Amelogenin-chitosan Hydrogel for Enamel Regrowth: An In Vitro pH-cycling Study

Objectives: We recently reported that amelogenin-chitosan (CS-AMEL) hydrogel promotes in vitro biomimetic enamel regrowth, with a dense enamel-restoration interface improving the effectiveness and durability of restorations. To examine the stability and efficacy of CS-AMEL hydrogel for biomimetic repair of human enamel with erosive or caries-like lesions in a pH-cycling system, and to explore its potential for the prevention, restoration, and treatment of defective enamel.
Methods: Erosive lesions were produced by etching tooth slices with 30% phosphoric acid for 30 seconds, while early caries-like lesions were created by immersing tooth blocks in a demineralization solution (pH 4.6) at 37°C for 3 days. All the samples were subjected to a standard regime of pH cycling at 37 °C for 7 days. During each 24-hr period, samples were immersed in the demineralization solution for 5 hours, then immersed in a remineralization solution (pH 7.0) for 18 hours. About 20 µl of CS-AMEL hydrogel was applied on the lesion surface before and after the demineralization period. The morphology and composition of newly-grown crystals were characterized by scanning electron microscopy and X-ray diffraction. The depths of carious lesions were determined before and after pH cycling by fluorescent microscopy.
Results: After completion of pH cycling, a synthetic layer composed of oriented apatite crystals was formed on enamel surfaces treated with CS-AMEL hydrogel in both the erosion and caries models. On the erosive lesion surface, the newly-grown crystals had a needle-like shape and were arranged parallel to each other. The depth of the caries lesion was significantly decreased from ~ 100 µm to ~ 50 µm following treatment with the CS-AMEL hydrogel in a pH-cycling system.
Conclusions: Our results demonstrate that the CS-AMEL hydrogel is stable in an acidic environment and is effective in restoring erosive and carious lesions.