Riboflavin-ultraviolet-A collagen crosslinking treatments in improving dentin bonding and resistance to enzymatic digestion

Background/purpose: The efficacy of riboflavin-ultraviolet-A (RF-UVA) treatment in crosslinking collagen and improving dentin bonding has been proven. However, biodegradation of the hybrid layer may compromise the bonding. The purpose of this study was to evaluate different RF-UVA treatments regarding their ability to preserve dentin bonding from enzymatic digestion. Materials and methods: Collagen subjected to different RF (0.1 %, 1 %)-UVA (1, 2, 5 min) treatments and 5 % glutaraldehyde (GA), without or with enzymatic digestion, were examined by gel electrophoresis (SDS-PAGE). Twenty-five teeth with exposed dentin were primed with one of three RF-UVA treatments (0.1 %RF/1-minUVA, 0.1 %RF/2-minUVA, and 1 %RF/1-minUVA), GA, or distilled water after acid-etching, then restored with an adhesive and a resin composite. After 24-h storage, these teeth were sectioned into microbeams. Half of them received an early microtensile bond strength (μTBS) test, while the other half was stored in enzyme solution for 7 days before testing. Nanoleakage and hybrid layer degradation were examined by TEM. Results: According to SDS-PAGE results, all groups showed the dissipation of intense γ bands of collagen after digestion. For the early bonded specimens and after enzymatic digestions, 0.1 %RF/2-minUVA treated group presented the highest μTBS and none of premature failure. Its TEM images showed less nanoleakage after digestion, which is contributed to the well suspended collagen fibrils and resin infiltration in the hybrid layer. Conclusion: RF-UVA treatment attained collagen crosslinking effects to improve resin-dentin bonding. 0.1 %RF/2-minUVA effectively enhanced dentin bond strength and resistance to enzymatic digestion by optimally expanding dentinal collagen matrix to facilitate hybrid layer formation.