The effect of direct and indirect water storage on the microtensile dentin bond strength of a total-etch and two self-etching adhesives

PURPOSE: To evaluate the effect of direct and indirect water storage on the microtensile dentin bond strength of one total-etch and two self-etching adhesives. METHODS: 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 (4 x 4 mm) was prepared in the occlusal surface with the pulpal floor extending approximately 1 mm into dentin. The teeth were divided into three groups (n = 12). Each group was restored with the resin composite Clearfil APX using one of the tested adhesives. For each experimental group three test procedures (n = 10) were carried out: Procedure A: the teeth were stored in water for 24 hours, then sectioned longitudinally, buccolingually and mesiodistally to get rectangular slabs of 1.0 - 1.2 mm 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 1 year before microtensile testing; Procedure C: the teeth were kept in water at 37 degrees C for 1 year before sectioning and microtensile testing. During microtensile testing the slabs were placed in a universal testing machine and load was applied at a cross-head speed of 0.5 mm/minute. RESULTS: For the 24-hour water storage groups there was no significant difference in bond strength between the three adhesives. After 1 year of indirect water storage, the bond strength decreased but the reduction was not significantly different from those of 24 hours. After 1 year of direct water storage, the mean bond strengths of Admira Bond and Hybrid Bond were significantly reduced compared to their 24-hour results. In contrast the average value of Clearfil SE Bond was not significantly affected.