Effect of Repeated Preheating and Light Curing Distance on Flexural Strength and Degree of Conversion of Two Resin-Based Materials

Abstract

Objective: This study was conducted to evaluate the effect of resin-based material, repeated preheating and light curing distance on flexural strength and degree of conversion. Materials and Methods:A total of 220 specimens were used in this study. One-hundred sixty rectangular specimens measuring 12mm x 2 mm x 2mm were dedicated for flexural strength (FS) using three-point bending test. Sixty disc-shaped specimens measuring 4mm x 2mm were dedicated for degree of conversion (DC) using ATR-FTIR spectrophotometer. Specimens were divided into two main groups according to material used; SPRG-containing Beautifil II LS and non-SPRG containing Filtek™ Z250 XT. Each group was subdivided into five subgroups according to the number of preheating cycles to which the syringe was exposed: no preheating, one, five, ten, or fifteen cycles of preheating. Then, each subgroup was further subdivided according to light curing distance (0mm and 10mm). Specimens were stored for 24 hours then subjected to the corresponding testing method (FS n=8, DC n=3). Data was statistically analyzed using three-way ANOVA followed by Tukey's post hoc test.Results: Nanohybrid composite recorded significantly higher FS (p<0.001). Also, a significant effect on FS was revealed for preheating (p=0.001), light curing distance (p=0.038), and the interaction between preheating and distance (p=0.027). Meanwhile, giomer recorded significantly higher DC (p<0.001). All other variables and their interactions were non-significant. Conclusion1. Material formulation has a significant effect on polymerization efficiency reflected in FS and DC.2. Preheating and light curing distance had a significant effect on FS, but not on DC.Clinical Relevance: Deeply situated margins require meticulous attention and care from the clinician in order to guarantee seal, adaptation, optimum cure and ultimately restoration success.