Effect of Delayed Light-Curing Through A Zirconia Disc on Microhardness and Fracture Toughness of Two Types of Dual-Cure Cement

Objectives: photopolymerization immediately sets dual-cure cements and prevents the continuation of chemical polymerization. delayed light-curing allows the chemical process to continue up to the point before starting irradiation; however, there is a controversy in this respect. the present study evaluates the effect of delayed light-curing through a zirconia disc on the microhardness and fracture toughness (kic) of two types of dual-cure cement. materials and methods: samples measuring 25×5×3 mm³ were prepared for fracture toughness test, and discs measuring 5 mm in diameter and 3 mm in thickness were prepared for microhardness test using bifix and biscem cements. light-curing protocols were as follows: immediate light-curing (group a), a 2-minute delay (group b), a 5-minute delay (group c), direct irradiation (group d), and no irradiation (group e). in groups a to c, light-curing was carried out through a zirconia disc. data were analyzed by two-way and one-way analysis of variance (anova), post-hoc tukey's test, and kruskal-wallis test at 95% confidence interval. results: there was a significant difference in the microhardness of the cements (p=0.00). delayed light-curing had no effect on microhardness (p=0.080). the microhardness of biscem in group e was significantly lower than that in group d (p=0.015). the fracture toughness of bifix in groups b and c was significantly different than that in group e and biscem groups. conclusions: under the limitations of our study, delayed light-curing had different effects on microhardness and fracture toughness. differences in light-curing protocols resulted in different effects based on the cement type. light-curing is recommended to achieve optimal mechanical properties.