Objectives: The aim of this study was to investigatge flexural fatigue strength of new generation of resin composite materials under cyclic loading. Materials & Methods: Disc specimens (13 mm. in diameter and 2 mm. in thickness) of 5 different resin composites [Admira (Voco), CereamX (Dentsply). Filtek Supreme Translucent (3M ESPE), Filtek Supreme Standard (3M ESPE) and Z250 (3M ESPE)] were prepared and stored in 37 degree celcius distilled water for 24 hours before testing. Bi-axial flexural strength test (a-ball-on-three-ball) was selected to evaluate the bi-axial flexural strength (n=15) using a universal testing machine. Flexural fatigue strength of resin composites were determined for 10,000 cycles under the same loading apparatus and support at a frequency of 2.0 Hz. (n=20). The staircase method was used for flexural fatigue strength evaluation. Results: Filtek Supreme translucent showed the highest bi-axial flexural strength value, while CeramX exhibited the lowest value. The bi-axial strength valuesof Supreme standard and Z250 were not significantly different. Z250 showed the highest flexural value. Both Z250 and Filtek Supreme standard were significantly higher the flexural fatigue strength than Filtek Supreme translucent. For each material, the initial strength was significantly higher than the fatigue strength. There was no linear correlation between initial and fatigue strength. Conclusions: The material which had the highest bi-axial flexural strength did not show the highest flexural fatigue strength. The resin composite materials responded to static force differently from cyclic loading since the applied forces were different in these two methods. The reaction depends on properties of materials such as stiffness and toughness. Because the resin composite materials used in oral cavity are subject to cyclic loading force, it is suggested that more consideration should be emphasized on the fatigue strength.
