ANALYTICAL AND QUANTITATIVE CYTOPATHOLOGY AND HISTOPATHOLOGY

1. 83
OBJECTIVE: To evaluate shear bond strength of 2
different fluoride-releasing sealants and their adhesive
remnant index (ARI).
STUDY DESIGN: A total of 105 extracted human max-
illary premolars were divided into 3 groups of 35. Slot
brackets (0.018-inch) were bonded to buccal surfaces of
teeth using Pro Seal, Opal Seal, and, as a control group,
Transbond XT. Transbond XT Composite was used only
as an adhesive material. All samples were subjected to
thermocycling for 5,000 cycles in water baths between
5°C and 55°C. Subsequently, the shear bond strengths
of specimens were determined under loads vertically at
0.5 mm/min crosshead speed until rupture occurred.
After the shear bond strength test, specimens were exam-
ined with a stereomicroscope at ×20 magnification and
grouped according to ARI analysis. Statistical analyses
were performed using one-way ANOVA analysis of
variance for shear bond strength data and Kruskal-
Wallis and Mann-Whitney U tests for ARI analysis.
RESULTS: There was no significant difference between
all the groups (p>0.05) with regard to shear bond
strength. According to ARI analyses, the control group
was statistically different from both the Pro Seal and
Opal Seal groups (p<0.05). However, there was no sig-
nificant difference between the Pro Seal and Opal Seal
groups for ARI analyses.
CONCLUSION: The results of this study showed that
the potential of caries and white spot lesions during
orthodontic treatment can be decreased by using new
fluoride-releasing sealants. However, this is an in vitro
study and these results should be supported with clin-
ical studies. (Anal Quant Cytopathol Histpathol
2021;43:83–89)
Keywords: bond strength, dental caries, fluoride,
Opal Seal, orthodontia, orthodontic appliances,
orthodontic brackets, Pro Seal, sealant, shear bond
strength, sodium fluoride dental bonding, white
spot lesions.
Tooth decay is one of most important problems of
dentistry, and this issue is of concern to patients
with orthodontic treatment and their orthodontists.
Orthodontists theorized that if bonded brackets
instead of bonded bands in fixed orthodontic treat-
ment were used, caries lesions might be encoun-
tered less often. However, that expected outcome
did not occur.
Although the relation of orthodontic treatment
and caries incidence was proven long ago,1 initial
caries lesions still maintain importance because
white spot lesions (WSLs) negatively affect the
dental esthetic, even many years after treatment.2
WSLs are one of the most important complica-
tions of long-term orthodontic treatment, and the
rate of WSLs in patients with orthodontic treat-
ment is high as compared to control groups.2-4 The
rate of WSLs in patients with orthodontic treatment
Analytical and Quantitative Cytopathology and Histopathology®
0884-6812/21/4302-0083/$18.00/0 © Science Printers and Publishers, Inc.
Analytical and Quantitative Cytopathology and Histopathology®
In Vitro Evaluation of Shear Bond Strength of
Two Different Fluoride-Releasing Sealants
Mehmet Doğru, Ph.D., and Afşin Salman, Ph.D.
From the Department of Orthodontics, Dicle University Faculty of Dentistry, Diyarbakır, Turkey.
Mehmet Doğru is Assistant Professor.
Afşin Salman is Specialist Dentist.
Address correspondence to: Afşin Salman, Ph.D., Şehreküstü Street, No. 4, Duran Apartment, A Block, Floor: 1, Flat No. 1, 16190
Osmangazi, Bursa, Turkey (afsinsalman6@gmail.com).
Financial Disclosure: The authors have no connection to any companies or products mentioned in this article.

2. is 72.9%.5 Risk factors for developing WSLs during
orthodontic treatment include appliance design,
excessive adhesive around the bracket, saliva flow
rate and content, bacterial plaque composition,
enamel mineral contents, and dietary habits.6-9
It has been shown that WSLs can occur within
4 weeks of beginning treatment.3,10,11 Even if those
small lesions can be remineralizated,12,13 their neg-
ative effect on esthetics can last for many years.3
Five years after debonding brackets, WSLs are still
resistant to remineralization.2
To prevent WSLs, fluoride can be used in dif-
ferent forms, like mouth washes, gel, toothpaste,
varnish, and sealants.14 All of these materials have
their own disadvantages, but fluoride-releasing
sealants have some superiority among the other
methods because they are not dependent upon pa­
tient compliance, they are easy to apply, and they
have the ability to recharge.
Although fluoride addition can prevent deminer-
alization, some researchers claim that fluoride has
a negative effect on bracket shear bond strength.15-17
It has been proven that application of sodium fluo-
ride, stannous fluoride, titanium tetrafluoride, and
zirconia tetrafluoride on acid-etched enamel reduce
bonding strength.18 Bishara et al19 and Al-Kawari
and Al-Jobair20 found that fluoride application
before or after acid etch reduce bonding strength.
The reason may be that the topical fluoride appli-
ance fills the interstitial space, and reaction prod-
ucts on the enamel create a physical barrier, both of
which reduce bonding strength.18,21
Pro Seal (Reliance Orthodontic Products, Itasca,
Illinois, USA) is a light-cure, fluoride-releasing,
highly filled sealant. It achieves 100% polymeriza-
tion, creates a smooth coating, prevents leakage,
and protects enamel. Several studies evaluated the
efficiency of this material on enamel surface pro­
tection and yielded controversial results.22-25 Opal
Seal (Opal Orthodontics, Ultradent, South Jordan,
Utah, USA) is a fluoride-releasing, glass ionomer,
nano-filled sealant. No studies are currently avail-
able comparing the effects of Opal Seal and Pro
Seal on bracket bonding strength.
While fluoride reportedly has a negative effect
on shear bond strength, Pro Seal and Opal Seal
materials are claimed to act differently. Because of
their slow and long-term fluoride-release action,
high filler content, abrasion resistance, and quality
of being oxygen inhibition layer–free, these ma-
terials can be used to prevent WSLs. The null
hypotheses were that (1) there is no statistical dif-
ference among the materials’ fracture strength and
(2) there is no statistical difference among the ma-
terials’ ARI scores.
Materials and Methods
The materials used in the study are shown in Ta-
ble I. Human maxillary premolar teeth (n=105)
without cracks, caries, and enamel irregularities
and which had been extracted for orthodontic and
periodontal reasons were used for the study. Tooth
diameter was measured with digital scale, and
similar teeth were chosen. Teeth were cleaned with
pumice and kept in deionized water for 3 months.
Three groups of 35 teeth were established. All teeth
were marked and embedded in self-curing acrylic
resin (Imicryl Dental, Konya, Turkey) 2 mm below
the cementoenamel junction. After polymerization,
the blocks were extracted from the molds.
The buccal surface of each tooth was etched
with 37% orthophosphoric acid for 15 seconds and
rinsed and dried until a frosty-white appearance
was obtained. In the control group Transbond XT
primer (3M Unitek, Monrovia, California, USA)
was applied. In the Opal Seal group, Opal Seal
was applied in a thin, uniform coat and dried for
2 seconds and then polymerized for 3 seconds with
the Valo Cordless Curing Light (Ultradent). In the
Pro Seal group, sealant was applied in the same
way and cured for 6 seconds. Stainless steel pre-
molar brackets were bonded to the middle of the
tooth with Transbond XT composite, excessive ad-
hesive was removed, and each tooth in the groups
was cured for 6 seconds.
All specimens were stored in deionized water
at 37°C for 24 hours. After this period, the speci-
mens were submitted to 5,000 cycles in a thermal
cycler with deionized water between 5°C and 55°C
(dwell time of 25 seconds, transfer time of 10 sec-
onds).
The specimens were secured in the lower jaw
of the machine so that the bonded brackets’ base
was parallel to the shear force direction. Force
applying chisel was secured in the upper jaw,
and specimens were stressed in an occlusogin­
gival direction at the bracket-tooth interface with
the help of chisel. The upper jaw was moved at
a crosshead speed of 0.5 mm/minute; the maxi-
mum load necessary to debond or initiate bracket-
tooth interface fracture was recorded in Newtons
and then converted into megapascals as a ratio
of Newtons to surface area of the bracket. Bond
strength MPa=Force (in Newton)/Surface area
84 Analytical and Quantitative Cytopathology and Histopathology®
Doğru and Salman

3. of the bracket (in mm2). After shear mode testing,
enamel surfaces of teeth were inspected indepen-
dently by one evaluator. An optical microscope
(stereomicroscope) at 20× magnification was used
to determine the adhesive remnant index (ARI)
score at the site of bond failure (Figure 1). This
Volume 43, Number 2/April 2021 85
Strength of Two Different Fluoride-Releasing Sealants
Table I Materials and Contents
Materials manufacturer Contents Percentage
Pro Seal (Reliance Orthodontic Products) Ethoxylate bisphenol-A diacrylate 10–50
Sealant (Lot: 14411) Urethane acrylic ester 10–40
Polyethylene glycol diacrylate 10–40
Glass particles of fluoride 5–40
Opal Seal (Opal Orthodontics, Ultradent) HPMA (2-hydroxypropyl methacrylamide) 17
Sealant (Lot: 905061) Ethyl alcohol 16
Glass ionomer and nano filler 38
Panora 200 (Imicryl Dental) (Lot: 15316) Orthophosphoric acid 37
Transbond XT (3M Unitek) Bis-GMA 45–55
Primer (Lot: N628038) TEGDMA 45–55
4-(dimethylamino)-benzene ethanol <3
DL-camphorquinone <3
Hydroquinone <3
Transbond Composite (3M Unitek) Bis-GMA 10–20
Adhesive resin (Lot: N660371) Bisphenol A bis(2-hydroxyethyl ether) DMA 5–10
Silanated quartz 70–80
Silanated silica <2
Difeniliodoium hexafluorophosphate <0.2
TEGDMA = triethylene glycol dimethacrylate.
Figure 1
Stereomicroscope images of
adhesive remnant index (ARI)
scores according to the Artun
and Bergland scale, in which
0=no adhesive remaining on
the tooth in the bonding area,
1=less than half the bonded
area covered by the adhesive,
2=more than half the bonded
area covered by the adhesive,
and 3=all adhesive remaining
on the entire bonded area.

4. scale ranges from 0 to 3 according to Artun and
Bergland,26 in which 0=no adhesive remaining
on the tooth in the bonding area, 1=less than half
the bonded area covered by the adhesive, 2=more
than half the bonded area covered by the adhesi-
ve, 3=all adhesive remaining on the entire bonded
area.
Statistical Analysis
All statistical analyses were performed with SPSS
software. The data were subjected to a Shapiro-
Wilk normality test and Levene’s variance homo­
geneity, showing a normal distribution and ho­
mogeneity of variance among groups. Hence, the
shear bond strength’s statistical analysis was eval­
uated with one-way ANOVA.
Adhesive remnant index data evaluation was
made with nonparametric analysis. Bonferroni cor-
rection Mann-Whitney U test was used for binary
comparation, and Kruskal-Wallis was performed
for intergroup comparison.
Results
Shear bond strength values are listed Table II. Ac-
cording to one-way ANOVA, there was no sta-
tistical difference between groups for shear bond
strength (p>0.05). The highest mean shear bond
strength value was in the control group (8.55 MPa).
The lowest value was in the Pro Seal group (8.11
MPa) (Figure 2).
In the ARI score evaluation, statistical results
showed a difference between the control group
versus the Pro Seal group and between the con-
trol group versus the Opal Seal group (p<0.05)
but no statistical difference between the Pro Seal
group versus the Opal Seal group (p>0.05) (Ta-
ble III).
Discussion
There are many studies on reducing the deminerali-
zation of enamel during orthodontic treatment. Flu-
oride is one of these methods, but patient cooperati-
on must be sufficient for the fluoride to be effective.
To control dental plaque without compromising the
shear bond strength of the braces before and during
fixed orthodontic treatment has long been a field
of research.27 With the advancement in bonding
technologies, fluoride-releasing sealants found new
areas for usage, like protecting hypoplastic enam­
el, around orthodontic brackets, and unharmed
enamel.25 Sealant application after acid etch would
increase shear bond strength and protect enamel
around the bracket.23 Also, sealants act as a barrier
to acid attacks for enamel28 and are chemically or
light cured. Using light-cure polymerization in-
stead of chemical polymerization ensures full enam­
el surface coverage without an oxygen inhibition
layer.29,30 For this reason, highly filled and light-
curing polymerization are two new materials that
Pro Seal and Opal Seal present to the dental mar­
ket. Pro Seal and Opal Seal sealants are quite suc-
86 Analytical and Quantitative Cytopathology and Histopathology®
Doğru and Salman
Table II Mean Shear Bond Strength Values and Standard
Deviation
Group Mean±SD Max Min
Control (n=35) 8.55±2.27 13.04 4.01
Opal Seal (n=35) 8.49±2.43 15.54 4.20
Pro Seal (n=35) 8.11±2.06 11.68 4.39
Figure 2 Graphic of shear bond strengths.
Table III ARI Scores for Groups
ARI Control Opal Seal Pro Seal
score group group group
0 3 (8.6%) 0 (0.0%) 2 (5.7%)
1 16 (45.7%) 2 (5.7%) 1 (2.9%)
2 15 (42.9%) 26 (74.3%) 25 (71.4%)
3 1 (2.9%) 7 (20.0%) 7 (20.0%)
ARI = adhesive remnant index.

5. cessful in preventing demineralization. Pro Seal
has been reported to be more successful than Opal
Seal, especially in preventing demineralization.31-33
The decrease in the protective effect of the Opal
Seal over time can be explained by a decrease in
fluoride release or the removal of the adhesive on
the tooth surface. Regarding the relationship be­
tween fluoride and shear bonding strength, in this
study we research two different sealants’ effect on
shear bond strength. Failure in bracket bonding
causes time, material, and patient inconvience. For
this reason, it is worthwhile to perform a research
study using the method that best mimics the oral
conditions since it will reflect clinical situations.
In dentistry it is necessary to investigate any
new dental material with in vivo and in vitro stud­
ies for all aspects such as bonding strength, mar-
ginal leakage, and biocompatibility. In vivo stud­
ies are difficult to standardize, and the time and
money demands for both the patient and physician
are disadvantages. For these reasons, researchers
tend to use in vitro methods. Accurate determina­
tion of bonding strength can only be achieved by
similar designing of the oral environment. Con-
sequently, similar tooth sizes were chosen for
study. All teeth were stored in deionized water
for 3 months maximum according to the Interna­
tional Organization for Standardization (ISO) ma-
nifesto.34 After bonding, all samples were stored
in 37°C deionized water for 24 hours. Deionized
water, saline, or artificial saliva have no effect on
shear bond strength as storage media.35 Bishara
et al36 found that thermocycling causes lower
shear bond strength values than storing samples
in water for 24 hours. For this reason, accelerated
aging method, thermocycling, was used in this
study according to ISO standards.34 There is no
standardization on temperature degrees and num-
ber of cycles.37,38 In this study researchers per­
formed 5,000 cycles at 5–55°C to demonstrate a
6-month period.
In this study, there was no statistical difference
between the sealants and control groups. According
to this result, it can be said that fluoride in seal-
ants does not adversely affect bonding strength.
This may be explained by the fact that these ma­
terials have increased mechanical properties and
less microleakage due to their higher filler con-
tent. There are other studies with similar results.
Paschos et al39 and Varlik et al40 analyzed Pro Seal’s
effect on shear bond strength and found no statis­
tical difference. Although there have been several
studies on Pro Seal, there are no studies on the ef-
fect of the Opal Seal bracket shear bond strength
relation.
Powers and Messersmith41 stated that orthodon-
tic adhesive materials’ shear bond strength should
be above 8 MPa. Reynolds42 found that 5.9–7.8 MPa
shear bond strength is enough for orthodontic ad­
hesives. In this study, shear bond strength values
are between the stated values. Consequently, it
can be said that there will not be any problems
with bonding failures in the routine use of Pro
Seal and Opal Seal.
It is a primary concern of clinicians to obtain a
smooth and sound enamel surface after removal
of orthodontic brackets.43 After debonding, it is
more favorable to have bonding failure between the
bracket-adhesive interface or in the adhesive itself
than in the enamel-adhesive interface in order to
avoid enamel cracks.44 The ARI scoring system is
a method developed to evaluate the amount of re-
sidual adhesive. Montasser et al45 found that there
was a tendency toward higher scores when viewed
at ×20 magnification and a tendency toward lower
scores at ×10 magnification or naked eye visual in­
spection. This is why ×20 magnification was used
for ARI score evaluation in this study. As a result,
a statistical difference was found between the con­
trol group and the experimental groups. However,
there was no significant difference between the Pro
Seal group and the Opal Seal group according to
ARI. ARI scores of the control group were stated
as Score 1 (45.7%). Therefore, it can be said that
after bracket debonding the enamel suffers much
more damage in the control group. ARI scores of
the Pro Seal and Opal Seal groups were stated as
Score 2 or Score 3—more than 50% of the com-
posite on the enamel surface. This is a more desir­
able result because it causes less damage to the
enamel surface.
When all of these results are taken into ac-
count, there is no statistical difference in bonding
strength, so Pro Seal and Opal Seal should be in­
troduced more frequently in order to incur less
damage to the dental tissue. However, it should
not be forgotten that this study is an in vitro
study and the oral enviroment is imitated in a
limited way, so the results should be evaluated ac-
cording to these deficiencies.
Conclusion
Within the limitation of this in vitro study, the fol-
lowing conclusion can be drawn: (1) there was no
Volume 43, Number 2/April 2021 87
Strength of Two Different Fluoride-Releasing Sealants

6. statistical difference among all groups in shear
bond strength, (2) there was a significant differ-
ence between the control group versus Pro Seal
group and the control group versus Opal Seal
group, and (3) there was no statistical difference
between the the Pro Seal group and the Opal Seal
group.
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