Monitoring demineralization and remineralization of human dentin by characterization of its structure with resonance-enhanced AFM-IR chemical mapping, nanoindentation, and SEM

Objective: This research aimed at monitoring demineralization and remineralization of dentin and its collagen matrix at the nanoscale by amorphous, microcrystalline, and in situ formed hydroxyapatite. Methods: The concurrent use of the resonance-enhanced atomic force microscopy coupled with infrared probe (AFM-IR) chemical mapping, nano-indentation, and scanning electron microscopy (SEM) provides a detailed insight into the structure of human dentin, as well as to the processes of its partial demineralization and remineralization. Results: The resonance-enhanced AFM-IR chemical mapping of dentin has shown to be a useful method to follow distribution of its collagen and hydroxyapatite components at the micro- and nanoscale levels, especially in conjunction with SEM imaging and nanoindentation. Dentin with a higher extent of natural dentin tubule occlusion tends to be harder and less elastic. The relative affinity of the collagen and hydroxyapatite components of dentin toward hydroxyapatite depends on its type (amorphous, microcrystalline, or formed in-situ). The gel mineralization technique allows for an even and controlled growth of hydroxyapatite guided by the completely demineralized collagen matrix of dentin. Significance: The observed trends of the affinity of collagen toward different forms of hydroxyapatite helps develop new remineralizing formulations. The employed methods of characterization may provide an insight to the natural processes of bone mineralization guided by its both hydroxyapatite and protein constituents.