Riboflavin-ultraviolet-A-induced collagen cross-linking treatments in improving dentin bonding

Objectives To evaluate the collagen cross-linkers, riboflavin-ultraviolet-A (RF/UVA) and glutaraldehyde, with regard to their efficacy in cross-linking the dentinal collagen and improving dentin bonding. Methods Glutaraldehyde and different RF/UVA protocols (0.1%RF/1-minUV, 0.1%RF/2-minUV, and 1%RF/1-minUV) were first evaluated by gel electrophoresis to determine their abilities of collagen cross-linking. The mechanical properties of acid-etched dentin receiving these cross-linking treatments were examined in either dry or wet condition by a nanoindentation test. Fifteen teeth with exposed occlusal dentin received the microtensile bond strength (μTBS) test. The teeth were primed either with RF/UVA or glutaraldehyde, followed by adhesive treatment and composite restorations, and then cut into resin-dentin microbeams. Half of the microbeams received the μTBS test after 24 h, and the other half received test after 5000 thermocycles. Nanoleakage at the bond interface was examined under TEM. The alignments of collagen fibrils in the hybrid layers were also defined by an image analysis. Results Gel electrophoresis showed that glutaraldehyde induced strong collagen gelation, while RF/UVA generated milder collagen cross-linking. Glutaraldehyde, 0.1%RF/2-min-UVA, and 1%RF/1-minUV showed higher stiffness compared to untreated and 0.1%RF/1-minUV in wet condition. All the crosslinking treatments improved early μTBS, but 0.1%RF/2-minUVA treatment maintained high μTBS after theromocycles. Under TEM, glutaraldehyde-treated dentin showed dense and enclosed collagen network on the adhesive interface. 0.1%RF/2-minUVA showed the least nanoleakage, and this could be associated with the suspended collagen fibrils in the hybrid layer. Significance 0.1%RF/2-minUVA treatment enhanced resin-dentin bond possibly through enhancing the stiffness and maintaining the expanding collagen matrix in the hybrid layer.