Because collagen is a major component of the hybrid layer, an improvement of its mechanical properties might be advantageous during bonding procedures. This study investigated the effect of three different cross-linking agents—glutaraldehyde (GA), grape seed extract (GSE), and Genipin (GE) (Wako Pure Chemical Industries, Osaka, Japan), a Gardenia fruit extract natural cross-linker—on resin-dentin tensile bond strengths (TBS).Materials and Methods:
Sixty-four sound human molars were collected and their occlusal surfaces were ground flat to expose dentin. The dentin surfaces were etched using 35 to 37% phosphoric acid for 15 seconds, rinsed and kept moist. Cross-linking agents were applied to the etched dentin (5% GA, 6.5% GSE, and 0.5% GE at a pH of 7.4), with phosphate buffer used as a control. The teeth were restored using either acetone-based One-Step Plus (Bisco, Inc., Schaumburg, IL) or ethanol-based Adper Single Bond Plus (3 M ESPE, St. Paul, MN) adhesive systems and a composite material in 2-mm increments to a total height of 5 mm to allow for gripping during tensile testing. After 24 hours of storage in distilled water, specimens were sectioned to produce a cross-sectional surface area of 1.0 mm2 and were tested for tensile bond strength. The debonded surfaces were classified as adhesive failure at the interface, cohesive failure in the composite or in adhesive. The micromorphology of the fractured interface was assessed using scanning electron microscopy.Results:
For Adper Single Bond, two of the cross-linking agents significantly increased mean TBS. There was an increase of more than double for the control, from 33.38 to 68.96 MPa for GA and 71.06 for GSE. Results were similar for One-Step Plus. Bond strengths increased from the control of 44.13 to 65.46 MPa for the GA treatment and 74.40 MPa for GSE. There was no statistically significant difference with the GE-treated samples. The mode of fracture at the interface showed that a majority were at the interface; however, the GSE and GA samples showed a distinct difference, with the fracture being at the top of the hybrid layer with a morphology showing that the bond had undergone excessive strain and plastic deformation.Conclusions:
The chemical modification to the dentin matrix promoted by GA and GSE, but not GE, resulted in significantly increased bond strengths. The application of selective collagen cross-linkers during adhesive restorative procedures might be a new approach to improve dentin bond strengths.