Fernandes Júnior VVB et al.
MICROTENSILE BOND STRENGTH OF TWO SELF-ADHESIVE CEMENTS TO ENAMEL AND DENTIN: BONDING EFFICIENCY AND THERMOCYCLING
EFFECT
Microtensile bond strength of two self-adhesive cements to enamel
and dentin: bonding efficiency and thermocycling effect
Microtração de dois cimentos auto-condicionantes (self-adhesive) sobre
esmalte e dentina: eficiência de adesão e efeito do envelhecimento
Virgílio Vilas Boas FERNANDES JÚNIOR
MsC - Restorative Dentistry - School of Dentistry of São José dos Campos - UNESP - Univ Estadual
Paulista - São José dos Campos - SP - Brazil.
José Roberto RODRIGUES
Associate Professor - School of Dentistry of São José dos Campos - UNESP - Univ Estadual
Paulista - São José dos Campos - SP - Brazil.
João Maurício Ferraz da SILVA
PhD in Dentistry - Department of Restorative Dentistry - School of Dentistry of São José dos Campos
- UNESP - Univ Estadual Paulista - São José dos Campos - SP - Brazil.
Clóvis PAGANI
Associate Professor - Department of Restorative Dentistry - School of Dentistry of São José dos
Campos - UNESP - Univ Estadual Paulista - São José dos Campos - SP - Brazil.
Henderson MALAQUIAS
DDS - Department of Restorative Dentistry - School of Dentistry of São José dos Campos - UNESP Univ Estadual Paulista - São José dos Campos - SP - Brazil.
Ivan BALDUCCI
Assistant Professor - Department of Social Dentistry and Pediatric Clinic - School of Dentistry of São
José dos Campos UNESP - Univ Estadual Paulista - São José dos Campos - SP - Brazil.
Abstract
The aim of this in vitro study was to evaluate the bonding efficiency between two self-adhesive cements to enamel
and dentine, with and without previous dental surface conditioning, before and after thermocycling. Thirty-six molars
were divided into 3 experimental groups and 01 control group. The self-adhesive resin cements selected for the
experimental groups were: RelyX Unicem (subgroups RE and RD) and Bifix SE (subgroups BE and BD). For control
groups, a conventional resin cement, Variolink II (subgroups VRE and VRD), was used. The specimens were submitted to
microtensile bond strength test. The results were submitted to analysis of variance (ANOVA) and Tukey’s test. The results
showed statistically significant differences between VR group and the others before and after thermocycling. According
to the results obtained, it can be concluded that self-adhesive cements, despite of their practicality and less sensitive
technique concerning to cementation, have lower adhesive resistance when compared to conventional resin cements.
Keywords
Dental cements; cementation; microtensile.
Braz Dent Sci 2012 jan./mar.; 15 (1) 33-38
33
Fernandes Júnior VVB et al.
MICROTENSILE BOND STRENGTH OF TWO SELF-ADHESIVE CEMENTS TO ENAMEL AND DENTIN: BONDING EFFICIENCY AND THERMOCYCLING
EFFECT
Introduction
Restorative Dentistry has been modified in
several aspects which seem to institute new rules to
the therapeutic modalities of indirect restorations,
especially for restorative ceramics [1,2] and resin
cements [3-5].
The appearance of dual cure resin cements
allowed a significant improving regarding to
problems in luting, such as marginal gap, inadequate
polymerization of the luting agent, secondary caries
and marginal leakage [6-8].
However, these cements demand skilled clinical
procedures, especially during the removal of the
excess cement prior to its complete polymerization,
making this technique a complicated and sensitive
procedure [9]. Additionally, to increase the bonding
of these cements, it has been recommended the
previous conditioning of the tooth surface and
restoration.
Aiming to facilitate the use of the technique for
resin cements, self-adhesive resin cements have
been launched into the market, whose goal is to
combine the easy handling of glass ionomer cements
with the mechanical, aesthetical and bonding
properties of the resin cements [10]. According to the
manufacturers, bonding to the tooth occurs without
any previous conditioning. This process is based on
a new monomer and organic matrix of methacrylatephosphoric acid which etch and infiltrate on tooth
surface, contributing to bonding.
Likewise to self-etching adhesive systems, as the
self-adhesive cements promote the demineralization
of the dentin, the primer and adhesive is
impregnated, decreasing the chances of causing a
layer of demineralized and non-impregnated dentin.
Additionally, problems such as the incomplete
removal of the acid after the washing and excessive
drying of the dentin do not occur with the use of these
systems because the absence of these steps decreases
the possibility of post-operative sensibility.
These systems are composed by weak acids which
tend to reduce its capacity of etching and bonding to
enamel due to the highly inorganic composition of
this tissue. In this process, there is the dissolution
of the enamel prisms and the enlargement of the
interprismatic spaces, allowing the interdiffusion of
the resin monomers and the hybridization of the intraand interprismatic enamel instead of the formation of
pure resin tags such as those occurring in the systems
which employ total etching. In dentin, because of the
smallest mineral content, the demineralization and
34
consequent bonding is improved.
Despite of their advantages mainly regarding to
their practicality and smaller chair time, self-adhesive
cements need further studies on their efficiency
regarding to long-term bonding. Therefore, the aim
of this study was to evaluate the bonding efficiency
between two self-adhesive cements to enamel and
dentine, with and without previous dental surface
conditioning, before and after thermocycling,
through microtensile bond strength test. The null
hypothesis was that there would be no statistically
significant difference between the self-adhesive
cements (Rely –X and Bifix) and the resin cement
(Variolink II) in bond strength.
Material and Methods
Tooth collection
Thirty-six sound third molars extracted because
of orthodontic reasons, after the approval of the
Ethical Committee (#067/2008-PH/CEP), were
selected. The teeth were cleaned and kept in saline
solution until their use
Preparation of the Specimens
For the enamel groups, the buccal surface of 18
third molars was flattened by 600-, 800- and 1200grit sandpaper in a polishing machine. The teeth
were then divided into three groups according to
the cements: RelyX Unicem (RE), Bifix (BE) and
Variolink (VRE).
For the dentin groups, the other 18 teeth had
their occlusal thirds removed with a diamond disc
(Microdont, São Paulo, Brazil, #34570) at low speed,
under refrigeration. Next, the surface was flattened
similarly to the aforementioned procedure for the
enamel groups. Following, the dentin surface was
observed regarding to the presence of enamel and
pulp tissues by using an optical microscope and then
divided into three groups according to the cements:
RelyX Unicem (RD), Bifix (BD) and Variolink
(VRD).
Prior to cementation, blocks of direct composite
resin (Z1OO, 3M ESPE, St Paul, MN,USA) were
light-cured inside a pre-fabricated silicon matrix
through small increments of 2 mm each and the
last portion was light-cured after the insertion of a
polyester strip to promote a flat and smooth surface.
The composition of the resin cements are
described in Chart 1.
Braz Dent Sci 2012 jan./mar.; 15 (1) 33-38
Fernandes Júnior VVB et al.
MICROTENSILE BOND STRENGTH OF TWO SELF-ADHESIVE CEMENTS TO ENAMEL AND DENTIN: BONDING EFFICIENCY AND THERMOCYCLING
EFFECT
Chart 1 – Resin cements and their composition
Variolink
II
Dual
cure
Ivoclar
Vivadent
BisGMA/UDMA/TEGDMA/
DMA/barium sulphate/BaAl-F-Si-glass/silica, Benzoyl
peroxide glycerin
Rely-X
U-CEM
Selfadhesive
3M
ESPE
glass powder, silica, calcium
hydroxide, pigments, pyridine
peroxide, methacrylate
phosphoric acid ester,
dimethacrylate, acetate,
stabilizer, initiator, acetate.
Maxcem
Selfadhesive
Kerr
Hawe
Neos
Orange
Resin matrix: self-adhesive
acid monomer (GPDM),
co-monomers, self-curing
initiators, photoinitiator,
stabilizer.
Inorganic matrix: 67 % vol.
Cementation
For the groups RE, BE, RD, BD, The cements
RelyX Unicem (3M ESPE/ St. Paul, MN, EUA)
and Bifix SE (Voco/GHBM, Germany) were mixed
according to the manufacturers’ instructions and
directly applied onto the tooth surface without any
previous conditioning. The blocks of composite
resin were then positioned and locked by a
standardized load by a mobile spindle. Following,
the excesses were removed and the set (toothcement-block) was light-cured for 40 seconds
(light-cure unit XL 3000, 3M ESPE, MN, USA;
500 mW/cm2) on each side of the interface cement/
tooth surface.
For the groups VRE and VRD, twelve teeth
received a conditioning by 35% phosphoric acid for
30 s and 15 s, respectively, followed by the copious
rinsing with air/water jet for 10 s and application of
the bonding agent (Adper Single Bond 2, 3M/Espe,
St. Paul, Mn, USA), following the manufacturer’s
instruction. The cement (Variolink II) was mixed at
1:1 proportion, for 10 seconds. Then, it was applied
onto the tooth surface and the resin block was placed
following the same procedure for the other groups.
After 24 hours of storage in distilled water at 37OC,
the samples (resin block/tooth) were sectioned
perpendicularly to the interface cement/tooth, in a
cutting machine (LabCut 1010, Extec, Enfield, CT,
USA) by using diamond discs (Microdont, São
Paulo, Brazil, #34570), at low speed, under copious
irrigation. The samples were placed in order that
the interface cement/tooth is perpendicularly to
the diamond disc of the machine. The first cut,
measuring about 1 mm, was discarded to standardize
the samples. Next, other three sections measuring
1.0 mm thick were prepared.
Braz Dent Sci 2012 jan./mar.; 15 (1) 33-38
After that, the fixation device of the samples
was rotated at 90 degrees, and other four cuts were
performed similarly to the aforementioned procedure.
In average, nine rectangular specimens with 1.0 mm2
and 8 mm length were obtained.
Half of the samples were analyzed just after
the cuts and the other half was submitted to
thermocycling (5,000 cycles; 5°C/55°C, time period:
30 s, transference time: 2 s) (Nova Etica, São Paulo,
Brazil).
Microtensile bond strength test
The samples were individually fixed by their
endings with a cyanoacrylate gel adhesive (Super
Bonder Gel, Loctite Ltd, Piracicaba, SP, Brazil), in the
microtensile bond strength machine (LA 2500, Erios,
São Paulo, SP, Brazil), by placing the bonding area
perpendicular to the long axis of the bond strength,
therefore avoiding the occurrence of torsion and
shear forces (Figure 1).
A
B
Figure 1 – Sample positioned in the machine, before (A)
and after (B) the test.
The test was performed at constant speed of 1mm/
min in a universal testing machine (DL200 MF, Emic,
São José dos Pinhais, Paraná, Brazil), with load of
10 Kg. At the moment of the fracture, the movement
was automatically stopped and the microtensile bond
strength values were recorded and tabulated for
statistical analysis.
At the ending of the test, the two parts of the
sample were stored to enable that the fracture pattern
be evaluated.
Statistical analysis
Three-way ANOVA and Tukey test for multiple
comparisons were applied for statistical analysis,
35
Fernandes Júnior VVB et al.
MICROTENSILE BOND STRENGTH OF TWO SELF-ADHESIVE CEMENTS TO ENAMEL AND DENTIN: BONDING EFFICIENCY AND THERMOCYCLING
EFFECT
considering the following factors: resin cement,
thermocycling, and tooth substrate. The level of
significance was set at 5% for all tests.
Results
The statistical analysis was carried out
comparing the effects: cement, cement x area,
cement x thermocycling and cement x area x
thermocycling. There was a statistically significant
difference in the interaction cement x area x
thermocycling. Means and standard deviation can
be analyzed in Graph 1.
Table
2
-
Homogenous
groups
with
thermocycling
Cement
Tooth
substrate
Mean
Homogeneous
Group
VR
D
23,800
A
VR
E
17,350
B
R
E
11,400
C
R
D
9,196
CD
B
E
8,815
CD
B
D
7,077
D
The analysis of the surface fracture demonstrated
for the experimental groups (Rely-X and Bifix SE),
predominantly adhesive failures; in control group
(Variolink II), the failures were predominantly mixed.
Discussion
Graph 1 - Column Graph (mean±standard deviation) of the
values obtained in the microtensile bond strength test in
MPa, according to the experimental conditions.
Considering the statistical difference, Tukey test
for multiple comparisons was applied with level of
significance set at 5%. There
was
statistically
significant difference among Variolink (both for
enamel and dentin) and the other groups before (VE:
18,411) (VD: 24,574) and after thermocycling (VE:
17,350) (VD: 23,800).
There was no statistically significant
difference between the self-adhesive cements,
except between groups RE and BD; (RE: 12,107
and 11,400), (RD: 11,400 and 9,196), (BE:
10,132 and 8,815), (BD: 7,752 and 7,077).
The means and the homogenous groups can be
verified in tables 1 and 2.
Table 1 - Homogenous
groups
without
thermocycling
36
Cement
Tooth
substrate
Mean
Homogeneous
Group
VR
D
24,574
A
VR
E
18,411
B
R
E
12,107
C
R
D
10,640
CD
B
E
10,132
CD
B
D
7,752
D
During the cementation of an indirect restoration,
the luting agent is placed between the tooth and
the restoration, creating two distinct interfaces:
restoration/cement and cement/tooth surface. Resin
cements are the materials of choice for indirect
cementation, mainly in cases of metal-free crowns
[10,11]. The bonding between the resin cements
and the indirect restorations is not a great concern
in clinical practice because surface conditioning has
been indicated to increase this bonding [12,13]. On the
other hand, the bonding between the tooth substrate
and the resin cement, required for the durability of the
tooth/restoration system [10,11,14,15], has been the
most critical and difficult step. In order to achieve a
proper bonding, surfaces conditioning, such as total
acid etching or the use of self-adhesive cements has
been commonly used [16-18].
In our study, the hypothesis that the application
of the experimental cements (Rely-X and Bifix)
through their simplified mode as indicated by their
manufacturers would not decrease the bond strength
in comparison with the conventional cements (here
represented by the control group) was not proved
because the results showed that there was a significant
difference between them, both in enamel and dentin,
before and after thermocycling.
This was proved by the highest bonding values of
the surfaces conditioned by phosphoric acid followed
by the application of the bonding system (control
group) in comparison with those obtained by the
experimental groups (self-adhesive cements). Also, in
this present study, several samples of the experimental
groups showed spontaneous failure during the cutting
Braz Dent Sci 2012 jan./mar.; 15 (1) 33-38
Fernandes Júnior VVB et al.
MICROTENSILE BOND STRENGTH OF TWO SELF-ADHESIVE CEMENTS TO ENAMEL AND DENTIN: BONDING EFFICIENCY AND THERMOCYCLING
EFFECT
procedures, suggesting low shear bond strength. Acid
etching creates microporosities on the interprismatic
enamel through where the hydrophobic monomers
of the bonding agent may penetrate originating high
micromechanical retention [14]. These results are
in agreement with those of other studies [16,19,20]
which demonstrated that the surface conditioning
prior to the application of the resin cement resulted
in high bond strength in comparison with non treated
substrates. The replacement of the acid phosphoric
etching by the acid monomers present in the selfadhesive cements promotes a low interprismatic
hybridization and, consequently, a weak bonding
[16,17,19,20]. This may explain the similar results
of the experimental groups, which demonstrated that
despite of the low pH of these cements (around 2 at
the first minute), an apparent demineralization of the
tooth surface did not occur. According to De Munck
et al [16], this is because of the high viscosity of these
materials with consequent deficiency of penetration in
function of the time. De Angelis et al [21] reported
that Rely-X Unicem showed the smallest number of
pre-test failures in relation to the other self-adhesive
cements (iCEM – Heraeus Kulzer, Maxcem – Kerr,
Enacem HF – Micerium). The authors also reported
that this cement did not show statistically significant
difference in relation to the other self-adhesive
cements, although it still presented statistically
smaller bond strength than the conventional multiple
step cements (Panavia F – Kuraray).
Concerning to bonding to dentin, De Munck
et al. [16] reported that Rely-X Unicem, applied in
a simpler way showed a bond strength similar to
control group (Panavia F). In other study, Sahar et al.
[22] obtained results without statistically significant
difference among Rely-X Unicem and Panavia F,
Variolink, Dyract Cem Plus; and results significantly
higher than Ketac Cem prior to thermocycling.
After thermocycling, the authors also reported the
increasing in the bond strength, statistically higher
than Panavia F, Dyract Cem Plus and Ketac Cem,
although smaller than Variolink. This is because of
the highest sensibility of the self-adhesive cements
without water as solvent [2] and to the possible acidbase reaction occurring among the acid monomers of
the bonding agents, especially those of Dyract Cem
Plus, inhibiting the initiation of the chemical curing
components of the cements [19].
In our study, we observed that Variolink also
presented a significantly higher bond strength than
the other self-adhesive cements, which was partially
in agreement with the results of a previous study
[22], because after thermocycling the bonding
values of Rely-X did not increase, according to
the author. In this study, the thermocycling did not
promote a significant reduction in the bond strength
values of all groups. Based on the results of this
study, further studies are necessary to explain the
interaction between self-adhesive cements and tooth
substrate, especially regarding to demineralization
and impregnation of the resin monomers and
consequently to bond strength.
Conclusion
Self-adhesive cements, despite of their
practicability, do not show yet bond strength values
similar to conventional resin cements.
Resumo
O objetivo deste trabalho foi analisar in vitro a eficiência de adesão através de ensaio de microtração, de dois cimentos
autocondicionantes (self-adhesive), sobre esmalte e dentina, antes e após termociclagem em comparação a um cimento
resinoso convencional. Foram utilizados 36 terceiros molares, separados em grupos experimentais, sendo 2 grupos com
cimentos resinosos auto-condicionantes (Rely X Unicem - 3M ESPE – subgrupos RE e RD) e Bifix SE - Voco/GHB –
subgrupos BE e BD) e 1 grupo controle, com o cimento adesivo (Variolink II – Ivoclair - subgrupo VRE e VRD). Para a
análise estatística do teste de adesão, foi utilizado ANOVA 3 fatores com teste de comparação múltipla de Tukey (5%). Os
resultados evidenciaram diferença significante entre os grupos VR, dos demais grupos, antes e após termociclagem. De
acordo com os resultados, podemos concluir que os cimentos autocondicionantes, apesar da sua praticidade, facilidade de
técnica e menor susceptibilidade de hidrólise, ainda possuem menor resistência adesiva em relação aos cimentos resinosos
convencionais.
Palavras-chave
Cimentos dentários; cimentação; microtração.
Braz Dent Sci 2012 jan./mar.; 15 (1) 33-38
37
Fernandes Júnior VVB et al.
MICROTENSILE BOND STRENGTH OF TWO SELF-ADHESIVE CEMENTS TO ENAMEL AND DENTIN: BONDING EFFICIENCY AND THERMOCYCLING
EFFECT
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Received: 16/07/2011
Accepted: 23/02/2012
Corresponding author:
Virgílio Vilas Boas Fernandes Júnior
Rua Enseada , 46 – Cidade Jardim
São José dos Campos – SP – Brasil. - CEP: 12230-630
virgiliovilas@hotmail.com
Braz Dent Sci 2012 jan./mar.; 15 (1) 33-38