Download Shear bond strengths of orthodontic brackets with a new

Journal of Orthodontics, Vol. 37, 2010, 37–42
SCIENTIFIC
SECTION
Shear bond strengths of orthodontic
brackets with a new LED cluster curing
light
Mariana Marquezan, Thiago Lau, Carina Rodrigues, Eduardo Sant’Anna,
Antônio Ruellas
Department of Pedodontics and Orthodontics, Federal University of Rio de Janeiro (UFRJ), Brazil
Marcela Marquezan
Federal University of Santa Maria (UFSM), Brazil
Carlos Elias
Militar Engeneering Institute (IME), Rio de Janeiro, Brazil
Objective: To evaluate the shear bond strength of orthodontic brackets bonded to bovine enamel using a new curing appliance
composed of an LED cluster.
Design: In vitro, laboratory study.
Materials and methods: Standard edgewise maxillary central incisor metal brackets (0.0220 slot) were bonded to 60 bovine
incisors which were arranged in a parabola, simulating the dental arch. The arches were randomly allocated to one of five
groups: three experimental groups in which a half arch was cured using the Whitening Lase Ortho LED Cluster light for 10, 20
and 40 s (EG10s, EG20s, EG40s) and two control groups. Control group 1 (CGH) were cured using a halogen light for 20 s
and control group 2 (CGL) were cured using a conventional LED light for 20 s per tooth. A shear debond test was performed
using an EMIC machine and the results were analyzed by ANOVA and post hoc Tukey multiple comparisons. The Adhesive
Remnant Index (ARI) was determined at 106 magnification.
Results: The one-way ANOVA showed a statistically significant difference between the groups (P,0.001). The post hoc Tukey
comparison showed that the bond strength for group EG10s was significantly lower than both the control groups CGH
(P,0.001) and CGL (P,0.001). There was no significant difference between the bond strengths for groups EG10s and EG20s
(P50.100). Neither were there any statistically significant differences detected between groups EG20s, EG40s, CGL and CGH
(P.0.05).The ARI analysis revealed a higher frequency of score 2 for groups CGL, EG10s, EG20s, a higher frequency of score
0 and 1 for the CGH group and a score of 1 was most frequent for the EG40s group.
Conclusion: The Whitening Lase Ortho LED Cluster light shows promise when bonding a half dental arch with a curing time
of 40 s.
Key words: Light-polymerization, LED/halogen, Shear bond strength, Orthodontic brackets
Received 10th December 2008; accepted 27th October 2009
Introduction
Light-polymerized orthodontic composites allow
the ease of bracket placement and removal of
excess resin.1,2 Most dental photoinitiator systems
use camphoroquinone as the diketone absorber, with
a peak of absorption at a wavelength of approximately 470 nanometres (nm).3 This is the region of the
visible light spectrum, which includes the quartztungsten-halogen light, light-emitting diodes (LED),
the argon laser and the xenon plasma arc light.
According to most manufacturers of composite resins
conventional halogen curing lamps need at least 20 s per
Address for correspondence: Dr Antônio Carlos Oliveira Ruellas,
Federal University of Rio de Janeiro, Brazil.
E-mail: [email protected]
# 2010 British Orthodontic Society
bracket to achieve sufficient bond strength.4 The plasma
arc and laser have a reduced polymerization time, but
the cost of the equipment remains high. Light-emitting
diode systems were proposed as an alternative curing
system in 1994.5 They are now well accepted by
clinicians and have a cost comparable with that of
conventional halogen lights. The advantages of LEDs
are: a lifetime of over 10,000 h with relatively little
degradation; they require little power to operate; they
are resistant to shock and vibration; and require no
filters to produce blue light.6,7 Undoubtedly, LED
systems are an excellent alternative to conventional
halogen lamps.
DOI 10.1179/146531207225022329
38
Marquezan et al.
Figure 1
Scientific Section
The specimens arranged in a parabola
A new generation of high-intensity LED units has
been introduced into the market.2,8 These consist of
multiple LEDs9 or LEDs with larger emission areas to
reduce the time needed to bond orthodontic attachments
and to optimize the bonding procedure.
The aim of this study was to evaluate the shear bond
strength of orthodontic brackets bonded to bovine
enamel using a new polymerization appliance composed
of an LED cluster (Whitening Lase Ortho DMC
Equipamentos, São Carlos, São Paulo, Brazil). The null
hypothesis was that there were no differences in the
force required to debond brackets between the new LED
cluster light and two other light curing systems tested.
Methods
A total of 60 extracted bovine incisors without any
visible defects were stored in 0.1% thymol solution at
Table 1
JO March 2010
room temperature. The crowns were individually
embedded in auto polymerizing acrylic resin (JET,
Clássico Artigos Odontológicos, São Paulo, Brazil) with
the labial surface touching a glass plate. After polymerization, this surface was abraded until an enamel
area of approximately 664 mm2 was exposed, using
abrasive paper 180 and then polished with abrasive
papers 400 and 600 (40 to 50 movements along the X
and Y axes). Each abrasive paper was divided into four
parts and each part used for only five teeth.
The specimens were embedded in plaster stone, in
groups of 6, forming a parabola to simulate the shape of
the dental arch (Figure 1). A square was used to check
whether the labial surface was perpendicular to the
floor. The specimens were randomly divided into five
groups according to Table 1.
Before bonding, the enamel was cleaned with a mixture
of water and pumice, rinsed with water and dried with oilfree air. At this time, the surface was etched with 37%
phosphoric acid gel for 30 s, rinsed with a water/spray
combination for 30 s, and dried until a characteristic
frosty white etched area was observed. The Transbond
adhesive primer (3M Unitek, Monrovia, CA, USA) was
applied, as recommended by the manufacturer, and
polymerized for 20 s. The surface was prepared to receive
the brackets. Standard edgewise maxillary central incisor
metal brackets (Dental Morelli Ltda, Sorocaba, São
Paulo, Brazil), slot 0.0220, were used. Composite resin
Transbond XT (3M Unitek, Monrovia, CA, USA) was
applied to each bracket base by a single operator. Then
the bracket was positioned on the tooth and lightly
pressed into the desired position using a Hollenback
carver. Excess adhesive was removed with a probe.
Distribution of specimens in the experimental and control groups according curing time and appliance.
Group
Number of specimens
Polymerization appliance
Curing time
CGH
CGL
EG10s
EG20s
EG40s
12
12
12
12
12
OrthoLux XT (3M Unitek)
Ultra Blue IS 600 mW (DMC Equipamentos)
Whitening Lase Ortho (DMC Equipamentos)
Whitening Lase Ortho (DMC Equipamentos)
Whitening Lase Ortho (DMC Equipamentos)
20
20
10
20
40
Table 2
s
s
s
s
s
per
per
per
per
per
teeth
teeth
half arch
half arch
half arch
Technical characteristics of the light curing units investigated in this study.
Curing unit
OrthoLux XT (3M Unitek)
Ultra Blue IS 600 mW (DMC Equipamentos)
Whitening Lase Ortho (DMC Equipamentos)
*According to the literature.12,20,21
**According to the manufacturer.
Type
Halogen
LED
LED
Light source out put
75 W
0,6 W
2,1 W (per cluster)
Tip dimensions (area)
2
0.5 cm
0.5 cm2
7.5 cm2
Light intensity
Wavelength
2
400–505 nm
400–480 nm
400–480 nm
.400 mW/cm *
1200 mW/cm2**
280 mW/cm2**
JO March 2010
Scientific Section
The effect of LED cluster on bond strength
39
Figure 4 Polymerization in the experimental groups
Figure 2 The Whitening Lase Ortho LED Cluster light (DMC
Equipamentos, São Carlos, São Paulo, Brazil)
The composite was polymerized using one of three
curing lights allocated to that group of teeth (Table 1).
The technical details of the lights are presented in Table 2.
Experimental groups: a Whitening Lase Ortho (DMC
Equipamentos, São Carlos, São Paulo, Brazil) (Figure 2)
curing light was used to polymerize the composite. This is
composed of an LED cluster (460–480 nm) disposed in a
half moon (Figure 3). The manufacturer recommends a
single shot to polymerize half a dental arch, therefore
three bovine teeth were arranged in a half parabola,
measuring 40 mm or approximately equivalent to the
distance between a maxillary central incisor and second
premolar in a human dental arch. The experimental
group was divided into three groups with polymerization
times of 10 s (EG10s), 20 s (EG20s) and 40 s (EG40s) for
half the arch (Figure 4).
Control groups: There were two control groups. One
group of teeth (CGH) was cured using a conventional
halogen light (OrthoLux XT, 3M Unitek, Monrovia, CA,
USA) and the second control group (CGL) was cured
using a conventional LED light (Ultra Blue IS 600 mW,
DMC Equipamentos, São Carlos, São Paulo, Brazil).
The cure time for both the groups was 20 s per tooth (10 s
for the mesial and 10 s for the distal of the bracket).
After bonding, the specimens were kept in distilled
water for 24 h before the shear test. The mechanical test
was performed using a universal mechanical testing
machine (EMIC DL2000, Curitiba, Paraná, Brazil).
Each specimen was then stressed at the junction of the
bracket and adhesive in an occlusogingival direction
with a 50 kg load cell at a crosshead speed of 0.5 mm/
min until the brackets were debonded.
Statistical analysis
A sample size calculation was undertaken using previous
data from the literature.2,10 It was determined that 12 teeth
were required to identify a significant difference of 3 MPa
in shear bond strength of orthodontic brackets with a
significance level of 5% and power of 80% (SD 3 MPa).
A one-way analysis of variance with post hoc Tukey
multiple comparisons was undertaken in order to detect a
significant difference in the shear bond strengths between
the groups. The adhesive remnant index (ARI) was
recorded according to the four-point scale introduced by
Årtun:11 0, no adhesive left on the tooth; 1, less than half
the adhesive left on the tooth; 2, more than half the
adhesive left on the tooth; 3, all the adhesive left on
the tooth with a distinct impression of the bracket mesh.
The teeth were examined independently by two judges at
106 magnification (binocular optic microscopy Nikon
Eclipse E600, Nikon Corporation, Tokio, Japan). The
degree of agreement was assessed using a weighted kappa
statistic and was considered good (0.91). Statistical
analyses were performed using SPSS Statistical Package
(SPSS 13, SPSS Inc., Chicago, IL, USA) and Quick Calcs
(GraphPad Software Inc., San Diego, CA, USA).
Statistical significance was set at P,0.05.
Results
Figure 3 The LED cluster arranged in a half moon
The results of the one-way ANOVA are presented in
Table 3. This showed that there was a statistically
40
Marquezan et al.
Scientific Section
significant difference in the shear bond strength between
the groups (P,0.001). The descriptive statistics are
given in Table 4. The post hoc Tukey comparison
showed that the bond strength for group EG10s was
significantly lower than both the control groups CGH
(P,0.001) and CGL (P,0.001). There was no significant difference between the bond strengths for groups
EG10s and EG20s (P50.100). Neither were there any
statistically significant differences detected between
groups EG20s, EG40s, CGL and CGH (P.0.05).
The microscopic evaluation of the bond failure site
showed that the majority of failures were of a cohesive
nature (ARI scores 1 and 2). The ARI scores for groups
CGL, EG10s, EG20s were mainly 2, whereas the scores
for CGH were mainly 0 and 1 and for EG40s was score
1 (Table 5). The numbers were too small for statistical
analysis.
Table 3
Frequency distribution of the adhesive remnant index.
Table 5
ARI
EG10s count
% within group
EG20s count
% within group
EG40s count
% within group
CGH count
% within group
CGL count
% within group
0
1
2
3
0
0%
0
0%
2
16.7%
4
33.3%
1
8.3%
1
8.3%
2
16.7%
7
58.3%
4
33.3%
2
16.7%
10
83.3%
10
83.3%
3
25%
3
25%
9
75%
1
8.3%
0
0%
0
0%
1
8.3%
0
0%
One-way ANOVA for shear bond strengths.
Between groups
Within groups
Total
Table 4
JO March 2010
Sum of squares
df
Mean square
F
P value
57.808
100.288
158.097
4
55
59
14.452
1.823
7.926
,0.001
Descriptive statistics of shear bond strengths.
95% confidence interval
Group
Mean (MPa)
Standard deviation
Group of comparison
Lower bound
Upper bound
P value
CGH
4.9
2.0
CGL
4.9
1.1
EG10s
2.2
0.8
EG20s
3.6
1.3
EG40s
4.0
1.4
CGL
EG10s
EG20s
EG40s
CGH
EG10s
EG20s
EG40s
CGH
CGL
EG20s
EG40s
CGH
CGL
EG10s
EG40s
CGH
CGL
EG10s
EG20s
21.5
1.1
20.3
20.6
21.6
1.1
20.3
20.6
24.2
24.2
22.9
23.3
22.8
22.8
20.2
21.9
22.5
22.5
0.7
21.2
1.6
4.2
2.8
2.5
1.5
4.2
2.8
2.5
21.1
21.1
0.2
20.2
0.3
0.3
2.9
1.2
0.6
0.6
3.3
1.9
1.000
,0.001
0.156
0.437
1.000
,0.001
0.167
0.458
,0.001
,0.001
0.100
0.023
0.156
0.167
0.100
0.974
0.437
0.458
0.023
0.974
*Groups with different letters are statistically different at a,0.05%.
JO March 2010
Scientific Section
Discussion
This in vitro study found that the shear bond strength of
brackets bonded to bovine enamel using the new
Whitening Lase Ortho LED cluster light was
comparable after 40 s for half an arch with those
obtained using a conventional halogen lamp for 20 s per
bracket. When the appliance was used for only 10 s, the
values were significantly lower. This could lead to a
potential saving of 60 s curing time per halfarch.
The literature supports the use of LED curing lights for
the polymerization of orthodontic composites.3,4,6,7,9,12–14
The results of this study suggest that the Whitening Lase
Ortho LED curing light may be a useful adjunct to
reduce the time necessary to bond an orthodontic appliance to a dental arch with light-polymerized composites.
Composed of an LED cluster, the manufacturers claim
that the light can cover an area of 40 mm, which should
be sufficient for half an arch. The appliance has a light
intensity of 280 mW/cm2, which is lower than the
400 mW/cm2 suggested by Rueggeberg et al.15 for the
polymerization of dental resin composites. Our results
concur with Usumez et al.7 who found comparable shear
bond strength values when curing with an LED source
for 20 and 40 s and lower values when cured for 10 s,
although there was no statistically significant difference
between EG10s and EG20s.
The ARI scores from this study differed among groups
that used different LED sources and different polymerization times. This is contrary to the findings of Usumez
et al.7 and Swanson12 who found no difference in the
ARI scores when varying time-polymerization and LED
sources. The experimental group that was cured for 10 s
had similar results to those of Thind et al.,16 who tested
an LED source with a 10 s polymerization time and
found ARI scores of mainly 2 and 3. The ARI scores for
the 20 s and 40 s cure times are in agreement with
Usumez et al.7 who found a higher frequency of score 1.
The conventional LED scores in our study were similar
to Swanson et al.12 who found a higher frequency of
score 2.
The ideal tooth to use for bonding studies is the
human maxillary central incisor. It has a nearly flat
bonding surface that is usually consistent from incisor to
incisor without the concern of fitting a bracket base to a
varying curved surface. However, it is increasingly
difficult to get non-carious, sound human incisors for
studies. Some studies have advocated the use of
premolars to standardize results.17 They are more easily
obtainable than other teeth as they are commonly
extracted for orthodontic treatment, but premolars vary
in the curvature of their labial surface and therefore
provide an additional variable of the bracket base not
The effect of LED cluster on bond strength
41
closely fitting the tooth.18 Bovine lower incisors are
easily obtainable and therefore are an inexpensive substitute for human incisors. They have been used in a
number of previous studies.18 Although bovine enamel
acts in a similar way to human enamel, the strength of
the bond to bovine enamel is lower than to human
enamel, probably due to differences in formation, leading to larger crystal grains, and more lattice defects.18
The actual shear bond strength values in this study
were lower than those found in other studies. This might
be due to differences in the bonding protocol adopted.
To facilitate the inclusion of the teeth, in a group of six,
in the same base filled with plaster stone, the crowns of
the teeth were included in acrylic resin and then the
labial surfaces were flattened to allow them to be located
perpendicular to the floor. This procedure has not been
used extensively in the literature limiting the comparison
of nominal values.19
Among the experimental groups there were increasing
bond strengths with increasing curing times, which
concurs with previous studies;4,12 although these were
not statistically significant between EG10s and EG20s
or between EG20s and EG40s. This increasing bond
strength is due to the higher conversion rate of
monomer to polymer with increasing polymerization
times.12 The statistically non-significant results can be
explained either by the fact that there is no true
difference between the samples or alternatively that
our sample was not large enough to detect a significant
difference. Using data from our study we are able to
determine that we would require a sample size of 47
specimens in order to detect a significant difference of
1 MPa between the EG40s and CGH or 21 specimens to
detect the same difference between EG10s and EG20s
(power of 80% and significance level P,0.05).
The advantage of an in vitro experiment is that it
allows the number of variables to be minimized.
Laboratory studies are a valuable screening tool, but
clinical evaluation is necessary before validation of any
product or technique. Further studies are also necessary
to evaluate the compatibility and physical characteristic
of various orthodontic adhesive when submitted to this
LED cluster polymerization procedure.
Conclusions
N
There were no significant differences in the bond
strengths when using the new Whitening Lase Ortho
curing light for 40 s for a half arch compared with
conventional halogen and LED curing lights used for
20 s per tooth. This could lead to a potential saving of
60 s curing time per halfarch.
42
N
Marquezan et al.
Scientific Section
Differences were observed for ARI scores when light
sources and polymerization time changed.
Acknowledgements
The authors would like to thanks Morelli Ortodontia
for the donation of the brackets and DMC
Equipamentos for lending the Whitening Lase Ortho
for this study.
Contributors
Mariana Marquezan, Carina Rodrigues, Thiago Lau
and Antônio Carlos Ruellas were responsible for the
study design. Carlos Elias provided the technical
support for the shear debonding test. Marcela and
Mariana Marquezan performed the statistical tests and
data interpretation. Critical revision and final approval
of the article were undertaken by Eduardo Sant’Anna
and Antônio Carlos Ruellas. Mariana Marquezan and
Antônio Carlos Ruellas are the guarantors.
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