Use of riboflavin/blue light in improving dentin bonding

Purpose: To evaluate the use of the photoreactive agent riboflavin (RF) combining blue light irradiation as a collagen cross-linker in improving dentin bonding. Methods and materials: Sixty extracted human molars were used. For each tooth, enamel was removed and crown was flattened with low-speed diamond saw under water irrigation. A standardized smear layer was created with wet 600-grit silicon-carbide paper. The top surface of dentin was etched for 15 s with 35% phosphoric-acid gel, rinsed with water before different collagen cross-linking treatments. These teeth were divided into six experimental groups: Control, no treatment; RF0.1UV2, 0.1% RF treatment followed by 2-min UVA irradiation; RF0.1BL1 and RF0.1BL2, 0.1% RF followed by 1or 2-min blue light irradiation; RF1BL1 and RF1BL2, 1%RF followedby 1or 2-minblue light irradiation. The treated dentin surfaces received bonding procedure with Singlebond (3M ESPE), and 4mm-thick resin composite cube were builtup in two layers. After storage in distilled water at 37 ◦C for 24h, these teeth were cut into microbeams and then subjected to a microtensile bond strength ( TBS) test at initial stage and after enzymatic degradation. In addition, the fractured dentin-composite microbeams were evaluated by SEM to analyze fracture mode. Additionally, 24 teeth were powdered and demineralized with 1% phosphoric acid for 10min. These dentin powders were divided into six parts to received one of those collagen cross-linking treatments. Proteins were extractedwith extraction buffer and concentratedwith 30kDa membrane, then receivedBradfordassay todetermine theprotein concentrations. Finally, MMP2 activity was checked with a zymography assay. Results: RF0.1BL1 and RF0.1UV2 showed significantly increased TBS. Fracturemodeanalysis showed that RF0.1UV2 and RF0.1BL1 groups presented the least adhesive fracture mode. The zymography analysis showed that the enzymatic activity was inhibited when the teeth was treated with RF0.1/BL1. Conclusion: The collagen crosslinking by riboflavin/blue light could improve the dentin bonding stability and inhibit the MMPs activity.