Microtensile Bond Strength of Self-Etch Adhesives with the Total-Etch Technique

Objective: To determine if the application of 35% phosphoric acid prior to the use of self-etching adhesives affects microtensile bond strength of composite to dentin.  Methods:  The coronal enamel of 25 extracted human molars was removed exposing dentin.  The flattened dentin was treated with Xeno IV (Dentsply) or iBond (Heraeus) with or without a 10-second phosphoric acid pre-etch and light cured with a quartz-tungsten-halogen curing light (Optilux 501, Kerr) for 10 seconds.   All-Bond 2 (Bisco) was used as a control.  Composite (Z-250, 3M/ESPE) was incrementally placed and cured to approximately 4 mm.  The specimens were sectioned into 1 x 1 mm beams (Isomet 5000, Buehler).    Five teeth were used per each of five groups and four beams were sectioned from each tooth (n=20).  The beams were separated in tension by a universal testing machine (Instron Model 5543) at a crosshead speed of 1 mm/min.  A mean (MPa) and standard deviation were determined per group.  Results:  A difference was found between groups using a one-way ANOVA (p < 0.0001).  Tukey Post-hoc test was used for multiple comparisons.  See Table below.  A 2-way ANOVA was performed (excluding AllBond 2) to examine the effects of bonding agent or etching on bond strengths.  A difference was found based on bonding agent (p < 0.0001) and etchant use (p = 0.001).  However, there was a significant interaction (p = 0.011).  Separate T-Tests were performed comparing the etched vs. nonetched groups of each bonding agent.  There was a significant difference between the etched and nonetched groups of Xeno IV (p = 0.0002) but not for iBond (p = 0.3).  Conclusions:  The effect of pre-etching of dentin with phosphoric acid is product specific.  Xeno IV showed a dramatic improvement in microtensile bond strength, however, iBond showed no difference.