Bond Strength and Failure Mode of Two Packable Resin Composites

"Objectives: " To compare the shear bond strength and failure mode of two packable composite systems to horizontal and vertical human dentin.

"Methods: " Thirty (30) dentin human third molars slices were randomly distributed into six subgroups of 5 specimens each:  2 subgroups for superficial horizontal dentin, 2 for deep horizontal dentin and 2 for vertical dentin. Cylinders of methacrylate (Filtek P60, 3M ESPE, St. Paul, Minnesota, USA) and silorane (Filtek P90, 3M ESPE, St. Paul, Minnesota, USA) based restorative systems were bonded to each type of dentin and after 24 hours submitted to 2500 thermal cycles. Subsequently, shear bond strength tests were performed applying the force (crosshead speed of 0.5 mm/min) at the composite/dentin interface using the universal testing machine (Instron 1011, Instron Corp, Norwood, MA, USA). Finally, dentin surfaces and composite cylinders were observed using a stereomicroscope (Stemi 2000C, Carl Zeiss, Göttingen, Germany)

"Results: " Shear bond strength to superficial horizontal dentin, showed a statistical significant difference (p=0,006) between the two composite systems, presenting higher values the methacrylate system (30,52 MPa vs. 19,66 MPa). No statistical difference was observed at deep horizontal and vertical dentin when both composites were compared (p>0.05). Failure mode for superficial horizontal dentin with P60 was predominantly cohesive while for P90 was predominantly adhesive (80% and 60% respectively). In deep horizontal dentin for P60 was predominantly adhesive while for P90 was cohesive (80% both). In vertical dentin slices, failure mode for both systems was predominantly adhesive.

"Conclusions: " Bond strength to different types of dentin and failure mode is influenced by the dental substrate pre-treatment and the chemical composition of the specific adhesive used by each composite packable system. There is a dependence relationship between shear bond strength and failure mode at superficial and deep horizontal dentin.