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

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Figure 4 (A) Scanning electron micrograph of the resin–
dentin interface bonded with One-Step with self-etch
technique after argon ion etching. Thickness of the hybrid
layer (3.5 mm) was similar to the One-Step total-etch
group (Fig. 3(A) and (B)). The unfilled adhesive layer was
only 2 mm thick (compare Fig. 2(A) and (B)). c, composite;
a, adhesive; h, hybrid layer; d, dentin. (B) Scanning
electron micrograph of the resin–dentin interface bonded
with One-Step with self-etch technique subjected to
sequential acid–base treatment. Thickness of the hybrid
layer (3.5 mm) was similar to the One-Step total-etch
group (Fig. 3(A) and (B)). c, composite; a, adhesive; h,
hybrid layer; d, dentin, g, gap induced in the adhesive
layer and between hybrid layer and adhesive layer.
adhesive failures (Fig. 6). Using total-etch technique,
the filled adhesive One-Step Plus (Fig. 5)
and unfilled adhesive One-Step (Fig. 7) showed
mostly mixed failures.
Discussion
E. Can Say et al.
Filled adhesives were expected to act as an
intermediate shock-absorbing elastic layer
between composite resin and dentin, thus increasing
the bond strength to dentin. 1,3,20 Many studies
evaluated comparisons between commercially
available filled and unfilled adhesives however,
the advantages of these adhesives as stress buffers
remain unpredictable 7 and have not been substantiated
with in vitro bond tests 25–29 and a clinical
trial. 30 Filler type, size, shape, its surface characteristics,
their interaction with the resin matrix and
various solvents in the adhesives may affect the
bond strength. 20,21,31–33 The unfilled adhesive One-
Step and filled adhesive One-Step Plus, used in this
study, utilizes acetone as a solvent. Besides, One-
Step Plus consists of 8.5% Glass fillers with an
average particle size of 1 mm. SEM observations of
the resin-dentin interfaces revealed that the
thickness of the hybrid layer created with One-
Step Plus was almost similar to that achieved with
One-Step both with total-etch (approximately
3 mm; Figs. 1(B) and 3(B), respectively) and selfetch
(approximately 3.5 mm; Figs. 2(B) and 4(B))
techniques. Conversely, the adhesive layer of the
filled adhesive was thicker (Figs. 1(A) and (B), 2(A)
and (B)) than the unfilled adhesive (Fig. 3(A) and
(B), 4(A)). Filler particles were found around the
tubular orifices and in some dentin tubules
(Fig. 1(A)) with the total-etch technique, however
they were not capable of penetrating into the
spaces between collagen fibers because the width
of interfibrillar spaces is about 20 nm. 9 The results
of the microtensile bond test showed that bond
strengths to dentin between filled adhesive One-
Step Plus and the unfilled adhesive One-Step were
not significantly different when they were used with
the total etch (38.8G12.2 and 33.9G8.5 MPa,
respectively) and with the self-etch technique
(22.4G4.0 and 26.4G7.5 MPa, respectively).
These results might indicate that the penetration
ability of the resin monomer and the evaporation
rate of water/solvent from dentin subsurface are
not so different between filled and unfilled
Table 4 Failure modes of the specimens after microtensile bond test.
Groups Adhesive Mixed Cohesive in dentin Cohesive in composite
One-Step Plus total-etch 3 15 2 –
One-Step Plus self-etch 17 3 – –
One-Step total-etch 5 15 – –
One-Step self-etch 14 6 – –
Adhesive, between resin and dentin; Mixed, partially adhesive, partially cohesive failure in bonding resin or hybrid layer; Cohesive in
dentin; Cohesive in resin.