Dual function of quercetin as an MMP inhibitor and crosslinker in preventing dentin erosion and abrasion: An in situ/in vivo study

The aim of the present study was to evaluate the in situ/in vivo effect of quercetin on dentin erosion and abrasion. Human dentin blocks (2 × 2 × 2 mm) were embedded and assigned to 6 groups: 75 μg/mL, 150 μg/mL and 300 μg/mL quercetin (Q75, Q150, Q300); 120 μg/mL chlorhexidine (CHX, positive control); and deionized water and ethanol (the negative controls). The specimens were treated with the respective solutions for 2 min and then subjected to in situ/in vivo erosive/abrasive challenge for 7 d as follows: in vivo erosion 4 times a day and then in vivo toothbrush abrasion after the first and last erosive challenges of each day. Dentin loss was assessed by profilometry. An additional dentin specimen was used to evaluate the penetration depth of quercetin into dentin by tracking the spatial distribution of its characteristic Raman peak. Moreover, dentin blocks (7 × 1.7 × 0.7 mm) were used to detect the impact of quercetin on dentin-derived matrix metalloproteinase (MMP) inhibition by in situ zymography, and the inhibition percentage (%) was calculated. Additionally, the potential collagen crosslinking interactions with quercetin were detected by Raman spectroscopy, and the crosslinking degree was determined with a ninhydrin assay. Fully demineralized dentin beams (0.5 × 0.5 × 10 mm) were used to evaluate the impact of quercetin on the mechanical properties of dentin collagen fibre by the ultimate micro-tensile strength test (μUTS). The data were analysed by one-way analysis of variance and Tukey’s test (α = 0.05). Compared to the negative controls, all treatment solutions significantly reduced dentin loss. The dentin loss of Q150 and Q300 was significantly less than that of CHX (all P < 0.05). The amount of quercetin decreased with increasing dentin depth, and the maximum penetration depth was approximately 25–30 µm. In situ zymography showed that quercetin significantly inhibited the activities of dentin-derived MMPs. The inhibitory percentages of Q75 and Q150 were significantly lower than that of CHX (all P < 0.05), but no significant difference was found between Q300 and CHX (P = 0.58). The collagen crosslinking interactions with quercetin primarily involved hydrogen bonding and the degree of crosslinking increased in a concentration-dependent manner. Statistically significant increases in μUTS values were observed for demineralized dentin beams after quercetin treatment compared with those of the control treatments (all P < 0.05). This study provides the first direct evidence that quercetin could penetrate approximately 25–30 µm into dentin and further prevent dentin erosion and abrasion by inhibiting dentin-derived MMP activity as well as crosslinking collagen of the demineralized organic matrix.