Multimodal imaging offers new insights into understanding ion penetration in dentin caries using an animal model

Dentin being an organic-inorganic composite, understanding how inorganic ions behave and bring about changes in the organic matrix is essential to clarify the pathogenesis of dentin caries. We developed a novel in vivo carious restoration model combining quantitative analysis and multimodal imaging to elucidate the pathology of dental caries and to investigate how multi-ions released from restorative materials promote dentin demineralization.

Carious lesions in maxillary first molars of Sprague-Dawley rats were restored using a glass ionomer cement. We quantified the elemental concentrations of calcium, fluoride, and zinc in the dentin using air-microparticle-induced X-ray and gamma-ray emissions (PIXE/PIGE) after 1 week or 3 months from the restoration. Multimodal imaging was performed on 3 months sample.

We found fluoride and zinc incorporation increased in areas of calcium loss. Zinc showed significant increases in depth and concentration over time (one-way analysis of covariance, p < 0.05), penetrating into dentin by up to 146.3 μm after 3 months Initial demineralization was sensitively detected in the form of low calcium intensity and reduced hydroxyapatite crystallinity by PIXE/PIGE and Raman spectroscopy analyses, respectively. Time-of-flight secondary ion mass spectrometry analyses demonstrated that fluoride remained in the glycine-rich area with calcium loss, but zinc passed through the demineralized area and penetrated sound dentin.

We successfully created a carious restoration model using quantitative elemental analysis and spatially resolved multimodal imaging.

This model enables comprehensive, non-destructive evaluation of ion dynamics and pathological responses in dentin caries, potentially offering insights to develop new restorative materials and techniques.