Download Can intracoronally bleached teeth be bonded safely?

ORIGINAL ARTICLE
Can intracoronally bleached teeth be bonded
safely?
Tancan Uysal,a Ozgur Er,b Burak Sagsen,b Ayca Ustdal,c and Gulsen Akdogand
Kayseri, Turkey
Introduction: Our objective was to determine the effects of intracoronal bleaching on the shear bond strength
and failure side location of metallic brackets at 2 times (bleaching immediately before bonding and 30 days
before bonding). Methods: Sixty freshly extracted mandibular incisors were randomly divided into 3 groups;
each group contained 20 teeth. After finishing canal preparation and root canal filling, the root fillings were removed to a level 2 mm apical to the cementoenamel junction. Glass ionomer base (Vitrabond, 3 M Dental Products, St Paul, Minn) was placed approximately 2-mm thick. Bleaching agent (Whiteness Perfect, FGM Dental
Products, Joinville, Brazil) was placed into the rest of the cavity for 4 days at 2 times. Shear bond strength of
these brackets was measured in megapascals. The adhesive remnant index (ARI) scores were determined after the brackets failed. Data were analyzed with analysis of variance (ANOVA), Tukey, and chi-square tests.
Results: The bond strengths of the group with no bleaching (mean, 20.25 6 7.06 MPa) were significantly
higher (P .0.001) than those of the group that had bleaching immediately before bonding (mean, 4.85 6
3.22 MPa) and the group that had bleaching 30 days before bonding (mean, 8.70 6 4.93 MPa). The results
of the chi-square comparisons indicated significant differences among the 3 groups. In the group with no
bleaching, there was a higher frequency of ARI scores of 2 to 4, indicating cohesive failures in the resin. In
the other 2 groups, the failures were mostly adhesive at the resin-enamel interface (ARI scores of 4 and 5).
Conclusions: Intracoronal bleaching with carbamide peroxide adversely affected the shear bond strength
and changed the site of failure during debonding when bonding was done immediately or 30 days after bleaching. (Am J Orthod Dentofacial Orthop 2009;136:689-94)
D
iscolored teeth, especially in the anterior region,
can cause considerable cosmetic impairment.
When the pulp is injured, blood extravasations
from ruptured vessels can invade the pulp chamber,
and erythrocytes can penetrate the dentinal tubules.
The erythrocytes undergo hemolysis and liberate hemoglobin; this releases iron.1 The iron is combined with
hydrogen sulfide to form iron sulfide, a black compound
that gives teeth the dark discoloration.2
In addition to invasive therapies, such as crowning or
veneers, whitening of teeth is an alternative therapeutic
From the Erciyes University, Kayseri, Turkey.
a
Associate professor and department chair, Department of Orthodontics,
Faculty of Dentistry.
b
Assistant professor, Department of Conservative Dentistry and Endodontics,
Faculty of Dentistry.
c
Research assistant, Department of Orthodontics, Faculty of Dentistry.
d
Teaching staff, Department of Mechanics; Kayseri Vocational College,
Kayseri, Turkey.
The authors report no commercial, proprietary, or financial interest in the
products or companies described in this article.
Reprint requests to: Tancan Uysal, Erciyes Üniversitesi Disxhekimliği Fakültesi,
Ortodonti A. D. Melikgazi, Kampüs Kayseri, 38039 Turkey; e-mail,
[email protected].
Submitted, October 2007; revised and accepted, November 2007.
0889-5406/$36.00
Copyright Ó 2009 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2007.11.033
method. The discoloration of teeth with nonvital pulp requires an effective treatment with chemical bleaching
agents.3 This chemical bleaching can be achieved with
both extracoronal and intracoronal bleaching techniques.
Based on clinical experience and research, extracoronal tooth bleaching is considered safe and effective,
and the most conservative method of improving the esthetics of discolored teeth.4,5 However, several studies
reported that extracoronal bleaching has some disadvantages, including tooth sensitivity, gingival irritation, and
recurrent discoloration after bleaching.6,7 In addition, alterations in enamel surface morphology and reductions
in bond strength of adhesives after bleaching have been
reported.8-11 These adverse effects are clinically critical
when bonding resin composites, porcelain veneers, and
orthodontic brackets to bleached enamel surfaces.12
Previous studies have shown a change in enamel
structure, composition, and bond strength when exposed to the bleaching agents used for extracoronal
bleaching.8,13,14 Torneck et al9 identified a substantial
reduction in bond strength to enamel shortly after its exposure to concentrated aqueous solutions of a bleaching
agent. In addition, intracoronal (nonvital, devital)
bleaching has been found to reduce the microhardness
of dentin and enamel15 and weaken the mechanical
properties of the tooth structures.16 Perinka et al17
689
690
Uysal et al
showed a relationship between the microhardness and
calcium concentration and bond strength.
In restorative dentistry, several studies have evaluated the shear bond strength of composite resins on
enamel and dentin after intracoronal bleaching, but
there is no consensus on its effects on bond
strength.18-21 Some studies showed that the bonding
strength of enamel decreases after intracoronal bleaching with carbamide peroxide in various concentrations,18,20,21 and some concluded that permanent
restoration can be accomplished safely immediately
after intracoronal bleaching.19
In the orthodontic literature, various study designs
were used to evaluate the effect of extracoronal (vital)
bleaching on the bond strength of orthodontic
brackets.22-27 Cacciafesta et al26 evaluated the effects
of bleaching on the bond strength values of resin-modified glass ionomer cements and found that bleaching before bonding significantly lowered the bond strength of
the resin-modified glass ionomer, Fuji Ortho LC. In a recent study, Uysal and Sisman27 found that the use of a carbamide peroxide bleaching agent immediately before
bonding significantly reduced the shear bond strength
values of orthodontic self-etching primer systems.
Since some adults who are interested in orthodontic
treatment might have also had their endodontically
treated teeth bleached or might want bleaching, it seems
important to determine whether this procedure would
significantly influence the bonding strength of orthodontic bracket adhesives to the enamel surface.
So far, to our knowledge, no studies have investigated the effect of intracoronal bleaching on the bond
strength values of metallic brackets.
The purpose of this in-vitro study was to determine
the effects of intracoronal bleaching on the shear bond
strength and the adhesive remnant index (ARI) scores
of metallic brackets at 2 times (bleaching immediately
before bonding and 30 days before bonding). The null
hypotheses to be tested were that there are no statistically significant differences in (1) bond strength and
(2) failure site locations of intracoronal bleached and
unbleached teeth at the 2 times.
MATERIAL AND METHODS
Sixty noncarious freshly extracted single-rooted
mandibular incisors were used in this study. Teeth
with hypoplastic areas, cracks, or gross irregularities
of the enamel structure were excluded. The criteria for
tooth selection dictated no pretreatment with a chemical
agent such as alcohol, formalin, or hydrogen peroxide,
or any other form of bleaching. Immediately after extraction, the teeth were scraped of any residual tissue
American Journal of Orthodontics and Dentofacial Orthopedics
November 2009
tags and washed under running tap water. The teeth
were stored in distilled water, and the water was
changed weekly to prevent bacterial growth. The teeth
were randomly divided into 3 groups of 20 teeth each.
All teeth were mounted vertically in self-cure acrylic
so that the crowns were exposed. The buccal surfaces
were cleaned and polished with a rubber cup and slurry
with pumice and water, followed by rinsing with water
spray and drying with compressed air.
Endodontic access cavities were prepared with ISO
(International Organisation of Standardization) 12 round
diamond bur (Diatech, Coltene Whaledent, Altststten,
Switzerland) with a high-speed handpiece under water
cooling. The root canals were made by using Protaper
nickel-titanium rotary instruments (Dentsply-Maillefer,
Ballaigues, Switzerland), and 1 mL of 2.5% sodium hypochloride irrigation was provided between each file. Final
irrigation was applied with saline solution, and the root
canals were dried with sterile paper points. The canals
were filled with an epoxy-resin root canal sealer AH 26
(Dentsply, De Trey, Konstanz, Germany) and gutta-percha (SPI Dental, Inchon, Korea) by using a cold lateral
condensation technique. Then the root fillings were
removed 2 mm apical to the cementoenamel junction.
Light-cured glass ionomer base (Vitrabond, 3M Dental
Products, St Paul, Minn) was placed approximately
2 mm thick. All specimens for bracket bonding were
prepared with 1 of the following procedures.
Group A (control): the access cavity was rinsed with
distilled water and dried, and final composite restoration
was finished. A 37% phosphoric acid gel (3M Dental
Products) was used for the acid etching of the 20 incisors for 30 seconds The teeth were then rinsed with water from a 3-in-1 syringe for 30 seconds and dried with
an oil-free source for 20 seconds.
Group B: intracoronal bleaching was performed according to the manufacturer’s instructions. The bleaching
agent (16% carbamide peroxide, Whiteness Perfect, FGM
Dental Products, Joinville, Brazil) was placed into the rest
of the cavity and closed by a temporary filling material
(Cavit, AG, D-82229, 3M ESPE, Seefeld, Germany). After 4 days, this procedure was repeated to simulate the clinical conditions when 1 more bleaching sequence is
needed. After 4 days, the temporary filling material was
removed, and, to neutralize the bleaching agent, calcium
hydroxide was placed for 1 more week. Then the access
cavity was rinsed with distilled water, and final composite
restoration was placed. The bracket bonding area was
etched with 37% phosphoric acid gel for 30 seconds.
Group C: this group was treated the same as group B,
except that, after bleaching and before etching, the teeth
were stored in artificial saliva for 30 days at room temperature. The artificial saliva was changed daily.
Uysal et al
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 136, Number 5
Sixty stainless steel mandibular incisor brackets
(3M Unitek, Monrovia, Calif) with a base surface area
of 6.82 mm2 were used in all groups. The mean base surface area of the brackets was calculated by measuring
the length and width and computing the area. After surface preparation, liquid primer of the Transbond XT
(3M Unitek) was applied to the etched surface, and
the brackets were bonded on the incisors with Transbond XT; any excess resin was removed with an explorer
before the resin was polymerized. Then a light-emitting
diode (Elipar Freelight 2, 3M ESPE) was used for curing
the specimens for 20 seconds.
After these procedures, the embedded specimens
were secured in a jig attached to the base plate of a universal testing machine (Hounsfield Test Equipment,
Salfords, United Kingdom). A chisel-edge plunger
was mounted in the movable crosshead of the testing
machine and positioned so that the leading edge was
aimed at the enamel-adhesive interface. A crosshead
speed of 0.5 mm per minute was used, and the maximum load necessary to debond the bracket was recorded. The force required to remove the brackets was
measured in newtons (N), and the shear bond strength
(1 MPa 5 1 N/mm2) was calculated by dividing the
force values by the bracket base area (6.82 mm2).
After debonding, all teeth and brackets were examined under 10-times magnification. Any adhesive remaining after bracket removal was assessed with the
ARI and scored according to the amount of resin adhering to the enamel surface.28,29 The ARI scale has a range
between 5 and 1: 5 indicates that no composite remained
on the enamel; 4, less than 10% of the composite remained on the tooth; 3, more than 10% but less than
90% remained on the tooth; 2, more than 90% of the
composite remained; and 1, all composite remained
on the tooth, with the impression of the bracket base.
Statistical analysis
All statistical analyses were performed with Statistical Package for Social Sciences software (SPSS for Windows, version 10.0.1, SPSS, Chicago, Ill). Descriptive
statistics, including means, standard deviations, and minimum and maximum values were calculated for the 3
groups of teeth. Comparisons of the means of the shear
bond strength values were made with analysis of variance
(ANOVA). Multiple comparisons were done by Tukey
tests. The chi-square test was used to determine significant differences in the ARI scores among the 3 groups.
RESULTS
The descriptive statistics for the shear bond strengths
of the groups are presented in Table I. The results of
691
Table I. Descriptive statistics and results of ANOVA
comparing shear bond strength of 3 groups
Bond strength (MPa)
Group
n
Mean
SD
Minimum
Maximum
Tukey*
A (control)
B (BO)
C (B30)
20
20
20
20.25
4.85
8.70
7.06
3.22
4.93
9.00
1.00
2.00
31.00
10.00
17.00
A
B
B
BO, Bonded immediately after bleaching; B30, bonded 30 days after
bleaching.
*Groups with different letters are significantly different from each
other.
ANOVA indicated statistically significant differences
among the 3 groups (F 5 45.579, P 5 0.000). Thus, the
first null hypothesis of this study was rejected. The Tukey
test showed that the bond strengths of group A (no bleaching; mean, 20.25 6 7.06 MPa) was significantly higher
(P .0.001) than those of group B (bleaching immediately
before bonding; mean, 4.85 6 3.22 MPa) and group C
(bleaching 30 days before bonding; mean, 8.70 6 4.93
MPa). We found no statistically significant differences
between groups B and C (P 5 0.065).
The ARI scores for the various groups tested are
listed in Table II. The results of the chi-square comparisons indicated significant differences among the 3
groups (chi-square 5 34.468, P 5 0.000). Therefore,
the second null hypothesis of this study was rejected.
In group A, there was a higher frequency of ARI scores
of 2 through 4, indicating cohesive failures in the resin.
In groups B and C, the failures were mostly adhesive at
the resin-enamel interface (ARI scores of 4 and 5).
DISCUSSION
Esthetics of the teeth including color are of great importance to patients. Orthodontists often face patients
who are dissatisfied not only with the appearance, but
also with the color, of their teeth. A number of methods
and approaches have been described for bleaching teeth.
These methods have various bleaching agents, concentrations, times of application, product format, application mode, and light activation.30 In the orthodontic
literature, different concentrations and bleaching agents
were investigated with the extracoronal bleaching
method related to shear bond strength of orthodontic
brackets. Some authors investigated the effect of 25%
to 35% hydrogen peroxide23,26 on the shear bond
strength of brackets bonded on the bleached enamel,
and some used 10% carbamide peroxide.24,31,32 In restorative dentistry, many studies have investigated the
effect of intracoronal bleaching on resin-enamel and
resin-dentin shear bond strength.18-21 However, a review
692
Uysal et al
Table II.
American Journal of Orthodontics and Dentofacial Orthopedics
November 2009
Frequency of distribution and comparisons of ARI scores (%)
ARI scores*
Group
A (control)
B (BO)
C (B30)
Multiple comparison
1
2
3
4
5
n
Group B
0 (0%)
0 (0%)
0 (0%)
10 (50%)
0 (0%)
0 (0%)
6 (30%)
0 (0%)
0 (0%)
4 (20%)
10 (50%)
5 (25%)
0 (0%)
10 (50%)
15 (75%)
20
20
20
†
Group C
†
NS
NS
BO, Bonded immediately after bleaching; B30, bonded 30 days after bleaching; NS, Not significant.
*ARI scores: 1, all composite, with impression of bracket base, remained on tooth; 2, more than 90% of composite remained on bracket base; 3,
more than 10% but less than 90% of composite remained on tooth; 4, less than 10% of composite remained on tooth surface; 5, no composite on
tooth; †P \0.001.
of the literature indicated no studies on the effect of intracoronal bleaching treatment on the bond strength of
metallic brackets bonded with orthodontic composites
to enamel.
Several authors reported significant decreases in the
bond strength of composite resin to carbamide peroxide
bleached enamel compared with unbleached
enamel.8,22,26,27,33 Most reports have evaluated the
physical changes in enamel after bleaching to provide
a possible explanation for the decreasd bond strength
caused by bleaching agents. Some studies suggested
that the lower bond strengths are created by the changes
in enamel structure resulting from increased porosity
manifesting as an overetched appearance and loss of
prismatic form.33,34 In addition, Lewinstein et al15 indicated that intracoronal bleaching reduces the microhardness of dentin and enamel by the loss of calcium
and alterations in the organic substance, and these factors might be important to cause decreased enamel
bond strengths. Another study showed a relationship between microhardness and calcium concentration and
bond strength.17 Consistent with these previous explanations, the results of our study demonstrated a statistically significant reduction in shear bond strength of
brackets for teeth bonded immediately after intracoronal bleaching compared with the control group.
It was proposed that residual oxygen from the
bleaching agent interferes with resin attachment and
inhibits resin polymerization.22,35 Although there are
remarkable variations among the recommended postbleaching times in different studies (24 hours-4 weeks),
some authors thought that a delay of at least 2 weeks is
needed after bleaching for the tooth structure to regain
its prebleaching adhesive properties.36 Uysal et al23
and Uysal and Sisman27 stored their samples in artificial
saliva for 30 days and suggested that a delay of bonding
for a minimum of 2 to 3 weeks might be beneficial.
Spyrides et al37 also reported that a 1-week delay in
bonding might not be sufficient to restore the reduced
bond strength of bleached structures. Therefore, they
speculated that the effect of bleaching might be more
permanent or take longer to eliminate. In the previous
studies, bleached surfaces were directly in contact
with distilled water or artificial saliva. However, in
our study, the pulp chamber and the access cavity
where the bleaching gel was placed were sealed before
immersion in artificial saliva. We thought that this might
retard the elimination of residual peroxide from the
tooth structure. We found that immersion of bleached
specimens in artificial saliva for 30 days increased the
shear bond strength of orthodontic brackets but not up
to the levels of the control group. We found similar
bond strength values with bonding immediately after
bleaching and statistically significant lower values
than the control.
Treating the bleached enamel surface with antioxidants (10% sodium ascorbate) before bonding reverses
the reduction in bond strength of composite resin, and
it might be an alternative to waiting and eliminate the
need to postpone bonding.31,32
Some researchers indicated that tooth crown fractures have also been observed after intracoronal bleaching, most probably due to extensive removal of the
intracoronal dentin.38 However, in our study, no enamel
fracture was observed during testing.
Reynolds39 suggested that the minimum bond
strength of 5.9 to 7.8 MPa is adequate for most clinical
orthodontic needs and routine clinical use. Most
brackets in group C actually met those minimum bond
strength requirements. Although higher failure rates
were expected, the bond strength was significantly
reduced but the strength was sufficient for clinical
bonding. However, clinical conditions might significantly differ from an in-vitro setting. This was an invitro study, and the test conditions were not like the
rigors of the oral environment. Heat and humidity in
the oral cavity are highly variable. Because of the differences between in-vivo and in-vitro conditions, a direct
comparison cannot be made with the findings of the
other studies.
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 136, Number 5
In the literature, 3 similar investigations evaluated
the ARI scores. Some authors22,23 showed a prevalence
of cohesive characteristics, but failures occurred at the
enamel-adhesive interface in 1 study.26 The results of
the ARI score comparisons in our study indicated significant differences among the 3 groups. In group A, there
was a higher frequency of ARI scores of 2 through 4, indicating cohesive failures in the resin. In groups B and
C, the failures were mostly showed adhesive (resinenamel interface) characteristics. Failures in the
bleached groups were mostly located at the adhesiveenamel interface. Therefore, we concluded that the
adhesive bond strength values for bleached enamel in
our study are more likely to be accurate.
CONCLUSIONS
1.
2.
3.
Intracoronal bleaching with carbamide peroxide
adversely affected the shear bond strength of orthodontic brackets when the bonding procedure was
performed immediately after bleaching.
A 30-day delay in bonding procedures after bleaching slightly improved the bond strength of orthodontic brackets but not up to the levels of the
unbleached group.
Bonding after intracoronal bleaching significantly
alters the sites of failure during debonding. Failures
in the bleached groups were mostly located at the
adhesive-enamel interface.
We thank Medifarm and 3M Unitek for their support
of this project.
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