In Vitro Action of Various Bleaching Agents on the Microhardness of Human
Djalma PECORA (email@example.com)
Damião de SOUSA-NETO
Gariba SILVA (firstname.lastname@example.org)
de Odontologia Ribeirão Preto University of São Paulo
publicado no Brazilian Dental Journal 5(2):129-134, 1994
Prelo, SP, Brasil
authors verifieda decrease in human dentin microhardness after application
of the following bleaching agents for 72 hours: sodium perborate + water,
sodium perborate + 3% hydrogen peroxide, sodium perborate + 30% hydrogen
peroxide, Endoperox (crystallized hydrogen peroxide), Proxigel (carbimide
peroxide), and 30% hydrogen peroxide. Sodium perborate + water and sodium
perborate + 3% hydrogen peroxide caused less of a decrease in dentin microhardness
than Endoperox, Proxigel and 30% hydrogen peroxide which caused the greatest
decreases in dentin microhardness. Sodium perborate + 30% hydrogen peroxide
fell into a statistically intermediate position.
words: bleaching agents, dentin microhardness, Endodontics.
surgeons seek to discover solutions and techniques capable of bleaching
teeth whose color has been altered after endodontic treatment and also
of bleaching teeth with live pulp which have changed color due to tetracycline
ingestion or an excess of fluoride during the calcification phase.
bleaching of endodontically treated teeth has been considered to be efficient;
however, recent evidence suggests that this procedure can result in significant
complications. Cervical resorption of roots has been attributed to the
toxic nature of 30% hydrogen peroxide, with can leak through the dentinal
tubules and reach periodontal tissues (Harrington and Natkin, 1979; Friedman
et al., 1988; Pécora et al., 1991; Dahlstrom, 1993).
et al. (1981) reported that 30% hydrogen peroxide caused destructive changes
of pulp tissue favoring internal resorption in vital teeth. Lado et al.
(1983) showed that 30% hydrogen peroxide denatures human dentin, rendering
this tissue immuologically unacceptable. Bowles and Thompson (1986) reported
pulp reactions when bleaching vital teeth with the use of hydrogen peroxide
with or without heat. Such reactions ranged from simple reversible inflammatory
reactions to necrosis. They reported that pulp enzymes are inhibited in
the presence of hydrogen peroxide, especially when associated with heat.
et al. (1992) verified that the association of sodium perborate and 30%
hydrogen peroxide increased dentin permeability and the addition of heat
increased the action of this solution, significantly increasing tissue
permeability. Rotstein et al. (1992) detected that 30% hydrogen peroxide
caused alteration in the dental structure of both cementum and dentin.
Canepa et al. (1993) reported that the association of sodium perborate
and 30% hydrogen peroxide with heat caused decreased dentin microhardness,
and that this was even more notable with repeated application of these
bleaching agents. Dahlstrom (1993) verified that hydrogen peroxide is capable
of generality highly reactive hydroxyl radicals which can destroy connective
tissue components, collagen and hyaluronic acid.
high percentage of teeth which are bleached present color regression over
a period of up to five years (Howell. l98L Lado et al., 1983; Friedman
et al., 1988).
present study investigates the action of various bleaching agents, during
72 hors, on human dentin microhardness.
total of 36 extracted human maxillary central incisors were used. They
were sectioned at the cemento-enamel junction to separate the crown from
the root. The cervical part of the root was sectioned transversely to prepare
a 1-mm thick disk. These 36 disks were placed in rapid polymerization acrylic
resin blocks so that one surface of the dentin disk was exposed to the
external surface. After polymerization of the resin, these blocks were
smoothed with 400, 500 and 600 sandpaper in order to obtain a smooth and
uniform dentin surface. Running water was used during this process to avoid
injuring the dentin. The smoothness of the dentin surface was verified
with the use of a 30X magnifier.
dentin samples were placed in a recipient containing deionized distilled
water at 370C until time for microhardness readings. Dentin
microhardness was measured with a Vickers hardness instrument (Wolpert,
Germany) with a load of 5O grams for 15 seconds. The samples were placed
in [this instrument so that the readings were always made in the same region.
microhardness was first read on normal dentin, without the application
of a bleaching agent. Ten measurements for each sample were made. A bleaching
agent was then applied on the dentin and this was stored on a Petri dish
which was placed in an incubator an 3 70C for 72 hours. This
sample was then washed with deionized distilled water to remove the bleaching
agent and microhardness was then measured. Ten readings were also made
of these samples to obtain a mathematical mean of microhardness. These
same steps were carried out wit1u all of the bleaching agents studied:
sodium perborate (NaBO2.H202.3H20;
Reagen) ± water, sodium perborate + 3% hydrogen peroxide, sodium
perborate + 30% hydrogen peroxide, Endoperox (Septodont), carbimide peroxide
(Proxigel Inodon) and 30% hydrogen peroxide (Vetec).
mean values of microhardness of each dentin disk before and after application
of the bleaching agents are shown in Table 1. Data were submitted to analysis
which verified the normally of the samples. Analysis of variance was carried
out for independent data (solutions) and dependent data (treatment, before
and after). Analysis of variance showed a statistically significant difference
at the level of 1% between bleaching agents and treatments (before and
after). Microhardness was greater before the application of bleaching agents.
The Tukey lest was applied to show differences among bleaching agents.
Sodium perborate + water and sodium perorate + either 3% or 30% hydrogen
peroxide were statistically similar. Endoperox, Proxigel and 30% hydrogen
peroxide were statistically similar and different from the previous group.
Sodium perborate + 30% hydrogen peroxide showed a microhardness between
the two other groups.
1 shows the action of bleaching agents on dentin microhardness after
72 hours. This graph of interaction of dependents factors (dentin microhardness
before and after treatment) with independent factors (bleaching agents)
shows the position of sodium perborate + 30% hydrogen peroxide, which is
closer to the solutions which decrease dentin microhardness to a lesser
degree. The great reduction of dentin microhardness 72 hours after the
application of Endoperox, Proxigel and 30% hydrogen peroxide is clearly
shown in Figure 1.
bleaching can bc performed in both live teeth and in endodontically treated
teeth Numerous techniques lave been reported and all use potent oxidizing
agents. Bleaching of teeth is nothing more than a chemical process of oxidation-reduction
has shown that dental bleaching can cause serious consequences, such as,
external resorption color reversibility and alteration in the collagen
structure of dentin (Howell, 1981; Lado el al., 1983; Friedman et al.,
1988; Pécora et al., 199 1; Saquy et al., 1992; Canepa et al., 1993).
present study shows that the action of sodium perborate associated with
water or with 3% hydrogen peroxide reduces dentin microhardness slightly.
Endoperox (crystallized 35% hydrogen peroxide), Proxigel (carbamide peroxide)
and 30% hydrogen peroxide greatly reduced dentin microhardness in comparison
to the other group. The association of sodium perborate with distilled
water has a pH of 9.8 and the association of sodium perborate with 3% hydrogen
peroxide a pH of 8.22.
association of sodium perborate with water and with 3% hydrogen peroxide
are statistically similar. The mixture of sodium perborate with 30% hydrogen
peroxide falls in a statistically intermediate position between sodium
perborate + water and the agents Endoperox and Proxigel. This intermediate
position may be explained by the fact that these solutions react among
themselves which lowers the deleterious effect of 30% hydrogen peroxide
on dentin. Sodium perborate presents an alkaline pH and hydrogen peroxide
an acid pH of 2.0. The mixture of these 2 agents results in a produce with
pH 5, which forms water and ionized oxygen. With time, the pH of this mixture
becomes alkaline. Thus, the alteration of pH depends on the quantity of
each of these agents, being more acid at the beginning if the quantity
of hydrogen peroxide is greater than that of sodium perborate. However,
with time and as water and oxygen are being formed, the mixture becomes
the Tukey test did not allow a definite position for the association of
sodium perborate with 30% hydrogen peroxide, the Scheffé test was
applied. This test did not alter the position of this mixture in relation
to the other bleaching agents studied.
graph of the interaction of dependent and independent factors (Figure 1)
clearly shows that the association of sodium perborate and 30% hydrogen
peroxide is displaced closer to the group of sodium perborate and water
and sodium perborate and 3% hydrogen peroxide, decreasing dentin microhardness
less than the bleaching agents Endoperox, Proxigel (10% carbamide peroxide)
and 30% hydrogen peroxide.
bleaching agents studied caused a reduce then in dentin microhardness.
The results of this study and those of other researchers, in spite of the
fact that they on in vitro, show the harmful affects of 30% hydrogen peroxide
on human dentin. Thus, researchers must seek an oxidation agent or reducing
agent which does not have a deleterious effect on dentin.
The bleaching agents tested in this study decreased human dentin microhardness.
The application of sodium perborate associated with water or with 3% hydrogen
peroxide caused less of a decrease in dentin microhardness than the use
of the other bleaching agents studied.
Endoperox (crystallized hydrogen peroxide), Proxigel (10% carbamide peroxide)
and 30% hydrogen peroxide decreased dentin microhardness in a statistically
similar manner and more than sodium perborate with water or with 3% hydrogen
The association of sodium perborate and 30% hydrogen peroxide falls into
an intermediate position between the other two groups.
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