Microtensile bond strength of a filled vs unfilled adhesive to dentin ...

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can be considered as a strong self-etching primer
because of its low pH, 1.0. 36 This high acidity
results in deeper demineralization and the hybrid
layer thickness using the self-etching primer Tyrian
SPE resembled those of the total-etch technique
both with filled and unfilled adhesives, whose
thickness is different from the other self-etch
primer/adhesive systems (i.e.: Clearfil SE Bond). 37
However as previously reported hybrid layer thickness
does not correlate with bond strength values 38
and microtensile bond strengths to dentin in
comparison to the total-etch technique was compromised
when the self-etching primer Tyrian SPE
was used (Table 3). In addition, the debonded
specimens of the Tyrian SPE groups showed mainly
adhesive failures (Figs. 6 and 8), whereas the totaletch
specimens showed mostly mixed failures
(Figs. 5 and 7). These lower bond strengths using
Tyrian SPE both with filled and unfilled adhesives
may be attributed to these factors: Tyrian SPE
contains a high concentration of ethanol and water.
Although it would be desirable to remove all water
and solvent at the end of the etching time, acidic
monomers, dissolved calcium and phosphate ions
may lower their vapor pressure. Residual water in
the dentin subsurface may interfere with polymerization
of the mixture of the self-etching primer
and the adhesive resin, thereby lowering the quality
of the hybrid layer. 39
In addition to this, the problem may be further
aggravated by the addition of One-Step Plus and
One-Step, which also contains a high concentration
of acetone. It has been shown that incomplete
removal of acetone from the adhesive layer of twostep
total-etch adhesives resulted in poor polymerization
of resin and crack formation in the
adhesive layer or between adhesive and hybrid
layer, leading to premature bond failure. 40–42 The
observed gaps in One-Step Plus (Fig. 2(B)) and One-
Step (Fig. 4(B)) self-etch groups may have been
originated from or may have been increased by air
drying and desiccating the specimens for SEM
observation. However since such gaps or cracks
were not evident in total-etch groups, and since all
specimens were treated in the same manner, they
may have been attributed to poorly polymerized
hybrid/adhesive layers.
In conclusion, the 8.5% glass-filled adhesive One-
Step Plus did not show any beneficial effect than the
unfilled adhesive One-Step on the mTBS to dentin
with total-etch and self-etch techniques. Irrespective
from the adhesive type, self-etch technique
revealed lower bond strengths than the total-etch
technique. Further research is necessary to compare
the effects of fillers in adhesives with the same resin
composition and solvent on bonding to dentin within
various cavity shapes and on the durability of the
resin-dentin bonds made with these adhesives using
total-etch and self-etch techniques.
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