Use of Photoreactive Riboflavin and Blue Light Irradiation in Improving Dentin Bonding-Multifaceted Evaluation

Abstract

Recently, photoactivated riboflavin (RF) treatments have been approved to improve resin-dentin bonding by enhancing dentinal collagen crosslinking. This study aimed to evaluate whether RF activated by blue light (BL, 450 nm) strengthens the collagen matrix, increases resistance to enzymatic degradation, and improves adhesion as effectively as ultraviolet A (UVA, 375 nm) activation. Six groups were examined: control (no treatment); RF0.1UV2 (0.1% RF with 2 min of UVA irradiation); RF0.1BL1, RF0.1BL2, RF1BL1, and RF1BL2 (0.1% and 1% RF with 1 or 2 min of BL irradiation). The effects of RF/BL on collagen crosslinking were validated by gel electrophoresis. A nanoindentation test showed that both RF/UVA and RF/BL treatments enhanced the elastic modulus and nanohardness of demineralized dentin. A zymography assay using collagen extracted from demineralized dentin also revealed significant matrix metalloproteinase-2 inhibition across all RF treatments. Microtensile bond strength (µTBS) tests conducted both post-treatment and after 7-day enzymatic degradation showed that three RF0.1 groups (RF0.1UV2, RF0.1BL1, and RF0.1BL2) maintained high µTBS values after degradation, while RF0.1BL1 generated a significantly thicker hybrid layer compared to other groups. These findings suggest that RF/BL is as effective as RF/UVA in crosslinking dentinal collagen and resisting enzymatic degradation, with 0.1% RF proving superior to 1% RF in enhancing dentin bonding.

Keywords: collagen crosslinking; dentin bonding; enzymatic degradation; microtensile bond strength; nanoindentation; riboflavin.

Figure 1

(a) The absorbance spectrum of riboflavin aqueous solution; (b) Spectra of UVA and BL units.

Figure 2

(a) Electrophoretogram (SDS-PAGE) of collagen receiving different treatments; (b) Density ratio plot of the SDS-PAGE. All the γ, β, and α bands are calibrated with the control (collagen).

Figure 3

Results of the nanoindentation test. (a) Elastic modulus; (b) Hardness values. Identical letters represent no significant differences among treatments.

Figure 4

(a) Zymogram of the control and experimental groups; (b) The percentage of latent and active form of MMP2, and their total amounts.

Figure 5

(a) Micromorphology of resin–dentin interfaces. (b) Average adhesive layer thicknesses (μm) in experimental groups. The same uppercase letters indicate no significant differences. Identical uppercase letters represent no significant differences among treatments. A: adhesive layer; R: resin composite; T: resin tags.