Flexure Strength and Relative Micro-Hardness of Two Bulk-Fill Resin Composites

Abstract

Objective: To evaluate the effect of increment thickness (IT) and light curing distance (LCD) on flexural strength (FS) and relative micro-hardness (RMH%) of two bulk-fill resin composites (RC).

Method:

For the FS testing, 160 specimens were prepared and divided into 8 groups (n=20) according to 1: RC, X-tra fil and X-tra base (XF and XB, VOCO, Germany), 2: IT, 2mm and 4mm and 3: LCD, 0mm and 10mm. The specimens were prepared with dimensions of 12mm length X 2mm width and stored (24h). Test was run at a crosshead speed of 0.5mm/min. For RMH%, 40 discs were prepared (5mm diameter) and divided in correspondence to the FS (n=5). Five measurements were taken from each top and bottom surface using Vicker’s micro-hardness tester (Nexus 4000TM, INNOVATEST Europe BV, Netherlands) with load (500g) and dwell time (15s). Data was analyzed using Three-Way ANOVA and t-test, p=0.05.

Result:

Three-way ANOVA for FS showed significant effect of material (p=0.009). Average mean for RC was: XF 133.9±16.3 MPa ˃ XB 127.6±14.3 MPa. There was no significant effect of IT, LCD and interactions (p=0.516, p=0.603 and p=0.781 respectively). Average means for IT were: 2mm 130.0±16.2 MPa = 4mm 131.5±15.0 MPa and average means for LCD were: 0mm 131.4±14.2 = 10mm 130.1±16.9 MPa.

Three-way ANOVA for RMH% results showed significant effect of RC (p=0.002), IT, LCD and interactions (p=0.0001). Average means for RC were: XB 86.6±10.1 ˃ XF 83.2±10.7. Average means for IT were: 2mm 92.0±4.3 ˃ 4mm 77.7±9.8 and average means for LCD were 0mm 90.0±6.5 ˃ 10mm 79.8±11.2.

Conclusion:

Based on the results of this study; FS depends on the resin composite type rather than increment thickness and light curing distance. On the other hand; RMH% is affected by resin composite type, increment thickness and light curing distance.