. (3) Conclusions. This protocol highlights the importance in aesthetic dentistry of a gender-specific approach and the limitations of gender-neutral models, revealing the existing gender differences in aesthetic self-perception. In addition, the colour-matching relationships between facial and dental colour characteristics will be explored. This approach improves the accuracy and personalization of aesthetic assessments in dentistry, by addressing personalized and gender-specific needs. A gender-inclusive methodology that takes a more nuanced and culturally aware approach to aesthetic dentistry is a useful adjunct to modern clinical practices.

Illuminant metamerism between natural teeth and zirconia restorations evaluated with a chromatic adaptation transform.

STATEMENT OF PROBLEM: Little is known about the effect of illuminant metamerism between natural teeth and zirconia restorations, despite their increasing clinical popularity. PURPOSE: The purpose of this in vitro study was to compare illuminant metamerism between pairs of natural teeth and layered zirconia restorations and pairs of natural teeth and monolithic zirconia restorations under 10 different illuminants and analyze their metameric potential. MATERIAL AND METHODS: Spectral reflectance factors were obtained from 10 pairs of extracted natural teeth and layered zirconia restorations and 28 pairs of extracted natural teeth and monolithic multilayer zirconia restorations. Each pair showed a color match that was within the visual threshold for clinical acceptability (CIEDE2000≤1.8). A special index of metamerism for the change of illuminant (Milm) was calculated from the CIEDE2000 color difference equation. Descriptive statistics and the one-sample t test were used to analyze the results for the Milm and for both groups of layered and monolithic zirconia restorations (α=.05). RESULTS: Layered zirconia restorations reached a mean ±standard deviation value for Milm=0.3 ±0.2 and Milm=0.5 ±0.4 for monolithic zirconia restorations (P<.01). CONCLUSIONS: The effect of illuminant metamerism between natural teeth and zirconia crowns was weak and generally within the clinical acceptability limit.

The effect of colour environments on visual tracking and visual strain during short-term simulation of three gravity states.

This study investigated the effects of nine colour environments on visual tracking accuracy and visual strain during normal sitting (SP), -12° head-down bed (HD) and 9.6° head-up tilt bed (HU). In a standard posture change laboratory study, fifty-four participants performed visual tracking tasks in nine colour environments while in the three postures. Visual strain was measured by means of a questionnaire. The results showed that in all colour environments, the -12° head-down bed rest posture significantly affected visual tracking accuracy and visual strain. During the three postures, the participants' visual tracking accuracy in the cyan environment was significantly higher than that in other colour environments, and their visual strain was the lowest. Overall, the study adds to our understanding of how environmental and postural factors impact on visual tracking and visual strain.

A model for assessing the efficacy of colour vision aids.

Optical filter aids are marketed which claim to improve colour discrimination in red-green colour vision defectives. An earlier model has been revised and used to assess 9 currently available aids. Spectral reflectances (400-700 nm) for 80 colours equally spaced in hue angle at four equally spaced saturations were synthesised from chromatically adjacent Munsell colours. Aid induced chromaticity changes for Protanomals and Deuteranomals were calculated. Five aids enhanced red-green discrimination significantly for Protanomals and six for Deuteranomals and one aid reduced it significantly for both defectives. Five aids enhanced blue-yellow discrimination in Protanomals and Deuteranomals for whom it is not needed.

The Effect of Correlated Colour Temperature on Physiological, Emotional and Subjective Satisfaction in the Hygiene Area of a Space Station.

The hygiene area is one of the most important facilities in a space station. If its environmental lighting is appropriately designed, it can significantly reduce the psychological pressure on astronauts. This study investigates the effect of correlated colour temperature (CCT) on heart rate, galvanic skin response, emotion and satisfaction in the hygiene area of a space station. Forty subjects participated in experiments in a hygiene area simulator with a controlled lighting environment. The lighting conditions included 2700 K, 3300 K, 3600 K, 5000 K and 6300 K; physiological responses (heart rate, galvanic skin response), as well as emotion and satisfaction, were recorded. The results showed that CCT significantly influenced the participants' physiological and subjective responses in the space station hygiene area. 6300 K led to the best emotion and satisfaction levels, the highest galvanic skin response and the lowest heart rate. The opposite was true for 2700 K.

Effect of Elevation and Surface Roughness on Naturalness Perception of 2.5D Decor Prints.

Naturalness is a complex concept. It can involve a variety of attributes. In this work, we considered the effect of elevation and surface roughness on naturalness perception of 2.5D decor prints for four material categories. We found that elevation has an impact on the naturalness perception of 2.5D decor prints and that it is linked with content. The observers found lower elevation to be more natural for wood and glass 2.5D prints while there was no clear tendency for stone and metal 2.5D prints. We also found the perceptual attributes used for naturalness assessment of 2.5D decor prints. The top five ones are color, roughness, gloss, elevation, and lightness. The obtained findings can be useful for companies that produce 2.5D prints.

What Elevation Makes 2.5D Prints Perceptually Natural?

Elevation plays a considerable role in naturalness perception of 2.5D prints. The necessary level of elevation to make 2.5D prints look perceptually natural may vary from application to application. Therefore, one needs to know the right elevation for specific applications to make the prints look perceptually natural. In this work, we investigated what elevation makes 2.5D prints of wood images perceptually natural. We worked with various wood content images such as wooden wicker, wall, roof, and floor. We found that the optimal elevation that makes 2.5D prints of wood images perceptually natural is content-dependent and in a range between 0.3 mm and 0.5 mm. Moreover, we found that the optimal elevation becomes 0.5 mm if we consider images of wood regardless of the wood content. In addition, there was a high correlation between majority of observers on naturalness perception of 2.5D prints of wood images.

In-vivo colour stability of enamel after ICON® treatment at 6 years of follow-up: A prospective single center study.

OBJECTIVES: This in-vivo clinical study provides subjective and objective documentation on colour stability of enamel after resin infiltration at a mean observation time of six years after treatment. METHODS: 76 teeth previously treated with ICON® due to hypomineralized lesions of enamel were recalled for a follow-up at the 1st Observation Unit of the Department of Oral and Maxillofacial Sciences, "Sapienza" University of Rome (Italy). Colour stability was assessed: i) subjectively by patients using FDI-colour matching criteria; ii) objectively by calculating CIEDE2000 colour differences between the affected/treated and sound enamel in each tooth at T0 (baseline), T1 (one year) and T2 (six years) based on spectrophotometric data. Analysis of correlation between FDI and CIEDE2000 data was performed. RESULTS: Two teeth were lost to follow-up prior to 72 months. No unwanted effects were reported by patients. Number of FDI scores 1 and 2 were 13.5%, 90.6% and 93.2% at T0, T1 and T2, respectively. ΔE00 was evaluated at 6.8 (SD3.8) at T0. ΔE00 was 5.8 (SD3.1) between T0 and T1 and 1.3 (SD0.6) between T1 and T2. ΔE00 reduction (T1-T0) was significantly but only fairly correlated with FDI scores at any follow-up. CONCLUSIONS: This study shows that caries infiltration satisfactorily masks aesthetically relevant lesions after longer follow-up. Subjective and objective outcomes showed a fair correlation mainly for the initial masking effect. CLINICAL SIGNIFICANCE: This prospective clinical trial demonstrates the excellent subjective and objective colorimetric stability of enamel treated with ICON® 6 years after treatment.

Investigation of hue effects in tooth whiteness perception.

OBJECTIVE: To identify the hue angles that provide the optimal perception of tooth whitening. METHODS: Thirty-three male/female adult observers with normal color vision were recruited to assess teeth images on a color calibrated display. Images of teeth were generated which simulated color changes in each of eight hue directions in the CIE a*b* plane, each equi-distant from a baseline tooth color. Using a paired comparison study design, observers were asked to indicate which of two images had whiter teeth. The data were converted into an interval scale using Thurstone's Law of Comparative Judgment. The relationship between the hue angles and the scores was modeled by curve fitting. RESULTS: The optimal hues were found in a region between green and blue in the CIE a*b chart. When the tooth color travels in an optimal hue direction, the same amount of color change will result in a greater change in whiteness perception than when traveling in other hue directions. CONCLUSIONS: The optimal hues for tooth whitening were identified from the visual perception study. The most effective tooth whitening direction is to change tooth color towards the greenish-blue hue direction. CLINICAL SIGNIFICANCE: This study gives clinicians and researchers a better understanding of tooth color hue effects in tooth whiteness perception.

Aroused and Impulsive Effects of Colour Stimuli on Lateral and Logical Abilities.

The purpose of this study was to explore the influence of environmental colour on people's lateral and logical abilities. This was done by evaluating study participants' response time and error rate when completing six types of psychometric tests that were performed in various hue backgrounds on a computer. To maximise the colour stimulation provided by the monitor, the experiment was carried out in a dark laboratory. Analysis of participants' response time and error rate showed that different colours could significantly influence arousal and impulsiveness, which suggests that colour has indirect impacts on cognitive abilities. Further analysis revealed that different colours had various effects depending on the type of psychometric test given. These findings suggest that future research on environmental design should consider how to effectively use colour to impact people's performance and behaviour.

Objective shade matching, communication, and reproduction by combining dental photography and numeric shade quantification.

OBJECTIVE: The subject of this case report is the application of a newly developed workflow for objective shade communication sans visual shade assessment or the use of shade guides. CLINICAL CONSIDERATIONS: Clinical complications stemming from issues relating to esthetic integration can present a burden on the restorative team, often resulting in strenuous relationships among its members. The faithful imitation of the optical appearance of dental hard tissues with direct- and indirect restorations has been at the center of interest in a great number of publications from the realm of esthetic dentistry over the past 40 years. The present report describes a new approach to objective shade communication, by transcending the role of dental photography from its purely descriptive purpose to the level of quantification, thus abandoning the use of the established shading regimes and replacing them with a patient personal shade recipe based on the CIELAB color space instead. CONCLUSIONS: Objective shade communication is possible with the eLAB system by combining numeric shade quantification with dental photography. CLINICAL SIGNIFICANCE: The eLAB system presents a viable alternative to the traditional approach to shade communication and shade matching in dentistry.

A Comparative Study of Colour Effects on Cognitive Performance in Real-World and VR Environments.

This research explores the influence of colour on cognitive performance and intellectual abilities (i.e., logical and lateral thinking abilities and people's attention to detail) in a conventional laboratory setting and an approximately identical virtual reality (VR) environment. Comparative experiments using psychological methods were carried out in both settings to explore the impact of immersive colour experience. This work builds on earlier studies that suggest that the VR environment enhances user experiences, with results evidencing that a considered approach to colour design can trigger a positive impact on user engagement. The experiments further evaluated the positive effects of immersive colour stimuli in VR by evaluating participants' logical and lateral thinking abilities, as well as their attention to detail. Their response time and error rate when completing each psychometric test were recorded with different hue backgrounds in both environments. The data collected from participants reveal the differential impacts of colour between the reality setting using standard colour imaging displays and in an approximately identical VR environment. Analysis of the psychometric tests shows the differential influence of colours on logical and lateral thinking abilities and people's attention to detail between the physical environment and the VR environment. Our findings add to the data demonstrating that a well-designed immersive colour experience in VR can trigger positive user engagement and, as explored in this study, improve cognitive performance. This again positions immersive colour experience as an important design tool to be fully considered in the creation of effective VR research and applications.

Designing Effective Warnings about Addiction on the Patient Information Leaflet of Over-the-Counter Codeine Sold in England to University Students.

(1) Background: The harm of misusing over-the-counter (OTC) codeine-containing medicines among university students in England is being increasingly recognized. Based on English university students, this paper aims to study the importance of information design on information communication, explore methods for effective warning design, and investigate university students' perception of OTC codeine. (2) Methods: The effective warning design is addressed through case studies, answering correctness by the heat map generated from the eye-tracking experiment (ETE), and the total time spent on the tasks. User perceptions are made though online surveys. (3) Results: Information design significantly affects the way user processes information. Therefore, two emphasized warnings displayed in the headline, and the "possible side effect (PSE)" sections and warning signs of addiction presented under the PSE are suggested as effective ways to display warnings. For students' perception of OTC codeine, 80% of university students are unfamiliar with the substance. After reading the patient information leaflets (PILs), 47% recommended tight regulation on codeine. (4) Conclusions: The misuse of OTC codeine could be a potential problem among English university students. The design of the PIL significantly influences the chance of unintentional medicine misuse. The display of warnings on the PILs of OTC codeine should be redesigned for better understanding.

A psychophysical measurement on subjective well-being and air pollution.

Although the physical effects of air pollution on humans are well documented, there may be even greater impacts on the emotional state and health. Surveys have traditionally been used to explore the impact of air pollution on people's subjective well-being (SWB). However, the survey techniques usually take long periods to properly match the air pollution characteristics from monitoring stations to each respondent's SWB at both disaggregated spatial and temporal levels. Here, we used air pollution data to simulate fixed-scene images and psychophysical process to examine the impact from only air pollution on SWB. Findings suggest that under the atmospheric conditions in Beijing, negative emotions occur when PM2.5 (particulate matter with a diameter less than 2.5 µm) increases to approximately 150 AQI (air quality index). The British observers have a stronger negative response under severe air pollution compared with Chinese observers. People from different social groups appear to have different sensitivities to SWB when air quality index exceeds approximately 200 AQI.

A yellowness index for use in dentistry.

OBJECTIVES: To develop an equation that predicts the perceptual yellowness of teeth. METHODS: A large set of new psychophysical yellowness data were generated from an experiment where 500 participants each ranked a set of 58 shade guide samples. Two existing equations (WIO and b*) and one new equation (YIO) were evaluated by comparing their values for the 58 shade guide tabs with the psychophysical data. Coefficient of determination (r2), '% wrong decisions', and STRESS were used as measures of performance. The YIO equation was optimized using these data to maximize the r2 value. A validation set of psychophysical data was prepared in an experiment where 40 participants each ranked 5 sets of 9 samples that were viewed on an emissive display. The candidate equations were evaluated using these data and the r2, %WD, and STRESS metrics. RESULTS: All three metrics YIO, WIO and b* were strongly correlated with perceptual yellowness. YIO and WIO both showed stronger correlation than b*. CONCLUSIONS: A new yellowness equation YIO has been developed to correlate with tooth yellowness. It is suggested that tooth yellowness and whiteness are highly related concepts.

Evaluation of colorimetric indices for the assessment of tooth whiteness.

OBJECTIVES: To evaluate the performance of existing equations that measure perceptual whiteness of teeth. METHODS: Three new psychophysical experiments were conducted and combined with two previously published experiments to form a large set of data to test performance of whiteness indices. Three whiteness indices (WIC, WIO, WID,) were compared with regard to their ability to measure perceived whiteness. Coefficient of determination (r2) and '% wrong decisions' were used as measures of performance. One of the new experiments involved 500 participants across five different countries to explore the effect of gender, age and culture on whiteness perception. RESULTS: Equations (WIO and WID) that have been optimized for use with tooth whiteness better correlated with visual perceptions of changes in tooth whiteness than the more general CIE whiteness index (WIC). The best performance was given by WIO (in terms of both r2 and % wrong decisions). No effect of age, gender or culture was found on whiteness perception. CONCLUSIONS: WIO is a robust method for assessing whiteness of human teeth.

Tooth color and whitening - digital technologies.

OBJECTIVES: To review the key concepts of color in the dental domain with specific reference to the use of digital technology to measure color and color appearance. MATERIALS AND METHODS: The literature on color assessment in dentistry is considered and methods for assessing whiteness, yellowness and color appearance are collated and described. RESULTS AND CONCLUSION: A variety of methods for assessing color have been shown to exist and be viable including digital imaging. Equations to predict whiteness are identified; there is evidence that they are effective but further evaluation may be needed.

Objective and subjective aesthetic performance of icon® treatment for enamel hypomineralization lesions in young adolescents: A retrospective single center study.

OBJECTIVES: An evaluation method is proposed to qualitatively and quantitatively evaluate the clinical outcome of the enamel hypomineralization treatment with infiltrative resin in young adolescents. The aesthetic outcome is assessed before and after treatment by visual evaluation using FDI-colour match criteria and by spectrophotometric analysis using the CIEDE2000 colour difference formula. The visual (subjective) results are compared with the spectrophotometric (objective) approach. MATERIALS AND METHODS: 76 teeth of patients of Sapienza University (Rome, Italy) presenting early caries lesions and/or developmental defect of enamel on the labial surface of clinical crown were subjected to resin infiltration. Three observers evaluated the aesthetic appearance of the teeth before and after treatment using FDI-colour match criteria. The spectrophotometric colour difference between the affected and sound enamel in each tooth was calculated before and after resin infiltration. A correlation between FDI criteria and the calculated CIEDE2000 colour difference (ΔE00) was performed. RESULTS: Mean FDI scores and ΔE00, evaluated before and after treatment, were large in all sample. A clear correlation was detected between visual inspections and spectrophotometric colour difference of clinical outcomes. CONCLUSIONS: On the basis of the present study results, the aesthetic outcome of resin infiltration proved to be highly effective, both with visual qualitative and spectrophotometric quantitative assessment. CLINICAL RELEVANCE STATEMENT: Hypomineralized enamel colour abnormalities affect patients' quality of life, therefore tissue preservative cosmetic treatments are requested. An evaluation method of resin infiltration clinical outcome by visual evaluation and spectrophotometry is proposed.

Investigation of the perceptual thresholds of tooth whiteness.

OBJECTIVE: To investigate the tooth whiteness perceptibility thresholds of the average observer to changes in the CIELAB values and an optimised whiteness Index for dentistry (WIO) based on psychophysical studies. METHODS: A psychophysical experiment based on visual assessments of digital images of teeth on a calibrated display with a group of observers (n=32) has been conducted to determine the perceptual thresholds in tooth whiteness. Digital simulations of a tooth that is identical in shape to the left incisor in the image of teeth were superimposed on to images. The colour of the simulated tooth was varied and observers were asked to respond whether there was a difference in whiteness between the left incisor and the simulated tooth. Thresholds for detection of differences in whiteness were independently determined in four conditions: ΔL*, Δa*, Δb* and a blue optical whitening direction. Raw data were fitted using a non-parametric approach and thresholds of CIELAB and WIO for each conditions were calculated. RESULTS: Estimates of the threshold of the four conditions of ΔL*, Δa*, Δb* and a blue covarine optical tooth whitening direction were 1.14, 3.24, 1.11 and 1.51 respectively, with the corresponding WIO thresholds of 2.77, 6.52, 3.09 and 1.99 respectively. CONCLUSIONS: The thresholds for tooth whiteness perception in CIELAB space and WIO space were determined. The findings demonstrate that for a whitening treatment with a blue covarine optical technology, a colour change of about 2 WIO units would be noticeable. CLINICAL SIGNIFICANCE: This study gives a better understanding of the tooth whiteness perception threshold, and will help clinicians identify perceivable differences in tooth colour during matching and whitening procedures.