The document is a proof cover sheet for a journal article on the influence of preheating bonding agents on the degree of conversion and bond durability in dental cavities. It requests that the author carefully check the proofs, limit changes to corrections of errors, and confirm that the author list is correct. It also includes two queries asking the author to provide an institutional email address and history date for the article.

1. PROOF COVER SHEET
Journal acronym: TAST
Author(s): Boniek Castillo Dutra Borges
Article title: Influence of the preheating of bonding agents on the degree of conversion and bond
durability in tridimensional dentin cavities
Article no: 736190
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Prefix
Given name(s)
Surname
Boniek Castillo
Dutra
Ana Raquel Rocha
Correia
Antônio Cavalcanti
Charry Alves da
Marco Antonio
Eduardo José
Mario Alexandre
Coelho
Rodivan
Marcos Antônio
Japiassú Resende
Borges
Vilela
Silva-Junior
Silva-Junior
Botelho
Souza-Junior
Sinhoreti
Braz
Montes
Suffix

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4. TAST
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Journal of Adhesion Science and Technology
Vol. X, No. X, XXXX 2012, XXX–XXX
Influence of the preheating of bonding agents on the degree of conversion
and bond durability in tridimensional dentin cavities
Boniek Castillo Dutra Borgesa*, Ana Raquel Rocha Correia Vilelab, Antônio Cavalcanti
Silva-Juniorb, Charry Alves da Silva-Juniorb, Marco Antonio Botelhoa, Eduardo José
Souza-Juniorc, Mario Alexandre Coelho Sinhoretic, Rodivan Brazb and Marcos Antônio
Japiassú Resende Montesb
AQ2
a
Laboratory of Nanotechnology, Post-Graduate Program in Biotechnology, Potiguar University
(Laureate International Universities), Av. Senador Salgado Filho 1610, Natal 59088-725, Brazil;
b
Department of Restorative Dentistry, Pernambuco Dental School, Pernambuco University, Camaragibe,
Brazil; cDepartment of Restorative Dentistry, Piracicaba Dental School, State University of Campinas,
Piracicaba, Brazil
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(Received 12 August 2012; final version received 29 September 2012)
Objectives: The aim of this study was to evaluate the degree of conversion (DC) of dental
bonding agents at different temperatures and the bond durability of restorations bonded
with preheated dental bonding agents. Materials and methods: Three multistep adhesive
systems, including one 3-step etch-and-rinse (Adper Scotchbond Multipurpose Plus) and
two 2-step self-etching systems (Clearfil SE Bond; Filtek Low-Shrinkage Adhesive System), were evaluated. Dental bonding agents were preheated at 25, 37, and 60 °C. Barshaped specimens (n = 5) were prepared for DC analysis. Fourier Transform Infrared/Attenuated Total Fluorescence spectra were obtained, and the DC was calculated by comparing
the aliphatic bonds/reference peaks of nonpolymerized and polymerized materials. For bond
durability analysis, tridimensional dentin cavities were prepared in 180 bovine incisors,
which were then restored. Samples were stored in water for 24 h, and half of them were
subjected to additional degradation with 10% NaOCl for 5 h. The push-out bond strength
test was performed in a universal testing machine until failure. Failure modes were analyzed by scanning electron microscopy. Data were analyzed by analysis of variance
(ANOVA) and Tukey’s tests (p < 0.05). Results: Dental bonding agents preheated at 60 °C
showed higher DC values than those preheated at 25 and 37 °C. The temperature of the
dental bonding agent did not influence the bond durability, although fewer adhesive failures
were observed in restorations bonded with dental bonding agents at 60 °C. Conclusion:
Although the preheating of dental bonding agents can increase the DC, it may not improve
the bond durability of dentin restorations.
15
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Keywords: preheating; degree of conversion; failure analysis; in vitro; stress
Introduction
One of the major concerns in adhesive dentistry is the durability of bonds to dentin, because
the bonding is established on a complex hydrated biological composite structure [1].
AQ1 Although 3-step etch-and-rinse and 2-step self-etching adhesives have shown better results
*Corresponding author. Email: boniek.castillo@gmail.com
ISSN 0169-4243 print/ISSN 1568-5616 online
Ó 2012 Taylor & Francis
http://dx.doi.org/10.1080/01694243.2012.736190
http://www.tandfonline.com
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than their simplified versions [2], continuous degradation of the resin–dentin bond has been
observed for both materials in vivo [3,4]. Thus, efforts should be made to improve the dentin
bond durability of these dental adhesive systems.
The degree of conversion (DC) of the adhesive system and stress at the adhesive interface
due to composite shrinkage fundamentally impact the bond stability over time. The presence
of large amounts of unreacted monomer can expedite water absorption and compromise the
integrity of the hybrid and adhesive layers [5]. As the composite cures, an increase in stiffness, due to volumetric changes that are confined by the cavity walls, results in stresses that
challenge the bond integrity between the composite restoration and the tooth, particularly in
high C-factor cavities [6]. Thus, obtaining a high DC with low stress levels at the adhesive
interface during composite polymerization could improve the dentin bond stability in high
C-factor cavities.
A relatively recent method to increase the DC of resin-based dental materials is to preheat
the materials before photoactivation. Although preheating composite resins up to 68 °C reportedly increases the DC [7–10], few studies have evaluated the DC values of preheated dental
bonding agents. Silorane-based low-shrinkage restoratives have been developed to overcome
the drawbacks associated with the polymerization-related shrinkage of traditional methacrylate-based composite resins. In this technique, a 2-step self-etching adhesive system is used to
bond the silorane-based composite to dental tissues. However, no study has evaluated the
bond durability of restorations in high C-factor dentin cavities when the bonding agent is preheated before polymerization. This study aimed to evaluate: (I) the DC of preheated dental
bonding agents and (II) the bond durability of restorations in high C-factor dentin cavities
bonded with preheated dental bonding agents and filled with methacrylate- or silorane-based
composite resins. The hypotheses tested were as follows: (I) higher temperature would favor
increased DC of the bonding agents and (II) the bond durability of restorations bonded with
preheated bonding agents would be higher.
Materials and methods
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Experimental design
This study tested: (1) the DC of preheated dental bonding agents and (2) the bond durability
of restorations in high C-factor dentin cavities bonded with preheated dental bonding agents
and filled with composite resins. The multistep adhesive systems utilized in this study were
Adper Scotchbond Multipurpose Plus (MP) (3M ESPE, St. Paul, MN, USA), Clearfil SE Bond
(SE) (Kuraray Osaka, Japan), and Filtek Low-Shrinkage (LS) (3M ESPE). The DC was evaluated with three different bonding agents (in MP, SE, and LS) at three different temperatures
(25, 37, and 60 °C). The push-out bond durability was evaluated with three different adhesive
systems (MP, SE, and LS) at three different temperatures of the bonding agents (25, 37, and
60 °C) and with two different aging methods (short-time water storage with or without
subsequent chemical degradation by sodium hypochlorite). The compositions, manufacturers,
and batch numbers of the materials are shown in Table 1.
Preheating of the bonding agents
45
One bottle of each dental bonding agent was kept in an oven (incubator) at 25, 37, or 60 °C
for 2 h before starting the adhesive procedure [11]. One bottle of each dental bonding agent
from the same batch number was used for each temperature, which was checked with a
thermometer before the restorative procedure.

6. Batch number
3-step etch-andrinse adhesive
system
2-step self-etching
adhesive system
2-step self-etching
adhesive system
Dimethacrylatebased composite
resin
Silorane-based
composite resin
Adper Scotchbond Multipurpose
Plus (3M ESPE, St. Paul, MN,
USA)
Clearfil SE Bond (Kuraray, Tokyo,
Japan)
Filtek Low-Shrinkage Adhesive
System (3M ESPE, St. Paul,
MN, USA)
Filtek Z250 (3M ESPE, St. Paul,
MN, USA)
Filtek Low-Shrinkage Composite
(3M ESPE, St. Paul, MN, USA)
Initial
Notes: HR: bonding agent; HEMA: 2-hydroxyethyl methacrylate; Bis-GMA: bisphenol-glycidyl methacrylate; 10-MDP: 10-methacryloyloxydecyl dihydrogen phosphate;
TEGDMA: triethylene glycol dimethacrylate; UDMA: diurethane dimethacrylate; TMPTMA: trimethylolpropane trimethacrylate; and Bis-EMA: bisphenol A polyethylene glycol
diether dimethacrylate.
Silane-treated quartz (60–70), 3,4-epoxycyclohexylcyclopolymethylsiloxane
(5–15), Bis-3,4-epoxycyclohexylethyl-phenyl-methylsilane (5–15), yttrium
trifluoride (5–15), products (<26)
Silane-treated silica (75–85), Bis-EMA (1–10), UDMA (1–10), Bis-GMA
(1–10), TEGDMA (<5)
9N115915BR
N139697
Primer: HEMA (15–25), Bis-GMA (15–25), phosphoric acidmethacryloxyhexylesters (5–15), ethanol (10–15), water (10–15), silane-treated silica
(8–12), 1,6-hexanediol dimethacrylate (5–10), (dimethylamino)ethyl
methacrylate (<5), copolymer of acrylic and itaconic acid (<5), phosphine
oxide (<5), camphorquinone (<5) HR: substituted dimethacrylate (70–80),
silane treated silica (5–10), TEGDMA (5–10), phosphoric acids-6methacryloxy-hexylesters (<5), 1,6-hexanediol dimethacrylate (<3),
camphorquinone (<3)
Primer: HEMA (10–30), 10-MDP (np), hydrophilic dimethacrylate (np),
water (np), accelerators (np), dyes (np), camphorquinone (np) HR:
Bis-GMA (25–45), HEMA (20–40), 10-MDP (np), hydrophilic
dimethacrylate (np), colloidal silica (np), initiators (np), accelerators (np),
dyes (np), camphorquinone (np)
Etchant: water (55–65), phosphoric acid (30–40), synthetic amorphous
silica (5–10) Primer: ethyl alcohol (70–80), water (20–30),
methacryloxypropyltrimethoxysilane (<2) HR: Bis-GMA (60–70), HEMA
(30–40)
Composition (% by weight) – np: not provided by the manufacturer
Primer: N130675 HR:
N137817
Primer: 00896A HR:
01321A
Etchant: 9NL Primer:
N124653 HR:
N195685
Type
Materials used in this study.
Material (Manufacturer)
Table 1.
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Degree of conversion analysis
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The DC was analyzed by Fourier Transform Infrared/Attenuated Total Reflectance (Spectrum
100, PerkinElmer, Shelton, USA) at 24 °C under 64% relative humidity. Silicon molds
(1 mm  1 mm  7 mm) were filled with one drop (10 μL) of the dental bonding agents at each
temperature (n = 5). A Mylar strip was placed on the mold to cover the dental bonding agents.
The specimens were photoactivated for 10 s with a high-radiance light-emitting diode (LED)
unit (Coltolux, Coltène/Whaledent, Allstätten, Switzerland) at 1264 mW/cm2. The specimens
were carefully removed from the silicon molds and stored dry in dark receptacles at 37 °C for
24 h. The absorption spectra of nonpolymerized and polymerized bonding agents were
obtained from the region between 4000 and 650 cmÀ1 with 32 scans at 4 cmÀ1. The DC (%)
was calculated with the following equation: DC (%) = 100 Â [1 À (R polymerized/R nonpolymerized)], where R represents the ratio between the absorbance peaks at 1638 and 1608 cmÀ1.
The final DC values were analyzed by two-way analysis of variance (ANOVA) (dental
bonding agent  temperature of the dental bonding agent), followed by Tukey’s test (p < 0.05).
Push-out bond strength analysis
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Samples were prepared according to a previously described method for the push-out bond
strength test [12]. Figure 1 is a schematic representation of sample preparation and methods
utilized in this study. A total of 180 bovine incisors, free from cracks and structural defects,
were selected. The teeth were disinfected in a 0.1% aqueous solution of thymol at 40 °C for
no longer than 1 week. The roots were removed with a water-cooled diamond saw (South
Bay Technology, San Clement, CA) coupled to a precision cutting machine (Isomet 1000;
Buehler, Lake Forest, IL). The buccal aspect of the crown was wet-ground with 400- and
600-grit SiC abrasive papers in a polishing machine (Labopol-21, Struers, Copenhagen,
Denmark) in order to obtain flat dentin surfaces.
Standardized conical cavities (2 mm top diameter  1.5 mm bottom diameter  2 mm
height) were prepared with conical diamond burs at high-speed, under air–water cooling. A
custom-made preparation device allowed the cavity dimensions to be standardized. The burs
were replaced after every five preparations. To expose the bottom surface of the cavities, the
lingual surfaces were ground in accordance to the procedure described for flattening the
buccal aspects. In this manner, a cavity with a C-factor magnitude of 2.2 was obtained [13].
The prepared specimens were assigned to 18 groups (n = 10), according to the factors
under study (dental adhesive system  temperature of the dental bonding agent  aging
method). The adhesive systems were applied, according to the manufacturers’ instructions, as
follows:
MP: Dentin was etched with 35% phosphoric acid (Scotchbond Etchant, 3M ESPE) for
15 s and thoroughly washed in water for 30 s. Excess water was blot-dried with absorbent
paper, leaving the dentin surface visibly moist (wet-bonding). One coat of the primer was
applied to the dentin and air dried for 10 s at 20 cm. One coat of the bonding agent was
applied and light cured for 10 s with a Coltolux LED at 1264 mW/cm2.
SE: One coat of the self-etching primer was applied to the dentin with slight agitation for
20 s and air dried for 10 s at 20 cm. One coat of the bonding agent was applied and light
cured for 10 s with a Coltolux LED at 1264 mW/cm2.
LS: One coat of the self-etch primer was applied to the dentin with slight agitation for
15 s, air dried for 10 s at 20 cm, and light cured for 10 s with a Coltolux LED at 1264 mW/
cm2. The bonding agent was applied and light cured for 10 s.
After application of the adhesive systems, the specimens were placed onto a glass slab.
The restorative procedures were performed with the composites, which were bulk-inserted

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Figure 1. Schematic representation of sample preparation and methods. To test each adhesive system
in each one of the three temperatures (25, 37, and 60 °C), 20 bovine incisors were used. The roots were
removed with a diamond saw. The buccal aspect of the crown was wet-ground with SiC abrasive papers
in a polishing machine to obtain flat dentin surfaces. Standardized conical cavities (2 mm top
diameter  1.5 mm bottom diameter  2 mm height) were prepared with conical diamond burs, and their
lingual faces were ground. The adhesive systems were applied following the manufacturers’ directions.
The teeth were restored with composite resin and the buccal and lingual aspects of the restorations were
finished with abrasive papers coupled to a polishing machine. The samples were stored in distilled water
at 37 °C for 24 h. Half of them were subjected to further chemical degradation with 10% NaOCl for 5 h
before initiating the push-out bond strength test in a universal testing machine.

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into the cavity from its wider side. For MP and SE, a methacrylate-based composite resin
was used (Filtek Z250, 3M ESPE). For LS, the LS composite resin (Filtek Low-Shrinkage,
3M ESPE) was used. Photoactivation was performed with a Coltolux LED at 1264 mW/cm2
for 20 s. The light tip was positioned directly on the restoration, which had been previously
covered with a Mylar strip. The restorations were finished with abrasive cups and diamond
pastes on the buccal and lingual aspects. The samples were stored in distilled water at 37 °C
for 24 h. Half of them were subjected to further chemical degradation with 10% NaOCl for
5 h [14]. The push-out test was performed in a universal testing machine (model 4411,
Instron, Canton, MA, USA). An acrylic device with a central orifice was adapted to the base
of the machine. Each specimen was placed in the device with the top of its cavity against the
acrylic surface. The bottom surface of the restoration was loaded with a 1 mm diameter cylindrical plunger, at a cross-head speed of 0.5 mm/min, until failure of the tooth–composite bond
occurred in the lateral walls of the cavity. The plunger tip was positioned so that it touched
only the filling material, without stressing the surrounding walls. The load required for failure
was recorded by the testing machine, along with the area of each cavity (transformed into
MPa). The data for the bond strength were analyzed by three-way ANOVA (dental adhesive
system  temperature of the dental bonding agent  aging method), followed by Tukey’s test
(p < 0.05).
Failure modes
The fractured specimens were cut in half with a water-cooled low-speed diamond saw (Isomet
1000, Buehler, Lake Bluff, IL, USA) to obtain two specimens. Both specimens were fixed to
aluminum stubs, with the fractured interfaces facing upward. Specimens were sputter-coated
with gold (SDC 050 Suptter Coater, Baltec) and evaluated by scanning electronic microscopy
(JEOL, JSM 5600LV, Tokyo, Japan) to determine the failure mode. The failure modes were
defined as adhesive failure, cohesive failure in composite, and mixed failure (adhesive and
cohesive in composite). The data for the failure modes were analyzed by Kruskal–Wallis
(p < 0.05).
Results
Dc
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For the DC, differences among dental bonding agents and among temperatures of the dental
bonding agents were observed (p < 0.01). Multiple comparisons are shown in Table 2. All of
the dental bonding agents presented higher mean DC values when they were preheated at
60 °C. The bonding agent of the LS dental adhesive system presented the lowest mean DC
value at all temperatures.
Table 2. DC of the preheated bonding agents.
Temperature
Bonding agent
MP
SE
LS
25 °C
37 °C
60 °C
83.0 (0.4) Ba
83.7 (1.8) Ba
75.7 (1.5) Bb
82.4 (0.7) Ba
84.3 (1.5) Ba
76.6 (1.8) Bb
89.1 (1.1) Aa
91.6 (1.6) Aa
82.5 (0.6) Ab
Notes: Data are shown as means (standard deviations). Different uppercase letters in rows and lowercase letters in
columns indicate statistically significant differences (p < 0.05).

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Push-out bond strength
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The push-out bond strength values showed differences in the dental bonding agent  temperature of the dental bonding agent  aging method interaction (p = 0.02). Multiple comparisons
are shown in Table 3. After storage for 24 h in water, the prepolymerization temperatures of
the dental bonding agents influenced the bond strength values only for LS. Tooth restorations
bonded with preheated dental bonding agents at 60 °C presented the highest bond strength
values. LS showed the highest bond strength compared to the other restorative systems,
regardless of the temperature of the dental bonding agent. MP and SE showed bonding
stability after 10% NaOCl degradation at all temperatures of the bonding agent. LS showed
bonding stability when the bonding agent was preheated at 25 or 37 °C.
10
Failure modes
15
The frequencies of the failure modes are shown in Table 4. There were no statistically
significant differences among the temperatures for each adhesive system.
Discussion
The first hypothesis tested in this study was validated, since dental bonding agents preheated
at 60 °C showed increased DC. However, since higher temperature of the bonding agents did
not provided increased bond durability of restorations, the second hypothesis tested was
rejected. The dental bonding agents are a solvent-free mixture of monomers, which are polymerized after photoactivation. All of the bonding agents showed significantly increased DC
values when they were preheated at 60 °C. Improved monomer conversion of resin-based
materials in response to increased prepolymerization temperature can occur for many reasons.
The viscosity of the material is decreased with increasing temperature, which enhances radical
mobility [7]. The higher the curing temperature (below the glass transition temperature), the
greater the collision of nonreactive groups with free radicals [8]. Temperatures of 25, 37, and
60 °C were chosen to simulate room temperature, body temperature, and properly heated
materials, respectively. Only samples that were preheated at 60 °C displayed improved DC
values, presumably because this temperature provided greater radical mobility and collision of
the nonreactive groups with free radicals. This is in agreement with previous studies
investigating composite resins, which obtained increased DC for preheated materials [7–10].
Table 3. Push-out bond strength of dentin cavities restored with preheated 358 bonding agents,
according to aging method.
Temperature
Aging method
Bonding agent
25 °C
37 °C
60 °C
24 h water storage
MP
SE
LS
10.1 (3.8) Ab
10.8 (3.4) Aab
15.2 (3.5) ABa
7.1 (4.0) Ab
11.3 (2.1) Aab
13.5 (1.8) Ba
9.9 (6.6) Ab
11.1 (4.7) Ab
17.1 (3.8) Aa
24 h water and 5 h
10% NaOCl degradation
MP
SE
LS
7.1 (2.5) Aa
8.6 (3.6) Aa
11.8 (5.7) Aa
7.0 (4.1) Aa
7.8 (2.8) Aa
13.3 (5.3) Aa
9.6 (3.5) Aa
9.3 (3.5) Aa
11.4 (4.4)⁄ Aa
Notes: Data are shown as means (standard deviations). ⁄Different from 24 h water storage by ANOVA for the same
bonding agent and temperature (p < 0.05). Different uppercase letters in rows and lowercase letters in columns
indicate statistically significant differences (p < 0.05).
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Table 4. Frequency of the failure modes.
Aging method
24 h water storage
Temperature of the bonding
agent
A
MP
25 °C
37 °C
60 °C
25 °C
37 °C
60 °C
25 °C
37 °C
60 °C
10
5
7
9
7
5
4
5
1
–
–
1
–
–
–
–
–
3
–
5
2
1
3
5
6
5
6
25 °C
37 °C
60 °C
25 °C
37 °C
60 °C
25 °C
37 °C
60 °C
8
7
6
10
6
5
9
7
6
–
–
–
–
–
–
–
–
–
2
3
4
–
4
5
1
3
4
SE
LS
24 h water storage and
5 h 10% NaOCl
degradation
Failure modes
Adhesive
systems
MP
SE
LS
CC M
p
ns
ns
ns
ns
ns
ns
Notes: A: adhesive failure; CC: cohesive failure in composite; M: mixed (adhesive and cohesive in composite). ns:
p > 0.05.
Regardless of the prepolymerization temperature, the dental bonding agent of the LS
adhesive system showed the lowest DC values, whereas those of MP and SE were similar.
The different DC values for the three materials can be attributed to differences in their chemiAQ3 cal compositions. HEMA and TEGDMA are diluent monomers that are frequently added to
AQ4 Bis-GMA mixtures to reduce resin viscosity and increase monomer mobility. These
conditions favor the kinetics of monomer conversion [15]. The bonding agents of MP and SE
10
contain higher amounts of HEMA/TEGDMA monomers than does LS, which is probably
why the LS bonding agent showed a lower DC value.
The LS bonding agent showed the lowest DC. However, teeth restored with the LS system
showed the highest immediate bond strengths. In contrast with all other adhesive systems
tested, the self-etching/primer agent of the LS system must be photoactivated. The polymeriz15
able, self-etching primer of the LS adhesive system may mimic a 1-step self-etching adhesive,
because it contains the three cardinal steps for bonding (i.e. etching, priming, and bonding),
leading to the proper impregnation of the dentin substrate and optimal polymerization [16]. In
fact, the DC of the primer layer is even higher than the DC of the adhesive layer in dentin
interfaces bonded with the LS adhesive system [16]. Moreover, because the bond strength was
20
evaluated in high C-factor dentin cavities, the low shrinkage rates of the LS composite [17]
might be related to the improved bond integrity, due to the low stress levels generated in the
adhesive interface. Both of these attributes likely contributed to increase the immediate bond
strength of samples restored with the Filtek low-shrinkage composite restorative.
Despite the bonding agents preheated at 60 °C had higher DC values than those preheated
25
at 25 and 37 °C, an increase in the immediate bond strength was only observed for LS restorations bonded with the bonding agent preheated at 60 °C. Most likely, the combination of
the increased DC of the bonding agent with the low stress levels in the adhesive interface
provided the higher immediate bond strength for these samples. On the other hand, whereas
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the bonding agents of MP and SE showed higher DC values when they were preheated at
60 °C, the higher stress levels generated by the polymerization-induced shrinkage of the traditional methacrylate-based composite resin could have decreased the immediate bond strength
of these samples.
The temperatures of the dental bonding agents provided statistically similar failure modes
for restorations with the same dental adhesive system. Moreover, most of the tested conditions showed statistically similar bond durability of the dentin restorations. In fact, the 3-step
etch-and-rinse and 2-step self-etching adhesive systems have been shown to display satisfactory short-time dentin bond stability [12]. Use of 10% NaOCl as an aging method can induce
oxidation, leading to the fragmentation of resin unprotected collagen fibrils and affecting the
bond integrity [5]. Moreover, 10% NaOCl can promote resin dissolution at the hybrid layer
of adhesive systems [18], decreasing bond integrity. A demineralized dentin zone that is
insufficiently infiltrated by resin at the bottom of the hybrid layer is classically related to
etch-and-rinse adhesive systems. Nevertheless, collagen fibers that are incompletely coated by
resin have also been observed beneath the hybrid layer in self-etching adhesive systems [16].
Thus, all of the adhesive systems tested in this study could have been exposed to both of
these scenarios under 10% NaOCl use.
The improved DC of the LS dental bonding agent preheated at 60 °C was not sufficient to
prevent NaOCl degradation of the adhesive interface. Polymers with high crosslink densities
(CLDs) are morphologically more compact than those with a linear character and are more
resistant to solvent degradation and liquid absorption [19]. Resin-based polymer networks
with different DC values can present similar CLDs [20]. It is likely that the LS dental bonding agent preheated at 60 °C presented an extremely high DC, but a low CLD. This scenario
would favor, to some extent, the increased absorption of NaOCl and resin degradation,
leading to decreased bond integrity.
Different methods, such as the shear and tensile bond strengths, have been used to
measure dentin bond integrity. One disadvantage of these methodologies is that they are
generally performed on flat surfaces. In such situations, the C-factor is very low and the
shrinkage stress is not directed at the bonding interface [13]. For these reasons, the push-out
bond strength test was employed in the present study. The advantage of using the push-out
test is that the bond strength can be evaluated in a high C-factor cavity (2.2), such as Class V
cavities, with high stress generation directed to the bonding area [11]. The entire bonding area
was subjected to the compressive force at the same time, allowing the shear bond strength to
be evaluated in the cavity. The method also provides a better estimation of the bond strength
than does the conventional shear test, because fracture occurs in parallel (not transverse) with
the dentin bonding interface, thereby simulating the clinical condition [21].
5
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25
30
35
Conclusion
40
The dental bonding agents tested showed higher DC values when they were preheated at 60 °
C. However, the increased prepolymerization temperature of the dental bonding agents did
not lead to enhanced bond durability in high C-factor dentin cavities. Therefore, increasing of
the DC of dental bonding agents is not sufficient to improve the bond durability of the dentin
restorations.
45
Acknowledgements
The authors are grateful to KG Sorensen for providing them with their burs and polishing materials.

13. TAST
736190
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Initial
CE: VK QA: CS
11 October 2012
B.C.D. Borges et al.
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