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Research Article
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Long-term efficacy of in-office and at-home bleaching:
A 2-year double-blind randomized clinical trial
L
IDIA YILENG TAY, DDS, MS, CARLOS KOSE, DDS, MS, DANIEL RODRIGO HERRERA, DDS, MS, ALESSANDRA REIS, DDS, PHD
& ALESSANDRO DOURADO LOGUERCIO, DDS, MS, PHD
A
BSTRACT: Purpose: This parallel, double-blind randomized clinical trial evaluated the 2-year bleaching efficacy and
sensitivity produced by at-home (AH) and in-office (IO) bleaching therapies. Methods: 60 participants with tooth color
darker than C2, without restorations in the anterior dentition and older than 18 years old, were randomly allocated into
two groups to receive either IO with 35% hydrogen peroxide or AH with 16% carbamide peroxide. Color was recorded
at baseline (BA); 1-week (1W); end of the treatment (ET); and 2 years (2Y) after bleaching, using the Vita Classical
shade guide. The perception of TS was recorded on a 0-4 scale during and 2Y after bleaching. The variation in shade
guide units ('SGU) from BA vs. 1W was compared to 'SGU from BA vs. 2Y using paired t-test. The percentage of
subjects who reported TS was evaluated by Fisher’s exact test. The intensity of TS was evaluated by a Mann-Whitney
test (=0.05). Results: Both bleaching techniques demonstrated equivalent and significant tooth color shade lightening.
No significant color rebound occurred after 2Y for both techniques (P= 0.77 and 0.87, for AH and IO respectively). The
absolute risk of TS was similar for IO and AH (P= 0.12), however the intensity of TS was significantly higher for IO
(P= 0.001). No subjects reported sensitivity after 2Y. (Am J Dent 2012:25:199-204).
C
LINICAL SIGNIFICANCE: In-office bleaching produced efficient and long-lasting whitening effect, as well as at-home
bleaching, however the in-office bleaching protocol showed a higher intensity of sensitivity.
: Prof. Alessandro Dourado Loguercio, Faculty of Dentistry, State University of Ponta Grossa, Av. Carlos
Cavalcanti, 4748 – Bloco M – Sala 64, Ponta Grossa, Paraná CEP 84030-900, Brazil. E-: aloguercio@hotmail.com
Introduction
Improvements in the standard of living have increased the
number patients seeking cosmetic dentistry therapies. As whiter
teeth are perceived as being associated with health and beauty,
tooth bleaching has been widely performed by professionals for
treatment of discolored teeth. Compared with other restorative
treatments, such as porcelain veneers, crowns or composite
bonding, this treatment is a very conservative approach.
1
Different techniques are available for tooth bleaching.
2
Although at-home bleaching achieves a high success rate
3
and
it is the most widely taught bleaching technique in the USA,
4
some patients do not adapt well to the at-home protocol as they
prefer not to use a bleaching tray or do not want to wait 2-3
weeks to see the results of the treatment. Besides that, the
compliance of some patients to the daily use of a bleaching tray
that is not under the dentist’s control may increase the treatment
time and costs. In other clinical scenarios, such as the presence
of extensive tissue recession or deep unrestored abfraction
lesions, patients still need to be closely monitored.
1
For these
circumstances, the in-office bleaching protocol may be more
adequate, since it allows close dentist control, avoidance of
soft-tissue exposure and material ingestion, reduced total
treatment time and greater potential for immediate results
enhancing patient satisfaction and motivation.
5
Clinical trials
6,7
have compared the performance of high and
low-concentrated agents used for at-home or in-office tooth
bleaching and the majority has shown a similar whitening effect
for both concentrations and techniques. Nevertheless, the
incidence of tooth sensitivity or gingival irritation is more
common when the agent concentration is higher.
7,8
As patients look for an effective esthetic treatment, they
also expect that the treatment chosen will last for a long period
of time. Although a regression of color over time has been
reported for the at-home bleaching,
9-12
there is a general per-
ception among clinicians that at-home bleaching produces more
long-lasting results than in-office bleaching without a
substantial support of scientific evidence. Comparing 9-month
clinical longevity of both bleaching therapies did not detect any
significant difference among both protocols.
13
Few randomized
clinical trials
8,13-15
have evaluated the longevity of the whiten-
ing produced by in-office bleaching and those available report
only short-term results.
The present randomized clinical trial evaluated and com-
pared the 2-year longevity of bleaching efficacy and sensitivity
produced by at-home and in-office bleaching therapies. This
study was prepared according to the Consolidated Standards of
Reporting Trials (CONSORT) statement.
16
Materials and Methods
Experimental design - This clinical investigation was approved
under protocol number 08272/08 by the Institutional Review
Board of the local Ethics Committee of the State University of
Ponta Grossa, Brazil. Based on pre-established criteria, 60
volunteers were selected for this study. Two weeks before the
bleaching procedures, all the volunteers received a dental
screening and a dental prophylaxis with pumice and water in a
rubber cup. All subjects signed an informed consent form.
Study design - This was a randomized, double-blind, clinical
trial with an equal allocation rate to receive either one of two
treatments. The study took place in the School of Dentistry of
the State University of Ponta Grossa, Brazil, from October
2007 to August 2010.
Inclusion and exclusion criteria - Subjects included in this
clinical trial were at least 18 years old and had good general
200 Tay et al
and oral health. A total of 202 participants were examined to
check for the inclusion and exclusion criteria. Participants
needed to have six caries-free maxillary anterior teeth without
restorations on the labial surfaces, be willing to sign a consent
form and have central incisors determined to be shade C2 or
darker, according to a value-oriented shade guide [Vita Lumin
Vacuum (now marketed as Vita Classical
a
)]. Subjects were
excluded from the study if they had undergone tooth-whitening
procedures, had labial anterior restorations, were pregnant or
lactating, had severe internal tooth discoloration (such as
tetracycline stains, fluorosis, pulpless teeth), had bruxism habits
or had any other pathology that could cause sensitivity (such as
recession, dentin exposure).
Sample size calculation - Calculation of the sample size was
based on data resulting from previous in-office and at-home
bleaching studies.
17,18
For both bleaching protocols, the primary
outcome was the variation in shade guide units (SGU). A
sample size of 26 participants were required for both groups to
detect a difference of 1 SGU with a 90% statistical power
using a standard deviation of 1.5 with a significance level of
5%. In order to account for follow-up losses, 30 participants
were selected for each group.
Study intervention - Participants were randomly allocated into
two experimental groups (n = 30) according to the bleaching
technique: in-office or at-home bleaching. The simple random-
ization process was performed by computer-generated tables by
a third person not involved in the research protocol. Once the
participant was eligible for the procedure, and completed all
baseline assessments, the allocation assignment was revealed
by the third person. Neither the participant nor the operator
knew the group allocation, being both blinded to the protocol.
The participants from the in-office bleaching received a
prophylaxis of all teeth. The lips, cheeks and tongue were
isolated using the ArcFlex
b
lip retractor. The operators then
isolated the gingival tissue of the teeth to be bleached by using
a light-cured resin dam (Top Dam
b
). They applied a 35%
hydrogen peroxide gel (Whiteness HP
b
) for a total of 45
minutes. Every 15 minutes during the 45-minute session, they
refreshed the in-office bleaching agent. Participants repeated
the in-office bleaching treatment 1 week later.
For participants assigned to the at-home group, an alginate
impression of each subject’s maxillary arch was prepared and
filled with dental stone. To produce study models, block-out
material was not applied to the labial surfaces of teeth.
15
A 1-
mm soft vinyl material was used, provided by the manufacturer,
to fabricate the custom-fitted tray for the whitening gel. The
excess of labial and lingual surfaces was trimmed 1 mm from
the gingival junction. The tray and 16% carbamide peroxide gel
(Whiteness Standard
b
) was delivered to each subject with oral
instructions for use. All subjects were instructed to wear the
tray with agent for at least 6 hours at night. In the morning,
subjects were instructed to remove the tray, wash it and brush
their teeth with the fluoride toothpaste. The subjects were
instructed to wear the custom-fitted tray for 4 weeks. All
participants were instructed to brush their teeth regularly with
fluoridated toothpaste (Sorriso Fresh Gel
c
).
Shade evaluation - The subjective evaluation of color was per-
formed using a shade guide (Vita Lumina) in the same room
under artificial lighting. The shade guide’s 16 tabs were ar-
American Journal of Dentistry, Vol. 25, No. 4, August, 2012
ranged from highest (B1) to lowest (C4) value, making the color
C2 as number 7. Although this scale is not linear in the truest
sense, the changes were treated as representing a continuous and
approximately linear ranking for the purpose of analysis. The
measurement area of interest for shade matching was the middle
one third of the facial surface of the anterior central incisor.
Two calibrated evaluators, blinded to the allocation
assignment, recorded the shade of each participant’s teeth at
baseline and immediately after the first and second appoint-
ments for the in-office bleaching. For the at-home protocol, the
evaluators recorded the shade at baseline, and after 2 and 4
weeks of bleaching protocol. The two examiners were required
to have an agreement of at least 85% (Kappa statistic) before
beginning the study evaluation.
Tooth sensitivity evaluation - Participants were asked to record,
on a daily basis, their tooth sensitivity, according to the 5-point
Numerical Rating Scale,
17,18
with the following criteria: 0=
none, 1= mild, 2= moderate, 3= considerable and 4= severe.
These values were averaged for statistical purposes and
grouped into two categories: the overall percentage of subjects
with tooth sensitivity and the overall intensity of tooth
sensitivity. At the 2-year recall subjects were also asked to
record their tooth sensitivity.
All participants were evaluated at baseline, 1 week after the
end of the treatment and 2 years after bleaching. A standardized
questionnaire related to diet and oral hygiene behavior was
used specifically for the participants at the 2-year recall
appointment. Subjects were asked about the usage of whitening
toothpaste after bleaching; if they underwent another bleaching
treatment after the active treatment was completed; and the
daily intake frequency and type of staining beverage and food,
such as coffee, tea, wine, cola, artificial juices, chocolate,
beetroot or spinach, and smoking habits.
Statistical analysis - The analysis followed the intention-to-treat
protocol and involved all participants who were randomly
assigned, even those that were not able to be analyzed in the
scheduled recall visits.
16
In this case, we filled in the missing
data carrying the last observed value of such patient. The
statistician was blinded to the study groups. The agreement
between examiners was evaluated using the Kappa statistic.
Tooth shade changes were determined by calculating the
shift in the number of SGU that occurred toward the lighter
end of the scale. Two SGU were calculated: one taking the
baseline color vs. the color 1 week after the end of the
bleaching protocol (SGU 1 week) and the other taking the
baseline color vs. color taken at the 2-year recall (SGU 2
year). A paired Student t-test was used to compare the SGU 1
week and SGU 2 year for each bleaching therapy. A Student t
test for independent data was used to compare the bleaching
efficacy (SGU) at each assessment point for both therapies.
The least square mean differences as well as the confidence
interval were calculated.
The relative risks of tooth sensitivity for both bleaching
therapies were compared using the Fisher’s exact test ( =
0.05). The median of the tooth sensitivity intensity experienced
by each patient throughout the 4-week at-home and the 2-week
in-office therapies was used for statistical purposes. The
intensity of tooth sensitivity of both bleaching therapies were
compared using the Mann-Whitney test ( = 0.05).
American Journal of Dentistry, Vol. 25, No. 4, August, 2012
Fig. 1. Flow diagram of the clinical trial including detailed information on the
excluded participants.
Table 1. Change in tooth shade (mean and standard deviation) between
assessment points for the two treatment groups (*).
____________________________________________________________________________________________________
SGU SGU Least square
(Baseline (Baseline mean difference
vs 1 wk) vs 2 yrs) P value* (95% CI)
____________________________________________________________________________________________________
At-home (n=30) 6.27 ± 1.5 6.02 ± 1.4 0.77 0.25 (-0.5 – 1.0)
In-office (n=30) 5.62 ± 0.9 5.32 ± 0.7 0.87 0.30 (-0.1 – 0.7)
P-value** 0.51 0.47
____________________________________________________________________________________________________
* Paired t-test; ** unpaired t-test; CI: Confidence interval.
Results
Figure 1 depicts the participant flow diagram. All 60
participants who began the study, completed it. The mean ages
of the participants were 21 ± 3.8 and 21 ± 3.2 years for at-home
and in-office groups respectively. Males comprised 47.8 and
26.6% of participants in the at-home and in-office groups,
respectively.
Table 1 depicts the SGU calculated after each assessment
point for both bleaching protocols. Both techniques yielded a
whitening of approximately five to six shade guide units. No
significant darkening occurred by the 2-year recall (P< 0.77 and
P< 0.87 respectively, for at-home and in-office techniques).
The bleaching efficacy of at-home and in-office bleaching was
not statistically significant either 1 week after the end of
treatment (P< 0.51) or 2 years later (P< 0.47).
Table 2 shows the number of subjects who reported tooth
sensitivity during bleaching treatment. Statistically similar (P =
0.12) absolute risk of tooth sensitivity was reported by subjects
Clinical efficacy of tooth bleaching 201
Fig. 2. Levels of sensitivity (%) perceived by the participants for both groups
immediately after the bleaching protocol. No severe sensitivity was observed
in this study.
Table 2. Comparison of the number of subjects who experienced tooth sensitivity
during the bleaching regimen as well as absolute and relative risk (*).
____________________________________________________________________________________________________
Tooth sensitivity
during treatment
_________________________
Absolute risk Relative risk
Yes No P value* (95% CI) (95% CI)
____________________________________________________________________________________________________
At-home 20 10 66.7 (48.8 – 80.7)
0.12 1.3 (0.97 – 1.7)
In-office 26 4 86.7 (70.3 – 94.7)
____________________________________________________________________________________________________
* Fisher’s exact test; CI: Confidence interval.
Table 3. Medians and interquartile range of the scores of tooth sensitivity
intensity for each bleaching technique.
____________________________________________________________________________________________________
Tooth sensitivity
Groups Median (1
st
/3
rd
interquartile) P value*
____________________________________________________________________________________________________
At-home 1(0/2) 0.043
In-office 2 (1/3)
____________________________________________________________________________________________________
* Mann Whitney test.
from the in-office and at-home bleaching. None of the
participants from either bleaching technique complained of
tooth sensitivity at 2 years (P = 1.0).
Regarding tooth sensitivity intensity (Table 3), there was a
statistical difference between the bleaching therapies (P =
0.001). Most of the participants from the at-home group
experienced none to mild sensitivity, while most in the in-office
bleaching group experienced mild to moderate sensitivity.
Figure 2 shows the levels of sensitivity (%) perceived by the
participants for both groups during the treatment. At 2 years,
none of the participants reported tooth sensitivity.
Ten subjects (33.3%) from the in-office group and 18
subjects (60%) from the at-home group consumed at least one
kind of staining beverage every day. Only one subject from the
in-office group and three subjects from the at-home group were
daily smokers. From the in-office group, one subject reported
using a new bleaching agent after treatment and none of them
202 Tay et al
Table 4. Behavior of participants throughout the 2 years after the end of the
bleaching therapy.
____________________________________________________________________________________________________
2-year evaluation
______________________________________
Parameter At-home In-office
____________________________________________________________________________________________________
Daily staining beverage consumption
Yes 18 (60%) 10 (33.3%)
No 12 (40%) 20 (66.7%)
Daily frequency of staining beverage intake
None 12 (40%) 20 (66.7%)
Once a day 5 (16.7%) 9 (30%)
Two or three times a day 13 (43.3%) 1 (3.3%)
Four or more times a day 0 (0%) 0 (0%)
Daily smoker
Yes 3 (10%) 1 (3.3%)
No 27 (90%) 29 (96.7%)
Tooth bleaching repeated
Yes 0 1 (3.3%)
No 30 (100%) 29 (96.7%)
Use of whitening toothpastes
Yes 4 (13.3%) 0
No 26 (86.7%) 30 (100%)
____________________________________________________________________________________________________
used tooth whitening paste, while in the at-home group none of
the subjects reported using a new bleaching agent, and four
(13.3%) subjects used a whitening toothpaste. Details of the
daily frequency of staining beverage and subject behavior are
shown in Table 4.
Discussion
Investigators have used different methodological
approaches to assess tooth shade and changes in tooth shade
resulting from bleaching treatments.
19
Recently, digital systems
(spectrophotometers, colorimeters or digital cameras) have
been used to measure tooth shades. These systems express
color in three-dimensional specifications and allow for more
accurate assessments. These digital systems are precise
instruments that produce highly reliable, easily evaluated
results. High cost and complex operation could be unique
disadvantages for some of these methods.
19,20
A recent study
7
evaluating the validity and reliability of
visual assessment of tooth color using a commercial shade
guide (Vitapan Classical shade guide) reported that despite its
subjectivity such visual assessment was a valid method, with
good reliability in differentiating between dark and light colors.
Other clinical studies
8,21-24
comparing the color change after
different bleaching techniques using a subjective method (shade
guide) and an objective method (spectrophotometer) usually
reported similar outcomes with both evaluation methods. In the
present study, the shade guide was used for color change
evaluation because it is an easy, fast and reliable method
supported by the literature.
14,25,26
The results of the present investigation showed that both
techniques were effective and reached similar results when
used following their respective protocols. At the end of the
treatment, a mean variation of 6.2 and 5.6 SGUs were observed
for the in-office and at-home techniques, respectively. Auschill
et al
6
showed that at-home bleaching with 10% carbamide
peroxide gel and in-office bleaching with 35% hydrogen
peroxide lightened teeth six shades on the Vita color scale,
which is in line with the present investigation and other
studies.
17,24,27,28
American Journal of Dentistry, Vol. 25, No. 4, August, 2012
The efficacy of a bleaching technique depends on the
concentration of the hydrogen peroxide and the application
duration.
19,29
However, the relationship between hydrogen
peroxide concentration and application time is not linear but
exponential.
30
This explains why for the 16% carbamide
peroxide ( 5% hydrogen peroxide) a 4-week treatment with at
least a 6-hour daily use ( a total of 168 hours) was required to
reach the same whitening effect produced by an overall 1½-
hour treatment time using of the 35% hydrogen peroxide gel.
This exponential relation was recently demonstrated in a
laboratory setting and means that bleaching gels with a higher
peroxide concentration needed fewer applications/reduced time
to produce a similar bleaching effect.
30
To the extent of the authors’ knowledge, no study has
evaluated the longevity of whitening produced by bleaching
with 35% hydrogen peroxide for prolonged periods, i.e. more
than 1 year. Previous findings
9,31
have already reported color
rebound for at-home bleaching. Ritter et al
9
reported that 38
months after the end of at-home bleaching treatment, 62% of
the participants reported slight darkening. Leonard et al
31
found
a color rebound of two shade guide units over a period of time
ranging from 6 to 47 months with 10% carbamide peroxide,
which was similar to the findings of other clinical trials.
6,27
It is
widely reported that with in-office bleaching the color reverses
in a few days.
21,32,33
This E reversal was shown to be of the
order of 51% and 65% after 1 and 6 weeks post-bleaching,
respectively for eight in-office products.
33
Many aspects may account for this long-term color reversal.
The effect of staining produced by beverages and food is
usually believed as explanation for the slight darkening that
follows bleaching over time.
7
However one should consider
that this staining is usually extrinsic and although it may affect
the overall perception of whiter teeth, this can be easily
removed by professional cleaning. In the present investigation
none of the consumption parameters were shown to be
associated with the longevity of the treatment. These findings
do not necessarily mean that these parameters do not influence
the longevity of the whitening, since the study design was not
planned to detect such association. Further studies should
address this question.
Color rebound can also result from reversal of oxidative
reactions so that the shorter and lighter molecules produced by
the bleaching therapy return to their original configuration and
yellower color. Another explanation for the color rebound is the
fact that as teeth get older, there is a continuous deposition of
secondary dentin by the pulp.
34
As the dentin thickness
increases, teeth appear yellower. Unfortunately, the length of
time that it takes to change one Vita shade tab due to deposition
of secondary dentin is unknown and may take longer than the
period of 2 years of the current study. Future studies need to be
done to test this hypothesis.
Surprisingly, however, the present investigation reported
that both techniques achieved stable results at the 2-year recall.
A 2-year follow-up may be a short recall time to detect the
effects of continuous deposition of secondary dentin on the
outcome of bleaching.
Another interesting finding of the present investigation was
that this study challenged the widespread concept that the at-
home bleaching may produce more long-lasting results than in-
American Journal of Dentistry, Vol. 25, No. 4, August, 2012
office bleaching, which is in agreement with a 9-month follow-
up study.
13
The result observed immediately after in-office
bleaching is the sum of the oxidative processes, tooth
dehydration and demineralization. When the immediate
bleaching result is compared to the color measured some weeks
later, an unrealistic color reversal is usually reported,
33
but this
does not mean ineffective bleaching, since it is due to
remineralization
35
and rehydration that occurs after each
bleaching session. It is known that isolation can cause the teeth
to dehydrate, and it takes at least 30 minutes for teeth to
rehydrate.
36
Also, most of the bleaching gels possess an acidic
pH ranging from 2.4 to 6.2 and therefore teeth are also
demineralized by the bleaching gels.
37,38
In order to gather more stable results with less color
reversal, more than one clinical session may be required and
this seems to be the key feature for the long-lasting results of
the present study. According to Shethri et al
32
only after a
second session of in-office bleaching treatment, tooth lightness
improved significantly. Therefore, a single in-office treatment
with 35% hydrogen peroxide seems to be not enough to bleach
teeth to the same rate of the well-accepted at-home technique.
33
Tooth sensitivity is the most common adverse side effect of
bleaching and according to Leonard et al
39
25-75% of subjects
receiving the active bleaching ingredient experience tooth
sensitivity. In the present study it was observed that the
incidence of tooth sensitivity in the at-home and in-office
bleaching was similar, which is in agreement with others.
21,24
However, significant differences were observed between
techniques when the intensity of tooth sensitivity was compared
as well as in a previous study.
8
While most of the participants
from the at-home bleaching experienced none to mild
sensitivity, most of the participants from in-office group
reported mild to moderate sensitivity.
Cooper et al
40
showed that a very fast passage of hydrogen
peroxide occurs through the dental structure; within 15 minutes
after application, hydrogen peroxide can be detected at the
pulp. Thus, using a higher hydrogen peroxide concentration,
there may be larger amounts of reactive species arriving to the
pulp, leading to a more intense inflammatory response and
tooth sensitivity. A previous laboratory study
41
demonstrated
that the cytotoxicity of carbamide peroxide bleaching gels was
dose-dependent, with the highest concentration causing the
most intense cytopathic effects to the cultured cells.
None of the participants from both bleaching techniques
reported tooth sensitivity in the 2-year recall. Generally, tooth
sensitivity caused by at-home bleaching occurs in the first 2
weeks of treatment,
42
often in the first few days and decreases
as the teeth are accustomed to the procedure, but occasional
single-day episodes of sensitivity may occur over the course
of the treatment.
42
For in-office bleaching, tooth sensitivity
usually occurs within the 24 hours following the bleaching
protocol.
8,17,43
The lack of tooth sensitivity after long-term
evaluation seems to be consistent in the literature. Most of the
studies that evaluated the longevity of tooth bleaching
reported that subjects did not report tooth sensitivity after the
end of the bleaching.
44
In the present study tooth sensitivity was assessed using a 5-
point numerical rating scale (NRS) as this has been used for
tooth sensitivity evaluation in the great majority of the clinical
Clinical efficacy of tooth bleaching 203
trials involving bleaching and therefore allows comparison with
the earlier results.
12,14,17,21,23,32,45
The other common scale for
tooth sensitivity evaluation is the visual analog scale
(VAS).
6,8,24,43
Although we have not found in the bleaching
literature any study that compared the VAS and 5-point NRS,
some earlier studies pointed out that both scales yield similar
results.
46,47
This lack of comparison between these two scales
should be the focus of future investigations regarding tooth
sensitivity from bleaching therapies.
It is worth mentioning the limitations of the present study.
The fact that the participants were taken from a convenient
sample (participants seeking professional dental treatment) may
lead to bias, since they are much more motivated than
participants taken from outside the school. In addition, most of
the participants were young adults, which affect the
generalizability of the findings of the present investigation to
the overall population.
In summary, both techniques were effective to whiten teeth
and produced long-lasting and satisfactory results. Thus, the
choice of the bleaching technique depends on the professional
as well as patient preferences. At-home and in-office bleaching
are effective protocols for vital teeth bleaching, however a
higher intensity of tooth sensitivity was reported for in-office
bleaching.
a. Vita Zahnfabrik, Bad Säckingen, Germany.
b. FGM Dental Products, Joinville, SC, Brazil.
c. Colgate-Palmolive Company, São Paulo, SP, Brazil.
Disclosure statement: The authors declared no conflict of interest.
Dr. Tay and Dr. Kose are graduate students, and Dr. Reis and Dr. Loguercio are
Adjunct Professors, Department of Restorative Dentistry. School of Dentistry.
State University of Ponta Grossa, Paraná, Brazil; Dr. Herrera is a graduate
student, Department of Restorative Dentistry, Endodontics. School of Dentistry
of Piracicaba. State University of Campinas, Campinas, São Paulo, Brazil.
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