Effect of Preheating on the Degree of Conversion of Nanohybrid Resin Based Composites

Objectives: The physical and mechanical characteristics of resin composites are greatly influenced by the extent of conversion obtained by polymerization. The attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) test can be utilized as a method to examine the degree of conversion (DC). The purpose of this research was to investigate the influence of three preheating temperatures on the degree of conversion of four different nanohybrid resin based composites.
Methods: The 20 samples for three commercial resin composites were arbitrarily subdivided into 4 subgroups, in which 5 samples were employed for each one {subgroup 1 = room temperature 25^oC, subgroup 2 = preheating temperature 37^oC, subgroup 3 = preheating temperature 60^oC and subgroup 4 = preheating temperature 80^oC}. The samples were photo-polymerized with LED light curing unit for 20 s from only one direction in order to prepare samples for DC measurements. DC measurements of top and bottom of each sample were recorded following the preheating process. ATR-FTIR test was conducted for both surfaces of the prepared sample.
Results: No significant change in DC was measured for the composite preheating at 37^oC compared to room temperature. For the composite preheating at 60^oC and 80^oC, DC increased at both top and bottom surfaces compared to room temperature.
Conclusions: Regardless of the resin composite material used, DC was improved by increasing temperature.