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Influence of illuminants on the color distribution of shade guides
Influence of illuminants on the color distribution of shade guides Ji-Hoon Park, DDS,a Yong-Keun Lee, DDS, PhD,b and Bum-Soon Lim, PhDc Department of Dental Biomaterials Science and Dental Research Institute, College of Dentistry, Seoul National University, Seoul, Korea Statement of problem. Although a shade tab in a shade guide is matched to a natural tooth in the order of value, hue, and chroma, there are limited data on the color distribution of currently available shade guides sorted by these 3 parameters. Furthermore, spectrophotometric color measurements of shade tabs differ depending on the standard illuminant employed. Purpose. The purpose of this study was to determine the color distributions of 2 shade guides in value (CIE L*), chroma (C*ab) and hue angle (ho) scale relative to the standard illuminants D65, A, and F2. Material and methods. Color of shade tabs (n=36) from 2 shade guides (Vita Lumin and Chromascop) were measured, and the distributions for CIE L*, C*ab and ho values were compared. Color differences of shade tabs depending on the illuminant were calculated. The distributions of the ratios of CIE L* and C*ab values of each shade tab compared with the lowest value tab or the lowest chroma tab were determined. The data for the value, chroma, and hue angle within each shade guide were analyzed with a 2-way ANOVA with the factors of shade designation and type of illuminant (a=.05). Color difference caused by change of illuminant was analyzed with a 2-way ANOVA with the factors of shade designation and pair of illuminants compared (a=.05). The Scheffe multiple comparison test was performed as a post hoc test. Results. CIE L*, C*ab and ho values were influenced by shade designation and type of illuminant in both shade guides. Color difference caused by change of the illuminant was influenced by the shade designation and pair of illuminants compared. The order of mean color differences of 16 Vita Lumin shade tabs by pairs of illuminants compared was as follows: DE*ab (D65/F2) = 1.63 , DE*ab (D65/A) = 2.22 , DE*ab (A/F2) = 2.46 (P,.05). The order of mean color differences of 20 Chromascop shade tabs was as follows: DE*ab (D65/F2) = 2.45 , DE*ab (D65/A) = 2.71 , DE*ab (A/F2) = 3.14 (P,.05). The distributions of value and chroma in both shade guides were arbitrary. Conclusion. Color distribution of 2 shade guides varied by the illuminant, and the range of color difference for shade tabs by the illuminant was 0.80 to 4.82, which may be clinically unacceptable (DE*ab . 3.7). Color distribution of 2 shade guides by the value and chroma was not logical. (J Prosthet Dent 2006;96:402-11.)
CLINICAL IMPLICATIONS Color distribution of conventional shade guides was not logical. Therefore, new shade guides with logically arranged value, chroma, and hue should be used for color matching, and the influence of illuminants on shade matching should be considered in clinical color matching.
T
he goals for esthetic dental restorations are to achieve morphologic, optical, and biologic acceptance. Color matching of an esthetic restorative material with natural teeth is routinely performed with the aid of a shade guide. Dental shade guides are used to identify and communicate color; however, these shade guides have numerous limitations, and the majority of dentists in a survey indicated a need for the development of a
Supported by a grant of the Korea Health 21 R&D Project, Ministry of Health and Welfare, Republic of Korea (03-PJ1-PG1-CH090001). a Graduate student, Department of Dental Biomaterials Science. b Professor, Department of Dental Biomaterials Science, Dental Research Institute. c Professor, Department of Dental Biomaterials Science.
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systematic shade guide.1 Sources of error preclude true color matching: (1) shade guides are not fabricated to match natural teeth and (2) shade guides do not match other shade guides.2 The range of shades in shade guides is not consistent with natural teeth; therefore, an error in shade selection is introduced since many tooth colors must be defined by approximation to the nearest shade of the guide.3,4 Color is usually described according to the Munsell color space in terms of hue, value, and chroma.5 Hue is the attribute of a color that enables the clinician to distinguish between different families of color, and value indicates the lightness of a color. Chroma is the degree of color saturation. When color is determined using the Munsell system, value is determined first and chroma is determined next with shade tabs that are close to the VOLUME 96 NUMBER 6
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measured value but are of increasing saturation of color. Hue is determined last by matching with shade tabs of the value and chroma already determined.5 Color matching in dentistry is routinely performed with a visual method. However, instrumental color measurement can render useful information that can aid visual color matching.6 The Commission Internationale de l’Eclairage (CIE) refined color space in 1976.7 CIE L* value is a measure of the lightness of an object such that a perfect black has a CIE L* value of zero and a perfect reflecting diffuser (white) has a CIE L* value of 100. CIE a* value is a measure of redness (positive value) or greenness (negative value), and CIE b* value is a measure of yellowness (positive value) or blueness (negative value).7 Spectrophotometric color measurements differ depending on the measuring geometry and the illuminant. Therefore, when any color measurements are made with an instrument, measured color values are sensitive to the methods employed.8 Several standard illuminants have been used to measure the color of dental materials.9,10 Standard illuminant D65 represents a phase of daylight with a correlated color temperature of approximately 6500 K, illuminant A represents light from the full radiator at absolute temperature 2856 K, and illuminant F2 represents light from fluorescent lamp of medium color temperature of 4230 K.10 Two standard illuminants are recommended for use in colorimetry.11 Illuminant A should be used in all applications of colorimetry involving the incandescent lighting, and D65 should be used in all colorimetric calculations requiring representative day light.12 Regarding the color difference by the illuminant, it was reported that the changes in optical properties of composite resins relative to the varied illuminants were different from those of dentin.13 Metameric color difference can be minimized if a restoration is matched under a combination of light, which was found to provide the best-perceived match.14 Accurate evaluation of the color of a shade guide is essential for good color matching. Instrumental color measurements of a shade guide are variable for several reasons: measurements are sensitive to the measured location within a shade tab because the tabs are not a uniform color; the shade guides vary between batches; the standard illuminant varies; and there are inherent difficulties with instrumental measurements of tooth materials.15 The disadvantages of using a colorimeter for measuring tooth color are that the instruments are designed to measure flat surfaces and small aperture colorimeters are prone to significant edge-loss effects.16-18 It has also been recommended that research is needed to develop and improve the instrument and technique for quantitative measurement of tooth color.19 These limitations for the instrumental tooth color measurements would cause similar problems with the color measurement for a shade tab. The Vita Lumin Vacuum shade guide (VITA Zahnfabrik, Bad Sackingen, Germany) is divided into DECEMBER 2006
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4 series designated by letters A, B, C, and D. According to the manufacturer, these shades have brown, yellow, gray, and red hues, respectively. Shade tabs of a specific letter group have similar hue, and each hue group includes several tabs of increasing chroma and decreasing value designated in numeric order, such as A1, A2, and A3.15 However, others have concluded that the visual distinction between Vita Lumin shade tabs was primarily due to a difference in luminance or brightness.20 The Chromascop (Ivoclar Vivadent, Schaan, Liechtenstein) shade guide is divided into 5 series, such as 100, 200, 300, 400, and 500. The 100 series is white, 200 series is yellow, 300 series is light yellow, 400 series is gray, and 500 series is dark brown. Within the series, chroma increases and value decreases as the middle number increases, as purported by the manufacturer. Various reports for the color of shade guides are found in the literature.20-22 Since the structure of current shade guides is largely illogical and without any rational use of color ordering,23-25 the arrangement of shade tabs according to color difference from light to dark provides a 1-dimensional color order system to dental shade guides.21 A simplified arrangement of shade tabs was explained, and the reported advantages of this technique were quick verification of color choice, ease of correction (increasing or decreasing hue, value, and chroma) to select the right shade, and ease of communication with the laboratory.26 Use of the Vita 3D-Master shade guide (VITA Zahnfabrik) allows the practitioner to better understand the primary tooth shade characteristics of value, chroma, and hue.27 There is a lack of agreement regarding the threshold levels for the color difference that can be visually perceivable or clinically acceptable. The threshold for acceptable color difference was 1.7 DE*ab units regardless of the shade,28 while 3.3 DE*ab units was considered as an acceptable threshold for composite resins.29 However, these thresholds were determined under optimal in vitro conditions, which may not apply to clinical settings. As a clinical acceptability threshold, the average CIELAB color difference (DE*ab) of those ratings judged a perfect match by the US Public Health Service criteria was found to be 3.7 DE*ab units for composite resin veneer restorations and their comparison teeth.30 In addition to the magnitude of color difference, the position of a shade in color space influenced the color matching. Individual shades in shade guides influenced the reliability and validity of measurements in a color matching process.31 Also, the ratios for value and chroma between pairs of shade tabs influenced the visual perception of color.32 Since shade tabs in a shade guide are matched to a natural tooth in the order of value, hue, and chroma, color distribution of shade tabs sorted by these 3 parameters can provide data for modeling a new systematic 403
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Fig. 1. Distribution of CIE L* and C*ab values of VITA shade guide (D65).
Fig. 2. Distribution of CIE L* and C*ab values of CHRO shade guide (D65).
Fig. 3. Distribution of CIE a* and b* values of VITA shade guide (D65).
Fig. 4. Distribution of CIE a* and b* values of CHRO shade guide (D65).
shade guide. However, there were few studies identified regarding the distribution of shade tabs in commercial shade guides in the 3 color parameters of value, chroma, and hue,26,27,33 and on the influence of illuminant on the color of shade guides. The purpose of this study was to determine the color distributions of 2 conventional shade guides in value, chroma, and hue scale relative to the standard illuminants D65, A, and F2. The null hypotheses of the present study were: (1) the distribution of 3 color parameters are in equal distances from the adjacent shade tab in each shade guide; and (2) the value, chroma, and hue of shade tabs are not influenced by illuminants such as the standard illuminants D65, A, and F2.
MATERIAL AND METHODS
404
Color of the shade tabs of 2 shade guides (Vita Lumin Vacuum shade guide [VITA]; VITA Zahnfabrik, and Chromascop [CHRO]; Ivoclar Vivadent) was measured after polishing the 4-mm-wide middle portion of the labial surface of each shade tab with up to #2400 silicon carbide papers (Buehler Ltd, Lake Bluff, Ill) to make the measuring surface flat. Based on preliminary experiments, flattening the measuring surface resulted in more consistent measured color (less coefficient of variation); therefore, the values based on the flattened surface were used in the present study. The color of the middle site of the shade tab was measured because the translucency of VOLUME 96 NUMBER 6
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Fig. 5. Distribution of ratios for CIE L* and C*ab values of VITA shade guide tabs sorted by CIE L* ratio (D65).
Fig. 6. Distribution of ratios for CIE L* and C*ab values of VITA shade guide tabs sorted by C*ab ratio (D65).
Fig. 7. Distribution of ratios for CIE L* and C*ab values of CHRO shade guide tabs sorted by CIE L* ratio (D65).
Fig. 8. Distribution of ratios for CIE L* and C*ab values of CHRO shade guide tabs sorted by C*ab ratio (D65).
the incisal edge would make the measured color background-dependent, and cervical measurement would reflect the dark color.12 External light was excluded by covering the shade tab specimens with a zero calibration box (Zero Calibration Standard; GretagMacbeth Instruments Corp, New Windsor, NY). CIE L*, a* and b* values were measured according to the CIELAB color scale relative to the standard illuminants D65, A and F2 on a reflection spectrophotometer (Color-Eye 7000A; GretagMacbeth Instruments Corp) with specular component excluded geometry. An ultraviolet (UV) filter was positioned to 100% UV position. The aperture size was 3 3 8 mm, and the illuminating and viewing configuration was CIE diffuse/8-degree geometry.7 Measurements were repeated 3 times for each shade tab and averaged.
The photometric range for this instrument is 0 to 175%, and the resolution is 0.01%. The repeatability in spectral reflectance is within 0.20% SD, and the chromaticity is within 0.05 DE*ab SD when the white calibration plate is measured 30 times at 10-second intervals after white calibration has been performed, as purported by the manufacturer. Distributions for the CIE L*, C*ab and ho values of VITA and CHRO guides were compared. Chroma was calculated as C*ab = (a*2 1 b*2)1/2, and hue angle was calculated as Dho = arctan (b*/a*).7 Distributions of CIE L* and C*ab values and those of CIE a* and b* values relative to the illuminant D65 for each shade guide were compared. To determine the distribution of the ratios of CIE L* and C*ab values of each shade tab compared with the lowest value tab or the lowest chroma
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Table I. Mean (SD) CIE L*, C*ab, and ho values of VITA shade guide tabs measured relative to standard illuminants D65, A, and F2 D65 Shade
A1 A2 A3 A3.5 A4 B1 B2 B3 B4 C1 C2 C3 C4 D2 D3 D4
L*
60.8 59.8 57.4 55.5 52.7 59.7 61.0 55.8 55.9 56.2 53.9 51.8 47.4 55.3 54.3 52.9
(0.2) (0.1) (0.2) (0.3) (0.5) (0.2) (0.1) (0.4) (0.1) (0.3) (0.1) (0.2) (0.0) (0.1) (0.2) (0.1)
A h
C*ab
6.6 9.4 12.2 14.0 14.3 5.3 9.8 14.9 16.1 7.0 10.0 11.1 13.0 5.5 8.6 12.2
(0.3) (0.3) (0.4) (0.0) (0.2) (0.2) (0.3) (0.2) (0.7) (0.2) (0.2) (0.1) (0.3) (0.0) (0.1) (0.2)
o
281.3 88.1 86.0 84.2 82.7 276.1 285.4 86.9 86.8 284.1 290.0 87.3 82.1 285.3 87.0 288.9
L*
(0.5) (0.6) (0.3) (0.1) (0.2) (0.5) (0.3) (0.4) (0.3) (0.2) (0.1) (0.2) (0.1) (0.2) (0.1) (0.2)
61.1 60.5 58.2 56.5 53.8 59.9 61.5 56.8 57.0 56.6 54.6 52.5 48.4 55.6 55.0 53.6
F2
C*ab
(0.3) (0.1) (0.1) (0.3) (0.5) (0.3) (0.1) (0.4) (0.2) (0.3) (0.1) (0.2) (0.0) (0.1) (0.2) (0.1)
6.6 10.2 13.3 15.4 15.9 5.1 10.0 16.1 17.3 7.1 10.6 12.0 14.5 5.7 9.4 12.8
(0.3) (0.4) (0.4) (0.0) (0.2) (0.2) (0.3) (0.2) (0.7) (0.2) (0.3) (0.2) (0.4) (0.1) (0.1) (0.2)
h
o
86.5 78.4 77.0 75.8 74.6 288.7 82.4 77.6 77.6 82.7 78.6 77.3 74.1 82.6 77.5 79.8
L*
(0.5) (0.5) (0.2) (0.1) (0.2) (0.5) (0.2) (0.3) (0.1) (0.1) (0.2) (0.2) (0.1) (0.1) (0.1) (0.1)
61.1 60.4 58.1 56.3 53.6 59.9 61.4 56.7 56.8 56.5 54.4 52.4 48.2 55.6 54.9 53.5
(0.3) (0.1) (0.2) (0.3) (0.5) (0.3) (0.1) (0.4) (0.2) (0.3) (0.1) (0.2) (0.0) (0.1) (0.2) (0.1)
ho
C*ab
7.5 10.7 13.8 15.9 16.2 5.9 11.1 16.9 18.2 7.9 11.3 12.6 14.6 6.3 9.8 13.9
(0.3) (0.4) (0.4) (0.0) (0.3) (0.2) (0.3) (0.3) (0.7) (0.2) (0.3) (0.1) (0.4) (0.0) (0.1) (0.2)
283.9 89.8 88.5 87.4 86.6 280.9 286.6 88.9 89.0 285.9 289.3 89.3 86.3 286.4 89.2 288.7
(0.3) (0.4) (0.2) (0.1) (0.1) (0.4) (0.2) (0.3) (0.2) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1)
Table II. Multivariate test results based on 2-way ANOVA for difference in CIE L*, C*ab, and ho values of VITA shade guide tabs by illuminant Color parameter
CIE L*
C*ab
ho
Source
Shade designation Type of illuminant Shade designation 3 Type of illuminant Shade designation Type of illuminant Shade designation 3 Type of illuminant Shade designation Type of illuminant Shade designation 3 Type of illuminant
Type III Sum of squares
df
Mean square
F
P
1677.20 13.84 2.17
15 2 30
111.81 6.92 .07
2131.75 131.94 1.38
,.001 ,.001 .122
1875.30 49.08 9.26
15 2 30
125.02 24.54 .31
1352.15 265.41 3.34
,.001 ,.001 ,.001
540879.51 102902.31 239761.34
15 2 30
36058.63 51451.15 7992.05
531020.60 757699.89 117695.54
,.001 ,.001 ,.001
P,.05 indicates significant difference.
tab, the ratios for CIE L* or C*ab values were calculated. For the VITA guide, the C4 tab had the lowest value and the B1 tab had the lowest chroma. For the CHRO guide, the 540 tab had the lowest value and the 110 tab had the lowest chroma. Color differences of each of the VITA and CHRO shade tabs depending on the pair of illuminants compared were calculated. Color difference was calculated with the equation: DEab ¼ ½ðDL Þ2 1 ðDa Þ2 1 ðDb Þ2 1=2 .7 In each of VITA or CHRO guide, the influence of the shade designation and the type of illuminant on the CIE L*, C*ab and ho values was determined with a 2-way analysis of variance (ANOVA) (a=.05). Homogenous subsets for the CIE L*, C*ab and ho values of VITA and CHRO shade tabs relative to the illuminant D65 were determined based on the Scheffe multiple comparison test (a=.05). 406
Color difference by the change in the illuminants was analyzed with 2-way ANOVA for the variables of the shade designation and the pair of illuminants compared (a=.05).
RESULTS The distribution of CIE L* and C*ab values of the VITA shade guide is presented in Figure 1. As the designation numbers increased in each shade group, such as A, B, C, and D, the C*ab values increased; however, the ratios of the increase varied by the shade group. Distribution of CIE L* and C*ab values of the CHRO shade guide is presented in Figure 2. As the middle numbers increased in each shade group, C*ab values generally increased, except for the 300 group. VOLUME 96 NUMBER 6
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The distribution of CIE a* and b* values of the VITA shade guide is presented in Figure 3. As the numerical designations increased in each shade group, CIE a* and b* values increased, except for the D group. The distribution of CIE a* and b* values of the CHRO shade guide is presented in Figure 4. As the middle numbers increased in each shade group, CIE a* and b* values increased in some shade groups; however, a general trend could not be determined. Distributions of the ratios for the CIE L* and C*ab values of the VITA shade guide tabs sorted by the CIE L* ratio or the C*ab ratio are presented in Figures 5 and 6. The range of the CIE L* ratio compared with the C4 tab was 1.09 to 1.29, and that of the C*ab ratio compared with the B1 tab was 1.04 to 3.03. The range for the chroma ratio was greater than that for the lightness ratio. Distributions of the ratios for the CIE L* and C*ab values of the CHRO shade guide tabs sorted by the CIE L* ratio or the C*ab ratio are presented in Figures 7 and 8. The range of the CIE L* ratio compared with the 540 tab was 1.03 to 1.28, and that of the C*ab ratio compared with the 110 tab was 1.14 to 2.60. The range for the chroma ratio was greater than that for the lightness ratio. The CIE L*, C*ab and ho values of the VITA shade guide tabs are listed in Table I. Difference in hue angle by the illuminant was clear (positive or negative values by the illuminant). The CIE L* value was influenced by the shade designation and type of illuminant (P,.001), but there was no significant interaction between these 2 variables (Table II). The mean CIE L* value of the 16 VITA shade tabs relative to the illuminant D65 was the lowest, followed by that relative to illuminant F2 and illuminant A (D65,F2,A, P,.05). The C*ab and ho values were influenced by the shade designation and type of illuminant, and there was significant interaction between the 2 variables (P,.001) (Table II). The mean C*ab value of the 16 VITA shade tabs relative to illuminant D65 was the lowest, followed by those relative to illuminant A and illuminant F2 (D65,A,F2, P,.05). The mean ho value of the 16 VITA shade tabs relative to illuminant D65 was the lowest, followed by those relative to illuminant F2 and illuminant A (D65,F2,A, P,.05). Homogenous subsets for the CIE L*, C*ab and ho values of the VITA shade tabs relative to illuminant D65 are listed in Table III. The CIE L* value distribution corresponded to the order based on the lightness purported by the manufacturer. The CIE L* and ho values of the 16 shade tabs were divided into 8 homogenous subsets (a to h), and the C*ab value was divided into 11 subsets (a to k). The CIE L*, C*ab and ho values of the CHRO shade guide tabs are listed in Table IV. The results for the 3 color coordinates for the VITA shade guide as influenced by shade and type of illuminant were similar to DECEMBER 2006
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Table III. Homogenous subsets for CIE L*, C*ab, and ho values of VITA shade guide tabs relative to standard illuminant D65 Shade
No-1
No-2
L*
C*ab
ho
A1 A2 A3 A3.5 A4 B1 B2 B3 B4 C1 C2 C3 C4 D2 D3 D4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
2 5 8 12 15 1 3 11 13 6 7 14 16 4 10 8
i, j h, i g f b, c h j f f f d b a e, f d, e c
b, c d, e g, h i, j j a d, e j, k k c e, f f, g h, i a, b d g, h
c h g f e d b h h b a g, h e b h a
No-1 indicates numbering based on order of A, B, C, and D grouping. No-2 indicates numbering based on value (lightness) purported by manufacturer. Same letters indicate homogenous groups based on Scheffe multiple comparison test (P,.05).
those for the CHRO shade guide; therefore, the statistical results table was not included. Homogenous subsets for the mean CIE L*, C*ab and ho values of the CHRO shade tabs are listed in Table V. The CIE L* and C*ab values of 20 shade tabs were divided into 10 subsets (a to j), and the ho value was divided into 13 subsets (a to m). Color differences (DE*ab) of the VITA shade guide tabs caused by the changes in 3 standard illuminants are listed in Table VI. Color difference caused by the change in illuminants was influenced by the shade designation and pair of illuminants compared (D65/A and so on), and there was significant interaction between the 2 variables (Table VII). The order of mean color difference of the 16 VITA shade tabs was as follows: DE*ab (D65/F2) = 1.63 , DE*ab (D65/A) = 2.22 , DE*ab (A/F2) = 2.46 (P,.05). Color differences of the CHRO shade guide tabs caused by the changes in 3 standard illuminants are listed in Table VIII. Color difference caused by the change in illuminants was influenced by the shade designation and pair of illuminants compared, and there was significant interaction between the 2 variables (Table VII). The order of mean color difference of the 20 CHRO shade tabs was as follows: DE*ab (D65/ F2) =2.45 , DE*ab (D65/A) = 2.71 , DE*ab (A/F2) = 3.14 (P,.05).
DISCUSSION The first null hypothesis that the distribution of 3 color parameters are in equal distances from the adjacent 407
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Table IV. Mean (SD) CIE L*, C*ab, and ho values of CHRO shade guide tabs measured relative to standard illuminants D65, A, and F2 D65 Shade
110 120 130 140 210 220 230 240 310 320 330 340 410 420 430 440 510 520 530 540
L*
67.9 65.6 61.8 62.0 60.4 61.9 57.3 59.2 58.8 57.5 59.3 54.5 58.4 58.6 57.2 56.4 56.4 54.7 56.1 53.1
(0.1) (0.5) (0.4) (0.2) (0.2) (0.1) (0.4) (0.3) (0.5) (0.2) (0.2) (0.8) (0.5) (0.6) (0.3) (0.2) (0.1) (0.4) (0.3) (0.4)
C*ab
8.5 9.7 9.9 12.1 13.6 13.9 14.7 17.0 15.7 17.5 22.1 19.0 10.8 11.4 12.2 13.8 15.4 19.2 19.0 8.8
(0.2) (0.3) (0.2) (0.1) (0.1) (0.0) (0.3) (0.1) (0.2) (0.4) (0.5) (1.2) (0.2) (0.3) (0.4) (0.2) (0.3) (0.3) (0.3) (0.2)
A h
o
285.4 289.7 288.9 86.5 87.0 81.2 80.6 78.7 88.0 85.0 83.5 78.7 82.2 88.1 85.8 84.5 81.8 80.8 71.8 83.8
L*
(0.2) (0.2) (0.2) (0.0) (0.2) (0.0) (0.0) (0.1) (0.2) (0.1) (0.1) (0.0) (0.2) (0.0) (0.3) (0.1) (0.0) (0.0) (0.1) (0.2)
68.4 66.2 62.4 62.8 61.3 63.0 58.5 60.6 59.8 58.7 60.8 56.0 59.3 59.4 57.9 57.3 57.4 55.9 57.5 54.8
C*ab
(0.1) (0.5) (0.4) (0.2) (0.2) (0.1) (0.4) (0.3) (0.5) (0.2) (0.2) (0.9) (0.5) (0.6) (0.3) (0.2) (0.1) (0.4) (0.3) (0.4)
Table V. Homogenous subsets for mean CIE L*, C*ab, and ho values of CHRO shade guide tabs relative standard illuminant D65
110 120 130 140 210 220 230 240 310 320 330 340 410 420 430 440 510 520 530 540
No
L*
C*ab
ho
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
j i h h g, h h d, e f, g e, f, g d, e, f f, g a, b e, f e, f d, e c, d c, d a, b, c b, c, d a
a a, b a, b c, d d, e d, e, f e, f g, h f, g, h h, i j i b, c b, c b, c c, d d, e, f e, f, g i i
c a b l l f, g f e m j i e h j m k j g, h f d
No indicates numbering based on order of shade designation numbers. Same letters indicate homogenous groups based on Scheffe multiple comparison test (P,.05).
shade tab in each shade guide was rejected because the distributions of 3 color parameters of the shade tabs in each shade guide were not equally distanced from the 408
8.8 10.3 10.4 13.2 14.7 15.6 16.4 19.1 16.7 19.0 24.0 21.3 12.1 12.1 12.3 13.3 15.2 17.1 21.3 21.9
(0.2) (0.3) (0.2) (0.1) (0.1) (0.0) (0.4) (0.1) (0.2) (0.5) (0.5) (1.3) (0.2) (0.4) (0.3) (0.4) (0.2) (0.3) (0.4) (0.4)
F2 h
83.8 80.8 81.1 78.0 78.3 74.2 74.0 72.6 78.5 76.5 75.8 72.9 75.1 77.2 79.4 77.7 76.8 74.7 74.2 68.4
o
L*
(0.2) (0.2) (0.1) (0.0) (0.2) (0.0) (0.0) (0.1) (0.2) (0.1) (0.1) (0.1) (0.1) (0.0) (0.0) (0.3) (0.0) (0.0) (0.0) (0.0)
68.4 66.2 62.4 62.7 61.3 62.9 58.4 60.4 59.7 58.5 60.6 55.8 59.2 59.3 57.9 57.2 57.3 55.8 57.3 54.5
C*ab
(0.1) (0.5) (0.4) (0.2) (0.2) (0.1) (0.4) (0.3) (0.5) (0.2) (0.2) (0.9) (0.5) (0.6) (0.3) (0.2) (0.1) (0.4) (0.3) (0.4)
9.7 11.1 11.3 13.9 15.6 15.9 16.7 19.3 17.9 20.0 25.2 21.5 12.3 12.6 13.1 13.9 15.8 17.6 21.8 21.1
(0.2) (0.4) (0.2) (0.1) (0.1) (0.0) (0.4) (0.1) (0.2) (0.5) (0.5) (1.4) (0.3) (0.4) (0.4) (0.4) (0.2) (0.3) (0.4) (0.4)
ho
286.5 289.1 288.6 88.7 88.9 85.4 85.2 83.8 89.5 87.6 86.8 84.0 86.2 88.0 89.9 88.5 87.7 85.9 85.2 79.7
(0.1) (0.1) (0.1) (0.0) (0.1) (0.0) (0.0) (0.1) (0.1) (0.0) (0.1) (0.0) (0.1) (0.0) (0.0) (0.2) (0.1) (0.0) (0.0) (0.0)
Table VI. Mean (SD) color difference of VITA shade guide tabs depending on illuminant DE*ab (D65/A)
A1 A2 A3 A3.5 A4 B1 B2 B3 B4 C1 C2 C3 C4 D2 D3 D4
1.44 1.95 2.46 2.78 2.87 1.18 2.20 2.96 3.16 1.66 2.22 2.35 2.62 1.24 1.79 2.66
(0.06) (0.07) (0.06) (0.00) (0.03) (0.04) (0.06) (0.04) (0.10) (0.04) (0.05) (0.03) (0.06) (0.01) (0.01) (0.04)
DE*ab (D65/F2)
0.97 1.47 1.92 2.23 2.31 0.80 1.43 2.28 2.44 1.01 1.46 1.66 2.12 0.82 1.34 1.76
(0.04) (0.06) (0.06) (0.01) (0.03) (0.02) (0.04) (0.03) (0.10) (0.03) (0.04) (0.02) (0.06) (0.01) (0.01) (0.04)
DE*ab (A/F2)
1.45 2.14 2.78 3.20 3.36 1.13 2.30 3.38 3.64 1.70 2.42 2.63 3.09 1.29 1.98 2.89
(0.07) (0.08) (0.08) (0.00) (0.04) (0.04) (0.07) (0.04) (0.13) (0.05) (0.06) (0.03) (0.08) (0.01) (0.01) (0.05)
DE*ab (D65/A) refers to color difference between CIE L*, a*, and b* values measured relative to standard illuminants D65 and A.
adjacent shade tab. For the VITA shade guide, the CIE L* ratio was 1.09 to 1.29, and the C*ab ratio was 1.04 to 3.03. For the CHRO shade guide, the CIE L* ratio was 1.03 to 1.28, and the C*ab ratio was 1.14 to 2.60. These illogical distributions are clearly observed in Figures 5 through 8. The second null hypothesis that the value, chroma, and hue of shade tabs are not influenced by illuminants VOLUME 96 NUMBER 6
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Table VII. Multivariate test results based on 2-way ANOVA for color difference by pair of illuminants compared for VITA and CHRO shade guides Shade guide
VITA
CHRO
Source
Type III Sum of squares
df
Mean square
F
P
Shade designation Pair of illuminants Shade designation 3 Pair of illuminants Shade designation Pair of illuminants Shade designation 3 Pair of illuminants
57.549 17.705 1.813
15 2 30
3.837 8.853 .060
1381.263 3187.129 21.762
,.001 ,.001 ,.001
92.242 14.709 2.184
19 2 38
4.855 7.354 .057
1049.792 1590.298 12.427
,.001 ,.001 ,.001
P,.05 indicates significant difference.
such as the standard illuminants D65, A, and F2 was also rejected because value (CIE L*), chroma (C*ab), and hue angle (ho) were influenced by the illuminant in both shade guides. Color differences caused by the changes in illuminant were in the acceptable range for the VITA shade guide based on the criteria of Johnston and Kao (DE*ab , 3.7),30 because the range of color differences were 1.18 to 3.16 for the D65/A pair, 0.80 to 2.44 for the D65/F2 pair, and 1.13 to 3.64 for the A/F2 pair. However, those for the CHRO shade guide were acceptable or not, depending on the pair of illuminants compared, because the range of color differences were 1.72 to 3.98 for the D65/A pair, 1.30 to 3.59 for the D65/F2 pair, and 1.81 to 4.83 for the A/F2 pair. However, it should be noted that color discrepancies by the illuminant were also influenced by the shade designations. In the CHRO shade guide, several of the color difference values were in the unacceptable range. Therefore, these discrepancies in color parameters caused by the illuminant should be considered in clinical color matching. Further study on the clinical implications of these discrepancies is needed. In the present study, a color difference value of 3.7 was regarded as the acceptable limit because this value was calculated based on clinical condition.30 The correlation between instrumentally measured color differences (DE*ab) and human observer assessment of color differences was determined. The results showed that the threshold acceptability of color difference was 1.1 DE*ab units for red-varying shades and 2.1 DE*ab units for yellow-varying shades, and mean value regardless of shades was 1.7 DE*ab units.28 Based on the previous study,28 it is clear that color difference value itself has limitations when relating DE*ab value with observer response. The effect of individual shades in shade guides on the reliability and validity of measurements in a color matching process was determined. Thus, the matching process with shades of different materials was not accurate enough. Some shades produce a more reliable and valid match than others, and teeth are matched with DECEMBER 2006
Table VIII. Mean (SD) color difference of the CHRO shade guide tabs depending on illuminant DE*ab (D65/A)
110 120 130 140 210 220 230 240 310 320 330 340 410 420 430 440 510 520 530 540
1.72 1.88 1.96 2.34 2.58 2.69 2.78 3.20 3.07 3.31 3.98 3.43 2.09 2.09 2.15 2.29 2.58 2.88 3.46 3.66
(0.04) (0.06) (0.04) (0.02) (0.01) (0.00) (0.06) (0.02) (0.04) (0.06) (0.06) (0.18) (0.04) (0.07) (0.06) (0.06) (0.03) (0.04) (0.05) (0.05)
DE*ab (D65/F2)
1.30 1.56 1.56 2.01 2.22 2.46 2.60 3.07 2.45 2.84 3.59 3.41 1.92 1.89 1.86 2.04 2.33 2.69 3.34 3.78
(0.03) (0.05) (0.03) (0.02) (0.02) (0.01) (0.06) (0.02) (0.04) (0.06) (0.08) (0.20) (0.03) (0.06) (0.05) (0.05) (0.04) (0.04) (0.06) (0.06)
DE*ab (A/F2)
1.81 2.05 2.14 2.63 2.94 3.09 3.23 3.76 3.53 3.91 4.83 4.13 2.37 2.37 2.44 2.63 3.00 3.42 4.19 4.32
(0.04) (0.07) (0.04) (0.02) (0.02) (0.01) (0.07) (0.02) (0.05) (0.09) (0.09) (0.24) (0.04) (0.08) (0.07) (0.07) (0.04) (0.06) (0.07) (0.07)
DE*ab (D65/A) refers to color difference between CIE L*, a*, and b* values measured relative to standard illuminants D65 and A.
relative difficulty.31 Moreover, the differences in value, chroma, and hue between 2 shades compared to one another would influence differently the observer responses by the color parameter. As indicated in the present study, the ratios for value and chroma between pairs of shade tabs were not consistent. This should influence the visual perception of color.32 Bioform (Dentsply, York, Pa) and Vita Lumin shade guides, and a combination of the 2, have been compared spectrophotometrically to the published shades of human teeth.22 As a result, the use of both shade guides in shade selection was recommended to reduce the coverage error, which is caused by the difference in the ranges of shades in shade guides and natural teeth.22 The pattern and range for the 3 color parameters 409
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were different between 2 shade guides of the VITA and the CHRO, based on the present study. If shade tabs from 2 shade guides were combined, more accurate color matching may be possible. However, the increased number of shade tabs would make the color matching process more complicated. As noted previously, the VITA shade guide is grouped by the hue15 or value.20 In each shade series from A to D of the present study, chroma increased and value decreased as the second shade designation number increased. However, it was unclear whether each shade series had corresponding hue because hue angle varied in each shade series (Table I). A systematically arranged shade guide system will be more helpful in selecting the correct tooth shade and in avoiding shade corrections.24 Therefore, the order of the VITA shade guide was rearranged by the value purported by the manufacturer in the present study. As a result, although lightness was ordered in this new arrangement, the other 2 parameters varied. Rearrangement by the chroma and hue would render a more clinically relevant shade guide. Total color difference in relation to the lightest tab, followed by tab division into an adequate number of groups, is recommended as a possible and universally applicable mode of tab arrangement in dental color standards.25 The VITA Company developed a more ordered shade guide (Vitapan 3D-Master). Compared to Vitapan Classical, chromaticity ranges of Vitapan 3DMaster were extended in the desired directions.33 Use of the Vitapan 3D-Master shade guide significantly improved the intrarater repeatability of general practitioners compared with the Vita Lumin Vacuum shade guide.34 However, a new order of the Vitapan 3DMaster shade guide tabs has been recommended in relation to whiteness for use in studies of whitening products.35 In the present study, the CHRO shade guide was a conventional type; therefore, the conventional counterpart from the VITA company was selected for comparisons. Further studies with additional ordered shade guides (Vitapan 3D-Master) should be performed.
CONCLUSION Within the limitations of the present study, the distribution and range of 3 color parameters of value, chroma, and hue were significantly different for the 2 commercial shade guides. The 3 color parameters varied significantly by the illuminant. The distributions of value and chroma in both shade guides were arbitrary without any logical order. REFERENCES 1. Goodkind RJ, Loupe MJ. Teaching of color in predoctoral and postdoctoral dental education in 1988. J Prosthet Dent 1992;67:713-7.
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2. Preston JD. Current status of shade selection and color matching. Quintessence Int 1985;16:47-58. 3. Analoui M, Papkosta E, Cochran M, Matis B. Designing visually optimal shade guides. J Prosthet Dent 2004;92:371-6. 4. Browning WD. Use of shade guides for color measurement in toothbleaching studies. J Esthet Restor Dent 2003;15:13-20. 5. Powers JM, Sakaguchi RL. Restorative dental materials. 12th edition. St. Louis: Mosby; 2006. p. 28-31. 6. Paul SJ, Peter A, Rodoni L, Pietrobon N. Conventional visual vs spectrophotometric shade taking for porcelain-fused-to-metal crowns: a clinical comparison. Int J Periodontics Restorative Dent 2004;24:222-31. 7. Commission Internationale de l’Eclairage (CIE). Colorimetry - Technical Report. CIE Pub. No.15, 2nd ed. Vienna (Austria): Bureau Central de la CIE, 1986 (corrected reprint 1996). p. 35-6. 8. Lee YK, Yoon TH, Lim BS, Kim CW, Powers JM. Effects of color measuring mode and light source on the color of shade guides. J Oral Rehabil 2002; 29:1099-107. 9. Lee YK, Powers JM. Color difference of four esthetic restorative materials by the illuminant. Am J Dent 2005;18:359-63. 10. Commission Internationale de l’Eclairage (CIE). Colorimetry - Official recommendations of the Commission Internationale de l’Eclairage. CIE Publication No. 15 (E-1.3.1). Vienna (Austria): Bureau Central de la CIE, 1996. 11. ISO 10526. CIE standard illuminant for colorimetry. Geneva (Switzerland): ISO; 1999. 12. ASTM E 308-90. Standard test methods for computing the colors of objects by using CIE system. West Conshohocken (PA): ASTM; 1990. 13. Lee YK, Powers JM. Metameric effect between resin composite and dentin. Dent Mater 2005;21:971-6. 14. Leow ME, Ng WK, Pereira BP, Kour AK, Pho RW. Metamerism in aesthetic prostheses under three standard illuminants—TL84, D65 and F. Prosthet Orthot Int 1999;23:174-80. 15. Schwabacher WB, Goodkind RJ. Three-dimensional color coordinates of natural teeth compared with three shade guides. J Prosthet Dent 1990;64: 425-31. 16. van der Burgt TP, ten Bosch JJ, Borsboom PC, Kortsmit WJ. A comparison of new and conventional methods for quantification of tooth color. J Prosthet Dent 1990;63:155-62. 17. ten Bosch JJ, Coops JC. Tooth color and reflectance as related to light scattering and enamel hardness. J Dent Res 1995;74:374-80. 18. Bolt RA, Bosch JJ, Coops JC. Influence of window size in small-window color measurement, particularly of teeth. Phys Med Biol 1994;39: 1133-42. 19. Li Y. Tooth color measurement using Chroma Meter: techniques, advantages, and disadvantages. J Esthet Restor Dent 2003;15:33-41. 20. Ferreira D, Monard LA. Measurements of spectral reflectance and colorimetric properties of Vita shade guides. J Dent Assoc S Afr 1991;46: 63-5. 21. O’Brien WJ, Groh CL, Boenke KM. One-dimensional color order system for dental shade guides. Dent Mater 1989;5:371-4. 22. O’Brien WJ, Boenke KM, Groh CL. Coverage errors of two shade guides. Int J Prosthodont 1991;4:45-50. 23. Sproull RC. Color matching in dentistry. 3. Color control. J Prosthet Dent 1974;31:146-54. 24. Hassel AJ, Koke U, Schmitter M, Beck J, Rammelsberg P. Clinical effect of different shade guide systems on the tooth shades of ceramic-veneered restorations. Int J Prosthodont 2005;18:422-6. 25. Paravina RD, Powers JM, Fay RM. Dental color standards: shade tab arrangement. J Esthet Restor Dent 2001;13:254-63. 26. Pizzamiglio E. A color selection technique. J Prosthet Dent 1991;66: 592-6. 27. Baltzer A, Kaufmann-Jinoian V. Shading of ceramic crowns using digital tooth shade matching devices. Int J Comput Dent 2005;8: 129-52. 28. Douglas RD, Brewer JD. Acceptability of shade differences in metal ceramic crowns. J Prosthet Dent 1998;79:254-60. 29. Ruyter IE, Nilner K, Moller B. Color stability of dental composite resin materials for crown and bridge veneers. Dent Mater 1987;3: 246-51. 30. Johnston WM, Kao EC. Assessment of appearance match by visual observation and clinical colorimetry. J Dent Res 1989;68:819-22. 31. Lagouvardos PE, Diamanti H, Polyzois G. Effect of individual shades on reliability and validity of observers in color matching. Eur J Prosthodont Restor Dent 2004;12:51-6.
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32. Nieves JL, Garcia-Beltran A, Romero J. Response of the human visual system to variable illuminant conditions: an analysis of opponent-color mechanisms in color constancy. Ophthalmic Physiol Opt 2000;20: 44-58. 33. Paravina RD, Powers JM, Fay RM. Color comparison of two shade guides. Int J Prosthodont 2002;15:73-8. 34. Hammad IA. Intrarater repeatability of shade selections with two shade guides. J Prosthet Dent 2003;89:50-3. 35. Lath DL, Wildgoose DG, Guan H, Lilley TH, Smith RN, Brook AH. Visual whiteness ranking of a Vitapan 3D Master shade guide by untrained assessors. J Clin Dent 2006;17:10-3. Reprint requests to: DR YONG-KEUN LEE DEPARTMENT OF DENTAL BIOMATERIALS SCIENCE DENTAL RESEARCH INSTITUTE
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COLLEGE OF DENTISTRY, SEOUL NATIONAL UNIVERSITY 28 YEONGEON-DONG, JONGRO-GU SEOUL, KOREA FAX: 82-2-740-8694 E-MAIL: [email protected] 0022-3913/$32.00 Copyright Ó 2006 by The Editorial Council of The Journal of Prosthetic Dentistry.
doi:10.1016/j.prosdent.2006.10.007
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CLINICAL IMPLICATIONS Color distribution of conventional shade guides was not logical. Therefore, new shade guides with logically arranged value, chroma, and hue should be used for color matching, and the influence of illuminants on shade matching should be considered in clinical color matching.
T
he goals for esthetic dental restorations are to achieve morphologic, optical, and biologic acceptance. Color matching of an esthetic restorative material with natural teeth is routinely performed with the aid of a shade guide. Dental shade guides are used to identify and communicate color; however, these shade guides have numerous limitations, and the majority of dentists in a survey indicated a need for the development of a
Supported by a grant of the Korea Health 21 R&D Project, Ministry of Health and Welfare, Republic of Korea (03-PJ1-PG1-CH090001). a Graduate student, Department of Dental Biomaterials Science. b Professor, Department of Dental Biomaterials Science, Dental Research Institute. c Professor, Department of Dental Biomaterials Science.
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systematic shade guide.1 Sources of error preclude true color matching: (1) shade guides are not fabricated to match natural teeth and (2) shade guides do not match other shade guides.2 The range of shades in shade guides is not consistent with natural teeth; therefore, an error in shade selection is introduced since many tooth colors must be defined by approximation to the nearest shade of the guide.3,4 Color is usually described according to the Munsell color space in terms of hue, value, and chroma.5 Hue is the attribute of a color that enables the clinician to distinguish between different families of color, and value indicates the lightness of a color. Chroma is the degree of color saturation. When color is determined using the Munsell system, value is determined first and chroma is determined next with shade tabs that are close to the VOLUME 96 NUMBER 6
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measured value but are of increasing saturation of color. Hue is determined last by matching with shade tabs of the value and chroma already determined.5 Color matching in dentistry is routinely performed with a visual method. However, instrumental color measurement can render useful information that can aid visual color matching.6 The Commission Internationale de l’Eclairage (CIE) refined color space in 1976.7 CIE L* value is a measure of the lightness of an object such that a perfect black has a CIE L* value of zero and a perfect reflecting diffuser (white) has a CIE L* value of 100. CIE a* value is a measure of redness (positive value) or greenness (negative value), and CIE b* value is a measure of yellowness (positive value) or blueness (negative value).7 Spectrophotometric color measurements differ depending on the measuring geometry and the illuminant. Therefore, when any color measurements are made with an instrument, measured color values are sensitive to the methods employed.8 Several standard illuminants have been used to measure the color of dental materials.9,10 Standard illuminant D65 represents a phase of daylight with a correlated color temperature of approximately 6500 K, illuminant A represents light from the full radiator at absolute temperature 2856 K, and illuminant F2 represents light from fluorescent lamp of medium color temperature of 4230 K.10 Two standard illuminants are recommended for use in colorimetry.11 Illuminant A should be used in all applications of colorimetry involving the incandescent lighting, and D65 should be used in all colorimetric calculations requiring representative day light.12 Regarding the color difference by the illuminant, it was reported that the changes in optical properties of composite resins relative to the varied illuminants were different from those of dentin.13 Metameric color difference can be minimized if a restoration is matched under a combination of light, which was found to provide the best-perceived match.14 Accurate evaluation of the color of a shade guide is essential for good color matching. Instrumental color measurements of a shade guide are variable for several reasons: measurements are sensitive to the measured location within a shade tab because the tabs are not a uniform color; the shade guides vary between batches; the standard illuminant varies; and there are inherent difficulties with instrumental measurements of tooth materials.15 The disadvantages of using a colorimeter for measuring tooth color are that the instruments are designed to measure flat surfaces and small aperture colorimeters are prone to significant edge-loss effects.16-18 It has also been recommended that research is needed to develop and improve the instrument and technique for quantitative measurement of tooth color.19 These limitations for the instrumental tooth color measurements would cause similar problems with the color measurement for a shade tab. The Vita Lumin Vacuum shade guide (VITA Zahnfabrik, Bad Sackingen, Germany) is divided into DECEMBER 2006
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4 series designated by letters A, B, C, and D. According to the manufacturer, these shades have brown, yellow, gray, and red hues, respectively. Shade tabs of a specific letter group have similar hue, and each hue group includes several tabs of increasing chroma and decreasing value designated in numeric order, such as A1, A2, and A3.15 However, others have concluded that the visual distinction between Vita Lumin shade tabs was primarily due to a difference in luminance or brightness.20 The Chromascop (Ivoclar Vivadent, Schaan, Liechtenstein) shade guide is divided into 5 series, such as 100, 200, 300, 400, and 500. The 100 series is white, 200 series is yellow, 300 series is light yellow, 400 series is gray, and 500 series is dark brown. Within the series, chroma increases and value decreases as the middle number increases, as purported by the manufacturer. Various reports for the color of shade guides are found in the literature.20-22 Since the structure of current shade guides is largely illogical and without any rational use of color ordering,23-25 the arrangement of shade tabs according to color difference from light to dark provides a 1-dimensional color order system to dental shade guides.21 A simplified arrangement of shade tabs was explained, and the reported advantages of this technique were quick verification of color choice, ease of correction (increasing or decreasing hue, value, and chroma) to select the right shade, and ease of communication with the laboratory.26 Use of the Vita 3D-Master shade guide (VITA Zahnfabrik) allows the practitioner to better understand the primary tooth shade characteristics of value, chroma, and hue.27 There is a lack of agreement regarding the threshold levels for the color difference that can be visually perceivable or clinically acceptable. The threshold for acceptable color difference was 1.7 DE*ab units regardless of the shade,28 while 3.3 DE*ab units was considered as an acceptable threshold for composite resins.29 However, these thresholds were determined under optimal in vitro conditions, which may not apply to clinical settings. As a clinical acceptability threshold, the average CIELAB color difference (DE*ab) of those ratings judged a perfect match by the US Public Health Service criteria was found to be 3.7 DE*ab units for composite resin veneer restorations and their comparison teeth.30 In addition to the magnitude of color difference, the position of a shade in color space influenced the color matching. Individual shades in shade guides influenced the reliability and validity of measurements in a color matching process.31 Also, the ratios for value and chroma between pairs of shade tabs influenced the visual perception of color.32 Since shade tabs in a shade guide are matched to a natural tooth in the order of value, hue, and chroma, color distribution of shade tabs sorted by these 3 parameters can provide data for modeling a new systematic 403
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Fig. 1. Distribution of CIE L* and C*ab values of VITA shade guide (D65).
Fig. 2. Distribution of CIE L* and C*ab values of CHRO shade guide (D65).
Fig. 3. Distribution of CIE a* and b* values of VITA shade guide (D65).
Fig. 4. Distribution of CIE a* and b* values of CHRO shade guide (D65).
shade guide. However, there were few studies identified regarding the distribution of shade tabs in commercial shade guides in the 3 color parameters of value, chroma, and hue,26,27,33 and on the influence of illuminant on the color of shade guides. The purpose of this study was to determine the color distributions of 2 conventional shade guides in value, chroma, and hue scale relative to the standard illuminants D65, A, and F2. The null hypotheses of the present study were: (1) the distribution of 3 color parameters are in equal distances from the adjacent shade tab in each shade guide; and (2) the value, chroma, and hue of shade tabs are not influenced by illuminants such as the standard illuminants D65, A, and F2.
MATERIAL AND METHODS
404
Color of the shade tabs of 2 shade guides (Vita Lumin Vacuum shade guide [VITA]; VITA Zahnfabrik, and Chromascop [CHRO]; Ivoclar Vivadent) was measured after polishing the 4-mm-wide middle portion of the labial surface of each shade tab with up to #2400 silicon carbide papers (Buehler Ltd, Lake Bluff, Ill) to make the measuring surface flat. Based on preliminary experiments, flattening the measuring surface resulted in more consistent measured color (less coefficient of variation); therefore, the values based on the flattened surface were used in the present study. The color of the middle site of the shade tab was measured because the translucency of VOLUME 96 NUMBER 6
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Fig. 5. Distribution of ratios for CIE L* and C*ab values of VITA shade guide tabs sorted by CIE L* ratio (D65).
Fig. 6. Distribution of ratios for CIE L* and C*ab values of VITA shade guide tabs sorted by C*ab ratio (D65).
Fig. 7. Distribution of ratios for CIE L* and C*ab values of CHRO shade guide tabs sorted by CIE L* ratio (D65).
Fig. 8. Distribution of ratios for CIE L* and C*ab values of CHRO shade guide tabs sorted by C*ab ratio (D65).
the incisal edge would make the measured color background-dependent, and cervical measurement would reflect the dark color.12 External light was excluded by covering the shade tab specimens with a zero calibration box (Zero Calibration Standard; GretagMacbeth Instruments Corp, New Windsor, NY). CIE L*, a* and b* values were measured according to the CIELAB color scale relative to the standard illuminants D65, A and F2 on a reflection spectrophotometer (Color-Eye 7000A; GretagMacbeth Instruments Corp) with specular component excluded geometry. An ultraviolet (UV) filter was positioned to 100% UV position. The aperture size was 3 3 8 mm, and the illuminating and viewing configuration was CIE diffuse/8-degree geometry.7 Measurements were repeated 3 times for each shade tab and averaged.
The photometric range for this instrument is 0 to 175%, and the resolution is 0.01%. The repeatability in spectral reflectance is within 0.20% SD, and the chromaticity is within 0.05 DE*ab SD when the white calibration plate is measured 30 times at 10-second intervals after white calibration has been performed, as purported by the manufacturer. Distributions for the CIE L*, C*ab and ho values of VITA and CHRO guides were compared. Chroma was calculated as C*ab = (a*2 1 b*2)1/2, and hue angle was calculated as Dho = arctan (b*/a*).7 Distributions of CIE L* and C*ab values and those of CIE a* and b* values relative to the illuminant D65 for each shade guide were compared. To determine the distribution of the ratios of CIE L* and C*ab values of each shade tab compared with the lowest value tab or the lowest chroma
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Table I. Mean (SD) CIE L*, C*ab, and ho values of VITA shade guide tabs measured relative to standard illuminants D65, A, and F2 D65 Shade
A1 A2 A3 A3.5 A4 B1 B2 B3 B4 C1 C2 C3 C4 D2 D3 D4
L*
60.8 59.8 57.4 55.5 52.7 59.7 61.0 55.8 55.9 56.2 53.9 51.8 47.4 55.3 54.3 52.9
(0.2) (0.1) (0.2) (0.3) (0.5) (0.2) (0.1) (0.4) (0.1) (0.3) (0.1) (0.2) (0.0) (0.1) (0.2) (0.1)
A h
C*ab
6.6 9.4 12.2 14.0 14.3 5.3 9.8 14.9 16.1 7.0 10.0 11.1 13.0 5.5 8.6 12.2
(0.3) (0.3) (0.4) (0.0) (0.2) (0.2) (0.3) (0.2) (0.7) (0.2) (0.2) (0.1) (0.3) (0.0) (0.1) (0.2)
o
281.3 88.1 86.0 84.2 82.7 276.1 285.4 86.9 86.8 284.1 290.0 87.3 82.1 285.3 87.0 288.9
L*
(0.5) (0.6) (0.3) (0.1) (0.2) (0.5) (0.3) (0.4) (0.3) (0.2) (0.1) (0.2) (0.1) (0.2) (0.1) (0.2)
61.1 60.5 58.2 56.5 53.8 59.9 61.5 56.8 57.0 56.6 54.6 52.5 48.4 55.6 55.0 53.6
F2
C*ab
(0.3) (0.1) (0.1) (0.3) (0.5) (0.3) (0.1) (0.4) (0.2) (0.3) (0.1) (0.2) (0.0) (0.1) (0.2) (0.1)
6.6 10.2 13.3 15.4 15.9 5.1 10.0 16.1 17.3 7.1 10.6 12.0 14.5 5.7 9.4 12.8
(0.3) (0.4) (0.4) (0.0) (0.2) (0.2) (0.3) (0.2) (0.7) (0.2) (0.3) (0.2) (0.4) (0.1) (0.1) (0.2)
h
o
86.5 78.4 77.0 75.8 74.6 288.7 82.4 77.6 77.6 82.7 78.6 77.3 74.1 82.6 77.5 79.8
L*
(0.5) (0.5) (0.2) (0.1) (0.2) (0.5) (0.2) (0.3) (0.1) (0.1) (0.2) (0.2) (0.1) (0.1) (0.1) (0.1)
61.1 60.4 58.1 56.3 53.6 59.9 61.4 56.7 56.8 56.5 54.4 52.4 48.2 55.6 54.9 53.5
(0.3) (0.1) (0.2) (0.3) (0.5) (0.3) (0.1) (0.4) (0.2) (0.3) (0.1) (0.2) (0.0) (0.1) (0.2) (0.1)
ho
C*ab
7.5 10.7 13.8 15.9 16.2 5.9 11.1 16.9 18.2 7.9 11.3 12.6 14.6 6.3 9.8 13.9
(0.3) (0.4) (0.4) (0.0) (0.3) (0.2) (0.3) (0.3) (0.7) (0.2) (0.3) (0.1) (0.4) (0.0) (0.1) (0.2)
283.9 89.8 88.5 87.4 86.6 280.9 286.6 88.9 89.0 285.9 289.3 89.3 86.3 286.4 89.2 288.7
(0.3) (0.4) (0.2) (0.1) (0.1) (0.4) (0.2) (0.3) (0.2) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1)
Table II. Multivariate test results based on 2-way ANOVA for difference in CIE L*, C*ab, and ho values of VITA shade guide tabs by illuminant Color parameter
CIE L*
C*ab
ho
Source
Shade designation Type of illuminant Shade designation 3 Type of illuminant Shade designation Type of illuminant Shade designation 3 Type of illuminant Shade designation Type of illuminant Shade designation 3 Type of illuminant
Type III Sum of squares
df
Mean square
F
P
1677.20 13.84 2.17
15 2 30
111.81 6.92 .07
2131.75 131.94 1.38
,.001 ,.001 .122
1875.30 49.08 9.26
15 2 30
125.02 24.54 .31
1352.15 265.41 3.34
,.001 ,.001 ,.001
540879.51 102902.31 239761.34
15 2 30
36058.63 51451.15 7992.05
531020.60 757699.89 117695.54
,.001 ,.001 ,.001
P,.05 indicates significant difference.
tab, the ratios for CIE L* or C*ab values were calculated. For the VITA guide, the C4 tab had the lowest value and the B1 tab had the lowest chroma. For the CHRO guide, the 540 tab had the lowest value and the 110 tab had the lowest chroma. Color differences of each of the VITA and CHRO shade tabs depending on the pair of illuminants compared were calculated. Color difference was calculated with the equation: DEab ¼ ½ðDL Þ2 1 ðDa Þ2 1 ðDb Þ2 1=2 .7 In each of VITA or CHRO guide, the influence of the shade designation and the type of illuminant on the CIE L*, C*ab and ho values was determined with a 2-way analysis of variance (ANOVA) (a=.05). Homogenous subsets for the CIE L*, C*ab and ho values of VITA and CHRO shade tabs relative to the illuminant D65 were determined based on the Scheffe multiple comparison test (a=.05). 406
Color difference by the change in the illuminants was analyzed with 2-way ANOVA for the variables of the shade designation and the pair of illuminants compared (a=.05).
RESULTS The distribution of CIE L* and C*ab values of the VITA shade guide is presented in Figure 1. As the designation numbers increased in each shade group, such as A, B, C, and D, the C*ab values increased; however, the ratios of the increase varied by the shade group. Distribution of CIE L* and C*ab values of the CHRO shade guide is presented in Figure 2. As the middle numbers increased in each shade group, C*ab values generally increased, except for the 300 group. VOLUME 96 NUMBER 6
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The distribution of CIE a* and b* values of the VITA shade guide is presented in Figure 3. As the numerical designations increased in each shade group, CIE a* and b* values increased, except for the D group. The distribution of CIE a* and b* values of the CHRO shade guide is presented in Figure 4. As the middle numbers increased in each shade group, CIE a* and b* values increased in some shade groups; however, a general trend could not be determined. Distributions of the ratios for the CIE L* and C*ab values of the VITA shade guide tabs sorted by the CIE L* ratio or the C*ab ratio are presented in Figures 5 and 6. The range of the CIE L* ratio compared with the C4 tab was 1.09 to 1.29, and that of the C*ab ratio compared with the B1 tab was 1.04 to 3.03. The range for the chroma ratio was greater than that for the lightness ratio. Distributions of the ratios for the CIE L* and C*ab values of the CHRO shade guide tabs sorted by the CIE L* ratio or the C*ab ratio are presented in Figures 7 and 8. The range of the CIE L* ratio compared with the 540 tab was 1.03 to 1.28, and that of the C*ab ratio compared with the 110 tab was 1.14 to 2.60. The range for the chroma ratio was greater than that for the lightness ratio. The CIE L*, C*ab and ho values of the VITA shade guide tabs are listed in Table I. Difference in hue angle by the illuminant was clear (positive or negative values by the illuminant). The CIE L* value was influenced by the shade designation and type of illuminant (P,.001), but there was no significant interaction between these 2 variables (Table II). The mean CIE L* value of the 16 VITA shade tabs relative to the illuminant D65 was the lowest, followed by that relative to illuminant F2 and illuminant A (D65,F2,A, P,.05). The C*ab and ho values were influenced by the shade designation and type of illuminant, and there was significant interaction between the 2 variables (P,.001) (Table II). The mean C*ab value of the 16 VITA shade tabs relative to illuminant D65 was the lowest, followed by those relative to illuminant A and illuminant F2 (D65,A,F2, P,.05). The mean ho value of the 16 VITA shade tabs relative to illuminant D65 was the lowest, followed by those relative to illuminant F2 and illuminant A (D65,F2,A, P,.05). Homogenous subsets for the CIE L*, C*ab and ho values of the VITA shade tabs relative to illuminant D65 are listed in Table III. The CIE L* value distribution corresponded to the order based on the lightness purported by the manufacturer. The CIE L* and ho values of the 16 shade tabs were divided into 8 homogenous subsets (a to h), and the C*ab value was divided into 11 subsets (a to k). The CIE L*, C*ab and ho values of the CHRO shade guide tabs are listed in Table IV. The results for the 3 color coordinates for the VITA shade guide as influenced by shade and type of illuminant were similar to DECEMBER 2006
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Table III. Homogenous subsets for CIE L*, C*ab, and ho values of VITA shade guide tabs relative to standard illuminant D65 Shade
No-1
No-2
L*
C*ab
ho
A1 A2 A3 A3.5 A4 B1 B2 B3 B4 C1 C2 C3 C4 D2 D3 D4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
2 5 8 12 15 1 3 11 13 6 7 14 16 4 10 8
i, j h, i g f b, c h j f f f d b a e, f d, e c
b, c d, e g, h i, j j a d, e j, k k c e, f f, g h, i a, b d g, h
c h g f e d b h h b a g, h e b h a
No-1 indicates numbering based on order of A, B, C, and D grouping. No-2 indicates numbering based on value (lightness) purported by manufacturer. Same letters indicate homogenous groups based on Scheffe multiple comparison test (P,.05).
those for the CHRO shade guide; therefore, the statistical results table was not included. Homogenous subsets for the mean CIE L*, C*ab and ho values of the CHRO shade tabs are listed in Table V. The CIE L* and C*ab values of 20 shade tabs were divided into 10 subsets (a to j), and the ho value was divided into 13 subsets (a to m). Color differences (DE*ab) of the VITA shade guide tabs caused by the changes in 3 standard illuminants are listed in Table VI. Color difference caused by the change in illuminants was influenced by the shade designation and pair of illuminants compared (D65/A and so on), and there was significant interaction between the 2 variables (Table VII). The order of mean color difference of the 16 VITA shade tabs was as follows: DE*ab (D65/F2) = 1.63 , DE*ab (D65/A) = 2.22 , DE*ab (A/F2) = 2.46 (P,.05). Color differences of the CHRO shade guide tabs caused by the changes in 3 standard illuminants are listed in Table VIII. Color difference caused by the change in illuminants was influenced by the shade designation and pair of illuminants compared, and there was significant interaction between the 2 variables (Table VII). The order of mean color difference of the 20 CHRO shade tabs was as follows: DE*ab (D65/ F2) =2.45 , DE*ab (D65/A) = 2.71 , DE*ab (A/F2) = 3.14 (P,.05).
DISCUSSION The first null hypothesis that the distribution of 3 color parameters are in equal distances from the adjacent 407
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Table IV. Mean (SD) CIE L*, C*ab, and ho values of CHRO shade guide tabs measured relative to standard illuminants D65, A, and F2 D65 Shade
110 120 130 140 210 220 230 240 310 320 330 340 410 420 430 440 510 520 530 540
L*
67.9 65.6 61.8 62.0 60.4 61.9 57.3 59.2 58.8 57.5 59.3 54.5 58.4 58.6 57.2 56.4 56.4 54.7 56.1 53.1
(0.1) (0.5) (0.4) (0.2) (0.2) (0.1) (0.4) (0.3) (0.5) (0.2) (0.2) (0.8) (0.5) (0.6) (0.3) (0.2) (0.1) (0.4) (0.3) (0.4)
C*ab
8.5 9.7 9.9 12.1 13.6 13.9 14.7 17.0 15.7 17.5 22.1 19.0 10.8 11.4 12.2 13.8 15.4 19.2 19.0 8.8
(0.2) (0.3) (0.2) (0.1) (0.1) (0.0) (0.3) (0.1) (0.2) (0.4) (0.5) (1.2) (0.2) (0.3) (0.4) (0.2) (0.3) (0.3) (0.3) (0.2)
A h
o
285.4 289.7 288.9 86.5 87.0 81.2 80.6 78.7 88.0 85.0 83.5 78.7 82.2 88.1 85.8 84.5 81.8 80.8 71.8 83.8
L*
(0.2) (0.2) (0.2) (0.0) (0.2) (0.0) (0.0) (0.1) (0.2) (0.1) (0.1) (0.0) (0.2) (0.0) (0.3) (0.1) (0.0) (0.0) (0.1) (0.2)
68.4 66.2 62.4 62.8 61.3 63.0 58.5 60.6 59.8 58.7 60.8 56.0 59.3 59.4 57.9 57.3 57.4 55.9 57.5 54.8
C*ab
(0.1) (0.5) (0.4) (0.2) (0.2) (0.1) (0.4) (0.3) (0.5) (0.2) (0.2) (0.9) (0.5) (0.6) (0.3) (0.2) (0.1) (0.4) (0.3) (0.4)
Table V. Homogenous subsets for mean CIE L*, C*ab, and ho values of CHRO shade guide tabs relative standard illuminant D65
110 120 130 140 210 220 230 240 310 320 330 340 410 420 430 440 510 520 530 540
No
L*
C*ab
ho
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
j i h h g, h h d, e f, g e, f, g d, e, f f, g a, b e, f e, f d, e c, d c, d a, b, c b, c, d a
a a, b a, b c, d d, e d, e, f e, f g, h f, g, h h, i j i b, c b, c b, c c, d d, e, f e, f, g i i
c a b l l f, g f e m j i e h j m k j g, h f d
No indicates numbering based on order of shade designation numbers. Same letters indicate homogenous groups based on Scheffe multiple comparison test (P,.05).
shade tab in each shade guide was rejected because the distributions of 3 color parameters of the shade tabs in each shade guide were not equally distanced from the 408
8.8 10.3 10.4 13.2 14.7 15.6 16.4 19.1 16.7 19.0 24.0 21.3 12.1 12.1 12.3 13.3 15.2 17.1 21.3 21.9
(0.2) (0.3) (0.2) (0.1) (0.1) (0.0) (0.4) (0.1) (0.2) (0.5) (0.5) (1.3) (0.2) (0.4) (0.3) (0.4) (0.2) (0.3) (0.4) (0.4)
F2 h
83.8 80.8 81.1 78.0 78.3 74.2 74.0 72.6 78.5 76.5 75.8 72.9 75.1 77.2 79.4 77.7 76.8 74.7 74.2 68.4
o
L*
(0.2) (0.2) (0.1) (0.0) (0.2) (0.0) (0.0) (0.1) (0.2) (0.1) (0.1) (0.1) (0.1) (0.0) (0.0) (0.3) (0.0) (0.0) (0.0) (0.0)
68.4 66.2 62.4 62.7 61.3 62.9 58.4 60.4 59.7 58.5 60.6 55.8 59.2 59.3 57.9 57.2 57.3 55.8 57.3 54.5
C*ab
(0.1) (0.5) (0.4) (0.2) (0.2) (0.1) (0.4) (0.3) (0.5) (0.2) (0.2) (0.9) (0.5) (0.6) (0.3) (0.2) (0.1) (0.4) (0.3) (0.4)
9.7 11.1 11.3 13.9 15.6 15.9 16.7 19.3 17.9 20.0 25.2 21.5 12.3 12.6 13.1 13.9 15.8 17.6 21.8 21.1
(0.2) (0.4) (0.2) (0.1) (0.1) (0.0) (0.4) (0.1) (0.2) (0.5) (0.5) (1.4) (0.3) (0.4) (0.4) (0.4) (0.2) (0.3) (0.4) (0.4)
ho
286.5 289.1 288.6 88.7 88.9 85.4 85.2 83.8 89.5 87.6 86.8 84.0 86.2 88.0 89.9 88.5 87.7 85.9 85.2 79.7
(0.1) (0.1) (0.1) (0.0) (0.1) (0.0) (0.0) (0.1) (0.1) (0.0) (0.1) (0.0) (0.1) (0.0) (0.0) (0.2) (0.1) (0.0) (0.0) (0.0)
Table VI. Mean (SD) color difference of VITA shade guide tabs depending on illuminant DE*ab (D65/A)
A1 A2 A3 A3.5 A4 B1 B2 B3 B4 C1 C2 C3 C4 D2 D3 D4
1.44 1.95 2.46 2.78 2.87 1.18 2.20 2.96 3.16 1.66 2.22 2.35 2.62 1.24 1.79 2.66
(0.06) (0.07) (0.06) (0.00) (0.03) (0.04) (0.06) (0.04) (0.10) (0.04) (0.05) (0.03) (0.06) (0.01) (0.01) (0.04)
DE*ab (D65/F2)
0.97 1.47 1.92 2.23 2.31 0.80 1.43 2.28 2.44 1.01 1.46 1.66 2.12 0.82 1.34 1.76
(0.04) (0.06) (0.06) (0.01) (0.03) (0.02) (0.04) (0.03) (0.10) (0.03) (0.04) (0.02) (0.06) (0.01) (0.01) (0.04)
DE*ab (A/F2)
1.45 2.14 2.78 3.20 3.36 1.13 2.30 3.38 3.64 1.70 2.42 2.63 3.09 1.29 1.98 2.89
(0.07) (0.08) (0.08) (0.00) (0.04) (0.04) (0.07) (0.04) (0.13) (0.05) (0.06) (0.03) (0.08) (0.01) (0.01) (0.05)
DE*ab (D65/A) refers to color difference between CIE L*, a*, and b* values measured relative to standard illuminants D65 and A.
adjacent shade tab. For the VITA shade guide, the CIE L* ratio was 1.09 to 1.29, and the C*ab ratio was 1.04 to 3.03. For the CHRO shade guide, the CIE L* ratio was 1.03 to 1.28, and the C*ab ratio was 1.14 to 2.60. These illogical distributions are clearly observed in Figures 5 through 8. The second null hypothesis that the value, chroma, and hue of shade tabs are not influenced by illuminants VOLUME 96 NUMBER 6
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Table VII. Multivariate test results based on 2-way ANOVA for color difference by pair of illuminants compared for VITA and CHRO shade guides Shade guide
VITA
CHRO
Source
Type III Sum of squares
df
Mean square
F
P
Shade designation Pair of illuminants Shade designation 3 Pair of illuminants Shade designation Pair of illuminants Shade designation 3 Pair of illuminants
57.549 17.705 1.813
15 2 30
3.837 8.853 .060
1381.263 3187.129 21.762
,.001 ,.001 ,.001
92.242 14.709 2.184
19 2 38
4.855 7.354 .057
1049.792 1590.298 12.427
,.001 ,.001 ,.001
P,.05 indicates significant difference.
such as the standard illuminants D65, A, and F2 was also rejected because value (CIE L*), chroma (C*ab), and hue angle (ho) were influenced by the illuminant in both shade guides. Color differences caused by the changes in illuminant were in the acceptable range for the VITA shade guide based on the criteria of Johnston and Kao (DE*ab , 3.7),30 because the range of color differences were 1.18 to 3.16 for the D65/A pair, 0.80 to 2.44 for the D65/F2 pair, and 1.13 to 3.64 for the A/F2 pair. However, those for the CHRO shade guide were acceptable or not, depending on the pair of illuminants compared, because the range of color differences were 1.72 to 3.98 for the D65/A pair, 1.30 to 3.59 for the D65/F2 pair, and 1.81 to 4.83 for the A/F2 pair. However, it should be noted that color discrepancies by the illuminant were also influenced by the shade designations. In the CHRO shade guide, several of the color difference values were in the unacceptable range. Therefore, these discrepancies in color parameters caused by the illuminant should be considered in clinical color matching. Further study on the clinical implications of these discrepancies is needed. In the present study, a color difference value of 3.7 was regarded as the acceptable limit because this value was calculated based on clinical condition.30 The correlation between instrumentally measured color differences (DE*ab) and human observer assessment of color differences was determined. The results showed that the threshold acceptability of color difference was 1.1 DE*ab units for red-varying shades and 2.1 DE*ab units for yellow-varying shades, and mean value regardless of shades was 1.7 DE*ab units.28 Based on the previous study,28 it is clear that color difference value itself has limitations when relating DE*ab value with observer response. The effect of individual shades in shade guides on the reliability and validity of measurements in a color matching process was determined. Thus, the matching process with shades of different materials was not accurate enough. Some shades produce a more reliable and valid match than others, and teeth are matched with DECEMBER 2006
Table VIII. Mean (SD) color difference of the CHRO shade guide tabs depending on illuminant DE*ab (D65/A)
110 120 130 140 210 220 230 240 310 320 330 340 410 420 430 440 510 520 530 540
1.72 1.88 1.96 2.34 2.58 2.69 2.78 3.20 3.07 3.31 3.98 3.43 2.09 2.09 2.15 2.29 2.58 2.88 3.46 3.66
(0.04) (0.06) (0.04) (0.02) (0.01) (0.00) (0.06) (0.02) (0.04) (0.06) (0.06) (0.18) (0.04) (0.07) (0.06) (0.06) (0.03) (0.04) (0.05) (0.05)
DE*ab (D65/F2)
1.30 1.56 1.56 2.01 2.22 2.46 2.60 3.07 2.45 2.84 3.59 3.41 1.92 1.89 1.86 2.04 2.33 2.69 3.34 3.78
(0.03) (0.05) (0.03) (0.02) (0.02) (0.01) (0.06) (0.02) (0.04) (0.06) (0.08) (0.20) (0.03) (0.06) (0.05) (0.05) (0.04) (0.04) (0.06) (0.06)
DE*ab (A/F2)
1.81 2.05 2.14 2.63 2.94 3.09 3.23 3.76 3.53 3.91 4.83 4.13 2.37 2.37 2.44 2.63 3.00 3.42 4.19 4.32
(0.04) (0.07) (0.04) (0.02) (0.02) (0.01) (0.07) (0.02) (0.05) (0.09) (0.09) (0.24) (0.04) (0.08) (0.07) (0.07) (0.04) (0.06) (0.07) (0.07)
DE*ab (D65/A) refers to color difference between CIE L*, a*, and b* values measured relative to standard illuminants D65 and A.
relative difficulty.31 Moreover, the differences in value, chroma, and hue between 2 shades compared to one another would influence differently the observer responses by the color parameter. As indicated in the present study, the ratios for value and chroma between pairs of shade tabs were not consistent. This should influence the visual perception of color.32 Bioform (Dentsply, York, Pa) and Vita Lumin shade guides, and a combination of the 2, have been compared spectrophotometrically to the published shades of human teeth.22 As a result, the use of both shade guides in shade selection was recommended to reduce the coverage error, which is caused by the difference in the ranges of shades in shade guides and natural teeth.22 The pattern and range for the 3 color parameters 409
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were different between 2 shade guides of the VITA and the CHRO, based on the present study. If shade tabs from 2 shade guides were combined, more accurate color matching may be possible. However, the increased number of shade tabs would make the color matching process more complicated. As noted previously, the VITA shade guide is grouped by the hue15 or value.20 In each shade series from A to D of the present study, chroma increased and value decreased as the second shade designation number increased. However, it was unclear whether each shade series had corresponding hue because hue angle varied in each shade series (Table I). A systematically arranged shade guide system will be more helpful in selecting the correct tooth shade and in avoiding shade corrections.24 Therefore, the order of the VITA shade guide was rearranged by the value purported by the manufacturer in the present study. As a result, although lightness was ordered in this new arrangement, the other 2 parameters varied. Rearrangement by the chroma and hue would render a more clinically relevant shade guide. Total color difference in relation to the lightest tab, followed by tab division into an adequate number of groups, is recommended as a possible and universally applicable mode of tab arrangement in dental color standards.25 The VITA Company developed a more ordered shade guide (Vitapan 3D-Master). Compared to Vitapan Classical, chromaticity ranges of Vitapan 3DMaster were extended in the desired directions.33 Use of the Vitapan 3D-Master shade guide significantly improved the intrarater repeatability of general practitioners compared with the Vita Lumin Vacuum shade guide.34 However, a new order of the Vitapan 3DMaster shade guide tabs has been recommended in relation to whiteness for use in studies of whitening products.35 In the present study, the CHRO shade guide was a conventional type; therefore, the conventional counterpart from the VITA company was selected for comparisons. Further studies with additional ordered shade guides (Vitapan 3D-Master) should be performed.
CONCLUSION Within the limitations of the present study, the distribution and range of 3 color parameters of value, chroma, and hue were significantly different for the 2 commercial shade guides. The 3 color parameters varied significantly by the illuminant. The distributions of value and chroma in both shade guides were arbitrary without any logical order. REFERENCES 1. Goodkind RJ, Loupe MJ. Teaching of color in predoctoral and postdoctoral dental education in 1988. J Prosthet Dent 1992;67:713-7.
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2. Preston JD. Current status of shade selection and color matching. Quintessence Int 1985;16:47-58. 3. Analoui M, Papkosta E, Cochran M, Matis B. Designing visually optimal shade guides. J Prosthet Dent 2004;92:371-6. 4. Browning WD. Use of shade guides for color measurement in toothbleaching studies. J Esthet Restor Dent 2003;15:13-20. 5. Powers JM, Sakaguchi RL. Restorative dental materials. 12th edition. St. Louis: Mosby; 2006. p. 28-31. 6. Paul SJ, Peter A, Rodoni L, Pietrobon N. Conventional visual vs spectrophotometric shade taking for porcelain-fused-to-metal crowns: a clinical comparison. Int J Periodontics Restorative Dent 2004;24:222-31. 7. Commission Internationale de l’Eclairage (CIE). Colorimetry - Technical Report. CIE Pub. No.15, 2nd ed. Vienna (Austria): Bureau Central de la CIE, 1986 (corrected reprint 1996). p. 35-6. 8. Lee YK, Yoon TH, Lim BS, Kim CW, Powers JM. Effects of color measuring mode and light source on the color of shade guides. J Oral Rehabil 2002; 29:1099-107. 9. Lee YK, Powers JM. Color difference of four esthetic restorative materials by the illuminant. Am J Dent 2005;18:359-63. 10. Commission Internationale de l’Eclairage (CIE). Colorimetry - Official recommendations of the Commission Internationale de l’Eclairage. CIE Publication No. 15 (E-1.3.1). Vienna (Austria): Bureau Central de la CIE, 1996. 11. ISO 10526. CIE standard illuminant for colorimetry. Geneva (Switzerland): ISO; 1999. 12. ASTM E 308-90. Standard test methods for computing the colors of objects by using CIE system. West Conshohocken (PA): ASTM; 1990. 13. Lee YK, Powers JM. Metameric effect between resin composite and dentin. Dent Mater 2005;21:971-6. 14. Leow ME, Ng WK, Pereira BP, Kour AK, Pho RW. Metamerism in aesthetic prostheses under three standard illuminants—TL84, D65 and F. Prosthet Orthot Int 1999;23:174-80. 15. Schwabacher WB, Goodkind RJ. Three-dimensional color coordinates of natural teeth compared with three shade guides. J Prosthet Dent 1990;64: 425-31. 16. van der Burgt TP, ten Bosch JJ, Borsboom PC, Kortsmit WJ. A comparison of new and conventional methods for quantification of tooth color. J Prosthet Dent 1990;63:155-62. 17. ten Bosch JJ, Coops JC. Tooth color and reflectance as related to light scattering and enamel hardness. J Dent Res 1995;74:374-80. 18. Bolt RA, Bosch JJ, Coops JC. Influence of window size in small-window color measurement, particularly of teeth. Phys Med Biol 1994;39: 1133-42. 19. Li Y. Tooth color measurement using Chroma Meter: techniques, advantages, and disadvantages. J Esthet Restor Dent 2003;15:33-41. 20. Ferreira D, Monard LA. Measurements of spectral reflectance and colorimetric properties of Vita shade guides. J Dent Assoc S Afr 1991;46: 63-5. 21. O’Brien WJ, Groh CL, Boenke KM. One-dimensional color order system for dental shade guides. Dent Mater 1989;5:371-4. 22. O’Brien WJ, Boenke KM, Groh CL. Coverage errors of two shade guides. Int J Prosthodont 1991;4:45-50. 23. Sproull RC. Color matching in dentistry. 3. Color control. J Prosthet Dent 1974;31:146-54. 24. Hassel AJ, Koke U, Schmitter M, Beck J, Rammelsberg P. Clinical effect of different shade guide systems on the tooth shades of ceramic-veneered restorations. Int J Prosthodont 2005;18:422-6. 25. Paravina RD, Powers JM, Fay RM. Dental color standards: shade tab arrangement. J Esthet Restor Dent 2001;13:254-63. 26. Pizzamiglio E. A color selection technique. J Prosthet Dent 1991;66: 592-6. 27. Baltzer A, Kaufmann-Jinoian V. Shading of ceramic crowns using digital tooth shade matching devices. Int J Comput Dent 2005;8: 129-52. 28. Douglas RD, Brewer JD. Acceptability of shade differences in metal ceramic crowns. J Prosthet Dent 1998;79:254-60. 29. Ruyter IE, Nilner K, Moller B. Color stability of dental composite resin materials for crown and bridge veneers. Dent Mater 1987;3: 246-51. 30. Johnston WM, Kao EC. Assessment of appearance match by visual observation and clinical colorimetry. J Dent Res 1989;68:819-22. 31. Lagouvardos PE, Diamanti H, Polyzois G. Effect of individual shades on reliability and validity of observers in color matching. Eur J Prosthodont Restor Dent 2004;12:51-6.
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32. Nieves JL, Garcia-Beltran A, Romero J. Response of the human visual system to variable illuminant conditions: an analysis of opponent-color mechanisms in color constancy. Ophthalmic Physiol Opt 2000;20: 44-58. 33. Paravina RD, Powers JM, Fay RM. Color comparison of two shade guides. Int J Prosthodont 2002;15:73-8. 34. Hammad IA. Intrarater repeatability of shade selections with two shade guides. J Prosthet Dent 2003;89:50-3. 35. Lath DL, Wildgoose DG, Guan H, Lilley TH, Smith RN, Brook AH. Visual whiteness ranking of a Vitapan 3D Master shade guide by untrained assessors. J Clin Dent 2006;17:10-3. Reprint requests to: DR YONG-KEUN LEE DEPARTMENT OF DENTAL BIOMATERIALS SCIENCE DENTAL RESEARCH INSTITUTE
DECEMBER 2006
THE JOURNAL OF PROSTHETIC DENTISTRY
COLLEGE OF DENTISTRY, SEOUL NATIONAL UNIVERSITY 28 YEONGEON-DONG, JONGRO-GU SEOUL, KOREA FAX: 82-2-740-8694 E-MAIL: [email protected] 0022-3913/$32.00 Copyright Ó 2006 by The Editorial Council of The Journal of Prosthetic Dentistry.
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