Interfacial Bond Strength and Fracture Behaviour of Bi-layered Composite Structures

Objectives: Injectable composites like everX Flow (GC Corporation) and SDR flow + (Dentsply-Sirona) are intended for use as dentin replacement (substructure) in large restorations. Unlike SDR flow + the filler fraction of everX Flow consists of both glass particles and discontinuous randomly oriented glass fibers. In the present study, the shear bond strength (SBS) of four particulate filler composites (PFCs) to the substructure composites were compared, followed by fracture analysis.
Methods: For SBS, 120 cylindrical cavities (diameter 6 mm and depth 4 mm) were prepared in acrylic blocks and filled with either a substructure material (everX Flow or SDR flow + or the proper PFC (control). After light-curing while exposed to air, about 2 mm cylindrical increment of the PFC [G-aenial Posterior (GP), G-aenial Universal Injectable (GUI), Essentia Universal (EU) and Ceram X (CX)] was placed on top and light-cured according to manufacturer’s recommendations. After SBS testing (speed 1mm/min), fracture surfaces were analyzed under the light microscope. Results were statistically analyzed with ANOVA and Tukey’s test (p<0.05).
Results: SBS between the two increments are shown in Table. FRC had statistically significantly (p<0.05) higher SBS values than PFC and SDR. SDR substructure failed cohesively before the overlaying PFC, whereas everX Flow substructure and overlaying PFC failed either as one block or adhesively.
Conclusions: Flowable composite with glass fibers (everX Flow) was a better bonding substrate for PFC than flowable composite with particulate fillers (SDR).