To evaluate marginal integrity of direct resin composite restorations before and after thermo-mechanical loading
in vitro, and before and after 6 years of clinical service in a prospective clinical trial.
For the in
vitro part, MO cavities with the proximal box beneath the cemento-enamel junction were prepared in 32 extracted human third
molars. The specimens were randomly assigned to four groups (n = 8) and received bonded resin composite restorations (two
groups each Grandio bonded with Solobond M and Tetric Ceram bonded with Syntac). Specimens were subjected to three different
aging protocols: 6-year water storage (WS), thermo-mechanical loading (TML; 100,000 × 50 N; 2500 × +5/+55 °C), and 6-year
water storage plus thermo-mechanical loading (WS + TML). Initially and after aging, marginal qualities in enamel and dentin
were evaluated using replicas at 200× magnification (SEM). For the in vivo part, 30 patients received 68 direct resin composite
restorations of the same materials in a prospective clinical trial. Replicas of 11 selected subjects per group were assessed
for marginal quality under a SEM at 200×.
in vitro, all initial results showed nearly 100% gap-free margins.
For TML, percentages of gap-free margins dropped to 87-90% in enamel and to 58-66% in dentin (p < 0.05). For WS, enamel
margins still were at 97-99% whereas dentin margins exhibited 67-75% gap-free margins, and for WS + TML, enamel margins were
at 85-87% and dentin margins at 42-52% gap-free margins. In vivo, gap-free enamel margins were reduced from initially 86-90%
to 74-80% after 6 years of clinical service (p < 0.05). Proximally exposed dentin margins were not recordable by impressions,
however, clinically no considerable problems like recurrent caries or discolorations were detected.
vitro, hydrolytic degradation supports mechanical fatigue in dentin-composite bonds over time. In vivo, wear phenomena are
superimposing marginal quality aspects. Gaps between enamel and resin composite did not play a major role.