Does "soft-start" curing mode really makes a difference?

Objectives: The aim was to determine how physical properties of nanohybrid composite material EmpressDirect (IvoclarVivadent, Schann, Liectenstien) will change if cured with different curing modes. Methods: Bluephase G2 polywave (IvoclarVivadent, Schann, Liectenstien) was used for polymerization with high power mode (1200 W/cm2), low power mode (650 W/cm2) and soft start mode (650 W/cm2 to 1200 W/cm2). Changes were recorded during polymerization process using laser interferometry. The Vickers test was performed to measure hardness of polymerized composite samples (10 g load for 10 seconds). The results were analyzed by ANOVA, and Tukey post hoc test was used for finding significance levels. Results:The highest shrinkage values were observed in case of composite polymerization using the soft start polymerization mode of the curing unit (9,03µm or 1.06%), while lowest results were obtained when low power mode was used (7,32µm or 0.86%). Average polymerization shrinkage in the case of using high power mode was 7,86µm or 0.92%. Initial expansion of samples was greatest when soft start mode was used (1,41 µm or 0.15%), while high and low power modes gave mean 0,56 µm or 0.07% shrinkage. The difference between samples cured with soft start mode and both low and high power mode is statistically significant (p=0.05).The hardest samples were those polymerized with high power light mode (24.47 HV) and the softest samples were obtained when low power mode was used (20.59 HV). Average Vickers Pyramid Number of samples cured with soft start mode is 23.62 HV. The difference between samples polymerized with low power mode and both soft start and high power mode is statistically significant with p=0.01. Conclusions: Based on obtained data physical properties of nanohybrid composites will not be superior if cured with soft-start curing mode. This study was supported by grants 065-0352851-0410 and 035-0352851-2854 of MZOS, Croatia.