Proanthocyanidins alter adhesive/dentin bonding strengths when included in a bonding system

To determine the effect of proanthocyanidins (PA) incorporation into a bonding system on dentin/adhesive bond stability following long-term storage in buffer and collagenase.

Human dentin surfaces were bonded with no PA (0-PA), PA incorporated in the primer (PA-primer), or PA incorporated in the adhesive (PA-adhesive), and composite build-ups were created. Following sectioning into beams, bonded specimens were stored in buffer or collagenase for 0, 1, 4, 26, or 52 weeks before being tested for microtensile bond strength (muTBS). ANOVA and Tukey's HSD post-hoc were performed. Fractured surfaces were viewed with scanning electron microscopy (SEM).

Both bonding system and storage time but not storage medium significantly affected muTBS. Initially, 0-PA and PA-primer were superior to PA-adhesive, and after 1 week both PA groups were inferior to 0-PA. However, after 4 weeks PA-adhesive had significantly increased and 0-PA significantly decreased such that all three groups were equal. Thereafter, both PA-primer/adhesive groups trended with an increase (the 0-PA group remaining consistent) such that at 52 weeks PA-primer samples were significantly stronger (P < 0.001) or nearly so (P = 0.08) when compared to 0-PA samples. SEM revealed that initial fractures tended to occur at the middle/bottom of the hybrid layer for 0-PA and PA-primer groups but at the top of the hybrid layer/in the adhesive for PA-adhesive. After 4 weeks, however, all groups fractured similarly at the middle/bottom of the hybrid layer.