The Influence of the Extent of Color-Vision Deficiency on Shade-Matching Ability.

OBJECTIVE: To evaluate the influence of the extent of color-vision deficiency on visual shade-matching ability.
MATERIALS AND METHODS: Six groups were investigated: the control group (N = 68), the protan medium deficiency (PMED) group (N = 5), the protan strong deficiency (PSTD) group (N = 5), the deutan mild deficiency (DMID) group (N = 5), the deutan medium deficiency (DMED) group (N = 5) and the deutan strong deficiency (DSTD) group (N = 8). The color vision of the participants was evaluated monocularly using the Hardy-Rand-Rittler (HRR) test and on an HMC Anomaloskop MR (Rayleigh test). The final exam on a Toothguide Training Box consisted of 15 lightness-chroma-hue tasks. The color difference (∆E*ab) and the shade-matching score (Σ∆E*ab) were computed. The means and the standard deviations for the Σ∆E*ab were calculated. An independent t-test was used for statistical analyses of the data and a comparison of means (α = .05) for protan groups and a one-way analysis of variance (ANOVA) and a post-hoc Bonferroni test (α = .05) for deutan groups.
RESULTS: The PSTD group had a mean Σ∆E*ab of 63.38 ± 9.52, which means their selections were significantly worse in comparison to the PMED group (Σ∆E*ab = 47.62 ± 9.88, p = 0.033). The selections of the control group were significantly better in comparison to all groups with color-vision deficiency (control - PMED, p = 0.031; control - PSTD, p < 0.0001; control - DMED, p < 0.0001; control - DSTD, p < 0.0001), except in comparison with DMID group (p = 0.082). The comparisons between deutan groups were not significantly different (DMID - DMED, p = 0.352; DMID - DSTD, p = 0.323; DMED - DSTD, p = 1.000).
CONCLUSION: Participants with strong protan color-vision deficiency are worse at shade matching than participants with medium protan color-vision deficiency.

Introduction

Shade matching is present in daily restorative and esthetic dentistry. Shade matching is performed by using visual and/or instrumental methods. Although many instruments have been developed for shade matching, it has been done most frequently using the visual method. The visual method is known as shade matching and is performed using dental shade guides. A tooth or restoration is compared with color standards, usually in a tooth-shape form, made of ceramics, acrylic or composite. The factors that influence the shade matching are more important for the visual method (). Congenital color-vision deficiencies affect visual shade matching (, ). Congenital color-vision deficiencies can be divided in protan red-green deficiency (predominantly red axis affected) and deutan red-green deficiency (predominantly green axis affected). Hardy-Rand-Rittler (HRR) test () identifies color-vision red-green and blue-yellow deficiencies and can differentiate the extent of the deficiency in mild, medium and strong, separately for red-green and blue-yellow color-vision deficiencies. To the present authors’ knowledge, the influence of the extent of the participant's color-vision deficiency measured with the HRR test on the visual shade-matching ability on Toothguide Training Box () (TTB) or VITA 3D-Master shade guide has yet not been published. The purpose of this study was to evaluate the influence of the extent of color-vision deficiency on the visual shade-matching ability. The null hypothesis was that shade-matching score, Σ∆E*ab, of participants with strong color-vision deficiencies would not differ from the score of participants with medium or mild color-vision deficiencies. The second null hypothesis was that shade-matching score, Σ∆E*ab, of the control group would not differ from the score of all other groups with color-vision deficiencies.

Materials and methods

The work has been approved by the appropriate Ethics Committee related to the institution in which it was performed. Informed consent was obtained for experimentation with human subjects. The study was presented in broader extent in a previous article by Pohlen et al (). The color vision of the participants was evaluated monocularly using the HRR test. The test is a color-vision-deficiency test with 24 pseudoisochromatic plates in a book. The participants with a color-vision deficiency found on the HRR test were also tested on an HMC Anomaloskop MR (Rayleigh test (OCULUS Optikgerate)) to confirm the diagnosis for red-green color-vision deficiency. Six groups were formed based on the results obtained on the HRR test: the control group (without color-vision deficiencies) (N = 68), the protan medium deficiency (PMED) group (N = 5), the protan strong deficiency (PSTD) group (N = 5), the deutan mild deficiency (DMID) group (N = 5), the deutan medium deficiency (DMED) group (N = 5) and the deutan strong deficiency (DSTD) group (N = 8). One color-vision-deficient participant (diagnosis based on the Rayleigh test on the anomaloscope) was excluded from the study, because no color-vision deficiencies were found on the HRR test.

The HRR test differentiates color vision into normal if correct responses were given to all six screening plates. Protan red-green deficiency (predominantly red axis affected) was classified if the total number of checks in the protan column was greater than in the deutan column. Deutan red-green deficiency (predominantly green axis affected) was classified if the total number of checks in the deutan column was greater than in the protan column. The extent of all the defects could be mild, medium or strong. The last group of plates in which errors occur gave the extent of the participant's color-vision deficiency ().

Color-vision deficient participants were also tested monocularly on an HMC Anomaloskop MR (Rayleigh test). An anomaloscope is an optical device designed to test color vision by matching a yellow light which may be varied in intensity with a combination of red and green lights of constant intensity.

The protocol on the Toothguide Training Box (5) was the same as in Pohlen et al (). The final exam was tested binocularly and it consisted of 15 lightness–chroma–hue tasks. These shade-matching results were recorded on a laptop computer connected to the TTB and were subsequently processed. The color difference (∆E*ab) between the task tab and the selected tab was computed as follows:

where ∆L*, ∆a* and ∆b* denote the differences in the lightness, chroma and hue coordinates.

The L*, a* and b* values of all 26 shade tabs were obtained from measuring three completely new shade guides with a spectrophotometer VITA Easyshade Advance. Each tab was measured three times under color-corrected light (Dialite Color, Eickhorst, Germany) with a color-correlated temperature of 5500 K, 1500 lux and 92 CRI. The average of all nine measurements was taken as the L*, a* and b* values of each of the 26 shade tabs, as in Pohlen et al () (Table 1).

Table 1

L*, a* and b* values of the 26 shade tabs from the VITA 3D-Master measured with the VITA Easyshade Advance spectrophotometer.

	L*	a*	b*
1M1	85.06	-1.91	11.43
1M2	85.46	-1.86	17.59
2M1	81.24	-0.76	12.96
2L1.5	80.97	-1.48	16.21
2L2.5	81.22	-1.26	21.61
2M2	81.58	-0.38	18.33
2R1.5	80.94	-0.06	15.34
2R2.5	80.68	0.09	21.2
2M3	81.21	-0.44	24.04
3M1	75.77	0.26	13.94
3L1.5	74.29	-0.1	17.88
3L2.5	75.26	0.52	23.77
3M2	76.79	1.07	21.07
3R1.5	75.01	1.17	16.06
3R2.5	75.21	1.63	22.84
3M3	76.69	1.38	26.32
4M1	70.62	1.57	15.34
4L1.5	71.2	1.27	19.64
4L2.5	70.91	2.1	25.7
4M2	71.57	2.48	21.97
4R1.5	71.22	2.83	18.93
4R2.5	70.99	3.46	24.7
4M3	71.47	3.24	29.3
5M1	65.99	2.52	16.87
5M2	67.16	4.2	24.56
5M3	68.06	5.54	33.3

The shade-matching score, Σ∆E*ab, for each participant was computed as the sum of the color differences (∆E*ab) between all the task tabs and the selected tabs. The lower Σ∆E*ab scores corresponded to better shade-matching results and vice versa. For a set of 15 exact matches this score would be zero. The means and the standard deviations for Σ∆E*ab were calculated.

An independent t-test was used for statistical analyses of the data and a comparison of means (α = .05) for protan groups and a one-way analysis of variance (ANOVA) and a post-hoc Bonferroni test (α = .05) for deutan groups. A one-way analysis of variance (ANOVA) and a post-hoc Bonferroni test (α = .05) was also used for comparison of all groups with the control group. The data analysis was performed using SPSS 22.0 for Windows (IBM).

Results

The PSTD group had a mean Σ∆E*ab of 63.38 ± 9.52, which means their selections were significantly worse in comparison to the PMED group (Σ∆E*ab = 47.62 ± 9.88, p = 0.033, Tables 2, 3, Figure 1). The selections of the control group were significantly better in comparison to all groups with color-vision deficiency (control – PMED, p = 0.031; control – PSTD, p < 0.0001; control – DMED, p < 0.0001; control – DSTD, p < 0.0001), except in comparison with DMID group (p = 0.082). The comparisons between deutan groups were not significantly different (DMID – DMED, p = 0.352; DMID – DSTD, p = 0.323; DMED – DSTD, p = 1.000) (Tables 2-4). The Σ∆E*ab of the final exam for all groups are presented in Table 2.

Table 2

The results of the final exam on the TTB (Σ∆E*ab ± Std. Deviation) and test statistics (independent test for protan groups and a one-way analysis of variance (ANOVA) for deutan groups) for Σ∆E*ab. Σ∆E*ab

Table 2: The results of the final exam on the TTB (Σ∆E*ab ± Std. Deviation) and test statistics (independent test for protan groups and a one-way analysis of variance (ANOVA) for deutan groups) for Σ∆E*ab. Σ∆E*ab		n	Mean	SD	t	df	p
Control		68	31.57	13.50
Protan	Mild (PMID)	0	0	0
	Medium (PMED)	5	47.62	9.88	-2.569	8	0.033
	Strong (PSTD)	5	63.38	9.52
	Sum	10	55.50	12.36
					F	df	p
Deutan	Mild (DMID)	5	47.92	11.93
	Medium (DMED)	5	64.73	13.20	1.831	2	0.194
	Strong (DSTD)	8	63.52	19.16
	Sum	18	59.52	16.76

Table 3

A one-way analysis of variance (ANOVA) for the control and protan groups.

F	df	p
16.224	2	< 0.0001

Figure 1

Σ∆E*ab for the final exam on the TTB.

Table 4

A one-way analysis of variance (ANOVA) for the control and deutan groups.

F	df	p
20.521	3	< 0.0001

Discussion

Approximately 8% of males have congenital color-vision deficiencies (-) in comparison with 0.5% females (-). Research on the effect of color-vision deficiencies on visual shade matching is rare, because congenital color-vision deficiencies are rare and are an “immensely well-kept secret” (). Secondly, research is mostly not able to discriminate different color-vision deficiencies (i.e. anomalous trichromats– protanomalia, deuteranomalia, tritanomalia from dichromats (more severe deficiency– protanopia, deuteranopia, and tritanopia)). In addition, it is not able to evaluate the extent of the subject's color-vision deficiency measured with the HRR test (i.e., mild, medium, strong) and its influence on visual shade-matching ability. Classifying by severity of the red-green color-vision deficiency is more useful for predicting the effect on performance (). Spalding () reported that subjects (medical doctors) with moderate and severe deficiencies had more difficulties compared with the results of those with mild deficiencies. The present study was able to evaluate the extent of the subject's color-vision deficiency measured by the HRR test and differentiate it in mild, medium or strong deficiency, separately for protan and deutan red-green deficiency. Five color-vision deficient groups were formed: the protan medium deficiency (PMED) group (N = 5), the protan strong deficiency (PSTD) group (N = 5), the deutan mild deficiency (DMID) group (N = 5), the deutan medium deficiency (DMED) group (N = 5) and the deutan strong deficiency (DSTD) group (N = 8). In addition, it was able to evaluate the influence of the extent of the subject's color-vision deficiency on visual shade-matching ability (Tables 2-4). The results of the present study showed that PSTD group (Σ∆E*ab = 63.38 ± 9.52) was significantly worse in shade matching than PMED (Σ∆E*ab = 47.62 ± 9.88, p = 0.033). To the present authors’ knowledge, the information that a greater protan color-vision deficiency extent has more influence on visual shade-matching ability on Toothguide Training Box (TTB) or VITA 3D-Master shade guide has yet not been published before. On the contrary to protan color-vision deficiency, there were not significant differences between deutan groups. This is the reason why the first null hypothesis can be rejected only for protan (predominantly red axis affected) color-vision deficiency.

The selections of the control group were significantly better in comparison to all groups with color-vision deficiency, except in comparison with mild deutan red-green color-vision deficiency group. The piece of information that color-vision deficiency affects shade matching is not new. It is in accordance with many previous studies, (, , -) and it is in fact “common sense”. This is the reason why the second null hypothesis can be rejected for all protan and deutan color-vision deficiency groups, except for DMID group. Further investigations with more participants with different extents of color-vision deficiencies are needed in future.

Conclusion

The extent of the participant's color-vision deficiency measured with the HRR test partially affects the visual shade-matching ability. Participants with strong protan red-green color-vision deficiency are worse in shade matching than participants with medium protan red-green deficiency. The selections of the control group were significantly better in comparison to all groups with color-vision deficiency, except in comparison with the mild deutan red-green color-vision deficiency group.