Restoring Subsurface Enamel Mineral Using Bioactive Nanoparticles in Non-Cavitated Lesions

Objectives: Remineralizing a demineralized (non-cavitated) carious lesion is challenging. This study used a novel, innovative technology, and a biomimetic restorative material, nano fluorapatite crystals (nFA), to restore the porous, sub-surface of caries-like lesions in enamel in one application.
Methods: Twelve extracted permanent molar human teeth were prepared with a 3x3mm enamel window on the buccal surface. The teeth were then placed in an acidic gel, pH 4.6, for ten days to create a subsurface lesion. Synthesized (nFA) crystals which are the same shape, size, and composition as human enamel crystals were tagged with Fluo-4 pentapotassium salt. Six carious lesions were exposed to 15% w/v nFA-Fluo-4 for 30 minutes and six were treated with only the Fluo-4 solution for the same time. All the teeth were rinsed in DI-water for two minutes. The teeth were illuminated with a composite light curing unit to determine fluorescence and photographed. The specimens were then examined with a Leica TCS SP8 2-Photon confocal microscope with FLIM & FCS and a 20x dry objective to verify nFA crystal penetration into the lesions.
Results: After demineralization, when nFA-treated samples were exposed to the composite curing light, the lesions fluoresced. The 2-photon microscopy z-stack images confirmed the extent of the penetration of the nFA crystals into the subsurface of the caries-like lesions in the enamel. The controls showed little or no fluorescence. More studies are required to confirm the long-term retention of the nanoparticles.
Conclusions: Applying Nano fluorapatite crystals directly to active non-cavitated caries-like lesions penetrated the subsurface of the lesion restoring the lost minerals of the enamel.