Effect of different fiber post surface treatments on microtensile bond strength to composite resin

Statement of problem: The interface of fiber post and composite resin is a site of potential failure of adhesion. Improving this interface adhesion through different pretreatments of the fiber post surface has been suggested, but the results are controversial.

Purpose: The purpose of this in vitro study was to evaluate the effect on the bond strength to composite resin of pretreating glass fiber post surfaces with hydrogen peroxide, phosphoric acid, and a silane coupling agent.

Material and methods: Glass fiber posts were treated for 1 or 5 minutes with 30% hydrogen peroxide or 35% phosphoric acid. Treated posts were divided into silanization and no silanization groups. Control groups included no treatment or treatment with silanization alone (total of 10 groups; n=14). Composite resin was bonded to the fiber posts, and the specimens were cut into beams with the fiber post in the middle and the composite resin at both sides. The beams were attached to a mechanical testing device, and microtensile bond strength was evaluated. Fracture modes were assessed using stereomicroscopy. Statistical analysis was done with 3- and 2-way ANOVA (α=.05). Additional specimens were evaluated with a scanning electron microscope (SEM) to evaluate the effect of treatments on the characteristics of fiber post surfaces.

Results: The highest bond strength values were found in the group treated with phosphoric acid for 5 minutes with silanization, followed by the group treated with silanization alone. ANOVA showed a statistically significant effect for silanization (P<.05), but no statistically significant effect for surface treatment. SEM evaluation revealed cracked and dislodged superficial fibers in all groups, with no obvious difference in fiber exposure among the groups.

Conclusions: The silane coupling agent had a significant effect on the bond strength of the tested glass fiber posts to composite resin, whereas 30% hydrogen peroxide or 35% phosphoric acid did not.