Effect of Gender, Experience, and Value on Color Perception Open Access

Achieving a harmonious smile has been one of the great challenges in restorative treatments, and in the search for excellent esthetics, the target of study by many researchers has been to reproduce the shade of natural teeth. Studies continue to be conducted in the endeavor to simulate natural teeth with restorative materials, and over the years, new possibilities have arisen. Nevertheless, it is still a challenging task to select the ideal shade for an esthetic restoration.

In 1801, Thomas Young learned about the trichromatic nature of human vision, presupposing the hypothesis that this phenomenon would be the result of the eye containing three light-sensitive mechanisms. Today it is known that this mechanism is related to the presence of light-receptor cells in the human retina, the cones and rods, which absorb the light by means of photosensitive pigments and transform it into a stimulus so that the brain perceives the color.¹ 

The evaluation of color occurs through the sequential processes of stimulation, sensation, and perception during color detection. These physical and psychological factors interact in order to enable color to be perceived.^2,3  The ability to select a shade varies from one individual to another and in the same individual at different times of visualization.^1,3,4  Due to variables in the environment and different personal evaluations and interpretations, dentists have found it challenging to select and communicate shades.

Shade selection depends on individual evaluation, which is subjective and consequently a clinically difficult process. Therefore, this is one of the reasons for developing standards for communicating shades and instruments that make it easier to measure them.⁵ 

At present, many methods are used to evaluate tooth shade. The comparison may be visual with the aid of scales, by means of instruments for measuring shade, or by digital image analysis.⁶  For the majority of dental professionals, a standard visual scale with a series of values continues to be the most commonly used method of shade selection, rather than computerized methods.^5,7 

Chromatic anomalies are factors that influence correct shade selection, and these defects are more frequently found among men.^8,9  Approximately 8% of all men and 0.5% of all women have some degree of defective color vision.⁹  This is one of the reasons women are considered more capable of matching shades than men are.^1,10,11 

It is known that men and women differ in their capacity to distinguish shades,^7,12,13  and traditionally women have been considered better at selecting shades than men.^11,14  The majority of studies have attached little or no importance to the observer's gender at the time of shade selection, even though this is a variable that can influence the end result of the selection process.^8,12,13 

Another variable to consider in shade matching is the observer's clinical experience, which can alter the capacity to reproduce the matching process.

The aim of this study was to investigate the importance of the observer's gender in the selection of shade. In addition, the study evaluated the extent to which the observer's clinical experience,^15-19  the ceramic shade,^20,21  and the value ^5,21 had an influence on the choice of shade.

Therefore, the null hypotheses to be tested were as follows: 1) gender is not a factor that significantly influences shade selection in ceramic restorations; 2) the observer's clinical experience is not related to the correct choice of ceramic shade; and 3) the value of the tooth does not influence the dentist's ability to select the ceramic shade.

Informed patient consent and ethics commission approval (Application No. 05/058 at São Leopoldo Mandic–School of Dentistry) were obtained for any in vivo experiments involved in this research.

A pilot study was conducted with 10 individuals in order to determine the power analysis of the sample size. A total of 99 student volunteers from the dental school were asked to participate in the project: 45 women (11 undergraduate and 34 postgraduate students from the restorative dentistry department) and 56 men (13 undergraduate and 43 postgraduate students). To eliminate possible errors resulting from congenital defects of color visualization, (eg, hereditary disorder linked to X-chromosome), each participant was submitted to a color vision test, using the Ishihara Test for Color Blindness.²²  The exam was performed by a calibrated examiner from the restorative dentistry department before the experiment was conducted, which excluded two men from the sample group, so that 54 individuals remained in the men's group.

Thirty-two ceramic samples (NobelRondo Alumina, Nobel Biocare, Göteborg, Sweden) were manufactured by the same certified dental technician, comprising 16 different shades of body ceramics (A0, A1, A2, A3, A3.5, A4, B0, B1, B2, B3, B4, C1, C2, C3, D2, D3), which were equally duplicated for performing shade matching. The final dimensions of the disks after finishing were approximately 2.9 mm thick and 11.0 mm in diameter.

The participants were asked to match the shades of one set of ceramic disks with those of the other set. The sets were placed on a neutral gray background that had 18% reflectance. No time limit was imposed on the evaluation, but the volunteers were advised of the possibility of fatigue of the retina cells if they stayed fixed on the samples for a long time. All the tests were performed on the premises of the São Leopoldo Mandic Postgraduation Center (Campinas, SP, Brazil) under the clinical lighting conditions that exist at the patient chair (fluorescent and natural light that comes through the window of the room) because it was the type of lighting most commonly found in dental offices and prosthesis laboratories.^23-26 

To analyze the association between the variables, the χ²  and Fisher exact tests were applied, adopting 5% as the level of statistical significance. Furthermore, an analysis of risk was performed, comparing the risk of wrong choices between the genders, among students with different levels of clinical experience, and between shades by the construction of intervals of confidence at a 95% probability.

The results are presented in Tables 1, 2, and 3. The results of the statistical analysis revealed that, with regard to gender, there was an association between the variables (χ²_= 5.5890 with 1 df, p=1.81%), rejecting the null hypothesis that they are independent. In the analysis of risk, it was verified that, among women, the risk of wrong choice was 29.58% and among men, 24.31% (Table 1). Thus, gender was a factor with a significant influence on choosing the ceramic shade.

A significant difference was found between the experienced observer and the beginners (Table 2). From the χ²  test results (χ²= 33.1628, p<0.01%) and the Fisher exact test (p=6.847⁻⁹), α dependence among the variables was shown. Thus, it was concluded that there was a significant association and that among undergraduate students, the risk of wrong choice was 38.02% and among the postgraduates, 23.08%.

Evaluating the influence of the shade of ceramic on the frequency of errors in the choice of shades (Table 3), the results of the χ²  test (χ²= 51.2835 , p<0.01%) showed statistical difference among the values. The Fisher exact test (p<0.01) showed that the frequency of errors rejected the null hypothesis that the variables are independent. In the risk analysis, it was verified that the risk of error in choice for the samples with light shades (A0, A1, A2, B0, B1, B2, C1, C2, D2) was 34.6%, and for the dark shades (A3, A3.5, A4, B3, B4, C3, D3) it was 18.69%, indicating a greater probability of error in selecting the light ones.

Selecting the shade of esthetic restorations is frequently based on visual perception by comparison with a shade guide in relation to the natural tooth, but there is great difficulty in transmitting the information obtained to the laboratory technician. In shade matching routinely done in dental offices, many uncontrolled variables are introduced into the evaluations made by human observers, such as the conditions of the environment, observer, or material evaluated.

In the current experiment, shade matching was performed using a fluorescent light source that, although not ideal, provided a standard necessary for the measurements, something not always possible with daylight. The results of some studies have shown a notable difference in correct shade selection under ideal lighting conditions.^9,23,24  Nevertheless, even the use of the ideal type of lighting does not guarantee precise shade matching, because the environment is not free of the natural light coming through the workroom window and mixing with the artificial light.³ 

The problems of shade perception are more common than one imagines and have different causes and variations. Because color blindness is a hereditary disorder linked to the X chromosome, men are 10 to 20 times more prone to having the deficiency than women,¹  which was also found in the current research, given that two men were excluded from the sample for reasons of daltonism (color blindness) as detected by the Ishihara test. The present data are in agreement with the data described by Barna and others²⁵  who, when examining several dentists with regard to color visualization defects, found that seven of the 50 participants had a chromatic anomaly. Moser and others⁸  in evaluating a group of 670 dentists, verified that 10% had some type of deficiency related to shade perception. This condition affects the ability to discriminate shades, which is in agreement with other studies.^7,8 

Although women are considered more capable than men with regard to shade selection,^10,11,13,26  some studies have demonstrated that there were no statistical differences with regard to the observer's gender in the ability to select color.^20,27,28  The results found in the present research, however, are in conflict with the previously described reports, because male observers obtained a higher frequency of correct results (75.69%) in matching the ceramic shades when compared with the female observers (70.42%). Donahue and others,¹²  when working with a similar methodology, found similar results, in which men showed slightly higher (63%) differences in comparison with women (58%) but without any statistical significance. Analyzing the space axes of shade and evaluating the dissimilarities perceived by each gender, Bimler and others¹³  concluded that men are less sensitive to stimuli on the green-red axis, but in compensation, are more sensitive along the axis of brightness. Because the value of shade is considered the most critical component of color when matching shades,^26,29,30  this is perhaps one of the reasons for the current results.

Dentists and dental students are required to select the shades of esthetic restorations in their work environment. The question to be discussed is whether these professionals, irrespective of their years of clinical experience, are equally capable of performing this task. According to some studies, the evaluators' years of clinical experience did not positively affect the capacity of shade selection.^{7,15,21,25,28}  Nevertheless, other studies found that this factor was relevant in the frequency of right choices of ceramic shade, which is in agreement with the findings of this current study.^16-19,31  Experienced clinicians were statistically significantly better at recognizing pairs of equal shades correctly (76.92%) than were the novices (61.98%). Therefore, one can speculate that training is a preponderant factor in correct shade selection.

Analysis of the risk of wrong choice when selecting a light or dark shade was also performed, with verification that the probability of wrongly choosing a light shade was greater. These results are in partial agreement with the data described by Lagouvardos and others,²¹  who verified that the shades at the beginning or end of each group evaluated (ceramic scale–Vita Classical, resin composite shade scale–Heraeus Kulzer, and extracted teeth) had more reliable results. The intermediate shades in the scales have little difference between them according to the color values (ΔE< 3.3).²⁸  Small differences in shade may not be perceived when there are differences below 3.7 units of ΔE, because these were evaluated as being equal in the oral cavity.³² 

A factor that could have affected the results obtained in this research was related to the use of fluorescent light. This could have been replaced by standardized corrected light to verify whether this parameter is essential in pairing the shades, because in order to discriminate colors, this is known to be essential.^9,19,23-25 

From analysis of the data in the literature and the results of the current study, any type of formula for transmitting data to the laboratory is with error, because there are a series of factors, both biological and technical, that must be considered when shade perception is involved. It is proposed that, irrespective of gender, professionals should consider getting a second opinion in shade selection in order to obtain more reliable results. Given the small number of studies in the literature similar to the present study, particularly with regard to the observer's gender, further investigations on the same subject should be conducted to validate and confirm the conclusions of this analysis.

1. 1

   Selection of the ceramic shade was influenced by the observer's gender, with the male gender tending to be more successful in discriminating the shades.

2. 2

   The participants with more clinical experience had a significantly higher number of correct choices than the novices.

3. 3

   For the shades evaluated, it was observed that darker shades were easier to distinguish than the lighter ones.

As a result of variations in accurate shade perception, considerations should be given to using multiple opinions to compensate for errors caused by gender or inexperience, especially when lighter shades are involved.