Keywords
tooth color - dehydration time - shade selection - color measurement
Introduction
Recently, dental demands shifted from functional dental treatments to more esthetic,
especially with more awareness and care toward individual oral health.[1] Social media has also proven to affect the perception and demand of dental esthetics
within the population.[2]
[3]
[4] Dental treatments including orthodontic treatment, prosthetics, and esthetic restorations
are all of high importance. Dental restorations, in particular, are more technically
sensitive especially in anterior teeth, due to the large variety of factors such as
teeth color, shape, and position which are affected by patients' preferences and sociodemographic;
gender, age, education level, and previous dental treatments affect patient satisfaction.[5] Many studies showed that ∼80% of patients were dissatisfied with their restoration
due to the color as they compared it with adjacent teeth.[6] Human teeth show unique opalescence, translucency, and fluorescence, which should
be restored by esthetic restorative materials.[7] Therefore, dental restorations should mimic the color and optical properties of
healthy teeth, especially in the anterior area.[8]
Accurate measurement of tooth color is essential for a successful aesthetic result.
Dentists must have adequate training in selecting tooth color and are aware of the
scientific aspects as well as the factors influencing tooth color and shade taking.
Color vision is a result of a complex process of stimulation, sensation, and perception.
Through optical phenomena, light is absorbed, reflected, and transmitted by the tooth
surface.[9] Color perception is influenced by three variables: the light source, the object,
and the observer's eyes and brain.[10] Object color is the result of a perception of light reflected or scattered from
its surface. Accordingly, the tooth color is a result of the perception of light scattered
within the tubules of dentin and hydroxyapatite crystals of the enamel.[11] Factors affecting the observer include eye fatigue, aging, emotional and physiological
issues, and light conditions of the surrounding environment will affect visual shade
selection.[12]
A variety of tools are used to determine color, including shade guides, spectrophotometers,
colorimeters, spectroradiometers, and digital image analysis.[13] A shade guide is a set of colored tabs which are used as a standard resembling teeth
structures.[14] It is a quick, easy, and cost-effective way to choose shades, but it is considered
subjective and inconsistent. Several factors can influence visual shade selection,
such as the lighting, color acuity, and eye fatigue.[15] These undesirable conditions can be overcome by using sophisticated instruments
such as spectrophotometers and colorimeters.
A spectrophotometer measures and records the amount and spectral composition of light
reflected from the tooth.[16]
[17] It is the most accurate and flexible instrument used for color matching.[18] Data are quantified and easily collected, but it is mostly used in research due
to its complexity and high costs.[19]
Dehydration of the teeth can increase enamel opacity, making them seem whiter.[10]
[20] Interprism spaces become filled with air instead of water, so light cannot scatter
between crystals.[21] Loss of translucency on dehydration results in more reflection, which masks the
underlying color of dentine, which makes it appear lighter.[22]
[23] Most dental procedures cause some dehydration of teeth.[20] It is recommended to record color before any restorative procedure.[24] Mismatches between restorations and natural teeth may result in remakes and increased
expense.
There is limited quantitative evidence in the current literature about the influence
of tooth dehydration on color measurements and shade selection mismatch. The primary
aim of this study was to assess the effect of dryness and dehydration on tooth color
using a spectrophotometer.
Materials and Methods
The present study was conducted at the Riyadh Elm University (REU) from June 13, 2021,
to August 16, 2021. The ethical approval was obtained from the Institutional Review
Board of REU with approval number SRP/2021/457/475. Twenty freshly extracted maxillary
central incisors were collected from several private clinics in Riyadh, Saudi Arabia,
and immediately soaked in normal saline for 24 hours. The selection criteria for the
teeth were the normal anatomical shape of the tooth and absence of visible defects,
restorations, stains, excessive abrasion, and caries on the labial surfaces. They
were extracted due to periodontal issues.
The Spectrophotometric Analysis
The color measurements were performed using the VITA Easyshade Advance 4.0 spectrophotometer.
The experiment was conducted in a dark room to minimize changes in light conditions
because any change can affect measurements due to the translucent nature of tooth
substance.[25] The spectrophotometer was calibrated and used according to the manufacturer's instructions
before each set of measurements and was used with the “Tooth Areas” setting to measure
color at the cervical, middle, and incisal areas. An infection control shield was
used to prevent any contamination and damage of the optical fibers. Spectrophotometer
measurements were performed for all teeth by a single operator, placing the probe
perpendicular to the tooth surface, pressing the measurement button, and holding the
probe tip against the tooth until two quick “beeps” can be heard to indicate completion
of the measurement. A total of three measurements were performed, baseline spectrophotometric
measurements were obtained (cervical, middle, and incisal), after that, the teeth
were dried at room temperature for 1 hour then 2 hours, respectively. Further spectrophotometric
measurements were performed (cervical, middle, and incisal). After all the teeth are
dehydrated naturally with air dry. The color data from Easyshade recoded by using
the International Commission on Illumination (CIE) L*a*b* coordinates, Chroma (c),
hue (h). The color difference (∆E) were calculated between two different dehydration
times by using: ∆E*ab = √ (L2∗ − L1∗)2 + (a2∗ − a1∗)2 + (b2∗ − b1∗)2. The CIE laboratory identifies light wavelengths as numbers represented in three
coordinates (L = lightness, a = green and red, and b = blue and yellow). The L coordinate
represents the lightness and darkness of the specimen, the greater the L*, the lighter
the specimen. The a coordinate measures the chroma within the red and green axis.
A positive a value corresponds to the amount of redness, whereas a negative a value
relates to the amount of greenness. And the b* coordinate measures of the chroma along
the yellow and blue axis, a positive b value relates to more yellowness, and a negative
b value relates to more blueish the color.[26]
Statistical Analysis
Descriptive statistics of mean (standard deviation) values were calculated for all
the color coordinates at a different time interval and compared across cervical, middle,
and incisal thirds of the teeth. A color change value ∆E was obtained ∆E*ab = √ (L2∗ − L1∗)2 + (a2∗ − a1∗)2+ (b2∗ − b1∗)2. Similarly, hue and chroma values were compared across different areas. All the data
collected on color measurements were entered into the statistical package for social
sciences (IBM-SPSS version 25, Armonk, New York, United States), and analysis was
performed. A p-value of less than <0.05 was considered significant for all the statistical tests.
The null hypothesis of this study is that there is no difference between tooth shade
before and after dehydration.
Results
The analysis of variance (ANOVA) indicated that there were no statistically significant
changes over time from the baseline, after 1 hour, and 2 hours of dehydration between
different areas of the tooth surface: cervical, middle, and incisal, respectively,
for color coordinates: L, C, h, a, b as shown in [Table 1]. From baseline to 1 hour of dehydration, there were no significant changes (p = 0.667) ([Fig. 1]). When comparing baseline to 2 hours of dehydration, there were no significant color
changes (p = 0.619) ([Fig. 2]), and finally, when comparing 1 hour of dehydration to 2 hours still no changes
were found (p = 0.888) ([Fig. 3]). However, there were statistically significant changes in the color difference
∆E with different time intervals: between baseline, after 1 hour, and 2 hours of dehydration.
Fig. 1 Color change from baseline to after 1 hour in different areas (F = 0.408, p = 0.667).
Fig. 2 Color change from baseline to after 2 hours in different areas (F = 0.483, p = 0.619).
Fig. 3 Color change from 1 hour to 2 hour in different areas (F = 0.119, p = 0.888).
Table 1
Descriptive statistics for color coordinates: L, C, h, a, b between different areas
of the tooth surface: cervical, middle, and incisal, at different time intervals
|
The color coordinates at different time intervals
|
|
Time
|
Color coordinates
|
Cervical
|
Middle
|
Incisal
|
|
Mean
|
SD
|
Mean
|
SD
|
Mean
|
SD
|
|
Baseline
|
L0
|
79.15
|
6.24
|
81.27
|
5.71
|
81.09
|
4.60
|
|
C0
|
19.21
|
5.54
|
17.65
|
6.37
|
17.28
|
7.17
|
|
h0
|
94.02
|
5.45
|
96.48
|
5.47
|
93.85
|
13.88
|
|
a0
|
−1.26
|
1.30
|
−1.30
|
1.34
|
−1.45
|
1.60
|
|
b0
|
19.21
|
5.52
|
17.59
|
6.38
|
17.26
|
7.15
|
|
1 h
|
L1
|
81.61
|
6.10
|
84.27
|
5.11
|
85.10
|
4.76
|
|
C1
|
20.91
|
5.19
|
19.14
|
6.20
|
18.53
|
7.41
|
|
h1
|
92.27
|
4.54
|
95.21
|
5.46
|
95.37
|
7.43
|
|
a1
|
−0.72
|
1.20
|
−1.02
|
1.21
|
−0.98
|
1.41
|
|
b1
|
21.31
|
5.80
|
19.12
|
6.21
|
18.52
|
7.41
|
|
2 h
|
L2
|
82.41
|
6.79
|
86.05
|
5.69
|
85.80
|
4.19
|
|
C2
|
21.78
|
5.54
|
20.13
|
6.33
|
19.68
|
7.57
|
|
h2
|
91.08
|
4.78
|
94.16
|
4.92
|
93.76
|
6.13
|
|
a2
|
−0.43
|
1.41
|
−0.70
|
1.26
|
−0.77
|
1.42
|
|
b2
|
21.55
|
5.51
|
20.06
|
6.29
|
19.63
|
7.55
|
Abbreviations: a, chromaticity coordinate for red–green; b, chromaticity coordinate
for yellow–blue; C, chroma value; h, hue value; L, lightness value; SD, standard deviation.
The ANOVA test indicated that there were statistically significant changes in the
∆E (p < 0.05) shown in [Table 2], as follows:
Table 2
Color change value at different time intervals
|
Paired differences in color change values (∆E)
|
|
Color change
|
Mean
|
SD
|
Standard error mean
|
95% confidence interval of the difference
|
Time
|
p-Value
|
|
Lower
|
Upper
|
|
∆E1 − ∆E2
|
−1.42
|
2.23
|
0.29
|
−1.99
|
−0.84
|
−4.912
|
<0.001
|
|
∆E1 − ∆E3
|
1.72
|
3.12
|
0.40
|
0.92
|
2.53
|
4.279
|
<0.001
|
|
∆E2 − ∆E3
|
3.14
|
2.90
|
0.37
|
2.39
|
3.89
|
8.371
|
<0.001
|
Abbreviations: ∆E1, color difference at baseline; ∆E2, color difference after dehydration
for 1 hour; ∆E3, color difference after dehydration for 2 hours; SD, standard deviation.
-
From baseline to 1 hour of dehydration: ∆E1 − ∆E2 (p < 0.001)
-
From baseline to 2 hours of dehydration: ∆E1 − ∆E3 (p < 0.001)
-
Between 1 hour and 2 hours of dehydration: ∆E1 − ∆E3 (p < 0.001)
In addition, results showed statistically significant changes in hue only between
1 hour and 2 hours of dehydration (p = 0.002) in [Table 3]. Chroma value also showed statistically significant changes over time of dehydration
from the baseline, after 1 hour, and 2 hours, respectively (p < 0.001) in all time intervals as shown in [Table 4].
Table 3
Paired differences in hue values at different time intervals
|
Paired differences in hue values at different time intervals
|
|
Hue
|
Mean
|
SD
|
Standard error mean
|
95% confidence interval of the difference
|
t-Value
|
p-Value
|
|
Lower
|
Upper
|
|
Between baseline and 1 h
|
0.50
|
7.82
|
1.01
|
−1.52
|
2.52
|
0.493
|
0.624
|
|
Between baseline and 2 h
|
1.78
|
7.95
|
1.03
|
−0.27
|
3.84
|
1.737
|
0.088
|
|
Between 1 h and 2 h
|
1.29
|
3.05
|
0.39
|
0.50
|
2.07
|
3.259
|
0.002
|
Abbreviation: SD, standard deviation.
Table 4
Paired differences in chroma values at different time intervals
|
Paired differences in hue values at different time intervals
|
|
Chroma value
|
Mean
|
SD
|
Standard error mean
|
95% confidence interval of the difference
|
t-Value
|
df
|
p-Value
|
|
Lower
|
Upper
|
|
Between baseline and 1 h
|
−1.49
|
1.50
|
0.19
|
−1.87
|
−1.10
|
−7.671
|
59
|
<0.001
|
|
Between baseline and 2 h
|
−2.49
|
2.12
|
0.27
|
−3.03
|
−1.94
|
−9.106
|
59
|
<0.001
|
|
Between 1 h and 2 h
|
−1.00
|
1.36
|
0.18
|
−1.35
|
−0.65
|
−5.685
|
59
|
<0.001
|
Abbreviations: df, degree of freedom; SD, standard deviation.
Discussion
In this study, Vita Easyshade Advance 4.0 spectrophotometer was used to record tooth
color changes in response to different dehydration time due to the limited number
of studies that have investigated the correlation between dehydration and tooth shade.
Electronic shade selection methods such as spectrophotometric shade analysis were
found more accurate, reliable, and reproducible compared with the conventional method
of human visual shade assessment.[27]
[28]
[29] The CIELAB system was selected to measure color variations due to its ability in
recording minor color variations.[30] The spectrophotometer and the CIE color system provided precise color difference
evaluations that surpassed the visual evaluations limitations.[31] Differences of CIE L*a*b* values between (cervical, middle, and incisal) regions
were clinically and statistically not significant in contrast to previous researches
in which there was an overall gradation in color from the cervical region which is
most opaque to the incisal region becoming more translucent[32] as shown in [Table 1]. This could be a result of the underlying absorption pattern of the tooth as dentin
and not only the enamel.[33]
To determine the change in tooth color due to dehydration, tooth shade was measured
at the baseline, after 1 hour, and 2 hours. The results indicated a significant change
in tooth color after 1 hour and 2 hours due to dehydration as shown in [Table 2]. At the different time intervals, the authors note that ∆E value increases gradually,
as it can be seen from baseline to 1 hour (∆E1 − ∆E2 = − 1.42), when compared with
the mean from baseline to 2 hours (∆E1 − ∆E3 = 1.72) and from 1 hour to 2 hours (∆E2 − ∆E3 = 3.14).
This interpretation validates the results of Burki et al, in which there were statistically
significant changes due to dehydration after 10 and 30 minutes.[24] After the statistical analysis, it was indicated that there is a significant rejection
of the null hypothesis which stated there is no change in the tooth color associated
with dehydration; however, the lightness (L) which represents the amount of light
reflected by an object, in this case the tooth surface, compared with a pure white
diffuser (an object that only reflects light rays) and a black absorber (an object
that only absorbs light rays),[34] showed no statistically significant changes, even though it is known that dehydration
leads to increase in the opacity of the tooth making it lighter.[10]
[20] As mentioned earlier, spectrophotometers reproduce accurate measurements compared
with visual assessment of tooth color, but it can give incorrect results if the investigator
is not trained with the instrument resulting in repositioning errors, as this could
be the case in this study. To limit the minor repositioning error during the teeth
assessment, it is important to orient the spectrophotometer probe in the same position
each time. A prior study noted the importance of using custom-made positioning jigs
for each subject to prevent the arbitrary placement of the probe.[24] Hue is the quality that differentiates one color from another.[35] The change in hue in this study was significant; we found a significant change between
1 hour and 2 hours of dehydration where p = 0.002 as shown in [Table 3]. The significance is possible because of a change in the reflectance spectrum of
the dehydrated enamel.[36] Chroma is a major determinant of color, defined as the saturation of a specific
color.[37] It changed significantly with dehydration as shown in [Table 4]. This significance is mainly due to the change of the refractive index within both
surfaces leading to more light scatter, thus appearing lighter.[22]
The spectrophotometer (Vita Easyshade Advance 4.0) is considered an extremely reliable
method to have accurate shade measurements and that is the reason we have used it
in this study.[38] However, according to Judeh and Al-Wahadni, further device improvements and software
upgrades would help dentists to select better shades.[39]
Limitations of the study include long time intervals between readings to measure the
dehydration effect. Additionally, a small sample size was used in the study, which
may have significant difference on the outcome when applied to a larger sample. Furthermore,
the experiment conducted on the sample was performed under ideal conditions, which
are not present in an actual clinical setting. Finally, the teeth used were not specific
as they were randomly collected from private clinics, so selected teeth had great
diversity of age, gender, and ethnicity; hence, tooth shades collected results were
affected. Additionally, the accuracy of the VITA Easyshade Advance 4.0 device might
have some minor defects that occur in electronic devices.
We recommend in future studies to decrease dehydration time intervals, since teeth
in the operative setting are subjected to continuous dehydration and rehydration effects.[36] For future in vitro studies increasing the sample could be beneficial to validate the results. Sample
selection could be from a specific age and ethnicity group with similar initial tooth
shade to make the study more precise and reveal a clearer picture regarding the different
dehydration patterns.[22] Additional recommendations include clinical application of the study with the use
of a rubber dam to evaluate the dehydration effect on teeth in clinical setting.
Conclusion
Dehydration time dramatically affects tooth color measurements, and the spectrophotometer
Vita Easyshade Advance 4.0 proved to be reliable in detecting tooth color changes
at different durations of dehydration. Postdehydration teeth appear brighter due to
the change in the refractive index caused by air replacing the interprism spaces within
the enamel; therefore, color measurements for shade selection should be taken as soon
as possible to ensure accuracy of shade selection and to provide a successful aesthetic
result. Dentists must have proper training in tooth color selection and be aware of
the scientific components as well as the factors that influence tooth color and shade
taking. Incompatibility between restorations and natural teeth will result in an increased
chance of remakes and higher expenses, as patients will not be satisfied with the
results.
