Fatigue fracture resistance of a short fiber-reinforced flowable resin composite in single-layer and incremental-layer blocks

Abstract

Objectives: The purpose of this study was to evaluate the effect of a short fiber-reinforced flowable resin composite (SFRFC) on fracture resistance when used as a base material in an incremental layering technique, and to compare it with bulk-fill flowable resin composites (BFRCs). Methods: Seven commercially available flowable resin composites were evaluated: one SFRFC (everX Flow; EFB), three Bulk fill flowable resin composites without fiber reinforcement: (Beautifil-Bulk Flowable; BBF, Omnichroma Flow Bulk; OFB, and SDR flow+ Bulk Fill Flowable; SDR), and three different types of conventional flowable resin composite (Gracefil ZeroFlo; GZ, Beautifil Unishade Flow; BU, and Omnichroma Flow; OU). Flexural strength, flexural modulus, and resilience modulus were measured using a three-point bending test. A fatigue flexural strength test was performed using repeated subcritical load stress at 20 Hz for 50,000 cycles. Additionally, Knoop hardness and wear resistance were evaluated for each individual composite. Results: The incremental-layer group tended to show higher flexural strength, resilience modulus, and fatigue flexural strength than the corresponding individual flowable resin composites. The combination of GZ and the SFRFC EFB showed a significantly higher flexural strength, resilience modulus, and fatigue flexural strength than the other combinations of flowable resin composites. Knoop hardness was material dependent, and GZ exhibited significantly higher wear resistance than the other materials in the simulated localized wear test. Significance: The combination of SFRFC and conventional flowable resin composite GZ appears to be the optimal material strategy for the incremental-layer technique using flowable resin composites, specifically offering superior mechanical properties and fracture resistance against external forces.