2010 Volume 53 Issue 6 Pages 611-618
One-step bonding adhesives currently available on the market tend to decrease the bond strength of resin to dentin when stored for a prolonged time or at high temperature. To clarify the cause of the decrease of bond strength of resin to dentin when treated with one-step bonding adhesives, the influence on the degradation of monomer contained in one-step bonding adhesives was examined by shear adhesive strength and nuclear magnetic resonance (13C NMR) techniques in this study. Bond Force (Tokuyama Dental) was used as a one-step bonding material and was stored at 40℃ for 0, 3, 7 and 14 weeks in an incubator to serve as a test sample. Bond Force 300mg and dimethyl sulfoxide 250mg as a test sample for 13C NMR were weighed accurately in an NMR tube, followed by shaking and mixing before analysis by using the 13C NMR technique. The shear adhesive strength was also measured for the same storage period. As a result, it was found that two NMR peaks, one corresponding to the carbonyl carbon of carboxyl methacrylate and the other to the methylene carbon of ethylene glycol, were detected when Bond Force solution was stored at 40℃ with their augmented NMR peak strengths when the storage duration was prolonged. When Bond Force was stored at 40℃ for 14 weeks, the methacryloxy ester group of HEMA was degraded by 22.39%, that is, the ester group of HEMA was hydrolyzed, subsequently producing methacrylic acid and ethylene glycol. In addition, the bond strength to enamel was 16.2MPa when stored for 0 day (control), but the value decreased gradually with longer storage and markedly to 5.5MPa when stored for 14 weeks. Similar to the bond strength of enamel, the value of the bond strength to dentin decreased from 12.7MPa to 6.0MPa with longer storage. The bond strength of resin to dentin thus seemed to decrease when HEMA in the one-step bonding material was altered by hydrolysis in response to the prolonged storage period. These results suggest that the decreased bond strength of resin to dentin was attributable to the degraded one-step bonding material.
