Pre-heating effect on micro-hardness and depth of cure for three bulk-fill composite resins: An in vitro study

This study aimed to evaluate the effect of preheating on the micro-hardness and depth of cure of three different bulk-fill composite resins: Filtek Bulk Fill (3M ESPE), Tetric EvoCeram Bulk Fill (Ivoclar Vivadent), and SDR (Dentsply Sirona). Three bulk-fill composite resins, Filtek Bulk Fill (3M ESPE), Tetric EvoCeram Bulk Fill (Ivoclar Vivadent), and SDR (Dentsply Sirona), were tested in this <i>in vitro</i> study. Each resin was divided into two groups: preheated and non-preheated. The preheating process was performed using a composite warmer at 68°C for 5 minutes. Micro-hardness was measured using a Vickers hardness tester, and the depth of cure was evaluated by measuring the hardness ratio at different depths (0.5 mm, 1 mm, and 2 mm). Pre-heating significantly increased the micro-hardness of all three bulk-fill composite resins (p < 0.05). For Filtek Bulk Fill, the micro-hardness value increased from 60 to 70 HV, for Tetric EvoCeram Bulk Fill from 55 to 65 HV, and for SDR from 58 to 68 HV. The depth of cure was also enhanced in the preheated groups. The hardness ratio at 2 mm depth was 0.85 for Filtek Bulk Fill, 0.80 for Tetric EvoCeram Bulk Fill, and 0.83 for SDR in the preheated groups, compared to 0.75, 0.70 and 0.72 in the non-preheated groups, respectively. Pre-heating bulk-fill composite resins improves their micro-hardness and depth of cure. This suggests that preheating could be beneficial in clinical settings to enhance the physical properties of composite restorations.