Effect of a 10% carbamide peroxide on wear resistance
of enamel and dentine: In situ study
Juliana Jendiroba Faraoni-Romanoa,*, Cecilia Pedroso Turssib, Mo ˆnica Campos Serraa
aDepartment of Restorative Dentistry, School of Dentistry of Ribeira ˜o Preto, University of Sa ˜o Paulo (USP), Ribeira ˜o Preto, Sa ˜o Paulo, Brazil
bLaboratory of Biomaterials Research, School of Dentistry, University of Uberaba (UNIUBE), Uberaba, Minas Gerais, Brazil
Appearance of the teeth is of great importance to patients that
seek esthetic treatments related to dental discoloration.
Among treatments, tooth bleaching has attracted the interest
of patients and dentists because it represents a non-invasive
option and is relatively simple to carry out.1At-home
bleaching technique, in particular, received worldwide accep-
percent carbamide peroxide is the bleaching agent most used
in this technique2as it is considered safe and effective.3As
whitening of vital teeth generally involves direct and frequent
contact of the bleaching agent with the outer enamel surface
andsometimeswith dentine foranextensiveperiodoftime,in
vitro studies have evaluated the effects of carbamide peroxide
texture,4–8mineral content,9–12chemical composition,6,13,14
and loss by toothbrushing abrasion.15
journal of dentistry 37 (2009) 273–278
a r t i c l e i n f o
Received 5 August 2008
Received in revised form
1 December 2008
Accepted 2 December 2008
10% carbamide peroxide
In situ study
a b s t r a c t
Objectives: This triple-blind, 2 ? 2 crossover in situ study, was undertaken to verify whether
the wear resistance of enamel and root dentine would be affected by bleaching with a 10%
carbamide peroxide agent and a placebo agent.
Methods: Thirty slabs of each substrate (2 mm ? 3 mm ? 2 mm) were selected for each
phase, after flattening and polishing procedures and microhardness test. After a 7-day
each one of 30 subject’s upper second premolars. The volunteers received instructions on
how to perform toothbrushing and applicationof gel in the tray. Fifteen volunteers bleached
their maxillary arch with a 10% carbamide peroxide bleaching agent for a 2-week period,
while the remainders used a placebo agent. After a 1-week washout period, a new set of
enamel and root dentine slabs were bonded to the premolars and volunteers were crossed
over to the alternate agent for 14 days. The resistance of enamel and root dentine to wear
following bleaching, toothbrushing and intraoral exposure was measured with a profil-
ometer, using reference areas.
Results: For enamel, ANOVA did not demonstrate significant difference between wear
provided by placebo and bleaching agent (p = 0.3713), but higher wear depth was observed
for bleached root dentine (p = 0.0346).
Conclusions: While overnight bleaching caused no alteration in wear resistance of enamel,
root dentine showed increased tissue loss.
# 2008 Elsevier Ltd. All rights reserved.
* Corresponding author at: Faculdade de Odontologia de Ribeira ˜o Preto, USP, Departamento de Odontologia Restauradora, Av. do Cafe ´, s/n,
Monte Alegre, CEP 14040-904, Ribeira ˜o Preto, SP, Brazil. Tel.: +55 16 3602 4075; fax: +55 16 3602 4781.
E-mail address: email@example.com (J.J. Faraoni-Romano).
0300-5712/$ – see front matter # 2008 Elsevier Ltd. All rights reserved.
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/jden
Additionally, some in situ studies, that represent an
have investigated the effects of bleaching treatment on
microhardness of dental enamel13,17–19and dentine.18,20Sur-
face morphology,13,21roughness21and calcium content in
enamel13have also been investigated. However, the effect of
whitening agents on wear of enamel and dentine, using an in
situ model, has still not been evaluated.
Considering that there are in vitro reports showing that
bleaching of enamel with 10% carbamide peroxide can cause
150 mm,9it could be assumed that the dental substrate could
be less resistance to wear processes. In fact, Wiegand et al.15
have already shown that bleaching increase the substrate loss
by toothbrushing. Nevertheless, no in situ study validated the
alteration and the increase of wear of enamel and dentine.
As in in situ studies the remineralization potential of
human saliva can minimize the adverse effects of bleaching
agents on enamel and dentine,18there are doubts if the
bleaching gel may increase the susceptibility of dental tissues
Therefore, this in situ study was conducted to evaluate the
effect of bleaching with 10% carbamide peroxide agent on
wear of enamel and root dentine.
2.Materials and methods
2.1. Ethical aspects and volunteers
The protocol of this study was reviewed and approved by the
Ethics Committee of the School of Dentistry of Ribeira ˜o Preto,
USP (process no. 2004.1.834.58.6). Thirty volunteers (28
females and 2 males, aged 19–43 years) who fulfilled the
inclusion criteria (normal saliva flow, absence of dental caries
and/or periodontal disease, willing to perform bleaching
treatment following the research schedule) without violating
the exclusion criteria (use of orthodontic appliances, presence
of fixed or removable denture, pregnant or nursing women,
smokers and dentine sensitivity) took part in this study after
signing an informed, written consent (Resolution no. 196 from
National Health Council, Brazil, 1996).
2.2. Experimental design
Each phase lasted 14 days and a washout period of 1 week
between each phase. The factor under study was bleaching
treatment at two levels: a 10% carbamide peroxide and a
placebo agent, as listed in Table 1. Volunteers were randomly
divided into two groups of 15, and each group received the
bleaching or the placebo agent in different sequence, in two
distinct periods (bleaching agent-placebo; placebo-bleaching
agent). The experimental units consisted of 60 bovine enamel
slabs and 60 bovine root dentine slabs, randomly assigned to
the 30 volunteers (one enamel slab and one dentine slab per
phase). Each volunteer was considered a statistical block. The
response variable was the wear depth (mm) evaluated
profilometricaly. The experimental set-up of this study is
shown in Fig. 1.
2.3.Preparation of dental slabs
tissue remnants and stored in 0.1% thymol (pH = 7.0). The
junction usinga lowspeed water-cooled diamondsaw (Isomet
(3 mm ? 2 mm ? 2 mm) were obtained from the middle third
2 mm ? 2 mm) were cut from the cervical third of the root
surface. Dental slabs were fixed with stick wax in acrylic resin
cylinders and the upper surface of the samples was then
flattened and serially polished with 400-, 600- and 1200-grit
Al2O3-abrasive papers and with 0.3- and 0.05-mm alumina
polishing suspensions (Alpha and Gamma Micropolish,
Buehler, Lake Bluff, IL, USA) on cloths in a water-cooled
mechanical grinder (Struers A/S, Rodovre, Denmark). To
remove polishing debris, specimens were placed in an
ultrasonic cleaner (T1440D, Odontobra ´s Ltda., Ribeira ˜o Preto,
SP, Brazil) with distilled water for 10 min. A stereomicroscope
(Nikon 88286, Tokyo, Japan) at 40? magnification was
employed to select and discard samples that presented pits
or cracks. Enamel and root dentine sections were then gas
sterilized (ethylene oxide).
dentineslabs(3 mm ?
2.4. Selection of enamel and root dentine slabs
After sterilization, microhardness measurements were per-
formed on sound substrates, through a Knoop indenter (HMV-
2, Shimadzu, Kyoto, Japan), under a 50-g load for enamel and
25-g load for root dentine applied for 30 and 10 s, respectively.
Four indentations, located 500 mm from the margin of the
dental slab and 250 mm apart, were made and the surface
microhardness (SMH) was calculated for each specimen. A
total of 60 slabs of enamel and 60 slabs of root dentine were
selected based on the mean values obtained for each dental
substrate (enamel and root dentine).
Table 1 – Bleaching treatments tested, their application protocol and pH.
Application protocol pHBatch #
(10% carbamide peroxide)
Placebo (Whiteness Perfect)
CP10%10% carbamide peroxide, neutralized
carbopol, glycerol and distilled water
Neutralized carbopol, glycerol and
8-h daily application, for 14 days6.14a
PLA8-h daily application, for 14 days6.28a
As provided by the manufacturer (FGM, Joinville, SC, Brazil).
aMeasured with mPA Tecnopon (mPA Tecnopon, MS Tecnopon Equipamentos Especiais Ltda., Piracicaba, SP, Brazil).
journal of dentistry 37 (2009) 273–278
Preparation of dental slabs for the experimental
In order to ensure the presence of reference surfaces (area
unexposed to the bleaching agent and to the oral cavity and
unbrushed) when measuring the depth of the abrasion
grooves, a thin layer of composite resin was applied over
the two ends of surface of the specimens, based on the
description of Amaechi and Higham,22leaving a window of
1 mm ? 2 mm ? 2 mm in their central area. The resin compo-
site (Herculite XRV, Kerr, Emigsville, PA, USA) was light-cured
On, 3M/Espe, St. Paul, MN, USA). Specimens were stored at
37 ? 0.5 8C in 100% relative humidity.
Upper and lower dental arch impressions were taken with
alginate using a stock tray and stone cast molds were made.
On the molds, vestibular reservoirs were generated with one
coat of nail varnish on all teeth, except on the second
premolars where reservoirs (3 mm ? 4 mm ? 3 mm) were
prepared with resin composite corresponding to the specimen
thatwould bebondedon thevolunteers’ teeth.Twotrayswere
manufactured for each volunteer using a 1-mm thick flexible
ethyl vinyl acetate polymer in a vacuum tray-forming
machine (P7/Bio-Art Equip Odontolo ´gicos Ltda., Sa ˜o Carlos,
2.7.Preparing the volunteers for the experimental phase
In the pre-experimental period or run-inphase, which lasted 1
week, each volunteer received a toothbrush (Oral-B Indicator
Plus 35, Gillette do Brasil Ltda., Manaus, AM, Brazil) and a
fluoridated dentifrice (Colgate Cavity Protection, Colgate-
Palmolive Ltda., Osasco, SP, Brazil, AO).
A completeprophilaxis was performedon each patient and
the initial color of his/her teeth was determined by Vita scale
(Wilcos do Brasil Indu ´stria e Come ´rcio Ltda., Petro ´polis, RJ,
2.8. Experimental phase
The 30 volunteers were randomly divided into 2 groups of 15.
First, the tray was tested, and when necessary, adjustments
were performed. After, two dental specimens – one of enamel
and one of root dentine – were randomly bonded to the
vestibular surfaces of the superior second premolars (if
absent, the upper first premolars) of each patient. The base
ofthe specimensandthe area corresponding to theplace to fix
it in the labial surface of the superior second premolar were
acid etched with phosphoric acid. In the sequence, an
Fig. 1 – Schematic drawing of the experimental set-up: using a low speed water-cooled diamond saw, bovine enamel and
root dentine slabs (3 mmT 2 mm T 2 mm) were obtained. Samples were fixed with stick wax in acrylic resin cylinders, and
ground flat and polished in a water-cooled mechanical grinder. Slabs were pretested using a microhardness tester. Two-
thirds of the surface area of specimens was covered with resin composite. The specimens were randomly fixed on the facial
surface of the maxillary second premolars of 30 volunteers. The volunteers were divided into 2 groups of 15: in the first
experimental phase, the Group I received the bleaching agent and the Group II received the placebo, for a period of 2 weeks.
In the second phase, after a washout of 1 week, the Group I received the placebo and the Group II received the bleaching
agent, characterizing a 2 T 2 crossover study. The composite resin was removed from the specimens and wear depth was
assessed in profilometer, in relation to the reference area.
journal of dentistry 37 (2009) 273–278
a resin cement (Rely-X, 3M/Espe, St. Paul, MN, USA) were
applied following the manufacturer’s instructions. The slab
was positioned on the correct area, the excess of the cement
was removed and light-cured. The volunteers were instructed
on how the bleaching treatment would be performed, the
manner to apply the bleaching gel (Whiteness Perfect 10%,
FGM, Joinville, SC, Brazil) or placebo gel (Whiteness Perfect,
FGM, Joinville, SC, Brazil) in tray, how to clean the tray after
removing it from the mouth and keep it in a container
provided. Moreover, with the aim to standardize the tooth-
brushing technique, instructions were given to the volunteers
on how to brush their teeth and bonded specimens. In the
experimental Phase 1, Group 1 applied the bleaching agent,
while Group 2 applied placebo agent in the tray and wore it
overnight for about 8 h. The volunteers were blind as to which
agent they were using.
After the bleaching period (14 days), the specimens were
carefully removed with orthodontic pliers and the residual
cement was removed with resin polishing carbide burs (Jet,
Beavers Dental, ON, Canada) and aluminum oxide discs (Sof-
Lex, Pop-On, 3M/Espe, St. Paul, MN, USA).
Volunteers were submitted to a washout period of 1 week
with the aim to eliminate the residual effects of the treatment
previously applied. Then, they received new toothbrushes and
dentifrices and the dental hygiene technique was reinforced.
In the experimental Phase 2, a new set of dental slabs were
randomly bonded in the same way as that used for experi-
mental Phase 1. New trays were distributed to the volunteers
to eliminate any possible residues left by the previously
applied agent. In this phase, the Group 1 applied the placebo
agent, while Group 2 used bleaching agent for another 2
in the Phase 1. After finishing the experimental Phase 2, the
volunteers began the bleaching treatment in the mandibular
arch. At the end of the bleaching treatment, photographs were
taken and some restorations were replaced for esthetic
2.9.Wear depth measurements
To determine wear, the composite resin was removed from
the specimens. As the acid etching/adhesive system was not
used, the composite resin was carefully and gently detached
from the enamel and root dentine surface, exposing the
untreated reference areas. The specimens were cleaned
ultrasonically for 10 min. The wear depth, on both tissues,
was measured using a profilometer (Surfcorder SE-1700,
Kosaka Corp., Tokyo, Japan) equipped with a diamond stylus
of 2 mm radius. Five profilometric traces at a constant speed of
0.1 mm/s and a load of 0.7 mN, perpendicular to the brushing
direction, were performed for each specimen. The average of
thesefivemeasurementswas usedas the weardepthvaluefor
2.10. Statistical analysis
Period and carryover effects were verified by paired t-tests. The
data were statistically evaluated using two-way analyses of
variance (ANOVA) with a significance level of 5%. Tukey’s test
was applied where significant differences were detected. The
software Statgraphics Centurion XV (Statgraphics Plus Soft-
ware, Manugistics, Rockville, MD, USA) was used to perform
the statistical analyses.
Thepairedt-testsverifiedthattheeffectsofperiod(p = 0.99for
enamel and p = 0.15 for root dentine) and carryover (p = 0.44
for enamel and p = 0.36 for root dentine) were not statistically
significant. Table 2 shows the means and standard deviations
of enamel and root dentine wear.
For enamel, ANOVA did not demonstrate significant
difference between wear provided by placebo and bleaching
agent (p = 0.3713), but higher wear depth was observed for
bleached root dentine (p = 0.0346).
Different protocols of in situ studies have been used to assess
the effects of bleaching treatment on dental hard tissues.
Among the described protocols in the literature, most of them
adopted the use of a removable palatal appliance containing
slabs of enamel13,17,19or dentine.20,23Some disadvantages
about this protocol may be identified such as the difficulty to
ensure that all volunteers followed it suitably; the fact that did
the oral cavity, as the appliance is removed during meals and
hygiene procedures and the abrasive effect that the tongue
can exert on dental tissues, increasing the overall loss of tooth
substance.24Moreover, another important constraint about
bleaching experiments in which removable palatal devices
were used17,19,20is that it is impossible to reject the probability
of contact of the bleaching gel with the control specimens or,
to avoid the residual effect of bleaching gel in the control
group, considering that the slabs were present in the same
device. In other researches, control specimens were removed
specimens were bleached in the mouth;23or the bleaching
treatment was performed outside the oral cavity and then
placed in the mouth of volunteers.13
In the present study, an in situ model was chosen to
simulate the bleaching treatment, as closely as possible of the
clinical situation, avoiding these above-mentioned problems.
The adopted protocol was similar to Basting et al.,18in which
Table 2 – Means (standard deviations) of surface wear
(mm) of enamel and root dentine exposed to 10%
carbamide peroxide and to placebo agents.
SubstrateEnamel Root dentin
Means connected by brackets did not differ from one another
(a = 0.05; l.s.d. = 0.55) for the same dental substrate.
journal of dentistry 37 (2009) 273–278
specimens of enamel and root dentine were fixed on the facial
surface of the maxillary second premolars. Another important
aspect related to the current study was the crossover
experimental design, in which each volunteer performed
the treatment with the bleaching and placebo gel, in different
periods, with a washout of 1 week to eliminate the residual
effect between the treatments. Thus, each volunteer was
considered one complete statistical block, eliminating the
different habits among them,25such as diet, toothbrushing
force, and biological factors including flow rate, buffering
capacity and composition of saliva.
Ten percent carbamide peroxide agent was used to
represent the gel most commonly used in home bleaching.
In this research, specialcare was taken in the choice of control
group, represented by a placebo, which was prepared by the
same industry of the bleaching agent. Thus, the placebo
presented exactly the same appearance, color, flavor, con-
sistency and composition, with exception of the 10% carba-
mide peroxide. The protocol of bleaching treatment was
performed according to manufacturer’s instructions.
A platform of composite was constructed on the two ends
of the selected slabs and then fixed on the teeth of the
volunteers, withthe aim ofserving as a referenceareato allow
latter evaluation of dental loss, and also providing protection
of the exposed area against the abrasion from soft tissues, as
proposed by Amaechi and Higham.22Slabs of enamel and root
dentine used in the present experiment were obtained from
composition to human teeth.26Moreover, bovine teeth are
easily obtained and manipulated, because of their large size.
In terms of wear, few studies in the literature have
Among the different methods used to assess the loss of dental
hard tissue, profilometry was chosen because it is a method of
high precision27and permits the measurements of wear in a
relatively simple way.28
With respect to enamel, the result of the current study did
not reveal a significant difference between the wear provided
by 10% carbamide peroxide and the placebo. This finding
corroborates a previous in vitro study in which 10% carbamide
the enamel wear produced by an oral wear simulator in
comparison with untreated specimens.29However, enamel
bleached with 10% carbamide peroxide and submitted to
cycles of toothbrushing showed slightly greater wear than
high concentration carbamide peroxide agents.29Despite of
the fact that the bleached differed from the unbleached group,
the magnitude of wear has been considered clinically
irrelevant.15In fact, the mean value obtained was around
0.207 mm, wear considered very small compared to values
observed in this in situ study (Table 2). The reports of Attin
et al.9and Efeoglu et al.,10have demonstrated that the 10%
carbamide peroxide are able to penetrate and diffuse through
enamel. Thus, demineralization and reduction of subsurface
microhardness have been observed up to 50 mm after 15-d
bleaching period10and 150 mm below the surface of the
enamel after 10-d bleaching period9. Possible explanations for
these alterations are the time of application of the bleaching
gel,15insufficient remineralizing period to repair subsurface
microstructural defects9and the result of the uncontrolled
reaction of the peroxide radical.10As a consequence of these
surface and subsurface changes, enamel could be more
susceptible to abrasive wear. However, due to the biological
factors of saliva – flow, buffering capacity, acquired pellicle,
composition – and to pH value of the bleaching agent does not
affect the enamel,30the increase of wear was not verified in
Some in situ investigations also are in agreement with the
absence of difference between bleaching and control treat-
ment in terms of microhardness,13,17micromorphology13,21
and content of calcium.13In contrast with these findings,
alterations on the microhardness18and surface roughness21
have been observed, probably because of the prolonged
contact between the bleaching gel and the dental tissue.18,21
Moreover, the carbopol present in the placebo and bleaching
agent may have caused changes in dental structure micro-
hardness and in its mineral content.21
With regards to root dentine, the specimens exposed to the
bleaching gel exhibited higher wear value than the placebo gel.
of this tissue,31which possess higher organic content than
enamel,26besides to present higher porosity and solubility.26,32
dentine which is in the range of 6.2 to 6.7.32In the current
than that established as critical for root dentine, the pH of the
occurs and, together with brushing, may increase dentine
surface wear. Changes on the dentine after the use of 10%
carbamide peroxide were also observed on surface morphol-
ogy,8microhardness11,12and mineral content14of in vitro
studies and onthemicrohardness ofaninsitustudy.20Probable
explanations for thesealterations are thelow pH,11,12composi-
tion of the bleaching agents12and protocol of the bleaching
treatment.8,14On the other hand, in some in vitro studies9,33,34
microhardness nor on the morphology and surface roughness
of dentine,33owing to the short-term regimens33,34and neutral
pH of bleaching agents.9The in situ studies of Basting et al.,18,21
also did not show significant difference on microhardness and
surface roughness, probably due to the pH of bleaching agent
At-home bleaching performed overnight with 10% carbamide
peroxide did not affect enamel wear, but caused higher wear
rates in root dentine.
This paper was based on part of a doctoral’s degree thesis
submitted by the first author to the University of Sa ˜o Paulo
(USP). This research was supported by CNPq (grant # 477419/
2004-6) and by FAPESP (grant # 04/15795-0). The authors would
like to thank all volunteers that took part of this study; to FGM
Produtos Odontolo ´gicos (Joinville/SC–Brazil); to the Ethylene
journal of dentistry 37 (2009) 273–278
OxideSterilization CentreoftheClinicalHospitaloftheSchool Download full-text
from the Department of Restorative Dentistry, USP. The
authors are indebted to Antonio Luiz Rodrigues Jr. for his
design of the flowchart.
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