Bilayered composite restoration: the effect of layer thickness on fracture behavior

Abstract

Purpose

By combining the increased toughness of a resin composite reinforced with discontinuous fibers and the surface wear resistance of a particulate filler composite (PFC), a bilayered composite technique was recently introduced. This study aimed to evaluate the effect of the thickness of the overlaying PFC placed over a fiber-reinforced composite (FRC) core, on the fracture-behavior of direct crown restorations.

Methods

Six groups of posterior crown restorations (n = 8/group) were fabricated having a discontinuous FRC-core (everX Flow) and a layer of surface PFC (Essentia U) with various thicknesses (0.5, 1.0, 1.5, 2.0 mm), with the remaining thickness of the bilayered being 6 mm. Control groups were only made of PFC or FRC materials. Restorations were statically loaded until fracture. Failure-modes were visually examined. Data were analyzed using ANOVA (p = .05) and regression analysis.

Results

The regression analysis showed that by decreasing the thickness of PFC layer, the load bearing capacity of restorations increased linearly (R²=0.7909). ANOVA revealed that crown restorations made only from everX Flow composite had significantly higher load-bearing capacities (3990 ± 331 N) (p < .05) among all the groups tested. With regard to the failure-mode analysis, crowns that had a FRC core material of everX Flow revealed delamination of the PFC surface composite from the core. Crowns which were made only of PFC i.e. with no fiber reinforcement, showed a crushing-like fracture pattern.

Conclusions

Restorations combining a thick FRC-core and a thin surface layer of PFC (0.5–1 mm), displayed promising performance related to fracture-behavior and load-bearing capacity.

Keywords:

• Fracture behavior
• bilayered restoration
• layer thickness
• fiber composite

Disclosure statement

Lippo Lassila and Sufyan Garoushi declare that they have no conflict of interests. Pekka Vallittu consults for Stick Tech – Member of GC Group in R&D and training. Eija Säilynoja and Roosa Prinssi work in research development and production Department at Stick Tech Ltd – Member of GC Group.