Methods: Dentin beams (1.5 x 0.5 x 6 mm) were obtained from sound extracted human molars. Beams were fully demineralized (10% phosphoric acid solution/5 h) and randomly assigned into 6 groups (n = 10). The purified oligomeric procyanidins (OPACs) A1, A2, B1, B2 (A-and B-type dimers) and C1 (B-type trimer) were tested. The compounds were prepared in 0.02 M HEPES to a final concentration of 0.65% (pH 7.2) and used for 1 hour incubation. Control group was treated with HEPES buffer solution. The apparent modulus of elasticity (E) was assessed on demineralized dentin beams (baseline) and following OPACs dentin modification treatment using a 3-point flexural test at 3% strain. Mass loss (%) was used to assess biodegradability of dentin matrix against bacterial collagenase (100 μg/ml Clostridium histolyticum) for 24 hours at 37oC. The fold increase of Eand mass loss after collagenase were statistically analyzed using one-way ANOVA and Games-Howell post-hoc tests at a 95% confidence level.
Results: Except for procyanidin A2 (1.45-fold), all other OPACs [C1 (5.11-fold), A1 (4.49-fold), B1 (3.14-fold), B2 (2.22-fold)] significantly increased the E of dentin matrix when compared to control (p <0.0001). Moreover, all PACs exhibited significant protective effect against collagenase digestion, ranging from 13.98 to 36.07% dry mass loss when compared to control (76.71%).
Conclusions: This compound-specific study confirms recent results with fractions containing PACs with various degrees of oligomerization, which indicated that medium-length OPACs are the most potent promoters of dentin enhanced mechanical properties and bio-stability.