Degradation of one step adhesives

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Objectives: The purpose of this study was to investigate the effect of aging temperature of one step adhesives on hydrolytic stability and dentin bond performance. Methods: Clearfil Tri-S Bond (TS) and Mega Bond (MB) were aged at 8, 20 and 40 ^oC for 14 weeks. ¹³C NMR observations of each aged adhesive were then performed by an EX-270 spectrometer. Furthermore, the shear bond strength of resin to dentin, conditioned with aged adhesives, was measured. Results: Table 1 shows the amounts of hydrolyzed HEMA utilized in both adhesives and the shear bond strength of to dentin conditioned by aged adhesives. The ester portion in HEMA hydrolyzed during aging period. This is because the protonated portion, caused by a dissociation of phosphoric acid group in MDP, acted as an accelerator for the hydrolysis of the ester portion. By raising the aging temperature, the hydrolyzed amount of HEMA increased. However, the hydrolysis speed of HEMA in TS was slower than in MB. Contrary, there was no significant difference in the shear bond strength among three aged adhesives, even though the hydrolyzed amounts of HEMA differed. Conclusions: The observed different hydrolysis speed was due to the difference in the amount of water and in the existence of ethanol in adhesive. The alteration of TS and MB, caused by the hydrolysis, didn't affect the dentin bond performance. This work was supported by a grant-in-aid for Developmental Scientific Research from the Ministry of Education, Science and Culture in Japan (#19592213)