Four-year water degradation of a total-etch and two self-etching adhesives bonded to dentin

To evaluate effect of direct and indirect water storage on the microtensile dentin bond strength of one total-etch and two self-etching adhesives.

The adhesive materials were: one total-etch adhesive; 'Admira Bond' and two self-etch adhesives; 'Clearfil SE Bond' and 'Hybrid Bond'. Freshly extracted human third molar teeth were used. In each tooth, a Class I cavity (4mmx4mm) was prepared in the occlusal surface with the pulpal floor extending approximately 1mm into dentin. The teeth were divided into three groups (n=18). Each group was restored with the resin composite 'Clearfil APX' using one of the tested adhesives. For each experimental group 3 test procedures (n=6) were carried out: Procedure A: the teeth were stored in water for 24h (control), then sectioned longitudinally, buccolingually and mesiodistally to get rectangular slabs of 1.0-1.2mm thickness on which a microtensile test was carried out. Procedure B: the teeth were also sectioned; however, the slabs were stored in water at 37 degrees C for 4 years before microtensile testing (direct water storage). Procedure C: the teeth were kept in water at 37 degrees C 4 years before sectioning and microtensile testing (Indirect water storage). During microtensile testing the slabs were placed in a universal testing machine and load was applied at cross-head speed of 0.5mm/min.

For the 24h control, there was no significant difference in bond strength between the three tested adhesives. After 4 years of indirect water storage, the bond strength decreased but the reduction was not significantly different from those of 24h. After 4 years of direct water storage, the bond strengths of all tested adhesives were significantly reduced compared to their 24h results.

All the tested adhesives showed no reduction in bond strength after indirect water exposure for 4 years. After 4-year direct water exposure, the bond produced by all tested adhesives was unable to resist deterioration.