Initial Fracture Strength and Cyclic Fatigue Resistance of Experimental Composites

Objectives: To evaluate the initial fracture strength (IFS) and cyclic fatigue resistance (CFR) of 3 experimental composites with different resin matrix composition.
Methods: Experimental composites were prepared with 30wt% of organic matrix and 70wt% of filler content constituted by silanated barium-glass fillers and silanized Ox-50 silica (90wt% and 10wt% respectively). The resin matrix composition of the groups was the following, Group EA: Bis-GMA:TEGDMA (60:40mol%), Group EB: Bis-GMA:TEGDMA:UDMA (35:30:35mol%) and Group EC: TEGDMA:UDMA (40:60mol%). To evaluate the IFS and CFR, disk-shaped specimens (15mm diameter x 1.1mm thickness) were made of each of the experimental composites. Top and bottom surfaces were covered with a Mylar strip and photoactivated for 40s on each side at 677 mW/cm² irradiance with a light-curing unit. The specimens were stored dry at room temperature for 24h and later their dimensions were recorded with a digital calipher. For IFS (in MPa) the specimens were loaded until fracture with a crosshead speed of 1 mm/min (n=15). To determine the CFR (in MPa) the “staircase” approach was used. For this test the specimens were subjected to 10⁴ cycles at a frequency of 2Hz (n=20). The maximum strength stress for the first specimen of each of the groups was set at 50% of the IFS value with further increment or decrease of 5Mpa according to whether the previous test resulted in failure or not. Data for IFS and CFR was analyzed by repeated measures analysis of variance (MIXED procedure) using the restricted maximum likelihood estimation method with post-hoc Tukey adjustments (α=0.05).
Results: see Table 1
Conclusions: The EC experimental composite yielded the highest values for both IFS and CFR parameters assessed in the present study suggesting a relationship between improved mechanical behavior and a non Bis-GMA-based experimental composite.