Long-term evaluation of water sorption and ultimate tensile strength of HEMA-containing/-free one-step self-etch adhesives

Objective

The objective of this study was to evaluate the water sorption (Wsp) and ultimate tensile strength (UTS) of HEMA-containing/free one-step self-etch adhesives after long-term water-storage.

Methods

Three HEMA-containing one-step self-etch adhesives (Bond Force (BF), Clearfil S³ Bond (S3) and OptiBond All-In-One (OP)), and one HEMA-free one-step self-etch adhesive, G Bond (GB) was used. After the solvents of each adhesive were evaporated, polymerised adhesive disks and dumbbell-shaped specimens of thirty-two each were prepared and divided into four groups of 14-, 90-, 180- and 360-day water-storage. After immersion in water for the designated storage periods, the disks were subjected to measurement of Wsp, and the dumbbell-shaped specimens were subjected to measurement of UTS. The data of Wsp and UTS were statistically analysed using a two-way ANOVA and Bonferroni test.

Results

Wsp of BF, S3 and OP increased over time, whereas for GB, there were no significant differences in Wsp among all the storage periods. Wsp of GB was lower than those of BF, S3 and OP in each period. The UTS of BF, S3 and OP decreased over time, whereas for GB, there were no significant differences in UTS among all storage periods. The highest UTS was initially seen in BF > GB = S3 = OP, and after 360-day water-storage, seen in BF = GB > OP = S3.

Conclusions

For the HEMA-containing adhesives, Wsp increased and UTS decreased over time. On the other hand, for the HEMA-free adhesive, Wsp and UTS did not significantly change even after 360-day water-storage.