Effect of curing modes on nano - mechanical properties and monomer conversion of dual - cured resin cements

Abstract

Objective To investigate the influence of different curing modes on nanohardness, elastic modulus, indentation creep and monomer conversion of two types of dual-cured resin cements. Methods Specimens of 5 mm diameter and 0.5 mm thickness were fabricated with two dual-cured resin cements: RelyX Unicem (RU) and PermaCem 2.0 (PC) , under four different curing modes: immediate light-curing mode (IML) , intermittent light-curing mode (ITL) , delayed light-cuing mode (DL) and chemical curing mode (CC) . After 24 hours′ storage in darkness at room temperature, nanohardness, elastic modulus and indentation creep were measured with a nanoindentation device under a 10 mN load for 20 s holding time. Monomer conversion was measured by Fourier transform infrared spectroscopy- attenuated total reflection. Data were analyzed by SPSS 16.0 software (α=0.05) . Results Curing modes showed significant influence on nanohardness and elastic modulus for both RU and PC (P DL>IML, ITL. For RU, there were no significant difference in monomer conversion among the four curing modes (F= 0.899, P= 0.447) . However, there were significant difference in monomer conversion among the four curing modes for PC (F= 20.76, P= 0.004) . Conclusions Lack of light activation resulted in an insufficient polymerization and compromised mechanical properties for dual-cured resin cements. Immediate and delayed light curing modes produce higher indentation creep. Curing modes had different levels of impact on the mechanical properties and monomer conversion of dual-cured resin cements with different components. Key words: Resin cements; Light-curing of dental cements; Self-curing of dental resins; Mechanical properties; Monomer conversion; Curing modes