Micro-tensile bond strength of adhesives bonded to class-I cavity ...

1006
etch and rinse control (Table 2; Fig. 2). Given the nonchanged
mTBS and fracture surface ultra-morphology
(Fig. 4), this adhesive also resisted to the thermocycling
regimen very well. This is consistent with in
vitro research, in which its predecessor Clearfil SE
(very similar in composition to Clearfil Protect Bond,
apart from the antibacterial monomer added to the
latter) performed very well. This two-step self-etch
adhesive resisted to 1 year in vivo functioning [26,27],
up to 30,000 thermo-cycles in a ‘shear-bond’ strength
test [5], and combined thermal and occlusal loading
[9]. Long-term water storage of prepared mTBSbeams
on the other hand, decreased the bond
strength to dentin [16,23]; other types of adhesive
did, however, decrease at least to the same extent in
a similar study [23]. Also in clinical class-V studies,
this adhesive performed very well [28,29].
iBOND was not able to produce a strong bond to
dentin at the bottom of an occlusal class-I cavity
(Table 2). For the control and the thermo-cycling/
stick group, all pre-testing failures occurred after
24 h during further specimen preparation. Because
of this low bonding effectiveness at baseline and
the low number of remaining specimens, no
conclusion can be drawn regarding degradation of
the resultant adhesive–tooth bond. Nonetheless,
the bond strength of this adhesive is too low to
resist the polymerization shrinkage of the restorative
composite in a class-I cavity. Analysis of the
fracture planes revealed that in all groups porosities
were observed in the adhesive resin near the
interface. This certainly must have weakened the
bond and is to a large extent responsible for the low
bonding effectiveness recorded. Similar porosities
were observed by Tay et al. [30,31]. These
porosities may be due to residual solvent (H2O)
that was not adequately removed because of
inefficient drying in a narrow cavity. Alternatively,
these porosities may also be caused by an osmotic
driven water uptake from dentin and/or the
environment, as these one-step self-etch adhesives
can act as semi-permeable membranes [30]. The
large amount and density, as seen in this study, may
be due to the storage in water for 20 days that
allowed this water uptake to take place to its full
extent. The bonding effectiveness after 24 h would,
however, not have been that different, as all pretesting
failures occurred during specimen preparation
1 day after adhesive procedures. The most
plausible explanation that follows out of recent
research [32,33] is that these porosities represent
water droplets that separated from the monomers
that no longer remained dissolved in water upon
evaporation of acetone.
In conclusion, thermo-cycling did not result in an
enhanced chemical or mechanical degradation of
the bonds to dentin produced by a two-step selfetch
and a three-step etch and rinse adhesive. The
bonding effectiveness of the one-step self-etch
adhesive tested was, however, too low to withstand
polymerization shrinkage stress, as produced in an
occlusal class-I cavity.
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