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N. ALGhazali* , G. Burnside†, P.W. Smith‡, A.J. Preston§ and F.D. Jarad¶
Abstract - Four different shades were used to produce 20 samples of resin-based composite and 20 samples of porce-
lain to evaluate the performance ability of an intra oral test spectrophotometer compared to a reference spectropho-
tometer. The absolute colour coordinates CIELAB values measured with both spectrophotometers were significantly dif-
ferent (p<0.001). However, a high correlation was found (p<0.001) despite the low concordance noticed. The colour
difference ΔE* values calculated between different shades also were significantly different between both spectrophotom-
eters (p< 0.05). Therefore, the Easy Shade can be used in dental practice and dental research with some limitations.
KEYWORDS: performance, spectrophotometer, composite, porcelain, colour, colour difference.
† PhD
‡ BDS, MDS, PhD, FDS, DRD, MRD, FDS(Rest Dent), RCS (Edin), ILTM
§ BDS PhD FDS FDS(Rest Dent) RCS (Eng) ILTHE
¶ BDS, PhD, MFDS RCS(Eng), MRD RCS (Edin) Endodontics, FHEA
Eur. J. Prosthodont. Rest. Dent., Vol.19, No. 4, pp 168-174 © 2011 FDI World Dental Federation
Printed in Great Britain doi:10.1922/EJPRD_1003Jarad07
One of the aims of restorative dentistry is to restore missing
tooth structure to its natural shape, function and appearance.
Reproducing the appearance of natural teeth is a challenging
process which requires a careful construction of the aesthetic
restoration in terms of shape, surface texture, colour and
translucency. However, it seems that a significant proportion
of the problems associated with aesthetic restorations are
those related to colour matching procedures 1.
The increased demand for aesthetic dental restorations
has raised the importance of reliable colour reproduction
procedures. Appropriate selection of shade and replicating
that shade is considered as the most essential step required
for achieving a good colour match between a restoration
and natural teeth. This in turn, is considered to be highly
dependent on the ability to determine tooth colour in a
consistent and precise way 2. The most traditional way used
for colour determination is via the use of shade guides.
However, shade guides serve as an intermediate tool and
therefore two main sources of error are produced; one
is in shade determination by a clinician and the other, in
shade reproduction by a technician 3.
The colour of an object is a visual perception of the visible
light that it reflects and/or transmits 2. Visual assessment of
tooth colour is considered greatly subjective and inconsist-
ent due to several variables which can be either an external
variables such as light conditions, or an internal variables
such as experience, age, fatigue of human eye 4,5, and other
physiological factors such as colour vision confusion (CVC),
often called colour blindness 6. Moreover, standardisation
of verbal means for visual colour determination is limited 1.
In spite of these limitations, the human eye can detect even
small colour differences between two substances.
The problems and short-comings related to visual colour
assessment may be overcome by using objective metric
techniques. Several colour-measuring instruments have
been developed for colour measurement under standard-
ised conditions 7. These instruments can be spectropho-
tometers, colorimeters, or digital cameras.
Several studies have evaluated different colour-measuring
instruments and compared the colour determination ac-
curacy of such devices to that of human observers. In
Paul’s study 5; it was revealed that the spectrophotometric
colour determination and communication can be used
effectively for producing of metal ceramic restorations.
Crowns produced with a spectrophotometric assessment
have a considerably better colour match and lower rate of
rejection due to shade mismatch in comparing to crowns
produced by using a conventional shade matching process
8. Additionally, it has been found that the spectrophotomet-
ric shade assessment is more accurate and more reliable
compared with human shade determination 5.
A spectrophotometer is measuring the spectral reflectance
or transmittance curve of an object. Light is released from a
light source in the spectrophotometer and then dispersed by
a prism into a spectrum of different wavelengths between
380-780 nm. The spectrophotometer then measure the
amount of the light reflected from the specimen for each
wavelength in the visible light, and convert the data into
numerical values of colour coordinates CIE L*, a* and b* 9.
The ability to measure colour of natural teeth and aesthetic
restorations reliably and accurately is the most important
consideration for selecting a colour-measuring instrument.
Reproducibility and precision indicate the consistency of
the instrument in matching the same object, and can be
assessed by comparing repeated measurements of the same
sample or standard. The accuracy of a colour-measuring
instrument indicates the ability of this instrument to pro-
169
ASSESSMENT OF VITA EASY SHADE SPECTROPHOTOMETER ON COLOUR MEASUREMENT OF AESTHETIC DENTAL MATERIALS
duce a correct match for a given sample. This can be
evaluated by comparing a test instrument to a reference
one which is considered to be correct 3. The accuracy of
a colour-measuring instrument (test instrument) are evalu-
ated by two means; firstly by comparing absolute colour
coordinates L*, a* and b* values for all samples measured
with the test instruments to those values made with the
reference instrument and this is called absolute accuracy;
secondly, by comparing the colour difference values calcu-
lated between different samples using the test instruments
to those values made with the reference instrument and
this is called relative accuracy 1.
Moreover, colour perception depends on psych-physiolog-
ical responses to the light, and it might differ from one ob-
server to another, thus, it is appropriate to assess the accuracy
of a colour-measuring instrument as well by evaluating the
degree of concordance of its measurements to the measure-
ments obtained with a widely-used reference machine 10.
Two types of errors influence colour measuring process
using a colour-measuring instrument: systematic errors and
random errors. Random errors, which tend to influence
the precision and reliability of the instrument, including
instrument drift, background noise, polarisation and prepa-
ration of the samples. On the other hand, systematic errors
including inaccurate calibration, wavelength, filter design,
detector sensitivity and linearity, fluorescence, and varied
geometries of colour measurements tend to influence the
accuracy of the instrument 11.
Different commercially available colour measuring instru-
ments were evaluated and different levels of accuracy were
noticed. The Easy Shade spectrophotometer was more
precise and accurate than colorimeters (IdentaColor II, and
ShadeEye) and digital cameras (ShadeScan and Ikam) been
evaluated 12. Moreover, it has been revealed that the Easy
shade spectrophotometer was the most accurate instru-
ment comparing to the other instruments used (Spectro-
shade (Spectrophotometer), ShadeVision, and ShadeScan
(Digital Cameras) 3. However, none of these studies have
evaluated the accuracy of this colour-measuring instrument
(Easy Shade spectrophotometer) by comparing its colour
measurements to those obtained by a reference machine.
The aim of this study was to evaluate the performance
ability of intra oral test spectrophotometer compared to a
reference spectrophotometer.
Four null hypotheses were devised for this study:
1- There is no difference in colour coordinates (L*, a*,
and b*) values for resin-based composite and porcelain
materials measured by test or reference spectrophotom-
eters (absolute accuracy).
2- There is no difference in ∆E* values calculated between
different shades of resin-based composite and porce-
lain when using test or reference spectrophotometers
(relative accuracy).
3- There is no correlation between colour coordinates (L*,
a*, and b*) values of resin-based composite and porce-
lain measured by test or reference spectrophotometers.
4- The test spectrophotometer used is not a precise in-
strument.
Four different shades were used to produce 20 samples
of commercially available resin-based composite and 20
samples of porcelain (five samples for each shade). CIE
L*, a* and b* coordinates for all samples were measured
using an intra oral test spectrophotometer (Easy Shade
spectrophotometer) and a reference spectrophotometer
(Minolta CM-2600d). Colour difference ∆E* values were
calculated between different shades within each material.
The colour coordinates L*, a* and b* values and the colour
difference ∆E* values obtained by both spectrophotometers
were then compared.
Four different shades (A1, A2, A3, and A3.5) of both resin-
based composite Filtek Z250 and dental porcelain Omega
900 were used to fabricate discs of 2.1 mm thickness and 13
mm diameter by using a mould made of polyvinyl siloxane
putty silicone (Figure 1). Five samples were produced for
each shade (20 samples in total).
Resin-based composite was packed into the silicone mould.
Samples were light cured at five different sites from both
sides each for 20 seconds (Curing light XL3000).
The porcelain powder (Omega 900) and modelling fluid
were mixed and packed with vibration into the silicone
mould. Excess moisture was removed using paper tissue
to minimize porosity of the samples. Then the condensed
samples were placed on a suitable tray and fired in a
vacuum furnace at a temperature of (950 °C) according to
the manufacturer instructions.
Resin-based composite and porcelain discs were then
ground to ± 0.05mm of the prescribed thicknesses 2 mm
and polished using 150-, 1000-, 1500-grit silicon carbide
papers (Rhynowet Plus) with running water. The thickness
of the samples was determined using a digital thickness
scale (Mitutoyo).
The putty silicone mould used to fabricate samples and a
resin-based composite disc .
170
N. ALGHAZALI , G. BURNSIDE, P.W. SMITH, A.J. PRESTON AND F.D. JARAD
Two different colour-measuring instruments were used
in this study:
The Easy Shade spectrophotometer (Vita Easy Shade)
which calculates CIELAB values for 2° observation and
D65 illumination curve. This instrument uses hand hold
probe with 5 mm measurement area and emits light using
one halogen lamp.
The single tooth measurement mode was selected to meas-
ure the samples. Calibration was performed by placing the
probe tip on the calibration port built in the machine (one
standard for calibration) before each specimen measure-
ment; and each specimen was measured by holding the
probe tip (5mm diameter) at 90 degrees to the surface in
the middle of the disc (Figure 2).
The reference spectrophotometer (Minolta CM-2600d)
which has an integrating sphere system which uses (d/8)
diffuse illumination and 8-degrees viewing geometry. An
integrating sphere is a spherical apparatus with its internal
surface covered with a white substance such as barium
sulphate, so the light is uniformly diffused in all directions.
The Minolta spectrophotometer was used in an almost
similar setting to that used with Easy Shade as follows: D65
illumination curve; 2° observation angle; specular compo-
nent excluded (SCE) as it is already excluded in Easy Shade
spectrophotometer; ultraviolet light (UV) included since
the D65 illumination used in Easy Shade states the average
daylight including ultra violet wavelength region; and small
aperture size (SAV) of 3mm/6mm measurement area since
the probe tip of Easy Shade is of 5mm measurement area.
Calibrations were performed as per the manufacturer
instructions using two different standards: the zero calibra-
tions and the white calibration (Figure 3).
The colour measurements were standardised by using
same black background, one operator, and same lighting
conditions. Three measurements for each sample was taken
and the means (L*, a*, and b*) were recorded.
Ten randomly selected samples (5 samples from each resin-
based composite and porcelain materials) were measured
again in the same day.
The accuracy of the test spectrophotometer was evaluated
in terms of absolute accuracy, relative accuracy, correlation
and concordance.
The precision of the test spectrophotometer was also
evaluated in terms of the consistency of its repeated
measurements.
The absolute accuracy of a colour measuring device is the
ability to perfectly achieve the absolute colour coordinates
L*, a* and b* measurements of individual sample. This was
assessed by statistically comparing the absolute colour
coordinates of each resin-based composite and porcelain
sample obtained with the test instrument and the corre-
sponding colour coordinates obtained with the reference
instrument using a paired t-test. Moreover, absolute colour
difference ∆E* values were calculated using the following
formula 13:
∆E*Rt = ((L*R-L*t) 2 + (a*R – a*t) 2 + (b*R-b*t) 2) 1/2
where L*R, a*R, and b*R express the values determined
using the reference machine (Minolta), and L*t , a*t , and
b*t express the values determined using the test machine
(Easy shade).
The relative accuracy of a colour measuring device is the
ability to correctly determine the colour difference values
between two different samples. This was evaluated by
statistically comparing the colour difference values calcu-
lated between each possible paired combination of the
four shades within porcelain and resin-based composite
groups obtained with the test spectrophotometer and the
corresponding colour difference values obtained using the
reference spectrophotometer using a paired t-test.
Colour difference values (∆Eab*) between each possible
paired combination of the four shades of both porcelain
and resin-based composite materials were calculated using
the following formula
Vita Easy Shade spectrophotometer.
Minolta CM2600d, Minolta Konica spectrophotometer.
( ) ( ) ( )
222 ******* bababaab bbaaLLE −+−+−=∆
171
ASSESSMENT OF VITA EASY SHADE SPECTROPHOTOMETER ON COLOUR MEASUREMENT OF AESTHETIC DENTAL MATERIALS
Where La*, aa*, and ba* are the mean colour coordinates
for one shade obtained with the test spectrophotometer,
and Lb*, ab*, and bb* are the mean colour coordinates of
another shade obtained with the same spectrophotometer.
Therefore, the relative accuracy were assessed by com-
paring ∆E*ab/1 and ∆E*ab/2 where ∆E*ab/1 was the colour
difference values between different shades obtained with
the test spectrophotometer, and ∆E*ab/2 was the correspond-
ing colour difference values obtained using the reference
spectrophotometer.
The absolute colour coordinates L*, a* and b* measure-
ments for all samples within resin-based composite and
porcelain groups obtained with the test instrument and
those obtained with the reference instrument were tested
for correlation using Pearson’s correlation coefficient, and
for concordance using Lin’s concordance coefficient 14.
Moreover, linear regression was conducted to determine
the formula parameters that may express the relation be-
tween colour measurements made with these two spec-
trophotometers.
The absolute colour coordinates L*, a* and b* measure-
ments of the ten randomly selected samples were com-
pared to those measurements made at the same day using
Lin’s concordance coefficient 14.
The absolute colour coordinates L*, a* and b* values meas-
ured with the test spectrophotometer and those measured
with the reference spectrophotometer were significantly
different for both resin-based composite and porcelain ma-
terials (p<0.001). The results based on paired samples t-test
are illustrated in Table 1. The absolute colour difference val-
ues (calculated between the absolute colour coordinates L*,
a* and b* values measured with the test spectrophotometer
and those measured with the reference spectrophotometer)
were ∆ERT*=13.95 (13.4-14.5 at 95% Confidence Interval)
for resin-based composite and ∆ERT*=14.7 (14-15.4 at 95%
Confidence Interval) for porcelain.
The colour difference values calculated between each pair
shades using the test spectrophotometer were significantly
different from those colour difference values calculated
between the corresponding pair shades using the refer-
ence spectrophotometer for both resin-based composite
and porcelain (p< 0.05). Results based on paired samples
t-test are shown in Table 2.
Significantly high correlations were found between all
CIELAB colour coordinates measured with the test spec-
trophotometer and those measured with the reference
spectrophotometer at p-value <0.001. The Pearson’s cor-
relation coefficients were illustrated in Table 3. However,
low concordance coefficients were found (Table 3).
The formula used to determine the relation between colour
coordinates CIELAB measured with both spectrophotom-
eters is: Y= a X+ b where the Y is the predicted colour
measurement of the reference spectrophotometer, X is the
real colour measurement made with the test spectropho-
tometer, a is the slope and b is the intercept. The slopes
and intercepts for each colour coordinate L*, a* and b*
was determined using the linear regression test, and they
are listed in Table 4.
Very high concordance was noticed between repeated col-
our measurements made with the test spectrophotometer
at the same day for both resin-based composites and por-
celain materials (p<0.001). Lin’s concordance coefficients
were (0.999, 0.996 and 1.0) for L*, a* and b* coordinates
respectively.
The first null hypotheses was rejected since the absolute
colour coordinate L*, a* and b* values measured with the
test instrument was statistically different from those meas-
ured with the reference instrument for both resin-based
composite and dental porcelain samples (p<0.001). The
absolute colour difference ∆ERT* values calculated between
absolute colour coordinates measured with the test and
reference instruments were 13.95 for resin-based composite
and 14.7 for porcelain, which are highly above the 1 ∆E*
unit presented as a perceptibility threshold 15 and 5.5 ∆E*
units presented as an acceptability threshold in clinical
conditions 16.
These significant differences may be explained by a
number of variables that can affect the absolute accuracy
of the test spectrophotometer. Measuring the colour of a
sample using the test spectrophotometer is accomplished
by holding the probe tip at 90 degrees to the sample sur-
face. Therefore, any minor angulations of the probe might
cause an edge-loss effect. In this effect, the illuminating
beam is scattered within the specimen beyond the edge
of the probe tip especially when measuring translucent
samples 17,18,19. In this study, the edge-loss effect caused
by using such probe spectrophotometer with translucent
samples of resin-based composite and porcelain materials
may result in some inaccuracy of the test spectrophotom-
eter in absolute colour measurements compared to the
reference instrument which uses an integrated sphere to
illuminate the samples.
Using more than one known standard to calibrate a
colour-measuring instrument will give the possibility that
the standards may have a varied translucency from the
sample and therefore, reduce the errors associated with
colour measurements of samples of different translucencies
20. Unlike the reference spectrophotometer which has two
different standards for calibration, the test spectrophotom-
eter is calibrated using just one standard, which might not
be sufficient for assure the accuracy of absolute colour
measurement of different shades of resin-based composite
and porcelain materials.
172
N. ALGHAZALI , G. BURNSIDE, P.W. SMITH, A.J. PRESTON AND F.D. JARAD
Other variables might have influenced the absolute ac-
curacy of the test spectrophotometer compared to the
reference instrument including: the spectral resolution is
25nm in the test instrument, while it is 10nm in the refer-
ence instrument which produce more accurate measure-
ments; and one tungsten lamp used as an illuminant in
Easy shade, while the three pulsed xenon lamps used in
Minolta can automatically compensate for any drifting in
the intensity of the illumination and result in more accurate
measurements 20.
The final assessment in any colour evaluation process is
always a visual one, and the most useful of colour data val-
ues are those that have some relations to visual judgement
1. Colour difference values are considered important and
more practically useful in dentistry than absolute colour
measurements, especially when comparing these colour
difference values to the practical parameters (perceptible
and clinically acceptable thresholds) 21,22.The second null
hypothesis was rejected as significant differences were
found between colour difference values determined us-
ing the test spectrophotometer and corresponding colour
difference values obtained with the reference spectropho-
tometer (p<0.05). The mean differences were 2.84 and 3.65
for resin-based composite and dental porcelain materials
respectively which are considerably perceptible. The same
mentioned variables may have also influenced the relative
accuracy of the test instrument in determining the colour
difference values between different shades.
The third null hypothesis was rejected and significantly
high correlations were found between both the test and
the reference instruments in determining the absolute
colour coordinates CIELAB values (p<0.001). However,
low concordance coefficients were found between them,
showing that the two spectrophotometers have given differ-
ent but correlated measurements. That, in turn, reflects the
standard relation between the absolute colour coordinates
measurements obtained with both spectrophotometers.
Based on linear regression model, for e.g, colour coordi-
nates L*, a* and b* values of the 5th sample of A3.5 shade
of resin-based composite were respectively (67.87, -2.4
and 22.73) when using the test spectrophotometer. The
Table 1. Significance p values based on paired t-test for the differences in absolute colour coordinates measured with Easy Shade
and Minolta spectrophotometers.
Absolute
accuracy
Composite Porcelain
Mean 95% Confidence Interval Significance Mean 95% Confidence Interval Significance
Lower Upper Lower Upper
L* 9.8 9.51 10.1 0.000 7.32 6.45 8.19 0.000
a* 1.46 1.59 1.33 0.000 1.31 0.9 1.72 0.000
b* 9.65 8.69 10.62 0.000 12.21 10.7 13.72 0.000
Table 2. Significance p values based on paired t-test for the relative differences between ΔE* values calculated using Minolta spec-
trophotometer and corresponding ΔE* values obtained using Easy Shade spectrophotometer.
Relative accuracy Mean difference Std. Deviation 95% Confidence Interval Significance
Lower Upper
Composite 2.84 1.76 0.99 4.68 0.011
Porcelain 4.89 3.65 1.06 8.71 0.022
Table 3. Displays the Pearson’s correlation coefficient and Lin’s concordance coefficient for absolute colour coordinates CIELAB meas-
urements of both resin-based composites and porcelain materials.
Composite Porcelain
Pearson’s correlation
coefficient
Lin’s concordance
coefficient
Pearson’s correlation
coefficient
Lin’s concordance
coefficient
L* 0.961 0.005 0.955 0.267
a* 0.976 0.222 0.974 0.385
b* 0.993 0.158 0.996 0.26
Table 4. Slopes and Intercepts based on linear regression test for each of the three colour coordinates CIELAB for both resin-
based composite and porcelain materials.
L* a* b*
Slope Intercept Slope Intercept Slope Intercept
Resin-based composite 0.743 -0.687 0.569 -0.392 0.335 1.464
Dental Porcelain 0.756 1.305 0.453 18.094 0.540 -1.186
173
ASSESSMENT OF VITA EASY SHADE SPECTROPHOTOMETER ON COLOUR MEASUREMENT OF AESTHETIC DENTAL MATERIALS
predicted values of the references spectrophotometer
using the formula (Y= a X+ b) will be respectively (58.8,
-1.09 and 9.88), which are quite close to the real values
measured using this references spectrophotometer (58.84,
-1.27 and 9.91 respectively). However, the small sample
size (20 sample for each material) and the small variety
of shades (4 shades of each material) used in this study
forms a limitations from using this formula in general, and
therefore, more studies are recommended.
The fourth null hypothesis were also rejected and signifi-
cantly high precision of the test spectrophotometer was
noticed in repeated measurements (p<0.001), which means
that this test spectrophotometer is significantly reliable in
colour measurements of both resin-based composites and
porcelain materials. This might be explained by the fact that
the drifting might happened in this test instrument were
very low as calibration of the instrument was performed
before each single colour measurement.
Within the limitations of this study, the ability of the Easy
Shade spectrophotometer in determining the absolute
colour coordinates L*, a* and b* values was not accurate
(absolute accuracy) and therefore it is not recommended to
be used in studies where the absolute colour coordinates
of samples are important to be evaluated (for instance,
studies investigating the lightness, hue and chroma of dif-
ferent shades of a dental material).
However, high correlation was found between both test
and reference spectrophotometers in determination of ab-
solute colour coordinate values. Additionally, the reliability
(precision) of the test spectrophotometer was found to be
excellent. Moreover, the test spectrophotometer was the
most accurate instrument comparing to other instruments
used in production a correct shade of a selected sample
3. Therefore, the test spectrophotometer can be used for
shade reproduction process and in studies evaluating
colour shifts or changes, in addition to the advantage of
using it intra orally.
Of more practical use, the ability of the test spectropho-
tometer in determining the colour difference ∆Eab* values
between different shades was not as accurate as the
references spectrophotometer. This shortcoming can be
overcome by establishing the perceptibility and clinically
acceptable thresholds related to the test spectrophotometer.
Therefore, further studies in determining such thresholds
for the test spectrophotometer and for each individual
colour measuring instrument available to use in dental
field are recommended.
The Easy shade spectrophotometer is considered of limited
accuracy in measuring absolute colour coordinates CIELAB
in comparing to the reference instrument. However, despite
the low concordance, the high correlation between colour
measurements obtained with both spectrophotometers
means that the Easy Shade can be used in dental practice
and dental research with some limitations. Colour dif-
ference ∆Eab* values determined using Easy shade were
different from those obtained using the reference instru-
ment, however, this can be overcome by establishing the
perceptibility and acceptability thresholds related to each
instrument. Easy Shade spectrophotometer is a reliable
precise instrument in colour measurements of resin-based
composites and porcelain materials.
• Filtek Z250, 3M ESPE, USA
• Omega 900, Vita, Germany
• Curing light XL3000, 3M ESPE, USA
• Modelling fluid, Vita, Germany
• Rhynowet Plus, Portugal
• Mitutoyo, Japan
• Vita Easy Shade, Vita, Germany
• Minolta CM-2600d, Konica Minolta, Japan
Nabiel ALGhazali is funded by Syrian Government, Uni-
versity of Aleppo.
Dr Fadi Jarad, Lecturer/Honorary Specialist Registrar in
Restorative Dentistry, Liverpool University Dental Hos-
pital, Pembroke Place Liverpool, L3 5PS. Email: fjarad@
liverpool.ac.uk
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