The aim of this in vitro study was to compare the dentin bond strength and
marginal adaptation of directly and indirectly inserted restorations. A con
ically modified push-out test was designed to consider polymerization shrin
kage and facilitate inlay placement. A total of 260 cavities were prepared
into disks of freshly extracted human third molars and filled with direct c
omposite resins or with adhesively luted ceramic inlays. Dentin adhesives o
f the third- (with self-etching primer: ART Bond, Syntac Classic), fourth-
(with total etching: Scotchbond Multi-Purpose Plus), and fifth-generation t
one-bottle adhesives: Syntac Single Component, Prime&Bond 2.1) were used in
combination with one hybrid composite (Tetric) or luting composite (Variol
ink Low). Control groups did not use an adhesive. Polymerization of the bon
ding agent was carried out prior to insertion of the filling/inlay or after
wards simultaneously with the composite/luting composite. The thickness of
the adhesive layer and luting composite was recorded, and after 7 days of s
torage and 24 hours of thermocycling (1150 cycles) replicas were made and e
xtrusion testing performed. Fracture modes were determined and replicas wer
e examined regarding marginal adaptation using SEM (X200 magnification).
Precuring of the bonding resin increased dentin bond strength independent o
f the material combination or insertion mode (P < 0.05). In general, third-
and fourth-generation dentin adhesives produced better results in bond str
ength achieved significantly higher push-out values than Syntac (P < 0.05),
but no better marginal adaptation. Cohesive fractures within the dentin we
re only observed in the inlay groups with precured resin.
Precuring of the bonding resin is an important factor for both direct and i
ndirect restorations. Nevertheless, precuring of the bonding resin prior to
insertion of adhesive inlays cannot be recommended clinically, because the
120-mu m luting spaces were too large. In simulated cavities, direct compo
site fillings with precuring achieved bond strengths similar to inlays with
out precuring. One-bottle adhesive systems performed poorly compared with m
ulti-step adhesives of the third and fourth generation.