Flexural-strength of FRCs as a function of composite-thickness, fiber-type, cyclic-loading

Objective: To evaluate the flexural strength of various fiber-reinforced composites (FRC) in combination with particulate filler composite (PFC) as a function of PFC thickness, FRC type with and without exposure to cyclic loading. Method: FRC-PFC combinations (N=160, n=10 per group) were produced using a polyethylene mold (thickness: 2.5, width: 3, length: 40 mm). Three types of FRCs (Voco FRC-VF; everStick-EF; Dentapreg PFU-DF) were combined with the PFC (Voco Grandio). Non-reinforced specimens made of PFC only acted as the control group. The thickness of the specimens increased in the order of 4 and 6 mm by incremental application of the PFC to the FRC. Subsequently, the polymerized specimens were randomly divided into two groups to be tested with and without exposure to thermo-mechanical cyclic loading (x1.200.000, 50 N, 5-55ºC). Flexural strength tests were performed in a universal testing machine (2 mm/min). Data were analyzed using ANOVA and Dunnett t-tests (alfa=0.05). Result: Under static loading, mean flexural strength (MPa) of 4 mm (272±28 - 285±21; p>0.05) and 6 mm thick (244±29 - 306±38; p>0.05) FRC-PFC assemblies was not significantly affected by the FRC type. After cyclic loading, mean flexural strength of 4 mm PFC only (252±37) showed significantly lower results (p<0.05) than those of other groups (269±56 - 293+66) but 6 mm thick (252±74 - 333±43; p>0.05) FRC-PFC assemblies showed no significant difference. Conclusion: Cyclic loading can distinguish the mechanical durability of FRC-PFCs combinations better than static tests.