The Impact of Repeated Preheating of Matrix Modifying Bulk Fill Resin Composite on Post-gel Polymerization Shrinkage Strain (in Vitro Study)

Abstract

Background: This study evaluated the effect of repeated preheating cycles of matrix-modifying bulk fill resin composites on the postgel polymerization shrinkage strain. Methods: Forty resin composite specimens were prepared using a Teflon mold (7 mm length x 4 mm width x 2 mm height). Each specimen was linked to a strain gauge and strain monitoring equipment (Strain-Meter PCD-300A Kyowa-Electronic Instruments Co, LTD, Tokyo, Japan) for measuring the postgel polymerizationshrinkage strain (um/m) of the resin composite. Preheating of the resin composite syringe was accomplished using Active Resin Heat (temperature of 68°C). According to the number of preheating cycles of the resin composite syringes, the specimens were divided into four equal groups: P0 (control), resin composite packed and cured at room temperature [23 ± 1°C], P1: preheated once, P2: preheated twice and P3: preheated three times prior to packing and curing for 30 seconds according to the manufacturer’s instructions. Statistical analysis was performed using Shapiro‒Wilk test for normality. ANOVA single factor was used as the test of significance followed by Tukey Hsd/Kramer with the level of significance set at 0.05. Results: Data analysis revealed insignificant differences in the postgel polymerization shrinkage strain among all tested groups (p≥0.05). Conclusions: The repeated preheating cycles of matrix-modifying bulk-fill resin composites prior to curing had no adverse effect on the induced postgel polymerization shrinkage strain. Clinical Relevance: The results of this study confirmed that clinicians can consider repeatedly preheating resin composites in dental practices. The information of comparable performance regarding postgel polymerization shrinkage when applying preheated composites as room temperature cured resin composites could be of utmost significance as the same resin composite syringe can clinically undergo numerous preheating cycles before it is completely consumed with the advantage of a transient reduction in viscosity, improving restoration adaptability to the cavity. Its use in routine care can be considered a good practice.