The effect of the presence and presentation mode of co-initiators on the microtensile bond strength of dual-cured adhesive systems used in indirect restorations

Abstract

This study compared the microtensile bond strength (uTBS) of indirect resin composite restorations to dentin when fifth-generation adhesive systems were either light-activated or left in the uncured state prior to cementation. The systems used in this study were Prime & Bond NT (NT-Dentsply) and Excite (EX-Ivoclar-Vivadent) or their dual-cured versions containing co-initiators with different presentation modes (as solution or salts) Prime & Bond NT Dual-cure (NTD-Dentsply) and Excite DSC (DSC-Ivoclar Vivadent). The bonding agents were applied to the flattened occlusal dentin surfaces of 40 human third molars according to the manufacturers' instructions and were light-activated (XL3000/3M ESPE) for 10 seconds (LP) or left in the uncured state (SP). The respective resin cements Calibra (Dentsply Caulk) and Variolink II (Ivoclar Vivadent) were applied to pre-cured resin composite discs (2 mm thick/Z-250/3M ESPE) that were fixed to the bonded dentin surfaces. The restored teeth were light-activated according to the manufacturers' instructions for five minutes after cementation and water-stored at 37°C for 24 hours. The teeth were then both mesial-distally and buccal-lingually sectioned to obtain bonded specimens (0.8 mm2). Each specimen was tested in tension at a crosshead speed of 0.5 mm/minute until failure. The data (MPa [SD]) were analyzed by 3-way ANOVA and Tukey's posthoc test (p >.05). The results showed that the presence of a co-initiator decreased uTBS for NT, while no significant difference in μTBS was noted between EX and DSC, regardless of the curing mode. All SP groups exhibited lower μTBS than the LP groups. The results suggest that coinitiators presented as a solution may decrease uTBS to dentin of the evaluated adhesive systems in indirect resin composite restorations. Light-activation of the adhesive layer prior to indirect cementation was crucial for higher μTBS on dentin. © Operative Dentistry, 2008.