Key words:
Shade guides - shade selection - spectrophotometers
INTRODUCTION
The increased emphasis on dental esthetics in recent years has developed the need
for accurate color replication methods.[1] Any error in reconstruction of teeth color can lead to patient dissatisfaction and
failure of the treatment. Studies showed that 80% of the patients are dissatisfied
with color differences between their restoration and adjacent teeth.[2]
[3] Therefore, precise shade selection and replication are critical in having successful
restorations.
Visual and instrumental methods are two ways to assess tooth color.[4] In the visual method, which is still the most popular method for dentists, the color
is selected by comparing tooth color with shade tabs made by different manufacturers
and choosing the closest color to the tooth. Two possible limitations are investigated
in this method. First, errors by dentist in shade selection, and second, shortcomings
inherent in shade tabs.[5] Factors affecting human perception of color, such as fatigue, aging, emotions, physiologic
problems, environmental light conditions, and metamerism, can cause problem in visual
shade selection. Several factors including surface texture, translucency, and the
color of surrounding environment make shade selection for natural teeth more difficult.[5]
[6]
[7]
[8]
[9]
[10] Another shortcoming of the visual method is that shade tabs do not cover all colors
present in natural teeth.[11]
Increasing public demand for cosmetic dentistry results in the progress of color determining
instruments. In recent years, several electronic shade-matching devices such as spectrophotometers
and colorimeters have been available for dental use.[12]
Spectrophotometers are among the most accurate, useful, and flexible instruments for
color matching.[13] A spectrophotometer functions by measuring the spectral reflectance or transmittance
curve of a specimen.[14]
[15] They are useful in the measurement of surface color.[12] A prism disperses white light from a tungsten filament bulb in the spectrophotometer
into a spectrum of wavelength bands between 5 and 20 nm. The amount of light reflected
from a specimen is measured for each wavelength in the visible spectrum. Spectrophotometers
have a longer working life than colorimeters and are unaffected by object metamerism.[12]
[16]
The reliability and accuracy of these instruments in precise shade matching are questionable.
There are several studies, which compare the visual and instrumental color matching
methods, but the findings are controversial because of using different instruments
or different methods of comparing. In 2008, Da Silva et al. compared Easyshade spectrophotometer with three visual shade guide systems. They
concluded that crowns fabricated using a spectrophotometer showed a significantly
better color match and a lower rate of rejection due to shade mismatching.[17] There are several other studies supporting instrumental methods in comparison with
visual ones.[6]
[18]
[19] In contrast with Da Silva et al., Yilmaz and Karaagaclioglu[20] show that visual method is more accurate than instrumental method.
The purpose of this study was to evaluate the accuracy of color measurements of two
dental electronic shade-matching devices against the visual method.
The null hypothesis for this study was composed of two different parts: (1) Color
analysis by means of a spectrophotometer device will improve color matching in comparison
with visual method and
(2) different spectrophotometer devices show different shade matching results.
MATERIALS AND METHODS
Thirteen patients who required a full coverage restoration in one of their central
incisors were entered into the study. The presence of an intact central incisor with
a contralateral incisor in need of a complete coverage restoration was the primary
inclusion criteria. The exclusion criteria were the presence of any decay, restoration,
or any sign of current or previous periodontal disease in the adjacent teeth. Three
metal ceramic crowns were fabricated for each patient. The first was fabricated using
visual shade matching, while the other two were fabricated using two different spectrophotometers.
The color match of each crown was analyzed.
After providing written consent, preliminary impression from upper and lower arches
was made using stock tray and irreversible hydrocolloid (Zhermack, Badia Polesine,
Italy). The casts were poured using Type IV dental stone (elite rock; Badia Polesine,
Zhermack Rovigo, Italy). Interocclusal wax records were used to mount the casts in
an articulator. A study wax-up was performed, and preparation indices were made using
condensational silicon material (speedex; coltane, Alstatten, Switzerland). The selected
tooth was prepared for metal ceramic restoration with a 1 mm wide 135-shoulder finish
line and 0.5 mm beneath gingival margin. Definitive impressions were made using additional
silicone material (putty and wash) (Elite HD, Zhermack, Badia Polesine, Italy) and
a stock tray. Provisional restoration was fabricated using Tempron (GC America, Alsip,
IL, USA) and luted with provisional cement (TempBond, Kerr Corp., Orange, CA, USA).
The impression was poured with Type V dental stone (elite rock; Badia Polesine, Zhermack
Rovigo, Italy). The poured cast was scanned using a 3D-laser scanner (3 shapeD810,
3shape, Copenhagen K, Denmark). The data were transferred to CAD Software (3 Shape’s
CAD Design Software, 3shape, Copenhagen K, Denmark) in which the frameworks were designed.
3 exactly same metal frameworks were then waxed-up using CAM machine (450 CAD/CAM,
Imes-icore, GmbH, Eiterfeld, Germany) for each tooth. The wax patterns then casted
using induction casting machine (Degudent, Hanau, Germany) with base metal alloy (For
all, Ivoclar Vivadent, Schaan, Liechtenstein).
Color selection and porcelain application
Three Crowns were made for each tooth. One crown was fabricated based on visual shade
matching by Vitapan classical shade guide (VITA Zahnfabrik, Bad Sackingen, Germany).
Two commercially available electronic shade-matching devices were used for the other
two crowns: Vita Easyshade and Degudent Shadepilot [Table 1]. Both devices were operated according to manufacturer’s instructions.
Table 1:
Devices evaluated
|
Device
|
Manufacturer
|
Type
|
|
Vita Easyshade
|
VITA Zahnfabrik, Bad Sackingen, Germany
|
Spectrophotometer
|
|
Shadepilot
|
Degudent, Hanau, Germany
|
Spectrophotometer
|
VITA Easyshade was calibrated by placing a probe tip on the calibration port aperture
before each specimen measurement. The targets were measured by holding the probe tip
at 90 degrees on the surface of the teeth. According to the manufacturer’s instructions,
the measurement was accepted when two consecutive, identical readings were generated
for each area.
After Degudent Shadepilot was calibrated, the device was put in the triple-zone measurement
mode. The targets were measured by placing the device mouthpiece at right angle to
the labial surface of the patient’s tooth. Again, the measurement was accepted when
2 consecutive, identical readings were generated for each area.
A single skilled dental technician with 15-year experience did all shade selections.
The technician was first screened for defective color vision using a color discrimination
test (Neitz test of color vision, western physiological services, Los Angeles, CA,
USA). All shade selections were done under D65 light source (judge2; GretagMacbeth,
Grand Rapids, MI, USA), between 10 and 12 am while the patients were positioned on
dental chair so that his/her mouth was at the same level and 40 cm apart from observers’
eyes. Shade selections were done in 3 areas of the tooth (incisal, middle, and cervical
third) [Figure 1].
Figure 1: Triple-zone measurement. Shade selections were done in three areas of the tooth (incisal,
middle, and cervical third)
Porcelain (Vita VM9; Ivoclar Vivadent, Liechtenstein, Germany) applications and firing
cycles were done by a skilled technician due to the current standards of metal ceramic
crown fabrication. Each crown was positioned on the patient’s tooth, and the color
was evaluated visually. Finished crowns were then glazed and send to the clinic for
evaluation.
Crowns evaluation
Each crown was seated on the tooth, and then, its color match with adjacent sound
tooth was evaluated [Figure 2]. The evaluations were done by five prosthodontists who do not have any color discrimination
disorders.
Figure 2:(a) Clinical evaluation of restoration fabricated by Vita Easyshade shade matching.
(b) Clinical evaluation of restoration fabricated by Shadepilot shade matching. (c)
Clinical evaluation of restoration fabricated by Vitapan classical shade matching
Each examiner was said to choose a score for color similarity of crown and adjacent
tooth on a scale of 1–10, with 10 as a perfect match; 1 as no match; ≥7, accepted;
<7, rejected. The final acceptance or rejection decision was based on the mean score
of the 5 examiners. Finally, a chart was completed for each crown by mean of scores
by 5 examiners. Examiners did not know the method of crown fabrication.
Statistical analysis
The means for different groups were compared using Wilcoxon test. All statistical
analyses were performed using SPSS 16.0 for Windows (SPSS 16.0 for Windows; SPSS Inc.,
Chicago, IL, USA).
RESULTS
About 7.6% of crowns fabricated by conventional method (1 out of 13) were deemed acceptable
by evaluators. By contrast, 73% of spectrophotometric crowns (19 out of 26) were deemed
acceptable. [Table 1] shows the means and standard deviations (SDs) of scores of examiners for each group.
[Table 2] shows the means and SDs of scores of examiners for each group: (1) Easyshade spectrophotometer.
(2) Shadepilot spectrophotometer. (3) Vitapan classical shade guide (no of specimen
= 13).
-
Comparison of first and third groups by Wilcoxon test showed a significant difference
between them (P = 0.008) with the first group showing significantly better results, so using Easyshade
spectrophotometer can improve color matching in comparison with visual method
-
Comparison of second and third groups revealed a significant difference between them
(P = 0.034) with the second group showing better results. These findings suggest that
using Shadepilot spectrophotometer can improve color matching in comparison with visual
method
-
Comparison of the first and second groups showed no significant differences (P = 0.844) between them, revealing no significant differences between Easyshade and
Shadepilot spectrophotometers.
Table 2:
Means and standard deviations of scores of examiners for each group: (1) Easyshade
spectrophotometer. (2) Shadepilot spectrophotometer. (3) Vitapan classical shade guide
(number of specimen=13)
|
Devices
|
Mean
|
SD
|
SEM
|
|
SD: Standard deviation, SEM: Standard error of mean
|
|
Vita Easyshade
|
7.2154
|
0.83850
|
0.23258
|
|
Shadepilot
|
7.3077
|
1.37020
|
0.38002
|
|
Vitapan classical
|
6.3077
|
0.37961
|
0.10528
|
DISCUSSION
The results of this study strongly support the acceptation of the first part of null
hypothesis since there was a significant improvement in color matching by means of
spectrophotometer in comparison with visual color determination method. However, no
significant difference was observed between the two spectrophotometers. Thus, the
data do support rejection of second part of null hypothesis.
In 2008, Da Silva et al.[17] compared visual and instrumental shade matching methods. They found color matching
by spectrophotometer more reliable than visual method. They said that it can also
significantly reduce the unacceptable results. In this study, better results achieved
by spectrophotometer device, but the only unacceptable result was in Easyshade spectrophotometer
group.
In 2002, Paul et al.[6] compared visual color matching method using Vitapan classical shade guide with spectroshade
spectrophotometer. They also achieved better results for spectrophotometer group.
They claimed that using a device rather than human vision is a good substitute for
color matching. In this study, the crowns made using a spectrophotometer were preferred
in 90% of cases rather than the crowns made by visual method. However, in our study,
Easyshade spectrophotometer showed better results in 85% of cases, and Shadepilot
spectrophotometer acted better in 70% of cases.
In Paul et al., Da Silva et al., and our studies better results were achieved in color matching when using a device.
One of the causes which can affect these results is a so-called “Hawthorne effect”
in which when color determination data are achieved from a spectrophotometer device,
more effort is done for color matching by the technician.[17]
This limitation was seen in both Da Silva et al. and our study although Paul et al., served the technician only the color not the way it was achieved.
In contrary, Li and Wang[18] compared visual color matching method using Vintage Halo shade guide and instrumental
method using Shade Eye calorimeter (shade eye, Shofa, Japan) in 2007. They reported
that none of these methods showed excellent color matching and there was no significant
difference between them. The reason they reached different results with our study
can be because they used different shade guide and device than our study.
This study was not free of limitations. Some of these limitations are discussed as
follows. First, the specimens were produced and tested under the ideal conditions,
which may not reflect actual clinical conditions. Second, the ease of use and degree
of technique sensitivity were not evaluated in this study, which are important factors
in clinical conditions. Third, the presence of metal framework beneath the porcelain
can affect the acceptability of color reproduction. It is recommended that future
studies on color matching take place on full ceramic crowns rather than metal ceramic.
Finally, we used Vitapan classical shade guide for visual color matching due to its
popularity and wide use by dentists. It is also suggested that future studies take
place on 3D-Master shade guide.
CONCLUSION
Within the limitations of this study, following conclusions were drawn:
-
The acceptance/rejection ratio of the crowns fabricated by spectrophotometric method
was significantly higher than the crowns fabricated by conventional method
-
There was no significant difference between color matching results of Easyshade and
Shadepilot spectrophotometers.
Acknowledgments
The authors would like to thank the Vice-Chancellery of Shiraz University of Medical
Sciences for supporting this research study (Grant#4601). The article is based on
a thesis by Dr. Ahmad Ghoreishian. The authors also thank Dr. Vosough from the Dental
Research Development Center, School of Dentistry for his contributions in the process
of statistical analysis.
Financial support and sponsorship
Nil.
