Effect of hydrogen-peroxide-basedhome bleaching agents on

Braz J Oral Sci. July-September 2006 - Vol. 5 - Number 18
Effect of hydrogen-peroxide-based
home bleaching agents on enamel
hardness
Isana Álvares Ferreira
Guilherme Carpena Lopes
Luiz Clovis Cardoso Vieira
Élito Araujo
Department of Operative Dentistry,
Universidade Federal de Santa Catarina,
Florianópolis, Brazil.
Received for publication: April 18, 2006
Accepted: August 24, 2006
Abstract
The aim of this in vitro study was to examine the effect of four
commercial hydrogen-peroxide-based home bleaching agents on
enamel microhardness. Fifteen human molars conserved in water for
no more than 3 months were sectioned mesio-distally. The buccal
and lingual surfaces were included in self curing acrylic resin, and the
30 specimens were ground until 600 grid (n=6). At baseline, 6
indentations (Vickers) were made on each of the 6 surfaces of each
group, under load of 100g for 30s. Bleaching procedure was performed
for 2 weeks with: 4.5% hydrogen-peroxide (Perfecta, Premier), 5.5%
hydrogen-peroxide (DayWhite, Discus Dental), 7.5% hydrogenperoxide (DayWhite, Discus Dental), a polyethylene-strip whitening
system containing 5.3% hydrogen-peroxide (Whitestrips,
Procter&Gamble) and 10% carbamide peroxide (Opalescence,
Ultradent) was used as control. After bleaching time, the specimens
were rinsed and maintained in fresh artificial saliva, changed daily. A
t-test compared each bleaching agent before and after treatment. The
results showed that none of the five commercial home bleaching
agents reduced the enamel microhardness. I t was concluded that all
the five commercial home bleaching agents evaluated in our study
showed no adverse effects on enamel microhardness.
Key Words:
hydrogen-peroxide, carbamide peroxide, bleaching, enamel, hardness
Correspondence to:
Isana Álvares Ferreira
Universidade Federal de Santa Catarina,
Centro de Ciências da Saúde
Departamento de Estomatologia, Dentística,
Campus Universitário, Trindade
CEP: 88015-000 - Florianópolis,
Santa Catarina, Brasil
Fax: 0055 48 234 1788
E-mail: [email protected]
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Braz J Oral Sci. 5(18):1090-1093
Introduction
The search for a more conservative cosmetic dentistry has
turned dental bleaching into the first option for the treatment
of teeth with changes in color. Teeth bleaching must not be
considered a new technique within dentistry, once it has
been performed for more than a century1. The home bleaching
technique, settled by Haywood and Heyman in 1989 2 ,
recommends the use of 10% carbamide peroxide with a custom
tray. Several changes regarding products and techniques
have been recently introduced thus disposing hydrogenperoxide-based bleaching agents in low concentrations and
techniques which make the traditional use of trays
unnecessary.
The 10% carbamide peroxide, when in contact with saliva
and oral fluids, dissociates itself in 7% of urea which
afterwards decomposes itself into ammonia and carbon
dioxide and 3% hydrogen peroxide3, which consequently
degrades itself into water and free nascent oxygen4.
Because they present acid characteristics, bleaching agents
may alter the mineral content of the teeth after bleaching3,5-6
and this would alter the enamel microhardness7, possibly
leading to a reduce on dental resistance to wear by abrasion,
attrition, abfraction and erosion. However, the effects that
home bleaching have on hard tissues, mainly on enamel, are
very contradicting8. Some researches state that the bleaching
treatment, containing carbamide-peroxide-based products,
does not affect the enamel microhardness9-12. New hydrogenperoxide-based materials available on market, present higher
concentrations than the hydrogen peroxide resulting from
the dissociation of the 10% carbamide peroxide. A recent
research on 3% hydrogen peroxide gel manipulated in a
pharmacy resulted on the enamel microhardness decrease13.
Besides, similar changes were reported in other researches
using 10% carbamide peroxide7-8,14-17. Thus, it can be assumed
that hydrogen peroxides tested on the present work, once
presenting a higher concentration of the active agent and
not presenting urea, which when degraded into ammonia
elevates the pH close to the dental surface18, could provide
similar or greater changes in microhardness. The main goal
of this study was to analyze the effect of four hydrogenperoxide-based bleaching systems on enamel microhardness.
Material and Methods
Fifteen human molars, stored in water for a maximum of 3
months, were sectioned in a mesio-distal direction in equal
halves. The buccal and lingual surfaces were embedded in
chemically-activated acrylic resin (AcryliMet, South Bay
Technology Inc., San Clemente, CA), an area of approximately
3 mm x 3 mm remaining exposed. The thirty specimens were
polished with sand-paper of 220, 360, 440, and 600-grit. Five
groups were prepared as per treatment modality (n=6): Group
1 – 4.5% hydrogen peroxide (Perfecta, Premier); Group 2 –
5.5% hydrogen peroxide (DayWhite, Discus Dental); Group
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Effect of hydrogen-peroxide-based home bleaching agents on enamel hardness
3 - 7.5% hydrogen peroxide (DayWhite, Discus Dental);
Group 4 - a polyethylene-strip whitening system containing
5.3% hydrogen peroxide (Whitestrips, Procter&Gamble); and
control, Group 5 - 10% carbamide peroxide (Opalescence,
Ultradent). The solutions had their pH measured using
pHmeter (Geaka, São Paulo, Brazil).
Prior to the experiment, 6 indentations (Vickers) were made,
separated 0.1 mm, on each of the 6 surfaces in each group,
using a Shimadzu hmv-2000 (Shimadzu, Tokyo, Japan).
Bleaching procedure was carried out for 30 minutes, twice a
day (30 minutes AM and 30 minutes PM) for 2 weeks, to the
exception of the control group that was carried for 2 hours
per day for 2 weeks. During the bleaching procedure the
specimens were put in a Tupperware containing artificial
saliva to active a more adequate simulation of the clinical
situation. The saliva did not cover the specimens. The
bleaching solutions were applied over the enamel. The
Tupperware was closed and maintained at 37ºC. Following
each daily bleaching session, the teeth were washed with
deionized water and stored in artificial saliva (Dermus
Pharmacy) at 37 °C, the saliva being changed daily.
At the end of the treatment period, the teeth had the Vickers
hardness measured, with 6 indentations separated 0.1 mm,
cut into each of the 6 surfaces of every group. A t-test
compared each bleaching agent pre and post treatment.
Results
Mean microhardness before and after treatment, as well as
the measured pH, are presented on Table 1. None of the five
commercial home bleaching agents reduced the enamel
microhardness when compared to the measurement
conducted prior to bleaching. However, specimens submitted
to bleaching with DayWhite 5.5% gel presented an increase
of enamel microhardness (p≤0.031).
Discussion
The effectiveness and safety of the hydrogen and carbamide
peroxides used in dental bleaching have been recently
researched 19-20. Contradicting results among laboratorial
works can be explained due to variations in the methodology
applied, such as time of exposure, pH of solution, type of
teeth and mainly the storage environment13. Some works
show that when the specimens are storage in artificial saliva
or exposure to oral environment in situ21, no changes in the
superficial hardness of enamel is observed9-12, considering
that the saliva presents a large remineralization potential.
The dynamism of the process may help to explain our results.
The enamel contact with the bleaching solution slightly
below the critical pH for a short period (30 minutes) followed
by the contact for a longer period with a hyper mineralized
solution of artificial saliva seems to be unable to result in
demineralization. Thus, in our study no reduce in the enamel
microhardness was noticed. On the other hand, an increase
Braz J Oral Sci. 5(18):1090-1093
Effect of hydrogen-peroxide-based home bleaching agents on enamel hardness
Table 1 - Mean microhardness values (SD in parentheses) before and after treatment
Bleaching Agents
pH
Microhardness (Baseline)
Microhardness (After Treatment)
Opalescence (Carbamide Peroxide10%)
6.5
332.1(33)a
331.4(34)a
DayWhite (7.5% Hydrogen Peroxide)
5.1
325.7(42)a
331.3(45)a
DayWhite (5.5% Hydrogen Peroxide)
6.6
324.6(35)a
350.8(42)b
Whitestrips (5.3% Hydrogen Peroxide)
6.0
332.2(25)a
340.1(27)a
Perfecta (4.5% Hydrogen Peroxide)
7.1
316.1(34)a
323.8(38)a
Values followed by different lower case letters mean statistical difference between the two evaluations at p<0.05
of about 8% in the microhardness of specimens from group
5.5%HP (Day White) was observed.
A research compared the effects of primary components
from 10% carbamide peroxide (3% of hydrogen peroxide and
7% urea) over the enamel13. In this study it was attained as
one of the results that the bleaching enamel with 3%
hydrogen peroxide (pH 6.4) presented a significant reduce
on its superficial microhardness 13. Based on this work, it
could be assumed that bleaching products used in the
present research based on hydrogen peroxide with higher
concentrations and lower pH could lead to a similar reduction
in the enamel microhardness. However, the results show that
none of the groups evaluated suffered any decrease. Two
possible conjectures could be done to explain the difference
between these two works. The first, time of exposure of the
gel over the enamel was three hours a day13, while in this
study, the period of time applied over the specimens was 30
minutes, twice a day. Second, the composition of the
commercial bleaching products seems to have solutions
which are able to perform a remineralization action. The
enamel demineralization happens in a pH of 5.5 (critical pH)22.
Thus, we could expect a reduction on the enamel hardness
of group 7.5% (Day White) once it presents a pH below the
critical (pH 5.1) and because it was the lowest of the products
tested (Table 1). However, some component of its formulation
makes its use unable to produce negative effects over the
enamel hardness.
Bleaching agents once presenting acid characteristics could
alter the mineral content of the teeth after bleaching (3,5,6)
and this would alter the enamel microhardness7. Bleaching
solutions with a pH moderately low reduce in vivo the saliva
pH during the first 5 minutes. After 15 minutes of treatment
the pH increases above the average23. This is possibly due
to chemical reactions of the carbamide peroxide, neutralizing
the saliva acidity24-25. So, it is believed that due to the presence
of urea, resulting from the carbamide peroxide breakdown
and responsible for the pH increase, the demineralization
does not occur and, consequently, there are no changes in
the enamel microhardness, a fact that was observed in the
carbamide peroxide group.
The findings of the present study demosntrated that the
bleaching systems evaluated showed no adverse effects on
enamel microhardness, being able to be safely indicated for
home dental bleaching.
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