Effect of Water Flow on Bond Strength of Zirconia to Tooth Structure.

Bond strength tests are used as predictors of the clinical longevity of dental restorations. However, the aging of bond strength specimens is often simulated with static water storage, even though the saliva flows over teeth and restorations in the mouth. This study investigated the effect of water under static and flow conditions on the bond strength between zirconia and tooth structure using different test designs. Ninety human molars with prepared flat dentin surfaces were randomly divided into three groups according to the test design: Tensile, Shear, and Crown pull-off. The Crown pull-off group received additional standard full crown preparations. Zirconia specimens milled according to the shape of each test design (n=30) were bonded to the tooth structure using resin cement. There were three subgroups (n=10) according to the artificial aging procedure: NA - no aging (24 hours); SW - static water (30 days); FW - water flow (30 days). Bond strength was assessed using a universal testing machine, and the load at failure was recorded. Data were analyzed using two-way ANOVA and Tukey post hoc tests (α=0.05), and the mode of failure was also classified. Two-way ANOVA revealed a significant effect of the test design (p<0.001). However, no effect was observed for the aging procedure (p=0.166). The interaction aging*test design was significant (p=0.019). FW significantly decreased the retention of zirconia crowns to tooth structure (p<0.05) but did not affect the other test design specimens. The mode of failure was adhesive (100%) at the zirconia/cement interface for all specimens and aging conditions, except for Crown pull-off / FW, which were predominantly mixed (60%). FW negatively affected the retention of Y-PSZ crowns to the tooth structure.