How UVA-activated Riboflavin Inhibits Demineralization of Human Dentin

Objectives: Root caries is becoming an increasingly important issue in aging societies. Strengthening type-I collagen, a major organic component of human dentin, may be effective in preventing root caries. The purpose of this study was to investigate how the exposure to riboflavin followed by UVA irradiation (riboflavin/UVA) affects the acid and enzymatic resistance of human dentin by producing collagen crosslinking.
Methods: Beam-shaped and disk-shaped dentin specimens were obtained from human third molars. These specimens were divided into two groups; half were exposed to 0.1% riboflavin followed by 365nm UVA irradiation (1600mW/cm²) for 10min (riboflavin/UVA group), and the others without such treatment served as controls. Beam-shaped specimens (n=7/group) were immersed in a demineralizing solution (pH5.0, 37°C) for 3 days. Mineral densities of the specimens before and after demineralization were analyzed by μCT. Dentin samples with or without riboflavin/UVA treatment were dissolved in pepsin from porcine gastric mucosa or collagenase from Clostridium histolyticum. After centrifuging the solutions, the resultant precipitations were analyzed by SDS-PAGE to assess the enzymatic resistance. The statistical differences were determined by Student’s t test (α=0.01).
Results: In μCT analysis, the amount of mineral loss after demineralization in the RF/UVA group (3.0±1.0mg/cm²) was significantly lesser than the control group (7.9±2.9mg/cm²). The depth of dentin surface after demineralization was significantly lesser in the RF/UVA group (25.4±14.6μm) comparing with the control group (75.9±29.3μm). In SDS-PAGE analysis, the collagen after the pepsin digestion and collagenase degradation was less soluble in the riboflavin/UVA group than in the control group because of new collagen crosslinking promoted by a radical reaction.
Conclusions: Riboflavin/UVA treatment was effective in enhancing the acid and enzymatic resistance of human dentin by producing new collagen crosslinking. (This study was supported by Grants-in-Aid for Scientific Research (25293387, 15K15700, and 25462957) from the JSPS.)