THE EFFECT OF INCREMENT THICKNESS AND LIGHT CURING DISTANCE ON FLEXURAL STRENGTH, MICROHARDNESS AND CYTOTOXIC BEHAVIOR OF TWO BULK-FILL RESIN-BASED MATERIALS

Abstract

For the flexural strength (FS) testing, 240 specimens were prepared and divided into 12 groups (n=20) according to 1: resin composite (RC), X-tra fil and X-tra base (XF and XB, VOCO, Germany), 2: increment thickness (IT), 2mm, 4mm, and 2mmX2mm and 3: light curing distance (LCD), 0mm and 10mm. The FS 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 relative microhardness (RMH%), 60 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). For testing of cytotoxic behavior, 24 specimens were prepared and divided in correspondence to FS & %RMH (n=2). Data was analyzed using Three-Way ANOVA and t-test, p=0.05. Three-way ANOVA for FS showed significant effect of material. There was no significant effect of increment thickness, light curing distance. Three-way ANOVA for RMH% results showed significant effect of material, increment thickness, light curing distance. Three-way ANOVA for cytotoxic behavior showed significant effect of increment thickness and light curing distance, but no significant effect of material was shown. Conclusions Based on the results of this study, several conclusions can be drawn: 1. Higher filler load contributes to higher flexural strength. 2. Effect of increment thickness and light curing distance may have been masked by overlapping cure during flexural strength specimen preparation. 3. Incrementation seems beneficial to cure efficiency of low-viscosity bulk-fill resin composite, reflected in relative microhardness and cytotoxic behavior. 4. Incrementation of high-viscosity bulk-fill resin composite enhanced microhardness especially at farther light curing distance, yet is detrimental to cytotoxic behavior. 5. Light curing distance has a detrimental effect on the relative microhardness of 4mm increment thickness of high- and low- viscosity bulk-fill materials, while only increasing cytotoxic behavior of low-viscosity bulk-fill.