Effect Of Interface Surface-texture On Fracture Behavior Of Bi-layered Composites

Objectives: Bi-layered composite structures [BLS] are growing rapidly in restorative dentistry. Materials such as bulk-fill and fiber-reinforced composites require dentists to place a final occlusal-composite layer made of a different material. This provides structural-integrity and longevity to the whole restoration. However, such a bi-layered system raises concerns about the interfacial segment between the two materials. Therefore, this study aimed to evaluate the effect of different interfacial-surface textures on the load-bearing capacity of such BLS.
Methods: Cylindrical (πx3.5²x5) specimens of BLS were prepared. Each specimen was made of a 3mm base composite (bottom layer) and 2mm occlusal composite (top layer) (n=60). Two different composite base materials where evaluated in this study; bulk-fill type SDR and fiber-reinforced composite everX Posterior [EVERX]. While hybrid-type composite Gænial Posterior was used as top layer in all the specimen fabricated. Three different interfacial-textures were used in this study; (i) Pyramidal, (ii) longitudinal parallel grooves and (iii) Perpendicular grooves. 3D-printed molds were fabricated to standardize the interfacial-texture between the top occlusal-composite and the bottom base composite materials. The base material was light-cured through the 3D-printed mold before application of the top-layer composite. The specimen where then statically-loaded with a steel ball (Ø 4mm) until fracture using a universal testing machine. Load values were evaluated using two-way ANOVA. Fracture types were classified into favorable or unfavorable bulk fracture.
Results: Load-bearing capacities showed variations with different surface-textures. SDR showed lower mean load bearing capacity when compared to EVERX in all the surface-textures. Two-way ANOVA revealed that material had a significant effect on the load bearing capacity (p=0.008), whereas surface texture did not have a significant effect (p>0.05). Fracture analysis has shown that EVERX demonstrated 80% favorable bulk-fractures whereas SDR demonstrated exclusively unfavorable bulk-fractures.
Conclusions: The presence of different interfacial-texture enhanced the fracture behavior of fiber-reinforced bi-layered composite structure.