Gingival irritation in patients submitted to at-home bleaching with different cutouts of the bleaching tray: a randomized, single-blind clinical trial

Abstract

Objectives
This split-mouth randomized, single-blind clinical trial evaluated the gingival irritation (GI) of at-home bleaching with individual trays of different cutouts, as well as the tooth sensitivity (TS) and color change.

Materials and methods
One hundred and twenty patients were randomized as to which side would receive the type of bleaching tray cutout: scalloped (in the gingival margin) and nonscalloped (extended from the gingival margin). The at-home bleaching was performed for 30 min with 10% hydrogen peroxide (HP) for 2 weeks. The absolute risk and intensity of GI and TS were assessed with a visual analog scale. Color change was assessed using a digital spectrophotometer and a color guide (α = 0.05).

Results
The proportion of patients who experienced GI was 57.5% (odds ratio 95% CI = 1.1 [0.7 to 1.8]), with no significant difference between groups (p = 0.66). The proportion of patients who experienced TS was 64.1% (odds ratio 95% CI = 1.0 [0.6 to 1.6]), with no significant difference between groups (p = 1.0). There is equivalence of scalloped and noscalloped groups for GI intensity (p < 0.01). Significant whitening was detected for both groups. Although some differences were observed between groups (CIELab and CIEDE00; p < 0.02), these were below of the considered clinically noticeable.

Conclusions
The different cutouts of trays proved to be equivalent when regarding gengival irritation and tooth sensitivity when 10% HP for at-home bleaching was used. Significant color change was observed in both groups. However, significant differences detected between groups are not considered clinically noticeable.

Trial registration
Brazilian Clinical Trials Registry (RBR-2s34685).

Clinical relevance
Scalloped or not, the individual trays for at-home bleaching could be considered a clinician’s decision.

Full text

Vol.:(0123456789)
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Clinical Oral Investigations
https://doi.org/10.1007/s00784-022-04401-4
ORIGINAL ARTICLE
Gingival irritation inpatients submitted toat‑home bleaching
withdifferent cutouts ofthebleaching tray: arandomized,
single‑blind clinical trial
TaynaraS.Carneiro1· MichaelW.Favoreto1· LaísG.Bernardi1· ElisamaSutil1· MichelWendlinger1·
GabrielleG.Centenaro1· AlessandraReis1· AlessandroD.Loguercio1
Received: 28 October 2021 / Accepted: 1 February 2022
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2022
Abstract
Objectives This split-mouth randomized, single-blind clinical trial evaluated the gingival irritation (GI) of at-home bleach-
ing with individual trays of different cutouts, as well as the tooth sensitivity (TS) and color change.
Materials and methods One hundred and twenty patients were randomized as to which side would receive the type of
bleaching tray cutout: scalloped (in the gingival margin) and nonscalloped (extended from the gingival margin). The at-
home bleaching was performed for 30min with 10% hydrogen peroxide (HP) for 2weeks. The absolute risk and intensity
of GI and TS were assessed with a visual analog scale. Color change was assessed using a digital spectrophotometer and a
color guide (α = 0.05).
Results The proportion of patients who experienced GI was 57.5% (odds ratio 95% CI = 1.1 [0.7 to 1.8]), with no sig-
nificant difference between groups (p = 0.66). The proportion of patients who experienced TS was 64.1% (odds ratio
95% CI = 1.0 [0.6 to 1.6]), with no significant difference between groups (p = 1.0). There is equivalence of scalloped
and noscallopedgroups for GI intensity (p < 0.01). Significant whitening was detected for both groups. Although some
differences were observed between groups (CIELab and CIEDE00; p < 0.02), these were below of the considered clini-
cally noticeable.
Conclusions The different cutouts of trays proved to be equivalent when regarding gengival irritation and tooth sensitiv-
itywhen 10% HP for at-home bleaching was used. Significant color change was observed in both groups. However, significant
differences detected between groups are not considered clinically noticeable.
Trial registration Brazilian Clinical Trials Registry (RBR-2s34685).
Clinical relevance Scalloped or not, the individual trays for at-home bleaching could be considered a clinician’s decision.
Keywords Bleaching tray· Hydrogen peroxide· Gingival irritation· Clinical trial
Introduction
Smile harmony is considered an important aspect of patients’
general appearance. Therefore, many patients who seek to
achieve it request bleaching procedures. This is the main
reason for these procedures’ growing popularity [1, 2]. In
a study that evaluated quality of life associated with tooth
bleaching, the number of patients dissatisfied with their
appearance decreased significantly after undergoing tooth
bleaching [3].
Among the techniques used to bleach vital teeth, the most
common is at-home bleaching, which consists of the applica-
tion of bleaching agents in low concentrations in individual
trays used by the patient outside the office environment
[4–6]. This technique reduces the clinical time in contact
with the patient, which reduces costs [5]. Furthermore, it is
considered the safest technique because at-home bleaching
uses low-concentration hydrogen peroxide (HP) [7], whereas
in-office bleaching techniques use higher concentrations of
HP [8, 9]. However, adverse effects are common among
* Alessandro D. Loguercio
aloguercio@hotmail.com
1 Department ofRestorative Dentistry, School ofDentistry,
State University ofPonta Grossa, Rua Carlos Cavalcanti,
4748 Bloco M, Sala 64-A, Uvaranas,PontaGrossa,
PR84030-900, Brazil
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Clinical Oral Investigations
1 3
patients, with tooth sensitivity (TS) and gingival irritation
(GI) being the most prevalent [10–12].
GI can be caused by direct contact of the bleaching gel
with soft tissues, where, due to its HP content, it has caustic
potential [13], and it may cause gingival burns and ulcera-
tions [13, 14]. These side effects are directly related to the
concentration of the bleaching gel and application time [15].
Poorly adjusted (i.e., nonscalloped) trays also influence GI
due to the trauma caused by contact with soft tissues [4, 15].
Many improvements have been proposed for the individual
trays used in at-home bleaching; among these are changes to
the type of material, the design of the trays, or the presence of
reservoirs [5, 7, 16, 17]. However, specifically in relation to
individual trays cutouts, there is no consensus in the literature.
Some authors have recommended that tray cutouts be designed
to skirt the gingival margin to create minimal mechanical con-
tact between the tray edge and the gingival tissue [5]. In addi-
tion, in this type of cutout, the excess of the extravasated prod-
uct is easily removed, reducing contact time with the gingival
tissue [7]. However, other authors have recommended that the
tray extend slightly over the gingival margin (nonscalloped)
without going around it [17]. In this way, it can act as an exter-
nal barrier, reducing contact between the bleaching gel and
saliva [18]. From a technical point of view, nonscalloped trays
such those used when performing an extension are easier to use
than trays that go around the gingival margin [17]. However,
only one clinical study found that tray cutouts (scalloped or
nonscalloped) did not assess GI [17].
Therefore, the aim of this single-blind, controlled, split-mouth
randomized clinical trial was to evaluate GI in various individ-
ual scalloped and nonscalloped trays (Fig.1), as well as TS and
bleaching effectiveness. The following null hypotheses were
tested: (1) the use of two (scalloped and noscalloped) customized
tray cutouts will not affect the absolute risk and intensity of GI
induced by at-home bleaching, (2) the use of two (scalloped and
noscalloped)customized tray cutouts will not affect the absolute
risk and intensity of TS induced by at-home bleaching, and (3)
the use of two (scalloped and noscalloped) customized tray cut-
outs will not affect color change after at-home bleaching.
Materials andmethods
Study design
This was a randomized, single-blind (evaluators), split-mouth,
equivalence trial with an equal allocation rate between groups.
This clinical trial was approved by the Local University Ethics
Committee (4.383.682) and it was registered in the Brazil-
ian Clinical Trials Registry (RBR-2s34685). This study was
prepared using the protocol established by the Consolidated
Standards of Reporting Trials statement, with extension
for noninferiority and equivalence trials and within-person
designs [19, 20]. This study was performed between January
2021 and July 2021 in the clinics of the school of dentistry at
the State University of Ponta Grossa, PR, Brazil.
Recruitment
Patients for this clinical trial were recruited through social
media. Volunteers that met the eligibility criteria read and
signed an informed consent form before being enrolled in
the study. To facilitate communication between the research
staff and the volunteers, we set up a social network group
via WhatsApp®.
Eligibility criteria
Patients included in this clinical trial were at least 18years
old, in good general and oral health, with anterior teeth free
of carious lesions, gingival recession, and periodontal dis-
ease, and with both canines with A2 or darker as judged by
comparison with a value-oriented shade guide (Vita Clas-
sical, Vita Zahnfabrik, Bad Säckingen, Germany; Fig.2).
Participants with anterior restorations or a dental prosthesis,
orthodontics apparatus, or severe internal tooth discoloration
(tetracycline stains, fluorosis, and pulpless teeth) and who
had previously undergone tooth bleaching procedures were
not included in the study. In addition, lactating/pregnant
women, participants with any other pathology that could
cause sensitivity (dentin exposure, such as recession or the
presence of visible cracks in teeth), habits such as bruxism,
or smokers were also excluded from this study [21, 22].
Sample size calculation
The primary outcome of this study was to assess the abso-
lute risk of gingival irritation from at-home bleaching
with HP, which was reported in approximately 29% in a
systematic review of randomized clinical trials [4]. For a
29% of gingival irritation in the control group and with a
20% equivalence limit, a minimum of 112 volunteers per
group was required with 90% study power and 5% alpha.
Fig. 1 Different designs used in the trays (left - scalloped and right -
nonscalloped)
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Clinical Oral Investigations
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A sample size of 120 volunteers was used to compensate
for any losses to follow-up.
Random sequence generation andallocation
concealment
Simple randomization was performed using a software pro-
gram freely available online (www . seale denve lope. com). For
each patient, the first group was randomized in one of the
two groups, and it was always applied to the patient’s right
hemi-arch. The name of each group was placed in a sealed
and opaque envelope, sequentially numbered. Randomiza-
tion and blinding were performed by a person not involved
in the research protocol. The allocation of the groups was
revealed with the opening of the envelopes minutes before
the delivery of the trays, in which the operator opened the
sealed envelope that defines the group in which the volunteer
is, and only then was the cutout made.
Blinding
This was a single-blind study in which only the evaluator did
not know the designation of the groups because he had not
participated in the study’s randomization and implementa-
tion process. Due to the tray test and demonstration of the
bleaching procedure, the operator and the participant could
not be blinded.
Study intervention
Three dentists with more than 5years of clinical experi-
ence performed the bleaching procedure. Participants were
instructed to perform prophylaxis prior to the intervention.
Two weeks before the start of the bleaching procedure, algi-
nate impressions were taken from the maxillary arch of each
participant (Avagel, Dentsply Sirona, Konstanz, Germany)
and after disinfection, the molds were leaked with a stone
plaster (Asfer, Asfer Chemical Industry Ltd., São Caetano
do Sul, SP, Brazil). From the plaster models, individual
trays were made with 1mm thick ethylene–vinyl acetate
(Whiteness Tray Plates, FGM, Joinville, SC, Brazil), in a
vacuum plasticizer (Plastivac P7, BioArt, São Carlos, SP,
Brazil).
The confection and cutout of the tray were performed by
a person who had no contact with the patient on the day of
delivery of the tray, and the cutout was performed only after
opening the envelope with the randomization of patients.
After performing the cutout that each side received (scal-
loped [23] [slightly below the gingival margin] or nonscal-
loped [23] extended from the gingival margin 2mm above
the cervical region of the canine [straight in the horizontal
direction]) (Fig.1), the trays were tested to ensure that they
were fully adapted in the patient’s dental arches and any
initial discomfort described by the patient was corrected.
Next, a syringe of 10% HP bleaching gel (White Class
Calcium 10%, FGM, Joinville, Brazil) was delivered to both
groups. Participants were instructed to use the bleaching gel
once a day for 30min for 14days. They were instructed to
dispense a drop of the product in the region corresponding
to the buccal surface of each tooth in the tray and in case
of extravasation, the excess should be removed. The entire
sequence was demonstrated by the research operator and
a video was sent on the social network WhatsApp® with
the aim of solving supposed doubts during the treatment.
The amount of gel used by research participants was 1.3g
per week on average (data not shown). After the bleach-
ing period, in order for the bleaching gel to be completely
removed, the instruction was given to remove the tray and
give a vigorous rinse with water, as well as to use dentifrices
without desensitizers and without bleaching agents for daily
brushing.
Gingival irritation (GI) evaluation
The GI was recorded using the visual analog scale (VAS;
0–10), where participants received a diary that corre-
sponded to 14days of treatment, being 0 = no irritation
and 10 = severe irritation [22, 24]. The participants were
instructed to record the GI, even if there was no irrita-
tion, marking with a vertical line the value corresponding
to the intensity of their GI, which was later measured in
Fig. 2 Canine color assessment
with subjectivescales
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Clinical Oral Investigations
1 3
centimeters with the aid of a millimeter ruler [24]. The worst
scores from the VAS weekly and during all bleaching treat-
ments were considered for statistical purposes, so that only a
single value was taken from the 2-week treatment. The val-
ues were arranged into two categories: absolute risk of GI,
which represented the percentage of patients who reported
GI at least once during treatment, and the GI intensity (first
and second week and worst overall scenario). Participants
received all the guidelines for a better perception and greater
description of the results in relation to GI.
Tooth sensitivity (TS) evaluation
Similar to GI, TS was recorded using the VAS (0–10), where
participants will receive a diary corresponding to the 14days
of treatment, being 0 = no sensitivity and 10 = severe sen-
sitivity [24, 25]; the participants were instructed to record
the worst result once a day, even if there was no sensitivity,
marking with a vertical line the value corresponding to the
intensity of their tooth sensitivity, which was later meas-
ured in centimeters with the aid of a millimeter ruler. The
worst scores from the VAS during all bleaching treatments
were considered for statistical purposes, so that only a single
value was taken from the 2-week treatment. The values were
arranged into two categories: absolute risk of TS, which rep-
resented the percentage of patients who reported TS at least
once during treatment, and the TS intensity (first and second
week and worst overall scenario). Participants received all
the guidelines for improving the description of the results
in relation to TS.
Color evaluation
The color was registered before and after 30days of the
end of the treatment. The color evaluation was carried out
through the subjective (Vita Classical and Vita Bleached-
guide 3D-MASTER; Vita Zahnfabrik) and objective (Vita
Easyshade spectrophotometer; Vita Zahnfabrik) methods.
Color evaluation was done in a room under artificial lighting
conditions without interference room outside light. For both
devices, color was checked at the middle third of the right
and left upper canines [21, 22].
The value-oriented Vita Classical color scale (Vita Zahn-
fabrik) consists of 16 color guides, arranged from the high-
est (B1) to the lowest (C4) [25, 26], and the Vita Bleached-
guide 3D-MASTER scale (Vita Zahnfabrik) is a proper
tooth bleaching scale, containing lighter colored tabs, being
arranged from the highest value (0M1) to the lowest (5M3)
[10, 24]. The evaluation of color change was performed
through the variation of Vita scale units (ΔSGU) organized
by value [10, 21].
For the objective evaluation, the Vita Easyshade spec-
trophotometer (Vita Zahnfabrik) was used, according to the
CIEL*a*b* system [9, 22] where L* represents the light-
ness value from 0 (black) to 100 (white), and a* and b*
represent the color, where a* is the measurement along the
green–red coordinate and b* is the measurement along the
blue-yellow coordinate. Through the spectrophotometer,
these values were provided and the device was calibrated
before each measurement. To standardize the measurement
of objective color, an impression of the upper arch of the
participants with condensation silicone (Perfil, Coltene, Rio
de Janeiro, RJ, Brazil) was performed to make a guide in
the upper anterior teeth. The matrix was perforated with
the aid of a 6-mm-diameter circular scalpel (Biopsy Punch,
Miltex, York, NJ, USA), similar to the active tip of the Vita
Easyshade spectrophotometer, in the vestibular region, in the
middle third, of the upper canines right and left. The differ-
ence between the colors registered before and 30days after
the end of the treatment was calculated using the formulas:
∆Eab = [(∆ L*)2 + (∆a*)2 + (∆b*)2]1/2 [27], ∆E00 = [(ΔL /
kLSL)2 + (ΔC / kCSC)2 + (ΔH / kHSH)2 + RT (ΔC*ΔH /
SC*SH)]1/2 [28], and ΔWID = (0.511L*) − (2.3424a*) − (1
.100b*) [29].
The two evaluators were calibrated before the study pre-
senting superior color-matching competency according to
the revisedISO/TR 28,642 [30]. This represents that they
had an agreement of at least 85% (kappa statistic) before
the start of the study evaluation (85% of correctly matched
pairs of tabs in shade guides). In case of disagreement dur-
ing the evaluation, they needed to reach a consensus before
the participant was dismissed.
Statistical analysis
The analysis followed the intention-to-treat protocol and
involved all participants who were randomly assigned [31].
The statistician was blind to the assessment of the groups.
The absolute risk of GI of both groups was compared using
the McNemar test. Odds ratios were also calculated, as well
as the 95% confidence interval (CI) and the Spearman cor-
relation was calculated. Two one-sided t-tests for paired
samples (TOST-P) were used to test the equivalence of
the study groups at the different assessment points for GI.
Such an approach includes a right-sided test for the lower
margin of the equivalence limit and a left-sided test for the
upper margin using one-sided 0.025 significance levels. The
overall p-value is taken to be the larger of the two p-values
from the lower and upper tests. Mean difference and 95%
CI were calculated between groups at each time assessment.
If both treatments differ by more than 2.0 units VAS inten-
sity in either direction, then equivalence does not hold. A
traditional Student’s paired t-test and the Pearson’s correla-
tion were employed for intensity ofGI to detect differences
between groups for each time (first and second week and
worst overall scenario).
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Clinical Oral Investigations
1 3
The absolute risk of TS of both groups was com-
pared using the McNemar test. Odds ratios were also
calculated, as well as the confidence interval (CI) and
the Spearman correlation were calculated. TS intensity
was analyzed using traditional Student’s paired t-test
and the Pearson correlation was calculated to detect
differences between groups for each time (first and sec-
ond week and worst overall scenario). Color change
between groups was compared using Student’s paired
t-test for the different instruments. In all statistical
tests, the alpha was preset at 5%.
Results
Characteristics ofincluded participants
Two hundred three participants were examined, and 120
of these were included in the clinical study (Fig.3).
Table1 outlines the baseline color of the participants’
teeth and the distribution of their genders and ages. In the
present study, no loss of participants was observed during
follow-up (Fig.3).
Gingival irritation
A little more than half of participants (57.5%) felt some dis-
comfort during treatment. Forty-eight participants reported
irritation in the nonscalloped group, and all participants
reported irritation in the scalloped group. Forty-eight par-
ticipants reported irritation in the scalloped group, and 12
reported no irritation in the nonscalloped group. Fifty-one
participants reported irritation on either arch side. In rela-
tive terms, the odds ratio for irritation was 1.1 (0.7 to 1.8;
Table2), so it did not reach statistical significance (p = 0.66).
The Spearman correlation coefficient for pairs of binary data
was moderate and significant (r = 0.65; p < 0.001).
Fig. 3 The CONSORT flow diagram of study design phases including enrollment and allocation criteria
Table 1 Baseline characteristics of the participants included in this
clinical trial
Abbreviations: SGU, shade guide unit measured by Vita Classical
scale
Groups (number of patients) Nonscal-
loped
(n = 120)
Scalloped (n = 120)
Baseline color (SGU; mean ± SD) 9.2 ± 2.8 9.4 ± 2.9
Gender (female; %) 73 (61%)
Average age (years; female/male) 25.3/24.6
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Clinical Oral Investigations
1 3
The TOST test demonstrated the equivalence of GI inten-
sity using a VAS. The two-sided 95% CI of the difference
between the means is within the predetermined equivalence
margins of − 2.0 and + 2.0 for VAS scale units. Statistical
analysis showed no significant difference in GI intensity in
the worst-case scenario in the first week (p = 0.57; Table3),
as well as in the second week (p = 0.05; Table3) and in
the worst-case overall (p = 0.52; Table 3). The mean dif-
ference in irritation intensity was, on average, 0.1 units for
the worst-case scenario in the second week and worst-case
scenario overall, and 0.06 for the worst-case scenario of the
first week, which was far from clinically important. Irritation
was positively correlated in both groups (Table3). Pearson’s
correlation was 0.78 (p < 0.001) for the worst-case scenario
in the first week and 0.79 (p < 0.001) for the worst-case sce-
nario in the second week and worst-case overall.
Tooth sensitivity
The majority of participants (64.1%) felt some discomfort
during treatment. Sixty-two participants reported TS in the
nonscalloped group, and all participants reported TS in the
scalloped group. Sixty-two participants reported TS in the
scalloped group and seven reported no TS in the nonscal-
loped group. Forty-three participants reported no TS on
either arch side. In relative terms, the odds ratio for TS was
1.0 (0.6 to 1.6; Table4), so it did not reach statistical sig-
nificance (p = 1.0). The Spearman correlation coefficient for
pairs of binary data was moderate and significant (r = 0.74;
p < 0.001).
Statistical analysis showed no significant difference in
TS intensity in the worst-case scenario in the first week
(p = 0.84; Table5), as well as in the second week (p = 0.61;
Table5) and in the worst-case overall (p = 0.35; Table5).
The mean difference in TS intensity was, on average, 0.02
units for the worst-case scenario in the first week, 0.04 units
for the worst-case scenario in the second week, and 0.07
units for the worst-case scenario overall. This difference was
far from being clinically important. TS was positively cor-
related in both groups (Table5). Pearson’s correlation was
0.83 (p < 0.001) for the worst-case scenario in the first week,
0.80 (p < 0.001) for the worst-case scenario in the second
week, and 0.85 (p < 0.001) for the worst-case overall.
Color change
The initial tooth color means in the treatment groups were
similar (Table1). The subjective and objective evaluations
showed a statistically significant degree of bleaching after
a 30-day evaluation period for both groups, with approxi-
mately 6 units on the Vita Classical scale (Fig.2), 7 units on
the Vita Bleachedguide, 9 units in the ∆Eab, 6 units in ∆E00,
and 12 units in the ∆WID (Table6). There was a signifi-
cant difference between the ΔEab and ΔE00 groups (Table6;
p < 0.02). The other groups evaluated showed no significant
difference (Table6; p > 0.09).
Table 2 Matched tabulation of the absolute risk of gingival irritation
for both groups along with the odds ratio and 95% confidence interval
(CI)
McNemar’s test (p = 0.66); Spearman’s correlation between paired
data (r = 0.65; p-value < 0.001)
Scalloped Odds ratio
(95% CI)
Positive Negative Total
Nonscalloped Positive 48 9 57 1.1 (0.7 to 1.8)
Negative 12 51 63
Total 60 60 120
Table 3 Means and standard deviations of intensity of gingival irritation for both groups and mean difference (95% confidence interval [CI]) and
correlation coefficient
* The p-value reported is the larger of the two p-values from the upper and lower one-sided tests (TOST test); **paired t-test
Main factor time Nonscalloped Scalloped Mean difference (95% CI) Equivalence (p-value)** p-value** Correlation
coefficient
(p-value)
First week 0.8 ± 1.8 0.8 ± 1.7 0.06 (− 0.1 to 0.3) Yes; p < 0.01 0.57 0.78; p < 0.0001
Second week 0.5 ± 1.3 0.4 ± 1.1 0.1 (0.0 to 0.2) Yes; p < 0.01 0.05 0.79; p < 0.0001
Worst overall scenario 1.0 ± 1.9 0.9 ± 1.8 0.1 (− 0.1 to 0.3) Yes; p < 0.01 0.52 0.79; p < 0.0001
Table 4 Matched tabulation of the absolute risk of tooth sensitivity
for both groups along with the odds ratio and 95% confidence interval
(CI)
McNemar’s test (p = 1.0); Spearman’s correlation between paired data
(r = 0.74; p-value < 0.001)
Scalloped Odds ratio
(95% CI)
Positive Negative Total
Nonscalloped Positive 62 8 70 1.0 (0.6 to 1.6)
Negative 7 43 50
Total 69 51 120
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Clinical Oral Investigations
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Discussion
This study was conducted to verify whether the scalloped
at-home bleaching tray using 10% HP for 30min per day
generates more GI when compared with nonscalloped
trays. For the study, a paired split-mouth design was cho-
sen, which removed the inter-individual variability from
the estimates of the treatment effect [32] and eliminated
the need for a large sample size. As far as the authors are
aware, this is the first well-designed study focused on com-
paring the two types of cutouts and proving that there was
no difference between them for all parameters evaluated
when 10% HP gel was used.
The presence of GI resulting from tooth bleaching can be
measured using reports of pain in the gingival tissue, which
may present burns or ulcerations [13, 14]. The study’s find-
ings indicated no significant differences in the risk of GI
for the different tray cutouts. Although the scalloped group
had a risk of 50%, the nonscalloped group’s risk was 47.5%.
These results are unexpected because the nonscalloped cut-
out extends over the gingival tissue and provides better seal-
ing for the tray [5], reduces the chance of excess bleaching
gel being removed, and thus maintains contact with the gum.
It has been reported that the bleaching agent that overflows
from the tray used in the at-home bleaching technique can
be ingested by the patient [7]. In this way, a nonscalloped
tray design, by being extended, acts as an external barrier
and reduces contact between the gel and saliva [18], being a
good option to avoid this ingestion.
However, on the other side, the scalloped cutout does
not keep the gel in contact with the soft tissues because,
in addition to the tray being cut slightly below the gingi-
val margin, the excess extravasated gel is easily removed
[7]. In a prior study, 25 to 30% of all participants had to
remove excess gel each time they underwent the procedure
[33]. Therefore, the excess whitening gel that overflows
from the tray is easily removed from the scalloped cutout
tray, but it remains in the nonscalloped cutout tray.
As pointed out in the “Introduction” section, only one
clinical study that evaluated different tray contours did not
assess GI, making difficult the comparison with literature
[17]. However, recently 10% HP gels available in prefilled
disposable tray have been launched in the market. In com-
parison with traditional bleaching trays, prefilled dispos-
able tray systems have a low cost, as the professional does
not need to fabricate a bleaching custom tray (impression,
model buildup, tray fabrication). However, as only one size
is available for all kind of patients and no cutout is recom-
mended by the manufacturer, it could be considered a type
of nonscalloped tray [10, 26, 34].
A closer view in the literature showed controversial
results when prefilled disposable trays were compared with
traditional scalloped trays [10, 26, 34]. In one clinical study
[26], higher GI for prefilled disposable trays was shown
when compared with traditional scalloped trays, and in
another clinical study, higher GI was observed for traditional
scalloped trays when compared with prefilled disposable
trays [10]. Also, the absolute risk of GI varies from 33–34%
[26, 34] to 75% [10] in these different clinical studies. For
instance, in the present study, approximately 57.5% of the
patients reported GI. In Cordeiro’s study [10], this number
increased for 75%. These differences could be related to
characteristics that differ between patients. A closer view of
Table 5 Means and standard
deviations of intensity of tooth
sensitivity for both groups
and mean difference (95%
confidence interval [CI]) and
correlation coefficient
* Paired t-test
Main factor time Nonscalloped Scalloped Mean difference (95% CI) p-value* Correlation
coefficient
(p-value)
First week 0.8 ± 1.5 0.8 ± 1.4 0.02 (− 0.1 to 0.2) 0.84 0.83; p < 0.0001
Second week 0.6 ± 1.2 0.5 ± 1.2 0.04 (− 0.1 to 0.2) 0.61 0.80; p < 0.0001
Worst overall scenario 1.0 ± 1.6 0.9 ± 1.5 0.07 (− 0.1 to 0.2) 0.35 0.85; p < 0.0001
Table 6 Means and standard
deviations of obtained from
color change and the mean
difference (95% confidence
interval [CI]) baseline vs.
1month
* Paired t-test
Color evaluation tool Groups Mean difference (95% CI) p-value*
Nonscalloped Scalloped
Vita Classical (ΔSGU) 6.3 ± 2.2 6.4 ± 2.2 − 0.1 (− 0.2 to 0.02) 0.09
Vita Bleachedguide (ΔSGU) 7.5 ± 3.2 7.5 ± 3.2 − 0.1 (− 0.3 to 0.1) 0.51
CIELAB (ΔEab)9.7 ± 4.1 9.0 ± 3.9 0.7 (0.1 to 1.3) 0.02
CIEDE (ΔE00)6.5 ± 3.1 5.9 ± 2.7 0.6 (0.2 to 1.1) 0.01
Whiteness Index (ΔWID)12.7 ± 7.7 11.9 ± 7.4 0.8 (− 0.6 to 2.1) 0.26
Content courtesy of Springer Nature, terms of use apply. Rights reserved.

Clinical Oral Investigations
1 3
Cordeiro’s study reveals that only adolescents (ages 12–18;
average 17years old) were included. In the present study,
young adults (> 18; average 25years old) were included.
Thus, it seems that younger people report more GI than
older people do, but future studies are necessary to prove
this hypothesis.
When comparing both tray cutouts, higher GI intensity
would also be expected for the nonscalloped group, mainly
because this tray design leads to greater contact between the
HP bleaching gel and the gingival tissues. However, based
on the results of the present study, this was not confirmed,
thus leading to accept the first null hypothesis. However,
GI intensity was usually mild (VAS = 1), which is in line
with observations from the other studies [26]. In addition,
GI disappeared immediately after the end of treatment in
the present study.
Together with GI, TS is among the most important
adverse effects of tooth bleaching described in the literature
[10–12]. Due to the low molecular weight of HP, it can eas-
ily penetrate enamel and dentin, reaching the pulp chamber
in a few minutes [35] and causing an inflammatory response
of the pulp [36] that leads a patient to report TS. The risk of
TS in the present study seemed to be higher (64.1%) for at-
home therapy. However, 10% HP, the highest-concentration
gel available for at-home bleaching, was applied. In com-
parison, Chemin etal. [25] reported a TS rate of 38% when
4% HP was applied versus 64% when 10% HP was used.
In general, the risk [25, 34, 37, 38] and intensity [25, 37,
38] of TS results observed in the present study are in line
with those of other studies that used similar HP concentra-
tions, and no significant difference was observed between
scalloped and nonscalloped trays, thus leading to accept the
second null hypothesis.
In this study, three tools were used to assess color change
in order to obtain a more reliable assessment. Spectropho-
tometry is an objective method that is less affected by the
variability and training of the observer [39]. The Vita Classi-
cal and Vita Bleachedguide 3D-MASTER scales used in this
study, as the most used in previous bleaching studies, facili-
tate comparisons between this study and previous research
[10, 25, 37]. Significant tooth bleaching was observed with
the use of HP 10%, similar to other studies [10, 25, 26, 37].
No significant difference in color change was detected in
the subjective evaluations (Vita Classical scale and Vita
Bleachedguide 3D-MASTER scale), regardless of the type
of tray used.
However, a greater whitening effect was detected for
the nonscalloped group compared to the scalloped group
when CIELab and CIEDE00 were applied, leading to partially
accepting the third null hypothesis. These results were unex-
pected because the tooth surface covered by both tray types
is identical. The study demonstrated a significant change in
color in both groups; although some significant differences
were observed between the groups, the color changes
between them were not necessarily clinically noticeable, as
the mean difference must be compared with the acceptability
and perceptibility of thresholds for dental color, as recom-
mended by Paravina etal. [40]. For the ∆Eab, the 50:50%
perceptibility threshold was 1.22 on average [40], which was
greater than the mean difference of 0.7 reported in this study,
and for ∆E00, the limit of 50:50% perceptibility threshold
was 0.81 units on average [40], which was also greater than
the mean difference of 0.6 reported in this study. Thus, for at
least half of the observers, these differences in color changes
that were detected when comparing the two evaluated groups
are not clinically noticeable.
However, it is worth mentioning that a new index has
recently been indicated for measuring the whiteness level of
tooth bleaching based on the CIELab color space [29]. The
Whiteness Index is a new formula that has a lower prob-
ability of error when evaluating whiteness [29]. When WID
was applied, no significant difference was observed between
the scalloped and nonscalloped groups. This index has been
introduced in the most recent clinical studies [16, 26] and
in the near future, it should be the most used measure of
whitening effects in clinical trials.
One limitation of this study relates to the use of bleach-
ing gel in only one concentration and commercial brand.
However, the bleaching gel used was of the highest con-
centration available for at-home bleaching. This means we
tested the worst-case scenario to evaluate the various tray
cutouts. Therefore, when lower concentrations of HP or car-
bamide peroxide are used, fewer adverse effects should be
expected. However, future studies are necessary to evaluate
this hypothesis.
Conclusions
The scalloped and nonscalloped cutouts proved equiva-
lent in terms of GI and TS for the highest-concentration
HP gel available for at-home bleaching. Significant color
change was observed in both groups; the color change in
some instruments was statistically significant; and it was
not clinically important because it was below the perceptible
threshold. Therefore, the choice of the individual tray cutout
for at-home bleaching should be at the clinician’s discretion.
Acknowledgements The authors would like to thank FGM Dental
Group for the generous donation of the bleaching products employed
in this study.
Funding This study was partially supported by the National Council
for Scientific and Technological Development (CNPq) under grants
303332/2017–4 and 308286/2019–7 and Coordenação de Aper-
feiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance
Code 001.
Content courtesy of Springer Nature, terms of use apply. Rights reserved.

Clinical Oral Investigations
1 3
Ethical approval The clinical investigation was approved (4.383.682)
by the scientific review committee and by the committee for the pro-
tection of human participants of the State University of Ponta Grossa
and was conducted in accordance with the protocol established by the
Consolidated Standards of Reporting Trials statement with extension
for within-person designs. All persons gave their informed consent
prior to their inclusion in the study. Details that might disclose the
identity of the subjects under study were omitted. It was registered in
the Brazilian Clinical Trials Registry (https:// ensai oscli nicos. gov. br)
under the identification number RBR-2s34685.
Declarations
Informed consent All persons gave their informed consent prior to
their inclusion in the study. Details that might disclose the identity of
the subjects under study were omitted.
Conflict of interest The authors declare no competing interests.
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