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Variation in color between intended matched shade and fabricated shade of dental porcelain
Variation in color between intended matched shade and fabricated shade of dental porcelain Alvin G. Wee, BDS, MS,a Peter Monaghan, DDS, PhD,b and William M. Johnston, PhDc College of Dentistry, The Ohio State University, Columbus, Ohio; and School of Dentistry, Marquette University, Milwaukee, Wisc. Statement of problem. The total quantifiable color difference between shade matching and shade duplication has not been investigated formally.
Purpose. The purpose of this in vitro study was to evaluate and compare the color difference of the total color replication process and the direction of the individual color parameters for 3 dental porcelain shade-matching systems. Material and methods. The shade of 11 porcelain master disks was determined visually and instrumentally using 3 porcelain shade-matching systems: (1) Vita Lumin/Vita VMK 68, (2) Vitapan 3D-Master/Vita Omega 900, and (3) Shofu ShadeEye-EX/Vintage Halo. Corresponding porcelain disks made of 4.5 mm opaque and 1 mm dentin porcelain were fabricated with each of the porcelain systems. The colors of the master disks and fabricated disks (CIE L* a* b* coordinates) were measured with a spectroradiometer with a 45°/0° configuration. Repeated-measures analysis of variance was used to evaluate within-group differences among the porcelain systems for the total color difference (∆E) and direction of the color parameters (∆L, ∆a, and ∆b). The Ryan-Einot-Gabriel-Welsch multiple range test was used for post-hoc analysis (α=.05). Results. The largest mean ∆E was recorded for the Vitapan 3D-Master system, which was significantly different from the other systems (P=.0024). A significant difference was found between the interaction of the different systems and the direction of color (P=.0024). The amount of change within each color parameter was dependent on the porcelain system, as well as the amount of change among the color parameters. Conclusion. Within the limitations of this study, the results suggest that reliable delivery of a properly matched restoration to existing porcelain restorations cannot be ensured regardless of the shade assessment method used (visual or computer-generated). (J Prosthet Dent 2002;87:657-66.)
CLINICAL IMPLICATIONS Shade determination, whether visual or computer-based, may not lead to the production of a porcelain restoration with a clinically acceptable color match. The best replication of dental porcelain color can be obtained with a shade-matching system similar to the porcelain restoration being matched.
T
he importance of dental appearance is well documented.1,2 It has been shown, for example, that This project was supported in part by the Ohio State University College of Dentistry’s Summer Research Program (NIH/NIDCR grant DE 07155-13) and the Ohio State University’s Clinical Research Curriculum (NIH/NHLBI grant K30 HL04162). The material was presented in part at the 78th General Session of the International Association for Dental Research, Washington, D.C., April 5-8, 2000. aAssistant Professor in Prosthodontics, Section of Restorative Dentistry, Prosthodontics, and Endodontics, The Ohio State University College of Dentistry. bAssistant Professor and Director of Graduate Biomaterials Program, Division of Dental Biomaterials, Marquette University School of Dentistry. cProfessor, Section of Restorative Dentistry, Prosthodontics, and Endodontics, The Ohio State University College of Dentistry. JUNE 2002
esthetic dental restorative treatment can enhance a patient’s self-esteem.3 Clinically, a successful color match is an important aspect of any esthetic dental restoration. According to results from clinical studies (Table I),4-7 however, the final color match of porcelain crowns to adjacent natural dentition remains problematic. In clinical practice, the color replication process for dental porcelain comprises a shade-selection phase followed by shade duplication (Fig. 1). Shade selection can be accomplished through either visual assessment or instrumental color analysis. Duplication of the selected shade is accomplished during the fabrication of the restoration in the dental laboratory. Visual shade selection is the most common method of color determination in dentistry,8 but color duplicaTHE JOURNAL OF PROSTHETIC DENTISTRY 657
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Fig. 1. Color replication process for dental porcelain.
Table I. Clinical studies that evaluated shade match of porcelain crowns Crown type
Color mismatch of cemented final restorations
Metal-ceramic (Procera) Metal-ceramic (Procera) All-porcelain (Dicor) All-porcelain (In-Ceram)
61% 63% 45% 44%
of of of of
40 44 98 80
Type of clinical study
crowns crowns crowns crowns
Two-year prospective Five-year prospective Five-year retrospective Four-year retrospective
Table II. Summary of studies relevant to dental color-matching tolerance Study
Color difference (∆E)
Results
Color perceptibility Kuehni and Marcus33 Seghi et al34 Johnston and Kao21
1.0 2.0 3.7
In vitro study. 50% of observers perceived a color difference. In vitro study. Porcelain specimens were correctly judged by observers 100% of the time. In vivo study. Found average color difference between compared teeth rated as a match in the oral environment.
Color acceptability Ragain and Johnston36 Ruyter et al35 Johnston and Kao21
2.72 3.3 6.8
In vitro study. Average 50:50 ∆E replacement rate for all subjects was found. In vitro study. 50% of observers considered the composite specimens to be unacceptable. In vivo study. Found average color difference between compared teeth rated as a mismatch within the normal range of tooth color in the oral environment.
tion via this process is plagued by unreliable and inconsistent results.9,10 The inadequacies of dental shade guides, in terms of the range11,12 and systemic distribution in the tooth color space,12-14 have been described.12,15,16 Inconsistencies in shade determination can result from multiple factors, including individual physiological and psychological responses to radiant energy stimulation,17 aging,18 and previous eye exposure/fatigue.19 Environmental and lighting conditions also play an important role in shade selection.9,12,20 Instrumental color analysis offers a potential advantage over visual color determination: instrumental readings are objective, quantifiable, and more rapidly obtainable. Although the extensive use of computer658
ized colorimeters and spectrophotometers has been reported in dental research,10,21-29 most devices currently are unsuitable for routine clinical dental use given their limited ability to measure the color of translucent objects8,30 (such as teeth) and their prohibitive cost/size.27-29 Shade matching, whether by visual or instrumental methods, requires an understanding of color harmony and tolerance—namely, what actual color difference (∆E) would be perceptible to the human eye. The CIELAB-based color difference formula, introduced in 1976 and recommended by the International Commission on Illumination,31 defines a color space (L*a*b*) in which L* represents lightness, a* represents the chromaticity coordinate for red-green (+a* is VOLUME 87 NUMBER 6
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Fig. 2. Flowchart of experimental design.
the red direction and –a* is the green direction), and b* represents the chromaticity coordinate for yellowblue (+b* is the yellow direction and –b* is the blue direction). Color difference, or ∆E, is defined by the following equation:32 ∆E = √(L*f – L*i)2 + (a*f – a*i)2 + (b*f – b*i)2
(1)
where the initial (i) and final (f) are color descriptors. This formula has been used extensively in dental research. Several studies that provide information regarding clinical color-matching tolerance are summarized in Table II.21,33-36 Errors associated with the shade duplication of dental porcelain are well documented. These errors are related to the underlying metal used,22,37-39 the batch of porcelain powder,40 the brand of porcelain,40-43 and the number of times glazing was performed.44 The total quantifiable color difference (∆E) between shade matching and shade duplication has not been investigated formally. It appears that no study has yet determined the quantifiable color difference for the shade-matching phase of visual shade determination. Only 2 studies have provided insight on the shade duplication process for porcelain. One study evaluated the color difference between Vita Lumin shade guides (Vident Inc, Brea, Calif.) and 4 fired porcelain systems on individualized ceramic shade tabs.43 An average color difference of 3 ± 0.8 was found for the 4 different metal-ceramic porcelain systems fabricated by 2 technicians. Another study evaluated the amount of porcelain thickness (standard JUNE 2002
0.5 mm opaque thickness) required to layer over highnoble metal to obtain an acceptable color difference to shade tabs.45 The 2 metal-ceramic porcelain systems tested exhibited an average color difference of 7.5 ± 2.1 at 1-mm thickness (data interpolated from figures in the published article).45 Vita Zahnfabrik (Bad Säckingen, Germany) recently introduced the Vitapan 3D-Master shade guide with a complementary new porcelain system to address some of the limitations of visible shade selection.16 According to the manufacturer, the guide was designed to include a more uniform coverage of shade tabs in virtually all existing natural tooth shades. It is systematically arranged in a 3-dimensional color space that makes shade selection simpler and more accurate. Shofu Dental Corporation (San Marcos, Calif.) claims that its new clinical colorimeter, the ShadeEye-EX Chroma Meter, is both precise and accurate for shade matching when used with the Vintage Halo porcelain system. (Information obtained from product guides.) The purpose of this in vitro study was to evaluate and compare the color difference of the total color replication process with 3 dental porcelain shadematching systems: (1) the Vita Lumin Vacuum shade guide and Vita VMK 68 porcelain system, (2) the Vitapan 3D-Master shade guide and Vita Omega 900 porcelain system, and (3) the Shofu ShadeEye-EX clinical colorimeter and Vintage Halo porcelain system. It was hypothesized that color differences (∆Ε) would exist between the master porcelain disks and those fab659
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Fig. 3. ShadeEye-EX chromameter used to measure master porcelain disk.
Fig. 5. Visual shade evaluation of master porcelain disk.
ricated with the 3 dental porcelain shade-matching systems and that different changes in color parameters (∆L*, ∆a*, and ∆b*) would be evident when the master porcelain disks were compared to those fabricated with the 3 test systems.
MATERIAL AND METHODS Eleven master porcelain disks of unknown shade fabricated from VMK 68, as used in a previous color experiment,46 were used to simulate metal-ceramic crowns. The disks were made with a 4.5-mm layer of opaque and 1-mm thickness of translucent dentin porcelain. Shade selection for these disks was carried out in 2 phases: instrumental and visual (Fig. 2). The manufacturers’ recommendations for use of the clinical colorimeter and 2 visual shade guides were followed precisely during the experiment. For instrumental shade selection, the ShadeEye-EX chromameter was used to measure the color of the 11 master porcelain disks in “porcelain” mode (Fig. 3). 660
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Fig. 4. New Vitapan 3D-Master shade guide.
Only one reading of the meter was used for porcelain fabrication. For visual shade selection, 2 conceptually different shade guides were used: the traditional Vita Lumin Vacuum guide and the new Vitapan 3D-Master shade guide (Fig. 4). Visual shade selections (Fig. 5) were performed in a viewing booth with color-corrected D65 lighting (Macbeth Spretra Light, Newburgh, N.Y.). The selections were made by 3 examiners: a general dentist, a prosthodontist, and a maxillofacial prosthodontist, none of whom had visual color deficiencies according to the American Optical Company Hardy-Rand-Ritter test. In a previous study, no significant differences (P=.7881) were found among these 3 examiners when they compared porcelain tabs to extracted teeth with the United States Public Health Service criteria.47 Each selector performed a total of 22 visual shade selections. For shade determination using the Vita Lumin Vacuum guide, selection was based on agreement between at least 2 of the 3 selectors or on consensus among the 3 selectors when 3 unique shades were chosen (Table III). For the Vitapan 3DMaster shade guide, the selected shade was derived from the median shade values of the 3 chosen shades (Table III). This method was used successfully in a previous study47 and is the shade-selection method recommended by the manufacturer when intermediate shades are fabricated by mixing porcelain powders at a 1:1 ratio. The practice of mixing porcelain to obtain a color that is “in between” the porcelain mixtures has been verified scientifically.27,48,49 The porcelain powders were measured on an analytical balance (AE 240; Mettler Instruments, Greifensee, Switzerland) with an accuracy of 0.01 mg. The ShadeEye-EX chromameter was used according to the manufacturer’s instructions, and as such, provided a formulation of the Vintage Halo porcelain to create the supposedly correct shade match. VOLUME 87 NUMBER 6
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Table III. Actual shades selected using the 3 porcelain shade-matching systems Vita Lumin Porcelain disks
1 2 3 4 5 6 7 8 9 10 11
3D-Master
ShadeEye
Consensus
Evaluator A
Evaluator B
Evaluator C
A3 A3 B2 A2 C4 B1 B1 D2 B2 A4 A3
2M2 2M2.5 1M2 1M2 4M2 1M1 1M1 2R1.5 1M2 4M2.5 3M2
3L2 3L2 2L1.5 3M2 5M1 2M1 2M1 3M1 2M1.5 5M2 4L1.5
3R2.5 3R2.5 2M2 2R2.5 4M2 1M2 2M1 2R1.5 2M2 4M2.5 3M2
Final
Shade
Value
Hue
3M2 3M2.5 2M2 2M2 4M2 1M1 2M1 2R1.5 2M2 4M2.5 3M2
3.3 3.0 2.0 2.0 3.8 1.0 1.0 2.0 1.5 4.0 3.3
± + ± + – ± ± – ± ± ±
Y1 Std Y1 R1 Std Std Std R1 Std Std Y1
0 1 0 1 2 0 0 1 0 0 0
Fabrication of porcelain disks Corresponding color-matching porcelain systems were used to fabricate the experimental porcelain disks: Vita VMK 68 for the Vita Lumin Vacuum system, Vita Omega 900 for the Vitapan 3D-Master system, and Vintage Halo for the ShadeEye-EX chromameter. For each of the 11 master disks, 1 experimental disk was fabricated for each porcelain system and its respective shade-selection method, yielding 33 disks for color measurement (Fig. 6). No porcelain disk was omitted during the fabrication procedure. During fabrication of the disks, the porcelain powders were dry compressed by hand into a fabricated mold with a plunger.42 Two to 3 drops of distilled water were added to the compressed powder to hold it together and facilitate removal. The specimens were extracted from the mold, set onto a sager tray, and fired with the manufacturer-recommended protocols in a high-temperature porcelain oven (Vita Vacuum 200; Vident Inc). The appropriate opaque powder was used first to fabricate an opaque disk. The opaque layers were approximately 4.5 mm thick and 15 mm in diameter. After the opaque disks were trimmed to shape, the respective dentin powder was added and fired in the porcelain oven. To simulate dental laboratory situations, 2 firing cycles for the opaque and dentin porcelain were performed. To eliminate the effect of surface texture variations on color,50 the dentin layer was polished to 1 mm thickness. All polishing was performed with a metallographic polishing system (Vari/Pol, VP-50; Leco Corp, St. Joseph, Mich.) from 400- to 1000-grit under continuous water cooling. A digital veneer caliper (model CD-6 BS; Mitutuyo Corp, Tokyo, Japan) was used for all thickness measurements. The disks were ultrasonically cleaned (Jelsonic; Jelenko, New Hyde Park, N.Y.) in a general-purpose cleaning solution (L & R Mfg Co, Kearny, N.J.) for 10 minutes JUNE 2002
Fig. 6. Six example sets of master and fabricated porcelain disks.
and then in distilled water for 10 minutes. After they dried, the disks were glazed in the porcelain furnace according to the manufacturers’ protocols.
Color measurement of porcelain disks The reflectance spectra of the 44 (11 master and 33 fabricated) porcelain disks were measured in a random order. Each disk was measured with a spectroradiometer (PR-705 SpectraScan; Photo Research Inc, Chatsworth, Calif.) at 380 to 780 nm with a 2-nm interval. The measurements were performed at a 0degree observer angle with a 45-degree illuminant angle arrangement, as recommended by Bolt et al30 for measuring the color of translucent materials. A 2light source (Model FO-150; FOSTEC Inc, Auburn, N.Y.) at 45 degrees from the observer yielded a diffuse illumination on the porcelain disks. For standardization, the spectral reflectance of a white reflectance standard (Target SRT-99-0100; Labsphere Inc, North Sutton, N.H.) traceable to the National Institute of Standards and Technology also was measured under this illuminant. Thus, a total of 45 spectral reflectance measurements were obtained. The absolute spectral power distribution of each 661
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Fig. 7. Mean ∆E, ∆L*, ∆a*, and ∆b* for porcelain shade-matching systems. Bars connected by horizontal lines were not significantly different. Vertical error bars represent standard deviations.
Table IV. ANOVA table of within-subject effects for mean color differences (∆E)
System Error
df
Sum of squares
Mean squares
F value
P value*
2 20
63.54 65.07
31.77 3.25
9.77
.0024
*Greenhouse-Geisser adjusted P value was used because the Greenhouse-Geisser value was not 1.
specimen was obtained by the relative reflectance spectra of the specimen compared to the white standard. With the use of a computer program, the X, Y, and Z tristimulus values were calculated for each of the 44 porcelain specimens from the spectral reflectance of their respective porcelain disks and the relative spectral power distribution of the illuminant. The CIELAB coordinates (L*, a*, and b*) then were calculated for each of the porcelain disks.
Statistical analyses Color differences (∆E) between the master and fabricated porcelain disks were determined with the use of Equation 1. A total of 33 differences for L*, a*, and b* were calculated. The total color difference (∆E) and color parameters (∆L*, ∆a*, and ∆b*) for all master/fabricated disk pairs were compared statistically with repeated-measures analysis of variance (ANOVA, α=.05) to evaluate the within-group effect (3 porcelain systems for the same specimen). Repeated-measures analysis was used to eliminate any possibility of dependency in the study design. Dependency could have arisen since the master disks were a common factor for the 3 porcelain systems during shade matching and during calculations for the outcome measures (∆E, ∆L*, ∆a*, and ∆b*) used in comparisons. There were no between-group effects, as the same master specimen was used to fabricate 3 matching disks. The post-hoc Ryan-Einot-GabrielWelsch multiple range test (REGWQ) was used to rank the groups’ mean and the mean color parameter
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differences (∆L*, ∆a*, and ∆b*). All statistical analyses and calculations were completed with the SAS statistical program (8th ed; SAS Institute Inc, Cary, N.C.).
RESULTS The mean color differences between the master and fabricated porcelain disks for the different systems are shown in Figure 7. Repeated-measures ANOVA revealed a highly significant difference among the mean for the within-group effect (systems) with an adjusted Greenhouse-Geisser P value of .0024 (Table IV). The adjusted P value was used because the Greenhouse-Geisser Epsilon value was .8248, which implied that the compound symmetry assumption was not satisfied for the ANOVA. Further analysis with the REGWQ (Fig. 7 and Table VI) revealed that use of the Vitapan 3D-Master guide resulted in a significantly greater mean color difference (6.8 ± 2.1 ∆E) than use of the ShadeEye-EX chromameter (4.5 ± 1.8 ∆E) or Vita Lumin guide (3.5 ± 2.8 ∆E). Mean color differences for the ShadeEye-EX and Vita Lumin systems were not significantly different. Differences in color parameters (∆L*, ∆a*, and ∆b*) between the master and fabricated porcelain disks also are shown in Figure 7. Repeated-measures ANOVA revealed a highly significant difference among systems (adjusted P<.0001) (Table V) and among color parameters (adjusted P=.0113). A highly significant difference also was found for the interaction of systems and different color parameters (adjusted P=.0024). Again, adjusted P values were used because
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Table V. ANOVA table of within-subject effects for mean direction of color (∆L*, ∆a*, and ∆b*)
System Error (system) Direction Error (direction) System * direction Error (system * direction) †Greenhouse-Geisser
df
Sum of squares
2 20 2 20 4 40
126.80 41.86 117.48 138.25 55.43 97.04
Mean squares
63.40 2.09 58.74 6.91 13.86 2.43
F value
P value†
30.29
<.0001
8.50
.0113
5.71
.0056
adjusted P value was used because the Greenhouse-Geisser value was not 1.
Table VI. Ryan-Einot-Gabriel-Welsch multiple range test for mean ∆E, ∆L*, ∆a*, and ∆b* Direction (∆)
E
L*
a*
b*
†Groups
System
N
Mean
SD
3D-Master ShadeEye Vita Lumin 3D-Master ShadeEye Vita Lumin 3D-Master ShadeEye Vita Lumin 3D-Master ShadeEye Vita Lumin
11 11 11 11 11 11 11 11 11 11 11 11
6.86 4.58 3.53 4.37 3.68 2.53 1.59 0.48 –0.07 4.06 2.18 –0.73
2.14 1.89 2.82 2.70 2.16 3.57 1.12 0.54 0.71 2.41 1.13 0.89
Tukey groupings†
A B B a a I I
b b II II
i ii iii
with the same letters were not significantly different.
the compound symmetry assumption was not satisfied (Greenhouse-Geisser Epsilon value = .8248). Because there was a highly significant interaction between systems and direction of color, the “simple effect” or single factor (for example, ∆L* for the Vitapan 3D-Master system) was of interest, and the main effects (system and color parameters) could not be interpreted individually. Thus, the amount of change within each color parameter was dependent on the system as well as the amount of change among the 3 color parameters. The REGWQ was used to evaluate the statistical significance within the individual color parameters (∆L*, ∆a*, and ∆b*) among the 3 systems. The Vitapan 3D-Master and ShadeEye-EX systems were significantly different for ∆L* and ∆a* (Table VI). All 3 systems were significantly different for ∆b* (Fig. 7).
DISCUSSION For the discussion of this study, ∆E=1 is considered a color difference perceivable by human observers33 and ∆E > 2.75 36 is considered a clinically unacceptable color difference (Table II). These stringent criteria for clinically acceptable color difference were selected over the 3.3 ∆E reported by Ruyter et al35 because their detailed methodology for obtaining the ∆E value could not be validated by the authors of the present study. Johnston and Kao21 performed the only JUNE 2002
other evaluation (thus far) of color acceptability in a clinical scenario. They reported that an average color difference of 6.8 ∆E between adjacent teeth and teeth veneered with composite rated as mismatch but was still within the normal range of tooth color. This value was not a “cut-off” point but an average within a range of 1.3 to 13.1 ∆E (SD 2.7 ∆E). Although the study was clinically relevant, a colorimeter was used and edge loss was not taken into account, thereby resulting in inaccuracies. The results do indicate, however, that the threshold for unacceptable color difference between a restoration and adjacent teeth is higher than 2.75 ∆E in an actual clinical scenario. Specimens used for extraoral evaluations are usually monochromatic, uniformly translucent, untextured, and viewed under ideal lighting conditions. Teeth, on the other hand, are polychromatic, non-uniformly translucent, textured, and viewed under ambient lighting conditions intraorally. Teeth are also clinically framed adjacent to other teeth with varying degrees of polychromaticity and translucency. Given these facts, a color difference above 2.7 ∆E may still be clinically acceptable depending on the degree of polychromaticity and translucency of adjacent teeth framing the restoration. If >2.75 ∆E is considered clinically unacceptable, then the present study found no clinically significant differences among groups with respect to mean ∆E; all 663
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fell within the clinically unacceptable range (Fig. 7). These results are consistent with a previous study47 in which color matches between extracted teeth and final fabricated porcelain shade tabs were evaluated by human observers using the same shade-selection systems tested in the present study. In the present study, the large error in mean ∆L* was the main contributor to errors in shade matching for the 3 systems tested. All of the systems produced large changes in L*, with the Vita Lumin system associated with the least change (Fig. 7). Douglas and Przybylska45 reported a similar finding. In their study, 70% of the color difference between porcelain specimens and corresponding shade tabs resulted from differences in L*. The authors found that 2 metalceramic systems (Vintage [3M, St. Paul, Minn.] and VMK 95 [Vita Zahnfabrik]) and a semi-opaque allceramic system (In-Ceram Alumina; Vita Zahnfabrik) demonstrated an increase in L* with decreasing translucent porcelain thickness. Douglas and Przybylska eloquently explained that as dentin porcelain thickness increases, the light that enters the porcelain increases in scattering and absorption. This phenomenon results in less light being reflected into the air by the opaque layer. With respect to ∆E, the Vita Lumin shade guide and Shade-Eye EX system were significantly different from the Vitapan 3D-Master guide but not significantly different from each another. When ∆E was broken down into different components, the Vita Lumin guide was superior to the other systems for ∆a* and ∆b* (–0.07 and –0.7, respectively). The Vitapan 3D-Master guide produced errors that were greater than 1 (1.5 ∆a* and 4.0 ∆b*) and thus would likely contribute to a clinically detectable ∆E. The ShadeEye-EX chromameter produced intermediate errors (0.4 ∆a* and 2.1 ∆b*). The ∆a* error probably would not contribute to a clinically detectable ∆E; the ∆b* error might contribute to a clinically detectable but not necessarily objectionable ∆Ε. Caution must be used when evaluating the individual error vectors (Fig. 7). The resolution of these vectors yields the total ∆E. However, the individual vectors do indicate something about color accuracy. Shade selection with the Vita Lumin guide seemed most accurate with respect to hue and chroma, being slightly off in the blue and green directions and significantly brighter. The ShadeEye-EX system measured color as slightly more red and significantly more yellow than in reality and also significantly brighter. The Vitapan 3D-Master system yielded shades similar to those selected with the ShadeEye-EX chromameter, but with greater magnitudes of differences in all directions. Within the limitations of this study, which was based on the results of a previous study,47 none of the 3 shade selection systems evaluated reliably yielded 664
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clinically undetectable porcelain shade matches, and none produced clinically acceptable color matches under the stringent criterion of 2.75 ∆E. Among the 3 systems, the Vita Lumin guide was associated with the least error (although its final mean ∆E of 3.5 was still relatively high). This finding is attributable to several factors. First, VMK 68 porcelain was used to fabricate the master disks, and the Vita Lumin shade guide is purportedly precisely matched to this porcelain. Second, Vitapan 3D porcelain is not matched to the Vita Lumin porcelain used to fabricate the master disks. Third, the Vitapan 3D-Master shade-selection system is relatively new to the market; the shade examiners had far less experience with this system than with the Vita Lumin system. A fourth factor is that, although the ShadeEye-EX chromameter eliminates any dependence on human vision and has a measurement mode strictly designed for porcelain, it still suffers from limitations. The instrument is a small-window colorimeter, which means it has a very small aperture through which both the illuminant light and the reflected light must pass. Small-window colorimeters can be inaccurate due to the effects of edge loss,30,51 a phenomenon that occurs during conventional reflectance measurements of translucent materials. Light from the illuminant travels through the translucent material and exits off the material. Thus, only part of the illuminant enters back into the window where reflectance is measured via the observation light path. Some of the signal is lost, although the manufacturers of the ShadeEye-EX chromameter claim to have accounted for this in their “conversion system” with use of the Vintage Halo porcelain system.52 In the present study, only the “porcelain” mode for the ShadeEye-EX chromameter was evaluated. The other mode of operation (“tooth”) was evaluated in a previous study.47 In both studies, the performance of the ShadeEye-EX chromameter did not match the manufacturer’s claims. Errors obtained with the 3 porcelain shadeselection systems tested (1.8 to 9.3 ∆E) were relatively large and represent the compounded value of errors during both the shade-matching and shadeduplication phases (Fig. 1). Other factors that contributed to this error include dentin porcelain thickness, which was 1 mm. Douglas and Przybylska45 used 1.4to 2.0-mm–thick translucent porcelain for metal-ceramic systems to achieve an acceptable color match. The large ∆Es found in this study may be explained by a lack of metal substructures for the test specimens. This factor also may have weakened the external validity of the study. Color error due to the underlying metal has been well documented in the literature.22,24,39,53,54 The application of different brands of porcelain24 or different shades44 of the same brand on VOLUME 87 NUMBER 6
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the same metal have affected the color of the porcelain in varied ways. Stavridakis et al39 reported decreased brightness of certain opaque porcelain with highpalladium alloys. Crispin et al55 found no significant color changes for an opaque group using high-gold, gold-palladium, nickel-chromium, palladium-silver, and palladium-copper-gallium alloys. Although the use of a metal substrate may be clinically relevant, deciding which metal to use would influence the direction and magnitude of color shift of the final porcelain disks fabricated. In the present study, the intention was to eliminate the effect of any underlying metal. Thus, as in previous studies,42,43,47 porcelain disks were fabricated without any metal substructure Another contributor to large ∆Es that also speaks to the external validity of the study relates to the tooth color space. In this study, the actual colors of the master disks were not equally distributed in the tooth color space. This unequal distribution may have resulted in an increased mean color difference for the visual shade-matching systems. Equal distribution would have provided a fairer evaluation of both visual shadematching systems. Color measurement and color replication have proven to be complex challenges in dentistry. The process of matching tooth structure to a completely different material is fraught with errors. Given these errors, a different or revised paradigm for achieving color replication should be investigated further.27-29 On a basic level, a similar investigation of the 3 systems tested in this study could be performed to validate the present findings. For instance, a comparison of master porcelain disks fabricated in shades from the tested systems with master disks made from a separate porcelain system within the tooth color space is suggested. Information gleaned may provide more insight about the replication of a color-matched metal-ceramic crown to adjacent porcelain crowns and about the performance of the 3 shade-matching systems evaluated in the present study.
CONCLUSIONS Within the limitations of this study, shade selection to match a porcelain-containing restoration was not proven to be clinically reliable with any of the 3 systems evaluated. Porcelain specimens fabricated after shade selection with the Vita Lumin, Vitapan 3D-Master, and Shofu ShadeEye-EX systems had color errors in excess of 2.75 ∆E when compared to the original master disks. Such color discrepancies are perceivable and could be considered clinically unacceptable under stringent criteria. With regard to individual color parameters, changes in L* were greater than changes in a* and b* for all systems evaluated, with a significant interaction between systems and color parameters. The best JUNE 2002
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results were obtained when the same shadeselection system was used with the original master disks and fabricated specimens (Vita Lumin/Vita VMK 68). We thank Mr Mark Halversen, a third-year dental student who participated in the Ohio State University College of Dentistry Summer Research Program (1999), for his assistance in the porcelain specimen preparation. We also express gratitude to Shofu for loan of the ShadeEye-EX chromameter and use of the Vintage Halo porcelain system.
REFERENCES 1. Watson JF, Crispin BJ. Margin placement of esthetic veneer crowns. Part III: Attitudes of patients and dentists. J Prosthet Dent 1981;45:499-501. 2. Carlsson GE, Wagner IV, Ödman P, Ekstrand K, MacEntee M, Marinello C, et al. An international comparative multicenter study of assessment of dental appearance using computer-aided image manipulation. Int J Prosthodont 1998;11:246-54. 3. Davis LG, Ashworth PD, Spriggs LS. Psychological effects of asethetic dental treatment. J Dent 1998;26:547-54. 4. Milleding P, Haag P, Neroth B, Renz I. Two years of clinical experience with Procera titanium crowns. Int J Prosthodont 1998;11:224-32. 5. Bergman B, Nilson H, Andersson M. A longitudinal clinical study of Procera ceramic-veneered titanium copings. Int J Prosthodont 1999;12:135-9. 6. Sjögren G, Lantto R, Tillberg A. Clinical evaluation of all-ceramic crowns (Dicor) in general practice. J Prosthet Dent 1999;81:277-84. 7. Haselton DR, Diaz-Arnold AM, Hillis SL. Clinical assessment of highstrength all-ceramic crowns. J Prosthet Dent 2000;83:396-401. 8. 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. 9. Culpepper WD. A comparative study of shade-matching procedures. J Prosthet Dent 1970;24:166-73. 10. Okubo SR, Kanawati A, Richards MW, Childress S. Evaluation of visual and instrument shade matching. J Prosthet Dent 1998;80:642-8. 11. O’Brien WJ, Boenke KM, Groh CL. Coverage errors of two shade guides. Int J Prosthodont 1991;4:45-50. 12. Sproull RC. Color matching in dentistry. II. Practical applications of the organization of color. J Prosthet Dent 1973;29:556-66. 13. Schwabacher WB, Goodkind RJ. Three-dimensional color coordinates of natural teeth compared with three shade guides. J Prosthet Dent 1990;64:425-34. 14. Ferreira D, Monard LA. Measurement of spectral reflectance and colorimetric properties of Vita shade guides. J Dent Assoc S Afr 1991;46:63-5. 15. Preston JD. Current status of shade selection and color matching. Quintessence Int 1985;16:47-58. 16. Miller L. Organizing color in dentistry. J Am Dent Assoc 1987;Spec No:26E-40E. 17. Judd DB, Wyszecki G. Color in business, science and industry. New York: John Wiley; 1975. p. 26-40. 18. Shinomori K, Schefrin BE, Werner JS. Age-related changes in wavelength discrimination. J Opt Soc Am A Opt Image Sci Vis 2001;18:310-8. 19. Sperling HG, Wright AA, Mills SL. Color vision following intense green light exposure: data and a model. Vision Res 1991;31:1797-812. 20. Preston JD, Ward LC, Bobrick M. Light and lighting in the dental office. Dent Clin North Am 1978;22:431-51. 21. Johnston WM, Kao EC. Assessment of appearance match by visual observation and clinical colorimetry. J Dent Res 1989;68:819-22. 22. Brewer JD, Akers CK, Garlapo DA, Sorensen SE. Spectrometric analysis of the influence of metal substrates on the color of metal-ceramic restorations. J Dent Res 1985;64:74-7. 23. Brewer JD, Garlapo DA, Chipps EA, Tedesco LA. Clinical discrimination between autoglazed and polished porcelain surfaces. J Prosthet Dent 1990;64:631-4. 24. Brewer JD, Glennon JS, Garlapo DA. Spectrophotometric analysis of a nongreening, metal-fusing porcelain. J Prosthet Dent 1991;65:634-41. 25. Goodkind RJ, Keenan KM, Schwabacher WB. A comparison of Chromascan and spectrophotometric color measurements of 100 natural teeth. J Prosthet Dent 1985;53:105-9. 26. Goodkind RJ, Schwabacher WB. Use of a fiber-optic colorimeter for in
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27.
28.
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32. 33. 34.
35. 36. 37.
38. 39.
40. 41.
42.
43.
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vivo color measurements of 2830 anterior teeth. J Prosthet Dent 1987;58:535-42. Ishikawa-Nagai S, Sato R, Furukawa K, Ishibashi K. Using a computer color-matching system in color reproduction of porcelain restorations. Part 1: Application of CCM to the opaque layer. Int J Prosthodont 1992;5:495-502. Ishikawa-Nagai S, Sawafuji F, Tsuchitoi H, Sato RR, Ishibashi K. Using a computer color-matching system in color reproduction of porcelain restorations. Part 2: Color reproduction of stratiform-layered porcelain samples. Int J Prosthodont 1993;6:522-7. Ishikawa-Nagai S, Sato RR, Shiraishi A, Ishibashi K. Using a computer color-matching system in color reproduction of porcelain restorations. Part 3: A newly developed spectrophotometer designed for clinical application. Int J Prosthodont 1994;7:50-5. Bolt RA, ten Bosch JJ, Coops JC. Influence of window size in small-window color measurement, particularly of teeth. Phys Med Biol 1994;39:1133-42. Recommendations on uniform color spaces, color difference equations, psychometric color terms. Supplement No 2. CIE Publication No. 15 (E13-1),1971 (TC-1.3). Paris: Bureau Central de la CIE; 1978. Berns RS. Billmeyer and Saltzman’s principles of color technology. 3rd ed. New York: John Wiley & Sons; 2000. p. 72. Kuehni RG, Marcus RT. An experiment in visual scaling of small color differences. Color Res Appl 1979;4:83-91. Seghi RR, Hewlett ER, Kim J. Visual and instrumental colorimetric assessments of small color differences on translucent dental porcelain. J Dent Res 1989;68:1760-4. Ruyter IE, Niler K, Moller B. Color stability of dental composite resin materials for crowns and bridge veneers. Dent Mater 1987;3:246-51. Ragain JC, Johnston WM. Color acceptance of direct dental restorative materials by human observers. Color Res Appl 2000;25:278-85. Herzberg TW, Gettleman L, Webber RL Moffa JP. Effect of metal surface treatment on the masking power of opaque porcelain. J Dent Res 1972;51:468-72. Barghi N, Richardson JT. A study of various factors influencing shade of bonded porcelain. J Prosthet Dent 1978;39:282-4. Stavridakis MM, Papazoglou E, Seghi RR, Johnston WM, Brantley WA. Effect of different high-palladium metal-ceramic alloys on the color of opaque porcelain. J Prosthodont 2000;9:71-6. O’Brien WJ, Kay KS, Boenke KM, Groh CL. Sources of color variation on firing porcelain. Dent Mater 1991;7:170-3. Rosenstiel SF, Johnston WM. The effects of manipulative variables on the color of ceramic metal restorations. J Prosthet Dent 1988;60:297303. Seghi RR, Johnston WM, O’Brien WJ. Spectrophotometric analysis of color differences between porcelain systems. J Prosthet Dent 1986;56:35-40. Groh CL, O’Brien WJ, Boenke KM. Differences in color between fired porcelain and shade guides. Int J Prosthodont 1992;5:510-4.
44. Jorgenson MW, Goodkind RJ. Spectrophotometric study of five porcelain shades relative to the dimensions of color, porcelain thickness, and repeated firings. J Prosthet Dent 1979;42:96-105. 45. Douglas RD, Przybylska M. Predicting porcelain thickness required for dental shade matches. J Prosthet Dent 1999;82:143-9. 46. Seghi RR, Johnston WM, O’Brien WJ. Performance assessment of colorimetric devices on dental porcelains. J Dent Res 1989;68:1755-9. 47. Wee AG, Kang EY, Johnston WM, Seghi RR. Evaluating porcelain color match of different porcelain shade-matching systems. J Esthet Dent 2000;12:271-80. 48. Johnston WM, O’Brien WJ, Tien TY. Concentration additivity of kubelkamunk optical coefficients of porcelain mixtures. Color Res Appl 1986;11:131-7. 49. White JM, O’Brien WJ. The colors of mixtures of dental opaque porcelains. J Dent Res 1989;68:1319-22. 50. Obregon A, Goodkind RJ, Schwabacher WB. Effects of opaque and porcelain surface texture on the color of ceramometal restorations. J Prosthet Dent 1981;46:330-40. 51. Johnston WM, Hesse NS, Davis BK, Seghi RR. Analysis of edge-losses in reflectance measurements of pigmented maxillofacial elastomer. J Dent Res 1996;75:752-60. 52. Yamamoto M. Development of the Vintage Halo computer color search system. Quintessence Dent Technol 1998;22:9-26. 53. Jacobs SH, Goodacre CJ, Moore BK, Dykema RW. Effect of porcelain thickness and type of metal-ceramic alloy on color. J Prosthet Dent 1987;57:138-45. 54. Crispin BJ, Seghi RR, Globe H. Effect of different metal ceramic alloys on the color of opaque and dentin porcelain. J Prosthet Dent 1991;65:3516. 55. Crispin BJ, Hewlett E, Seghi R. Relative color stability of ceramic stains subjected to glazing temperatures. J Prosthet Dent 1991;66:20-3. Reprint requests to: DR ALVIN G. WEE SECTION OF RESTORATIVE DENTISTRY, PROSTHODONTICS, AND ENDODONTICS THE OHIO STATE UNIVERSITY COLLEGE OF DENTISTRY 305 POSTLE HALL, W 12TH AVE PO BOX 182357 COLUMBUS, OH 43210-1241 FAX: (614)292-9422 E-MAIL: [email protected] Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 + 0. 10/1/125727
doi:10.1067/mpr.2002.125727
New product news The January and July issues of the Journal carry information regarding new products of interest to prosthodontists. Product information should be sent 1 month prior to ad closing date to: Dr. Glen P. McGivney, Editor, UNC School of Dentistry, 414C Brauer Hall, CB #7450, Chapel Hill, NC 27599-7450. Product information may be accepted in whole or in part at the discretion of the Editor and is subject to editing. A black-and-white glossy photo may be submitted to accompany product information. Information and products reported are based on information provided by the manufacturer. No endorsement is intended or implied by the Editorial Council of The Journal of Prosthetic Dentistry, the editor, or the publisher.
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Purpose. The purpose of this in vitro study was to evaluate and compare the color difference of the total color replication process and the direction of the individual color parameters for 3 dental porcelain shade-matching systems. Material and methods. The shade of 11 porcelain master disks was determined visually and instrumentally using 3 porcelain shade-matching systems: (1) Vita Lumin/Vita VMK 68, (2) Vitapan 3D-Master/Vita Omega 900, and (3) Shofu ShadeEye-EX/Vintage Halo. Corresponding porcelain disks made of 4.5 mm opaque and 1 mm dentin porcelain were fabricated with each of the porcelain systems. The colors of the master disks and fabricated disks (CIE L* a* b* coordinates) were measured with a spectroradiometer with a 45°/0° configuration. Repeated-measures analysis of variance was used to evaluate within-group differences among the porcelain systems for the total color difference (∆E) and direction of the color parameters (∆L, ∆a, and ∆b). The Ryan-Einot-Gabriel-Welsch multiple range test was used for post-hoc analysis (α=.05). Results. The largest mean ∆E was recorded for the Vitapan 3D-Master system, which was significantly different from the other systems (P=.0024). A significant difference was found between the interaction of the different systems and the direction of color (P=.0024). The amount of change within each color parameter was dependent on the porcelain system, as well as the amount of change among the color parameters. Conclusion. Within the limitations of this study, the results suggest that reliable delivery of a properly matched restoration to existing porcelain restorations cannot be ensured regardless of the shade assessment method used (visual or computer-generated). (J Prosthet Dent 2002;87:657-66.)
CLINICAL IMPLICATIONS Shade determination, whether visual or computer-based, may not lead to the production of a porcelain restoration with a clinically acceptable color match. The best replication of dental porcelain color can be obtained with a shade-matching system similar to the porcelain restoration being matched.
T
he importance of dental appearance is well documented.1,2 It has been shown, for example, that This project was supported in part by the Ohio State University College of Dentistry’s Summer Research Program (NIH/NIDCR grant DE 07155-13) and the Ohio State University’s Clinical Research Curriculum (NIH/NHLBI grant K30 HL04162). The material was presented in part at the 78th General Session of the International Association for Dental Research, Washington, D.C., April 5-8, 2000. aAssistant Professor in Prosthodontics, Section of Restorative Dentistry, Prosthodontics, and Endodontics, The Ohio State University College of Dentistry. bAssistant Professor and Director of Graduate Biomaterials Program, Division of Dental Biomaterials, Marquette University School of Dentistry. cProfessor, Section of Restorative Dentistry, Prosthodontics, and Endodontics, The Ohio State University College of Dentistry. JUNE 2002
esthetic dental restorative treatment can enhance a patient’s self-esteem.3 Clinically, a successful color match is an important aspect of any esthetic dental restoration. According to results from clinical studies (Table I),4-7 however, the final color match of porcelain crowns to adjacent natural dentition remains problematic. In clinical practice, the color replication process for dental porcelain comprises a shade-selection phase followed by shade duplication (Fig. 1). Shade selection can be accomplished through either visual assessment or instrumental color analysis. Duplication of the selected shade is accomplished during the fabrication of the restoration in the dental laboratory. Visual shade selection is the most common method of color determination in dentistry,8 but color duplicaTHE JOURNAL OF PROSTHETIC DENTISTRY 657
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Fig. 1. Color replication process for dental porcelain.
Table I. Clinical studies that evaluated shade match of porcelain crowns Crown type
Color mismatch of cemented final restorations
Metal-ceramic (Procera) Metal-ceramic (Procera) All-porcelain (Dicor) All-porcelain (In-Ceram)
61% 63% 45% 44%
of of of of
40 44 98 80
Type of clinical study
crowns crowns crowns crowns
Two-year prospective Five-year prospective Five-year retrospective Four-year retrospective
Table II. Summary of studies relevant to dental color-matching tolerance Study
Color difference (∆E)
Results
Color perceptibility Kuehni and Marcus33 Seghi et al34 Johnston and Kao21
1.0 2.0 3.7
In vitro study. 50% of observers perceived a color difference. In vitro study. Porcelain specimens were correctly judged by observers 100% of the time. In vivo study. Found average color difference between compared teeth rated as a match in the oral environment.
Color acceptability Ragain and Johnston36 Ruyter et al35 Johnston and Kao21
2.72 3.3 6.8
In vitro study. Average 50:50 ∆E replacement rate for all subjects was found. In vitro study. 50% of observers considered the composite specimens to be unacceptable. In vivo study. Found average color difference between compared teeth rated as a mismatch within the normal range of tooth color in the oral environment.
tion via this process is plagued by unreliable and inconsistent results.9,10 The inadequacies of dental shade guides, in terms of the range11,12 and systemic distribution in the tooth color space,12-14 have been described.12,15,16 Inconsistencies in shade determination can result from multiple factors, including individual physiological and psychological responses to radiant energy stimulation,17 aging,18 and previous eye exposure/fatigue.19 Environmental and lighting conditions also play an important role in shade selection.9,12,20 Instrumental color analysis offers a potential advantage over visual color determination: instrumental readings are objective, quantifiable, and more rapidly obtainable. Although the extensive use of computer658
ized colorimeters and spectrophotometers has been reported in dental research,10,21-29 most devices currently are unsuitable for routine clinical dental use given their limited ability to measure the color of translucent objects8,30 (such as teeth) and their prohibitive cost/size.27-29 Shade matching, whether by visual or instrumental methods, requires an understanding of color harmony and tolerance—namely, what actual color difference (∆E) would be perceptible to the human eye. The CIELAB-based color difference formula, introduced in 1976 and recommended by the International Commission on Illumination,31 defines a color space (L*a*b*) in which L* represents lightness, a* represents the chromaticity coordinate for red-green (+a* is VOLUME 87 NUMBER 6
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Fig. 2. Flowchart of experimental design.
the red direction and –a* is the green direction), and b* represents the chromaticity coordinate for yellowblue (+b* is the yellow direction and –b* is the blue direction). Color difference, or ∆E, is defined by the following equation:32 ∆E = √(L*f – L*i)2 + (a*f – a*i)2 + (b*f – b*i)2
(1)
where the initial (i) and final (f) are color descriptors. This formula has been used extensively in dental research. Several studies that provide information regarding clinical color-matching tolerance are summarized in Table II.21,33-36 Errors associated with the shade duplication of dental porcelain are well documented. These errors are related to the underlying metal used,22,37-39 the batch of porcelain powder,40 the brand of porcelain,40-43 and the number of times glazing was performed.44 The total quantifiable color difference (∆E) between shade matching and shade duplication has not been investigated formally. It appears that no study has yet determined the quantifiable color difference for the shade-matching phase of visual shade determination. Only 2 studies have provided insight on the shade duplication process for porcelain. One study evaluated the color difference between Vita Lumin shade guides (Vident Inc, Brea, Calif.) and 4 fired porcelain systems on individualized ceramic shade tabs.43 An average color difference of 3 ± 0.8 was found for the 4 different metal-ceramic porcelain systems fabricated by 2 technicians. Another study evaluated the amount of porcelain thickness (standard JUNE 2002
0.5 mm opaque thickness) required to layer over highnoble metal to obtain an acceptable color difference to shade tabs.45 The 2 metal-ceramic porcelain systems tested exhibited an average color difference of 7.5 ± 2.1 at 1-mm thickness (data interpolated from figures in the published article).45 Vita Zahnfabrik (Bad Säckingen, Germany) recently introduced the Vitapan 3D-Master shade guide with a complementary new porcelain system to address some of the limitations of visible shade selection.16 According to the manufacturer, the guide was designed to include a more uniform coverage of shade tabs in virtually all existing natural tooth shades. It is systematically arranged in a 3-dimensional color space that makes shade selection simpler and more accurate. Shofu Dental Corporation (San Marcos, Calif.) claims that its new clinical colorimeter, the ShadeEye-EX Chroma Meter, is both precise and accurate for shade matching when used with the Vintage Halo porcelain system. (Information obtained from product guides.) The purpose of this in vitro study was to evaluate and compare the color difference of the total color replication process with 3 dental porcelain shadematching systems: (1) the Vita Lumin Vacuum shade guide and Vita VMK 68 porcelain system, (2) the Vitapan 3D-Master shade guide and Vita Omega 900 porcelain system, and (3) the Shofu ShadeEye-EX clinical colorimeter and Vintage Halo porcelain system. It was hypothesized that color differences (∆Ε) would exist between the master porcelain disks and those fab659
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Fig. 3. ShadeEye-EX chromameter used to measure master porcelain disk.
Fig. 5. Visual shade evaluation of master porcelain disk.
ricated with the 3 dental porcelain shade-matching systems and that different changes in color parameters (∆L*, ∆a*, and ∆b*) would be evident when the master porcelain disks were compared to those fabricated with the 3 test systems.
MATERIAL AND METHODS Eleven master porcelain disks of unknown shade fabricated from VMK 68, as used in a previous color experiment,46 were used to simulate metal-ceramic crowns. The disks were made with a 4.5-mm layer of opaque and 1-mm thickness of translucent dentin porcelain. Shade selection for these disks was carried out in 2 phases: instrumental and visual (Fig. 2). The manufacturers’ recommendations for use of the clinical colorimeter and 2 visual shade guides were followed precisely during the experiment. For instrumental shade selection, the ShadeEye-EX chromameter was used to measure the color of the 11 master porcelain disks in “porcelain” mode (Fig. 3). 660
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Fig. 4. New Vitapan 3D-Master shade guide.
Only one reading of the meter was used for porcelain fabrication. For visual shade selection, 2 conceptually different shade guides were used: the traditional Vita Lumin Vacuum guide and the new Vitapan 3D-Master shade guide (Fig. 4). Visual shade selections (Fig. 5) were performed in a viewing booth with color-corrected D65 lighting (Macbeth Spretra Light, Newburgh, N.Y.). The selections were made by 3 examiners: a general dentist, a prosthodontist, and a maxillofacial prosthodontist, none of whom had visual color deficiencies according to the American Optical Company Hardy-Rand-Ritter test. In a previous study, no significant differences (P=.7881) were found among these 3 examiners when they compared porcelain tabs to extracted teeth with the United States Public Health Service criteria.47 Each selector performed a total of 22 visual shade selections. For shade determination using the Vita Lumin Vacuum guide, selection was based on agreement between at least 2 of the 3 selectors or on consensus among the 3 selectors when 3 unique shades were chosen (Table III). For the Vitapan 3DMaster shade guide, the selected shade was derived from the median shade values of the 3 chosen shades (Table III). This method was used successfully in a previous study47 and is the shade-selection method recommended by the manufacturer when intermediate shades are fabricated by mixing porcelain powders at a 1:1 ratio. The practice of mixing porcelain to obtain a color that is “in between” the porcelain mixtures has been verified scientifically.27,48,49 The porcelain powders were measured on an analytical balance (AE 240; Mettler Instruments, Greifensee, Switzerland) with an accuracy of 0.01 mg. The ShadeEye-EX chromameter was used according to the manufacturer’s instructions, and as such, provided a formulation of the Vintage Halo porcelain to create the supposedly correct shade match. VOLUME 87 NUMBER 6
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Table III. Actual shades selected using the 3 porcelain shade-matching systems Vita Lumin Porcelain disks
1 2 3 4 5 6 7 8 9 10 11
3D-Master
ShadeEye
Consensus
Evaluator A
Evaluator B
Evaluator C
A3 A3 B2 A2 C4 B1 B1 D2 B2 A4 A3
2M2 2M2.5 1M2 1M2 4M2 1M1 1M1 2R1.5 1M2 4M2.5 3M2
3L2 3L2 2L1.5 3M2 5M1 2M1 2M1 3M1 2M1.5 5M2 4L1.5
3R2.5 3R2.5 2M2 2R2.5 4M2 1M2 2M1 2R1.5 2M2 4M2.5 3M2
Final
Shade
Value
Hue
3M2 3M2.5 2M2 2M2 4M2 1M1 2M1 2R1.5 2M2 4M2.5 3M2
3.3 3.0 2.0 2.0 3.8 1.0 1.0 2.0 1.5 4.0 3.3
± + ± + – ± ± – ± ± ±
Y1 Std Y1 R1 Std Std Std R1 Std Std Y1
0 1 0 1 2 0 0 1 0 0 0
Fabrication of porcelain disks Corresponding color-matching porcelain systems were used to fabricate the experimental porcelain disks: Vita VMK 68 for the Vita Lumin Vacuum system, Vita Omega 900 for the Vitapan 3D-Master system, and Vintage Halo for the ShadeEye-EX chromameter. For each of the 11 master disks, 1 experimental disk was fabricated for each porcelain system and its respective shade-selection method, yielding 33 disks for color measurement (Fig. 6). No porcelain disk was omitted during the fabrication procedure. During fabrication of the disks, the porcelain powders were dry compressed by hand into a fabricated mold with a plunger.42 Two to 3 drops of distilled water were added to the compressed powder to hold it together and facilitate removal. The specimens were extracted from the mold, set onto a sager tray, and fired with the manufacturer-recommended protocols in a high-temperature porcelain oven (Vita Vacuum 200; Vident Inc). The appropriate opaque powder was used first to fabricate an opaque disk. The opaque layers were approximately 4.5 mm thick and 15 mm in diameter. After the opaque disks were trimmed to shape, the respective dentin powder was added and fired in the porcelain oven. To simulate dental laboratory situations, 2 firing cycles for the opaque and dentin porcelain were performed. To eliminate the effect of surface texture variations on color,50 the dentin layer was polished to 1 mm thickness. All polishing was performed with a metallographic polishing system (Vari/Pol, VP-50; Leco Corp, St. Joseph, Mich.) from 400- to 1000-grit under continuous water cooling. A digital veneer caliper (model CD-6 BS; Mitutuyo Corp, Tokyo, Japan) was used for all thickness measurements. The disks were ultrasonically cleaned (Jelsonic; Jelenko, New Hyde Park, N.Y.) in a general-purpose cleaning solution (L & R Mfg Co, Kearny, N.J.) for 10 minutes JUNE 2002
Fig. 6. Six example sets of master and fabricated porcelain disks.
and then in distilled water for 10 minutes. After they dried, the disks were glazed in the porcelain furnace according to the manufacturers’ protocols.
Color measurement of porcelain disks The reflectance spectra of the 44 (11 master and 33 fabricated) porcelain disks were measured in a random order. Each disk was measured with a spectroradiometer (PR-705 SpectraScan; Photo Research Inc, Chatsworth, Calif.) at 380 to 780 nm with a 2-nm interval. The measurements were performed at a 0degree observer angle with a 45-degree illuminant angle arrangement, as recommended by Bolt et al30 for measuring the color of translucent materials. A 2light source (Model FO-150; FOSTEC Inc, Auburn, N.Y.) at 45 degrees from the observer yielded a diffuse illumination on the porcelain disks. For standardization, the spectral reflectance of a white reflectance standard (Target SRT-99-0100; Labsphere Inc, North Sutton, N.H.) traceable to the National Institute of Standards and Technology also was measured under this illuminant. Thus, a total of 45 spectral reflectance measurements were obtained. The absolute spectral power distribution of each 661
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Fig. 7. Mean ∆E, ∆L*, ∆a*, and ∆b* for porcelain shade-matching systems. Bars connected by horizontal lines were not significantly different. Vertical error bars represent standard deviations.
Table IV. ANOVA table of within-subject effects for mean color differences (∆E)
System Error
df
Sum of squares
Mean squares
F value
P value*
2 20
63.54 65.07
31.77 3.25
9.77
.0024
*Greenhouse-Geisser adjusted P value was used because the Greenhouse-Geisser value was not 1.
specimen was obtained by the relative reflectance spectra of the specimen compared to the white standard. With the use of a computer program, the X, Y, and Z tristimulus values were calculated for each of the 44 porcelain specimens from the spectral reflectance of their respective porcelain disks and the relative spectral power distribution of the illuminant. The CIELAB coordinates (L*, a*, and b*) then were calculated for each of the porcelain disks.
Statistical analyses Color differences (∆E) between the master and fabricated porcelain disks were determined with the use of Equation 1. A total of 33 differences for L*, a*, and b* were calculated. The total color difference (∆E) and color parameters (∆L*, ∆a*, and ∆b*) for all master/fabricated disk pairs were compared statistically with repeated-measures analysis of variance (ANOVA, α=.05) to evaluate the within-group effect (3 porcelain systems for the same specimen). Repeated-measures analysis was used to eliminate any possibility of dependency in the study design. Dependency could have arisen since the master disks were a common factor for the 3 porcelain systems during shade matching and during calculations for the outcome measures (∆E, ∆L*, ∆a*, and ∆b*) used in comparisons. There were no between-group effects, as the same master specimen was used to fabricate 3 matching disks. The post-hoc Ryan-Einot-GabrielWelsch multiple range test (REGWQ) was used to rank the groups’ mean and the mean color parameter
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differences (∆L*, ∆a*, and ∆b*). All statistical analyses and calculations were completed with the SAS statistical program (8th ed; SAS Institute Inc, Cary, N.C.).
RESULTS The mean color differences between the master and fabricated porcelain disks for the different systems are shown in Figure 7. Repeated-measures ANOVA revealed a highly significant difference among the mean for the within-group effect (systems) with an adjusted Greenhouse-Geisser P value of .0024 (Table IV). The adjusted P value was used because the Greenhouse-Geisser Epsilon value was .8248, which implied that the compound symmetry assumption was not satisfied for the ANOVA. Further analysis with the REGWQ (Fig. 7 and Table VI) revealed that use of the Vitapan 3D-Master guide resulted in a significantly greater mean color difference (6.8 ± 2.1 ∆E) than use of the ShadeEye-EX chromameter (4.5 ± 1.8 ∆E) or Vita Lumin guide (3.5 ± 2.8 ∆E). Mean color differences for the ShadeEye-EX and Vita Lumin systems were not significantly different. Differences in color parameters (∆L*, ∆a*, and ∆b*) between the master and fabricated porcelain disks also are shown in Figure 7. Repeated-measures ANOVA revealed a highly significant difference among systems (adjusted P<.0001) (Table V) and among color parameters (adjusted P=.0113). A highly significant difference also was found for the interaction of systems and different color parameters (adjusted P=.0024). Again, adjusted P values were used because
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Table V. ANOVA table of within-subject effects for mean direction of color (∆L*, ∆a*, and ∆b*)
System Error (system) Direction Error (direction) System * direction Error (system * direction) †Greenhouse-Geisser
df
Sum of squares
2 20 2 20 4 40
126.80 41.86 117.48 138.25 55.43 97.04
Mean squares
63.40 2.09 58.74 6.91 13.86 2.43
F value
P value†
30.29
<.0001
8.50
.0113
5.71
.0056
adjusted P value was used because the Greenhouse-Geisser value was not 1.
Table VI. Ryan-Einot-Gabriel-Welsch multiple range test for mean ∆E, ∆L*, ∆a*, and ∆b* Direction (∆)
E
L*
a*
b*
†Groups
System
N
Mean
SD
3D-Master ShadeEye Vita Lumin 3D-Master ShadeEye Vita Lumin 3D-Master ShadeEye Vita Lumin 3D-Master ShadeEye Vita Lumin
11 11 11 11 11 11 11 11 11 11 11 11
6.86 4.58 3.53 4.37 3.68 2.53 1.59 0.48 –0.07 4.06 2.18 –0.73
2.14 1.89 2.82 2.70 2.16 3.57 1.12 0.54 0.71 2.41 1.13 0.89
Tukey groupings†
A B B a a I I
b b II II
i ii iii
with the same letters were not significantly different.
the compound symmetry assumption was not satisfied (Greenhouse-Geisser Epsilon value = .8248). Because there was a highly significant interaction between systems and direction of color, the “simple effect” or single factor (for example, ∆L* for the Vitapan 3D-Master system) was of interest, and the main effects (system and color parameters) could not be interpreted individually. Thus, the amount of change within each color parameter was dependent on the system as well as the amount of change among the 3 color parameters. The REGWQ was used to evaluate the statistical significance within the individual color parameters (∆L*, ∆a*, and ∆b*) among the 3 systems. The Vitapan 3D-Master and ShadeEye-EX systems were significantly different for ∆L* and ∆a* (Table VI). All 3 systems were significantly different for ∆b* (Fig. 7).
DISCUSSION For the discussion of this study, ∆E=1 is considered a color difference perceivable by human observers33 and ∆E > 2.75 36 is considered a clinically unacceptable color difference (Table II). These stringent criteria for clinically acceptable color difference were selected over the 3.3 ∆E reported by Ruyter et al35 because their detailed methodology for obtaining the ∆E value could not be validated by the authors of the present study. Johnston and Kao21 performed the only JUNE 2002
other evaluation (thus far) of color acceptability in a clinical scenario. They reported that an average color difference of 6.8 ∆E between adjacent teeth and teeth veneered with composite rated as mismatch but was still within the normal range of tooth color. This value was not a “cut-off” point but an average within a range of 1.3 to 13.1 ∆E (SD 2.7 ∆E). Although the study was clinically relevant, a colorimeter was used and edge loss was not taken into account, thereby resulting in inaccuracies. The results do indicate, however, that the threshold for unacceptable color difference between a restoration and adjacent teeth is higher than 2.75 ∆E in an actual clinical scenario. Specimens used for extraoral evaluations are usually monochromatic, uniformly translucent, untextured, and viewed under ideal lighting conditions. Teeth, on the other hand, are polychromatic, non-uniformly translucent, textured, and viewed under ambient lighting conditions intraorally. Teeth are also clinically framed adjacent to other teeth with varying degrees of polychromaticity and translucency. Given these facts, a color difference above 2.7 ∆E may still be clinically acceptable depending on the degree of polychromaticity and translucency of adjacent teeth framing the restoration. If >2.75 ∆E is considered clinically unacceptable, then the present study found no clinically significant differences among groups with respect to mean ∆E; all 663
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fell within the clinically unacceptable range (Fig. 7). These results are consistent with a previous study47 in which color matches between extracted teeth and final fabricated porcelain shade tabs were evaluated by human observers using the same shade-selection systems tested in the present study. In the present study, the large error in mean ∆L* was the main contributor to errors in shade matching for the 3 systems tested. All of the systems produced large changes in L*, with the Vita Lumin system associated with the least change (Fig. 7). Douglas and Przybylska45 reported a similar finding. In their study, 70% of the color difference between porcelain specimens and corresponding shade tabs resulted from differences in L*. The authors found that 2 metalceramic systems (Vintage [3M, St. Paul, Minn.] and VMK 95 [Vita Zahnfabrik]) and a semi-opaque allceramic system (In-Ceram Alumina; Vita Zahnfabrik) demonstrated an increase in L* with decreasing translucent porcelain thickness. Douglas and Przybylska eloquently explained that as dentin porcelain thickness increases, the light that enters the porcelain increases in scattering and absorption. This phenomenon results in less light being reflected into the air by the opaque layer. With respect to ∆E, the Vita Lumin shade guide and Shade-Eye EX system were significantly different from the Vitapan 3D-Master guide but not significantly different from each another. When ∆E was broken down into different components, the Vita Lumin guide was superior to the other systems for ∆a* and ∆b* (–0.07 and –0.7, respectively). The Vitapan 3D-Master guide produced errors that were greater than 1 (1.5 ∆a* and 4.0 ∆b*) and thus would likely contribute to a clinically detectable ∆E. The ShadeEye-EX chromameter produced intermediate errors (0.4 ∆a* and 2.1 ∆b*). The ∆a* error probably would not contribute to a clinically detectable ∆E; the ∆b* error might contribute to a clinically detectable but not necessarily objectionable ∆Ε. Caution must be used when evaluating the individual error vectors (Fig. 7). The resolution of these vectors yields the total ∆E. However, the individual vectors do indicate something about color accuracy. Shade selection with the Vita Lumin guide seemed most accurate with respect to hue and chroma, being slightly off in the blue and green directions and significantly brighter. The ShadeEye-EX system measured color as slightly more red and significantly more yellow than in reality and also significantly brighter. The Vitapan 3D-Master system yielded shades similar to those selected with the ShadeEye-EX chromameter, but with greater magnitudes of differences in all directions. Within the limitations of this study, which was based on the results of a previous study,47 none of the 3 shade selection systems evaluated reliably yielded 664
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clinically undetectable porcelain shade matches, and none produced clinically acceptable color matches under the stringent criterion of 2.75 ∆E. Among the 3 systems, the Vita Lumin guide was associated with the least error (although its final mean ∆E of 3.5 was still relatively high). This finding is attributable to several factors. First, VMK 68 porcelain was used to fabricate the master disks, and the Vita Lumin shade guide is purportedly precisely matched to this porcelain. Second, Vitapan 3D porcelain is not matched to the Vita Lumin porcelain used to fabricate the master disks. Third, the Vitapan 3D-Master shade-selection system is relatively new to the market; the shade examiners had far less experience with this system than with the Vita Lumin system. A fourth factor is that, although the ShadeEye-EX chromameter eliminates any dependence on human vision and has a measurement mode strictly designed for porcelain, it still suffers from limitations. The instrument is a small-window colorimeter, which means it has a very small aperture through which both the illuminant light and the reflected light must pass. Small-window colorimeters can be inaccurate due to the effects of edge loss,30,51 a phenomenon that occurs during conventional reflectance measurements of translucent materials. Light from the illuminant travels through the translucent material and exits off the material. Thus, only part of the illuminant enters back into the window where reflectance is measured via the observation light path. Some of the signal is lost, although the manufacturers of the ShadeEye-EX chromameter claim to have accounted for this in their “conversion system” with use of the Vintage Halo porcelain system.52 In the present study, only the “porcelain” mode for the ShadeEye-EX chromameter was evaluated. The other mode of operation (“tooth”) was evaluated in a previous study.47 In both studies, the performance of the ShadeEye-EX chromameter did not match the manufacturer’s claims. Errors obtained with the 3 porcelain shadeselection systems tested (1.8 to 9.3 ∆E) were relatively large and represent the compounded value of errors during both the shade-matching and shadeduplication phases (Fig. 1). Other factors that contributed to this error include dentin porcelain thickness, which was 1 mm. Douglas and Przybylska45 used 1.4to 2.0-mm–thick translucent porcelain for metal-ceramic systems to achieve an acceptable color match. The large ∆Es found in this study may be explained by a lack of metal substructures for the test specimens. This factor also may have weakened the external validity of the study. Color error due to the underlying metal has been well documented in the literature.22,24,39,53,54 The application of different brands of porcelain24 or different shades44 of the same brand on VOLUME 87 NUMBER 6
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the same metal have affected the color of the porcelain in varied ways. Stavridakis et al39 reported decreased brightness of certain opaque porcelain with highpalladium alloys. Crispin et al55 found no significant color changes for an opaque group using high-gold, gold-palladium, nickel-chromium, palladium-silver, and palladium-copper-gallium alloys. Although the use of a metal substrate may be clinically relevant, deciding which metal to use would influence the direction and magnitude of color shift of the final porcelain disks fabricated. In the present study, the intention was to eliminate the effect of any underlying metal. Thus, as in previous studies,42,43,47 porcelain disks were fabricated without any metal substructure Another contributor to large ∆Es that also speaks to the external validity of the study relates to the tooth color space. In this study, the actual colors of the master disks were not equally distributed in the tooth color space. This unequal distribution may have resulted in an increased mean color difference for the visual shade-matching systems. Equal distribution would have provided a fairer evaluation of both visual shadematching systems. Color measurement and color replication have proven to be complex challenges in dentistry. The process of matching tooth structure to a completely different material is fraught with errors. Given these errors, a different or revised paradigm for achieving color replication should be investigated further.27-29 On a basic level, a similar investigation of the 3 systems tested in this study could be performed to validate the present findings. For instance, a comparison of master porcelain disks fabricated in shades from the tested systems with master disks made from a separate porcelain system within the tooth color space is suggested. Information gleaned may provide more insight about the replication of a color-matched metal-ceramic crown to adjacent porcelain crowns and about the performance of the 3 shade-matching systems evaluated in the present study.
CONCLUSIONS Within the limitations of this study, shade selection to match a porcelain-containing restoration was not proven to be clinically reliable with any of the 3 systems evaluated. Porcelain specimens fabricated after shade selection with the Vita Lumin, Vitapan 3D-Master, and Shofu ShadeEye-EX systems had color errors in excess of 2.75 ∆E when compared to the original master disks. Such color discrepancies are perceivable and could be considered clinically unacceptable under stringent criteria. With regard to individual color parameters, changes in L* were greater than changes in a* and b* for all systems evaluated, with a significant interaction between systems and color parameters. The best JUNE 2002
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results were obtained when the same shadeselection system was used with the original master disks and fabricated specimens (Vita Lumin/Vita VMK 68). We thank Mr Mark Halversen, a third-year dental student who participated in the Ohio State University College of Dentistry Summer Research Program (1999), for his assistance in the porcelain specimen preparation. We also express gratitude to Shofu for loan of the ShadeEye-EX chromameter and use of the Vintage Halo porcelain system.
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44. Jorgenson MW, Goodkind RJ. Spectrophotometric study of five porcelain shades relative to the dimensions of color, porcelain thickness, and repeated firings. J Prosthet Dent 1979;42:96-105. 45. Douglas RD, Przybylska M. Predicting porcelain thickness required for dental shade matches. J Prosthet Dent 1999;82:143-9. 46. Seghi RR, Johnston WM, O’Brien WJ. Performance assessment of colorimetric devices on dental porcelains. J Dent Res 1989;68:1755-9. 47. Wee AG, Kang EY, Johnston WM, Seghi RR. Evaluating porcelain color match of different porcelain shade-matching systems. J Esthet Dent 2000;12:271-80. 48. Johnston WM, O’Brien WJ, Tien TY. Concentration additivity of kubelkamunk optical coefficients of porcelain mixtures. Color Res Appl 1986;11:131-7. 49. White JM, O’Brien WJ. The colors of mixtures of dental opaque porcelains. J Dent Res 1989;68:1319-22. 50. Obregon A, Goodkind RJ, Schwabacher WB. Effects of opaque and porcelain surface texture on the color of ceramometal restorations. J Prosthet Dent 1981;46:330-40. 51. Johnston WM, Hesse NS, Davis BK, Seghi RR. Analysis of edge-losses in reflectance measurements of pigmented maxillofacial elastomer. J Dent Res 1996;75:752-60. 52. Yamamoto M. Development of the Vintage Halo computer color search system. Quintessence Dent Technol 1998;22:9-26. 53. Jacobs SH, Goodacre CJ, Moore BK, Dykema RW. Effect of porcelain thickness and type of metal-ceramic alloy on color. J Prosthet Dent 1987;57:138-45. 54. Crispin BJ, Seghi RR, Globe H. Effect of different metal ceramic alloys on the color of opaque and dentin porcelain. J Prosthet Dent 1991;65:3516. 55. Crispin BJ, Hewlett E, Seghi R. Relative color stability of ceramic stains subjected to glazing temperatures. J Prosthet Dent 1991;66:20-3. Reprint requests to: DR ALVIN G. WEE SECTION OF RESTORATIVE DENTISTRY, PROSTHODONTICS, AND ENDODONTICS THE OHIO STATE UNIVERSITY COLLEGE OF DENTISTRY 305 POSTLE HALL, W 12TH AVE PO BOX 182357 COLUMBUS, OH 43210-1241 FAX: (614)292-9422 E-MAIL: [email protected] Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 + 0. 10/1/125727
doi:10.1067/mpr.2002.125727
New product news The January and July issues of the Journal carry information regarding new products of interest to prosthodontists. Product information should be sent 1 month prior to ad closing date to: Dr. Glen P. McGivney, Editor, UNC School of Dentistry, 414C Brauer Hall, CB #7450, Chapel Hill, NC 27599-7450. Product information may be accepted in whole or in part at the discretion of the Editor and is subject to editing. A black-and-white glossy photo may be submitted to accompany product information. Information and products reported are based on information provided by the manufacturer. No endorsement is intended or implied by the Editorial Council of The Journal of Prosthetic Dentistry, the editor, or the publisher.
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