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10.5005/jp-journals-10021-1192
ORIGINAL ARTICLE
Puneet Yadav et al
Evaluation and Comparison of the Color
Stability of Various Esthetic Brackets,
When Exposed to Various Food Dyes:
An in vitro Study
1
Puneet Yadav, 2Pushpa Vinay Hazarey, 3Seema Grover, 4Maninder Sidhu, 5Vikas Malik
ABSTRACT
Aim: Due to an increased demand for better esthetic during orthodontic treatment, tooth colored brackets were introduced. Esthetic brackets
can be either ceramic or composite, but their color stability remains main concern for clinicians and patients. The present in vitro study was
conducted to investigate, evaluate and compare color stability of various esthetic brackets when exposed to various food dyes. Further, effect of
time on color stability of esthetic brackets was evaluated.
Materials and methods: Total 120 upper central incisor brackets were taken for study. They were divided into three Groups of 40 brackets each.
Group I, ceramic brackets of American orthodontics, Group II, ceramic brackets of 3M Unitek and Group III composite brackets of Libral traders.
Frequently used beverages; drinking water, tea, coffee, coke were used in study. For control value, color of all brackets at 0 day was noted. Then
brackets of all groups were immersed in different solutions for 24 (1 day), 72 (3 days), and 144 hours (6 days) respectively and compared with
control value.
Results: All brackets showed significant color changes on sixth day. Group I showed 'E value of 5.18 for coffee, 5.17 for tea indicating more
staining with coffee than tea. Group II showed 'E-value of 5.05 for tea, 4.16 for coffee suggesting more color variation with tea than coffee.
Group III 'E values were 6.11 for coffee, 8.63 for tea. Hence, color variations were more prominent with tea than coffee in all groups. Coke and
water discolorations were least in all groups on sixth day.
Keywords: Esthetic, Bracket, Dyes.
How to cite this article: Yadav P, Hazarey PV, Grover S, Sidhu M, Malik V. Evaluation and Comparison of the Color Stability of Various
Esthetic Brackets When Exposed to Various Food Dyes: An in vitro Study. J Ind Orthod Soc 2013;47(4):382-389.
INTRODUCTION
The growing population of adult orthodontic patients not only
wants an improved smile, but also better esthetics during the
treatment. Over the years, the esthetic appearance of fixed
orthodontic appliance has become a vital concern. As the
number of adults seeking orthodontic treatment increased, the
esthetic brackets were introduced.1 Three types of orthodontic
bracket are currently available; metal, ceramic and plastic. The
metal brackets although provide good mechanical properties,
esthetically they are not appreciated.2
Although various modalities have been incorporated in
orthodontics to improve esthetics during the treatment, but
1,5
Senior Lecturer, 2,4Professor and Head, 3Professor
Department of Orthodontics, SGT Dental College, Gurgaon
Haryana, India
2
Department of Orthodontics, Sharad Pawar Dental College, Wardha
Maharashtra, India
1,3-5
Corresponding Author: Puneet Yadav, Senior Lecturer, Department
of Orthodontics, SGT Dental College, Gurgaon, Haryana, India
e-mail: drpuneetyadav@gmail.com
Received on: 3/3/12
Accepted after Revision: 27/6/12
382
composite and ceramic brackets remain the most popular
options preferred by the patients. Composite bracket are made
up of polycarbonate which adsorbed water during orthodontic
treatment. In the mid 1980s, first ceramic bracket made of
monocrystalline and polycrystalline materials became widely
available.3 An increased strength is a major advantage of
ceramic brackets over composite brackets. Nevertheless, the
use of ceramic brackets may result in problems with excessive
bond strength and damage the enamel during removal due to
their brittle nature.4
The color stability of these esthetic brackets has remained
the main concern for clinicians as well as patients. Though,
the ceramic brackets had similar disadvantages of getting
stained in the oral environment over a period of time, they
were more resistant to various stresses and torquing forces.
There are two types of discoloration of esthetic brackets:
Internal (endogenous) and external (exogenous).5 The external
discoloration is chiefly due to color dyes, such as food dyes,
tea stains, coffee, colored mouth rinses, etc.6 The material,
structure, filler content and surface roughness plays a decisive
role in the extent of external discoloration.7 The chief culprit
for internal discoloration was found to be UV radiations and
thermal energy.8,9
JIOS
Evaluation and Comparison of the Color Stability of Various Esthetic Brackets, When Exposed to Various Food Dyes
Two general methods can be used to analyze the color of
an object; visual and instrumental. Visual color determination
is based on visual comparisons of the object with standard
color. This method is most frequently applied in dentistry.10
Visual color assessments are a result of physiological and
psychological responses to radiant energy stimulation.
Alteration in perception can occur as a result of uncontrolled
factors, such as fatigue, aging, emotions, lighting conditions
and metamerism.11 It is the most scientific and practical
method to assess color stability.12
Colorimetry is the branch of science concerned with
numerically specifying the perceived color of the object as
well as differences in perceived color between two objects
judged to be different. 11 Reflected color is calculated
according to Commission Internationale de l’ Eclairage (CIE)
LAB color scale by measuring the ratio of reflected light to
incident light (spectral reflectance) under specified geometric
conditions. One of the most important features of CIELAB
system is its arrangement as an approximately uniform three
dimensional color space.13 The amount of color change can
be influenced by number of factors, including oral hygiene,
water sorption, incomplete polymerization and surface
roughness.
The purpose of the present in vitro study was to investigate
the influence of various food dyes on ceramic brackets, and
to evaluate and compare the color stability of various esthetic
brackets, when exposed to various color dyes. Further effect
of time on color stability of esthetic brackets was also
evaluated.
The samples were analyzed according to CIELAB color
scale and the exact color changes on their surfaces were
determined and compared with other experimental subgroups.
MATERIALS AND METHODS
A total of 120 upper right central incisors esthetic brackets
were taken for the study. These brackets were divided into
three groups according to their manufacture name. The ceramic
brackets were included in this study were polycrystalline in
nature.
• Group I: 40 ceramic brackets of American orthodontics
• Group II: 40 ceramic brackets of 3M Unitek
• Group III: 40 composite brackets of Libral Traders Pvt.
Ltd.
Solutions: Four solutions were chosen as they are the most
frequently used beverages in the daily life.
1. Packaged drinking water (Bisleri)
2. Tea (Lipton)
3. Coffee (Nescafe)
4. Cold drink (Coca Cola)
Distilled water used was Diet Aqua, India.
These groups were subdivided into following subgroups:
Total 120
samples
Drinking Tea
Coffee Cold
water
(10 no.) (10 no.) drink
(10 no.)
(10 no.)
40 ceramic
brackets (Group I)
40 ceramic
brackets (Group II)
40 composite
brackets (Group III)
Ia
Ib
Ic
Id
IIa
IIb
IIc
IId
IIIa
IIIb
IIIc
IIId
For the control value, or the base value, each bracket group
was analyzed for its original color value at 0 day interval, before
its immersion into the solution. The values were recorded and
were taken as the standard values for the further comparison
with the experimental groups.
Method for Analyzing the Samples
Three customized porcelain stands, with desired slot size of
each bracket type were fabricated so as to accurately fit the
brackets in them. This was essential for error free readings as
no external light sources could underpass the stand and thus
interfere with the analysis and the readings. Each subgroup
was then dipped in their respective solutions and were analyzed
for the color changes at the time intervals of 1 day (24 hours),
3 days (72 hours) and 6 days (144 hours) respectively. For
analyzing the samples, at the determined time interval, the
brackets from each subgroup were taken out of the solution
and rinsed for 20 minutes with deionized water (distilled water)
to remove the excessive stains. It was then gently dabbed by
filter paper to dry them. This method was followed for each
subgroup in the study.
The color measurements were carried out using the
Spectrolino™ Spectrophotometer (Figure 1 Spectrolino™
Spectrophotometer GretagMacbeth TM ) with a pinhole
diaphragm diameter of 4 mm according to the CIE L * a * b *
system (Commission Internationale de l’Eclairage, 1976).
Next, the brackets were placed in the slots of customized
porcelain stands and were placed under the spectrophotometer.
A color graph consisting of L *, a * and b* coordinates can be
produced by means of mathematical transformations. In the
CIELAB color space, L* is a measure of the lightness of an
object and is quantified on a scale such that perfect black has
an L* value of zero and a perfect reflecting diffuser an L*
value of 100.
The CIE a* value is a measure of redness or greenness,
and b* is a measure of yellowness or blueness. As a* becomes
more positive in value, the color is more red; as a* becomes
more negative in value, the color becomes more green. As b*
becomes more positive in value, the color becomes more
yellow; as b* becomes more negative in value, the color
The Journal of Indian Orthodontic Society, October-December 2013;47(4):382-389
383
Puneet Yadav et al
becomes more blue. Absolute measurements can be made in
L*a*b* coordinates and color change calculated as 'E
(L*a*b*). 'E value of 3.7 or less is considered to be clinically
acceptable.
The formula used for calculating the value of the change
in color is
'( >'L'a)2 + ('b)2]1/2
The obtained values were then subjected to statistical
analysis.
RESULTS
A total sample comprising of 120 brackets were used in this
study. Groups I and II consisted of 40 ceramic brackets.
Group III consisted of 40 composite brackets. These groups
were divided into subgroups as per the solution in which they
were immersed. The color measurements were carried out
using the Spectrophotometer according to CIE L*a*b* color
system.
The results and the statistic values are enumerated in the
form of tables.
Table 1 shows comparison between base values for
ceramic bracket Group I with that of subgroup Ia (drinking
water), Ib (tea), Ic (coffee) and Id (coke) at first, third, and
sixth day. On comparing Group I with Ia, there was a
statistically significant change in the color of brackets when
compared to their base values, this variation was most
significant on the sixth day and the color changes on first and
third day were not significant. However, the variation in the
color change was not relevant clinically as the base value for
the sixth day was 2.24, which is clinically acceptable. The
change in color is clinically perceptible only when equal to,
or above 3.5 to 3.7.14 When compared with Ib and Ic on third
and sixth day, “E value was higher for coffee (4.54 and 5.18)
than tea (4.96 and 5.17) showing more stains with coffee when
used in Group I brackets (Fig. 2).
Table 2 shows comparison between base values for
ceramic brackets of Group II with that of subgroup IIa, IIb, IIc
and IId. When compared with IIa (drinking water) at first, third
and sixth day. It showed that the variation in color on sixth day
was significant when compared to base value. When Group II
was compared with subgroup IIb (tea) at first, third and sixth
day, statistic analysis revealed significant variation in colors
for all the three time intervals as compared to the control
(base) values. However, highest value was seen on sixth day as
5.05. Similar findings were observed with subgroup IIc
Table 1: Comparison of base values of Group I with its subgroups Ia, Ib, Ic, Id on first, third and sixth day respectively
Group I
No. sample
Mean E
Base value
1st day
3rd day
6th day
–
10
10
10
2.20
1.49
1.79
2.24
0.82
1.31
0.32
0.51
0.26
0.41
0.10
0.16
–
0.89
0.13
2.13
–
0.384
0.895
0.032
Group Ib
1st day
3rd day
6th day
10
10
10
4.31
4.96
5.17
1.03
1.64
0.56
0.32
0.51
0.17
5.02
4.74
9.38
0.000
0.000
0.000
Group Ic
1st day
3rd day
6th day
10
10
10
2.68
4.54
5.18
0.78
0.42
1.39
0.24
0.13
0.44
1.33
15.20
5.80
0.199
0.000
0.000
Group Id
1st day
3rd day
6th day
10
10
10
3.09
3.51
3.51
0.76
0.49
0.49
0.24
0.15
0.15
2.49
4.27
4.27
0.022
0.000
0.000
Group Ia
Std. deviation
Std. error mean
T
p-value
p < 0.05, Significant
Table 2: Comparison of base values of Group II with its subgroups IIa, IIb, IIc, IId on first, third and sixth day respectively
Group II
No. sample
Mean E
Std. deviation
Std. error mean
T
p-value
Base value
–
1.81
0.60
0.19
–
–
Group IIa
1st day
3rd day
6th day
10
10
10
1.13
1.46
1.74
0.83
0.88
0.39
0.26
0.27
0.12
1.07
0.22
3.00
0.295
0.823
0.008
Group IIb
1st day
3rd day
6th day
10
10
10
3.08
3.59
5.05
0.46
0.77
0.62
0.14
0.24
0.19
5.27
5.71
11.81
0.000
0.000
0.000
Group IIc
1st day
3rd day
6th day
10
10
10
3.61
3.63
4.16
1.02
0.55
0.58
0.17
0.32
0.18
4.81
6.92
8.81
0.000
0.000
0.000
Group IId
1st day
3rd day
6th day
10
10
10
1.98
2.26
2.46
0.87
0.43
0.47
0.27
0.13
0.14
1.921
0.689
1.647
0.071
0.499
0.117
p < 0.05, Significant
384
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Evaluation and Comparison of the Color Stability of Various Esthetic Brackets, When Exposed to Various Food Dyes
Fig. 1: Spectrolino™ Spectrophotometer Gretag MacbethTM
Fig. 2: Comparison of base values with Subgroups of Ia, Ib, Ic and Id
at first, third and sixth days
Fig. 3: Comparison of base values of Group II with subgroups IIa, IIb,
IIc and IId at first, third and sixth days
(coffee), where highest value observed on sixth day was 4.16
and least on first day being 3.61. Whereas no statistically
significant color variation was observed on any day with
subgroup IId (coke). The maximum “E for coke subgroup was
2.46 (Fig. 3).
Fig. 4: Comparison of base values of Group III with subgroups IIIa,
IIIb, IIIc and IIId at first, third and sixth days
Table 3 shows comparison of composite brackets base
values Group III with subgroup IIIa, IIIb, IIIc and IIId on first,
third and sixth day. When compared with IIIa (drinking water),
statistically significant color change was observed on third
and sixth day. The E value for this day was 3.05, hence, color
change was clinically acceptable. Tea and coffee showed
highest values 8.63 and 6.11 on sixth day respectively (Fig. 4).
Table 4 shows the statistical intragroup comparison of
Group I when immersed in various solutionsat day 1. Although
color change was clinically insignificant for all the subgroups
analyzed, color variation was significantly noticeable between
subgroups Ia and Ib having value of –2.54, between Ia and Id,
value of E being –1.32. However, the color variation between
subgroups Ia, Ic and Id were not significant having value
–0.92 and –0.40 respectively. On sixth day, statistically
significant variation in color change was observed between
subgroups Ib and Id. The mean difference was found to be
maximum between the Groups Ia, Ib which was –3.68 followed
by Groups Ia and Id which was –2.01.
Table 5 shows the comparison in between subgroups of
Group II when immersed in various solutions on 1st, 3rd and
sixth day. On first day, maximum statistical variation in the
color change was seen between subgroups IIa, IIc which was
of value –2.16 followed by subgroups IIa, IIb having a value of
–1.61. On 3rd day, statistically significant color variation was
noticed between subgroups IIa, IIc (–1.87) followed by
subgroups IIa, IIb (–1.85). This suggests that color variation
was higher in coffee than tea. However, the variations in the
color stability were insignificant between the Groups IIa, IId,
and subgroups IIb and IIc. On 6th day, a statistically significant
color variation between all the subgroups was analyzed.
Maximum variations was seen in subgroups IIa, IIb (–3.91)
followed by subgroups IIa and IIc (–3.02).
Table 6 shows the comparison between subgroups of Group
III when immersed in various solutions on first, third and sixth
day. In the present study on 1st day, the maximum variation in
The Journal of Indian Orthodontic Society, October-December 2013;47(4):382-389
385
Puneet Yadav et al
Table 3: Comparison of base values of Group III with its subgroups IIIa, IIIb, IIIc, IIId on first, third and sixth days respectively
Group III
No. of sample
Base value
Mean E
Std. deviation
Std. error mean
T
p-value
0.81
0.44
0.13
Group IIIa
1st day
3rd day
6th day
10
10
10
0.98
2.63
3.05
0.29
0.46
0.18
0.09
0.14
0.05
0.99
9.01
14.79
0.333
0.000
0.000
Group IIIb
1st day
3rd day
6th day
10
10
10
5.26
8.20
8.63
0.69
0.56
0.44
0.21
0.17
0.14
17.14
32.55
39.39
0.000
0.000
0.000
Group IIIc
1st day
3rd day
6th day
10
10
10
4.71
5.54
6.11
0.50
0.25
0.28
0.15
0.08
0.09
18.41
29.24
31.80
0.000
0.000
0.000
Group IIId
1st day
3rd day
6th day
10
10
10
3.01
4.50
4.76
0.42
0.32
0.45
0.13
0.10
0.14
11.38
21.36
19.76
0.000
0.000
0.000
p < 0.05, significant
Table 4: Intragroup comparison of Group I when immersed in various solutions at days 1, 3 and 6
Groups
Ia
Ib
Ic
Mean difference
Ib
Ic
Id
Ic
Id
Id
p-value
Day 1
Day 3
Day 6
Day 1
Day 3
Day 6
–2.54
–0.92
–1.32
1.62
1.21
–0.40
–4.03
–3.61
–2.57
0.41
1.45
1.03
–3.68
–3.68
–2.01
–0.006
1.66
1.67
0.000
0.187
0.026
0.005
0.047
0.801
0.000
0.000
0.000
0.747
0.007
0.079
0.000
0.000
0.000
1.00
0.000
0.000
p < 0.05, significant
Table 5: Intragroup comparison of Group II when immersed in various solutions at days 1, 3 and 6
Groups
IIa
IIb
IIc
Mean difference
IIb
IIc
IId
IIc
IId
IId
p-value
Day 1
Day 3
Day 6
Day 1
Day 3
Day 6
–1.61
–2.16
–0.99
–0.54
0.62
1.16
–1.85
–1.87
–0.23
–0.02
1.61
1.63
–3.91
–3.02
–1.08
0.89
2.83
1.94
0.001
0.000
0.050
0.458
0.346
0.016
0.000
0.000
0.864
1.000
0.000
0.000
0.000
0.000
0.000
0.003
0.000
0.000
p < 0.05, significant
Table 6: Intragroup comparison of Group III when immersed in various solutions at days 1, 3 and 6
Groups
IIIa
IIIb
IIIc
Mean difference
IIIb
IIIc
IIId
IIIc
IIId
IIId
p-value
Day 1
Day 3
Day 6
Day 1
Day 3
Day 6
–4.27
–3.72
–2.03
0.54
2.24
1.69
–5.56
–2.90
–1.86
2.66
3.70
1.03
–5.57
–3.05
–1.70
2.52
3.87
1.35
0.000
0.000
0.000
0.085
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
p < 0.05, significant
color stability was seen in subgroups IIIa, IIIb again suggesting
that tea caused the most significant change in color having
value of –4.27 followed by subgroups IIIa and IIIc having value
of –3.72. On 3rd day, similar results were found with
386
maximum variation in subgroups IIIa, IIIb with value of –4.27
followed by subgroups IIIb and IIId with value of 2.24. The
least significant variation was observed between the Groups
IIIc and IIId having a value of 1.69 followed by subgroups IIIa
JIOS
Evaluation and Comparison of the Color Stability of Various Esthetic Brackets, When Exposed to Various Food Dyes
and IIId having value of –2.03. On 6th day, maximum significant
variation was seen in IIIa and IIIb having value of –5.57 followed
by subgroups IIIa and IIIc with value of –3.05.
Statistical analysis was carried out for the comparison of
the various esthetic brackets to find out the significant
difference between color stability within the Groups. Oneway ANOVA, Turkey multiple comparison test and Students
t-test were used for the analysis of results.
DISCUSSION
Color stability is an important parameter for modern esthetic
brackets. Color measurements can be evaluated with various
instruments. Since, instrument measurements eliminate the
subjective interpretation of visual color comparison,
spectrophotometers and colorimeters have been used to
measure color change in dental materials. The CIE L*a*b*
was chosen to record color differences because it is well suited
for determination of small color differences. Commonly
E values differing by 1 unit are considered a color match,
because they cannot be identified by independent observers.11
Values of E of 2 to 3 represent color difference that are slightly
perceptible. E values greater than or equal to 3.3 are visually
perceptible and clinically unacceptable.15 Hence, in this study
E value below 3.3 were considered clinically acceptable color
change.
The literature on color stability of orthodontic materials
is limited.16,17 In restorative and prosthetic dentistry, various
techniques have been described to study discoloration of dental
products. Accelerated aging methods and immersion solutions
such as coffee, tea, grape juice and chlorhexidine are used for
in vitro simulations.18,19 It has been shown that the type of
immersion solution and the exposure time influence the degree
of color change. Tea and coffee seem to cause the most
significant staining.20 In the present study Group I ceramic
brackets showed maximum stains with coffee with E value of
5.18 on 6th day than tea with E value of 5.17, whereas Group II
brackets revealed maximum stains with tea carrying E value
of 5.05 than coffee with E value of 4.16. The composite
brackets showed maximum stains with both tea and coffee with
“E value of 8.63 and 6.11 consecutively on 6th day. This could
be explained due to hydrophilic nature of resin matrix in
composite brackets. It is known that composite material allows
water to penetrate the matrix and the filler matrix interface.21,22
The interface between resin and particles is a weak point of a
composite material with high sensitivity to water sorption.23
Therefore, the hydrophilic degradation of this interface might
lead to enhanced water uptake of highly filled brackets. Water
acts as a carrier, and, as a result, solvent food dyes could
penetrate the composite and discolor the bracket. Hence, the
composite brackets attained more stains than ceramic
brackets.
The color stability of composites can be affected due to
many variables.24 Ferracane et al25 investigated the cause of
yellow discoloration and found that yellowing of the polymer
was accompanied by a reduction in the quantity of residual
unreacted double bonds in the resins. They stated that possible
explanation for the yellowing could be an oxidation of the
unreacted C = C to produce colored peroxide compounds.
Thus, the polymeric structure and filler content as well as the
polymerization conversion, seem to be the most important
factors, which influence the color stability of dental polymers.
Sham et al13 believed that changes in the optical properties in
the polymer could be responsible for color change.
The discoloration could be either due to extrinsic or
intrinsic factors. Extrinsic factors include adsorption or
absorption of colorants as a result of contamination from
exogenous sources. Extrinsic factors for discoloration are
known to cause staining of oral tissues and restorations
especially in combination with dietary factors. Among these
tea, coffee, nicotine and beverages have been reported. In the
present study, discoloration of resin-based composite brackets
by tea was mainly due to surface adsorption of the colorants
and discoloration by coffee was due to adsorption and also
due to absorption of colorants by investigated materials.
Absorption and penetration of colorants into the organic phase
of the resin-based materials are probably due to compatibility
of the polymer phase with the yellow colorants of coffee.
There was a small increase in the discoloration of the
brackets on the 1st day, and it increased with time that is on
6th day, and this correlated with the present study findings.26,27
Also Groups II and III brackets showed maximum discoloration
with tea rather than coffee on 6th day having E value of 5.05
and 8.63 consecutively. This is in contrast to studies done by
authors who used tea, coffee as chromogenic agents for resin
restorative material and concluded coffee to stain more than
tea.20,28 In a study done by Ruyter et al29 staining of resin based
veneering materials with three heat cured and two light cured
resins on test materials showed more discoloration by tea than
coffee over an observation period of 48 hours. But at the same
time, it reported that staining with tea was superficial and more
easily removed in comparison to coffee stains after cleansing
treatment with soap and toothbrush.
In the present study, the discoloration with composites
brackets was more than Group II and I brackets having E value
of 8.63 and 6.11 with tea and coffee respectively on 6th day.
Gharamanlooet al30 stated that porcelains resist discoloration
whereas composites are susceptible to extrinsic and intrinsic
stains. They acknowledged that high glossy surface is less
susceptible to staining, other surface conditions as incomplete
polymerization of the resin matrix may lead to surface staining
of composites. Microcracks, microvoids or interfacial gaps
located at the interface between filler and matrix are the
penetration pathways for stains.
When Groups I, II and III were compared with subgroups
tea, coffee, coke and drinking water on 1st, 3rd and 6th day, tea
and coffee stained more than coke and drinking water
respectively. With coffee staining more than tea, are similar to
findings by Lu et al31 and Guler et al.5 On 3rd day, the maximum
The Journal of Indian Orthodontic Society, October-December 2013;47(4):382-389
387
Puneet Yadav et al
changes in the color stability was observed between the Groups
Ia, Ib having values –4.03 and Ia, Ic (–3.61) which was similar
to results shown by Faltermiere et al.1
Coffee stained more than other subgroups which was in
accordance with findings by Gupta et al.32 Koksal and Dikbas2
suggested that coffee stained the brackets the most. The least
significant variation was seen between subgroups IIb and IIc
having value of 0.89.
Faltermeier et al33 investigated the influence of electron
beam irradiation with an energy dose of 100 kGy on the
mechanical properties and color stability of conventional
polymer brackets and experimental filled composite brackets.
The influence of electron beam postcuring on Vickers hardness
(VH) of the polymer brackets was investigated and possible
discoloration of the brackets after electron beam irradiation
was determined according to the three-dimensional L* a* b*
color space. These results demonstrated that the mechanical
properties of polymer brackets could be modified by electron
beam irradiation but clinical use of electron beam postcuring
might be restricted because of unacceptable color changes.
The color stability of ceramic and composite brackets was
found to depend on many factors, such as filler level and type
of discoloration. According to Lee YK the kind of material
and crystal structure for ceramic brackets did not influence
color stability, but color stability was mainly branddependent.34
Despite our results, the clinical performance of brackets
depends on various synergistic effects in the oral environment
that cannot be simulated precisely by in vitro investigations.
When discussing the clinical application of these results, it
must be considered that the oral environment differs in several
ways from in vitro conditions. Factors such as variety of foods,
thermal and mechanical stresses and their interactions may
intensify the discolorations in vivo. Since a limited data is
available in orthodontics, further in vivo studies should be
carried out for a longer period of time in this field to evaluate
discoloration as well as clinical color stability.
CONCLUSION
The brackets of Group I showed maximum variation in the
color stability when immersed in coffee solution, which was
followed by tea and coke respectively. However, this variation
was clinically insignificant whereas the brackets of Group II
showed maximum variation in the color stability when
immersed in tea solution. Group III showed maximum variation
in the color stability when immersed in tea solution, which
was followed by coffee, coke solutions and drinking water
respectively. Composite brackets showed overall poor color
stability with all the solutions.
According to Ruyter et al14 a 'E* of 3.3 is visually
perceptible and therefore clinically unacceptable. In this
in vitro investigation, maximum exposure time of 6 days was
chosen. In spite of this short exposure period, almost all
388
investigated esthetic brackets showed undesirable
discoloration. Nevertheless, it should be remembered that this
was an in vitro study, and care should be taken in interpreting
the results to those that might occur in the oral cavity.
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