Contact cyclic loading of restorative composites

The study evaluated the effect of contact cyclic loading on the flexural strength of a fiber reinforced, a microfilled, and a hybrid restorative dental composite in different testing conditions.; This investigation included three different filler reinforcements (fiber, hybrid, and microfilled); two aging times (0 and 3 months aging, in the respective testing media), four chemical medias (air, distilled water, artificial saliva, and 50/50 % by volume mixture of ethanol and distilled water); three load magnitudes (30-50, 60-80, and 90-110 N); three levels of cyclic loading (1, 100, and 100,000 cycles); and two loading radii (3.18 and 100 mm). Specimens were loaded in compression, in a contact load setting, supported along their entire span. Each groups consisted of 10 specimens. Following load cycling; the specimens were tested in three-point bending. Statistical analysis consisted of General Linear Model analysis followed by Tukey tests for multiple comparisons.; The results of this study indicated a superior mechanical performance of the fiber reinforced, followed by the hybrid and microfilled composite, respectively. Aging generally decreased the flexural strength of restorative composites. Aging in distilled water and ethanol mixture demonstrated the most detrimental effect on the flexural strength of all aged composites. No consistent results in regard to the effect of load magnitude on the flexural strength of dental composites were observed for the load ranges tested. The effect of number of cycles on the flexural strength appeared to be influenced by the loading morphology, as well as, being predominantly manifested in unaged specimens. Fiber reinforced composite demonstrated a predominant decrease in the flexural strength with increasing number of cycles. Hybrid composite demonstrated a predominant increase in the flexural strength with increasing number of cycles. The effect of number of cycles on the flexural strength of unaged microfilled composite was less predominant and more variable. The effect of the loading radius on the flexural strength of restorative composites was dependent on the type of filler reinforcement and mostly manifested in unaged fiber reinforced and hybrid composites.