Effect of water storage on seventh-generation dentin adhesives

Objectives: This study compared the bond strength of self-etching 7^th-generation adhesive systems after one day and one week of water storage.

Methods: Forty extracted human teeth were mounted, cut to expose superficial dentin and polished (600-grit SiC) under water. Specimens were divided into four groups (n=10) according to adhesives: Optibond All-In-One (OP, Kerr), Clearfil S3 BOND (CS3, Kuraray), Bond Force (BF, Tokuyama) and Xeno IV (XIV, Dentsply Caulk). Each adhesive was applied according manufacturers' instructions. Composite (Z100, 3M ESPE) was placed using bonding apparatus (Ultradent, 2.3-mm diameter) and light-cured for 40 s in two increments. Subgroups (n=5) were stored in distilled water at 37° C for 24 hours and 7 days and tested in shear with a testing machine (Instron) at a crosshead speed of 0.1 cm/min. Bond strengths were calculated in MPa and analyzed using two-way ANOVA at the 0.05 level of significance.

Results: Fisher's PLSD for comparisons of means among adhesives and between storage times (p<0.05) were 4.9 and 3.5 MPa, respectively. At 24 hours, bond strengths for OP and CS3 were statistically higher than those for BF and X4. At 7 days, the bond strength of CS3 and BF was statistically higher than X4. The bond strength of  CS3 was higher than those of X4,OP and BF when stored for 7 days in water. OP had significantly lower bond strength whereas BF had increased bond strength after storage for 7 days in water. The bond strengths of CS3 and X4 did not change over the storage time.

Bonding Agent	Bond Strength at 24 h, MPa	Bond Strength at 7 d, MPa
CS3	33.8(5.8)	36.2(3.5)
OP	31.9(5.4)	26.1(5.5)
XIV	24.7(5.2)	22.0(7.5)
BF	20.7(6.1)	30.4(2.8)

Conclusions: Water storage time had different effects on short-term bond strength in all adhesives tested.