Time-dependent polymerization of dual-cured luting agent beneath ceramic

Objectives: This study investigated the real-time degree of conversion (DC) of a dual-cured luting agent (RelyX-ARC) beneath a leucite-reinforced-ceramic (Empress-Esthetic; 0.7, 1.4 and 2mm-thick discs), and evaluated the light irradiance and spectrum of wavelengths transmitted through ceramic. Methods: The luting agent was photo-activated for 40s through each disc (XL3000; 600mW/cm²), defining the groups C-0.7, C-1.4 and C-2. Dual (DUC) and chemically-cured (CC) control groups were obtained, and also a group in which light-activation was performed after 5min (exposure delay–ED). Polymerization was analyzed using infrared spectroscopy equipped with an attenuated total reflectance device. DC (%) was evaluated right after 40s, 1, 2, 4, 6, 8 and 10min (12 scans, 4cm^-1 resolution). Light irradiance and spectrum were obtained using a power-meter and a spectrometer. Data were submitted to two-way RM-ANOVA and Tukey's test (5%). Results: A decrease in irradiance was observed with increasing ceramic thickness: 19% for 0.7, 35% for 1.4 and 57% for 2mm disc. No significant change in the emission profile through ceramic was detected: a spectrum between 400-510nm (peak at 484nm) was detected. At 40s, all groups showed DC higher than 66% (DUC=69.5%, C-0.7=66.8%, C-1.4=68.1%, C-2=69.7%), except for ED (8.3%) and CC (7.9%). At 10min, the DC for all groups (DUC=82.1%, C-0.7=80.6%, C-1.4=76.6%, C-2=78.9%, ED=77.9%, CC=61.1%) was significantly higher than at 40s. No significant differences were detected for DUC compared with C-0.7, C-1.4 and C-2. Generally, CC showed significantly lower DC than all groups. No significant effect was detected for ED. When observing the DC in the course of time, a significant increase was detected only until 4min. Conclusions: A decrease in irradiance was observed with increasing ceramic thickness. The luting agent depended on light exposure and time to obtain improved DC. Neither the indirect activation nor the ED procedure presented significant influence on the final DC values.