Genipin-induced cross-linking and dentin bond strength

The achievement of a strong and stable bonding between composite resin and dentin collagen matrix remains a challenge in restorative dentistry. It has been reported that the treatment of collagen with a natural cross-linker, genipin (GE), significantly improves the ultimate tensile strength of dentin. However, its effect on dentin bond strength at the dentin/resin interface is not well understood. Objective: To evaluate the extent of GE-induced collagen cross-linking on amino acid composition  and dentin bond strength. Method: The demineralized bovine dentin collagen was treated with 0.5% GE for 1, 4 and 12 hrs, hydrolyzed with 6N HCl and subjected to amino acid analysis. In another set of experiment, the effect of GE cross-linking on micro tensile bond strength (MTBS) was investigated by using extracted human molars that were etched, treated with PBS (control), or 0.5% GE for 1, 4 or 12 hrs prior to build-up with resin. Specimens were incubated at 37 °C for 24 hrs. Result: The results of amino acid analysis showed that the contents of lysine (Lys) and hydroxylisine (Hyl) in the GE treated group were significantly decreased in a time dependent manner.  The MTBS was significantly increased in the 4 and 12 hrs GE treatment groups (58.5 ± 17.7 MPa and 44.3 ±16.8 MPa, respectively) when compared to that of control (15.1 ± 8.5 MPa) (p<0.001). The MTBS of the 1hr treatment group was not significantly different from control. Conclusion: GE-mediated cross-linking involves the Lys and Hyl residues of collagen and the 0.5% GE treatment for 4 hrs could be sufficient to exert efficient bond strength.