Influence of the preheating of bonding agents on the degree of conversion and bond durability in tridimensional dentin cavities

Objectives: The aim of this study was to evaluate the degree of conversion (DC) of dental bonding agents at different temperatures and the bond durability of restorations bonded with preheated dental bonding agents. Materials and methods: Three multistep adhesive systems, including one 3-step etch-and-rinse (Adper Scotchbond Multipurpose Plus) and two 2-step self-etching systems (Clearfil SE Bond; Filtek Low-Shrinkage Adhesive System), were evaluated. Dental bonding agents were preheated at 25, 37, and 60 degrees C. Bar-shaped specimens (n=5) were prepared for DC analysis. Fourier Transform Infrared/Attenuated Total Fluorescence spectra were obtained, and the DC was calculated by comparing the aliphatic bonds/reference peaks of nonpolymerized and polymerized materials. For bond durability analysis, tridimensional dentin cavities were prepared in 180 bovine incisors, which were then restored. Samples were stored in water for 24h, and half of them were subjected to additional degradation with 10% NaOCl for 5h. The push-out bond strength test was performed in a universal testing machine until failure. Failure modes were analyzed by scanning electron microscopy. Data were analyzed by analysis of variance (ANOVA) and Tukey's tests (p<0.05). Results: Dental bonding agents preheated at 60 degrees C showed higher DC values than those preheated at 25 and 37 degrees C. The temperature of the dental bonding agent did not influence the bond durability, although fewer adhesive failures were observed in restorations bonded with dental bonding agents at 60 degrees C. Conclusion: Although the preheating of dental bonding agents can increase the DC, it may not improve the bond durability of dentin restorations.