Multi-resolution Correlative Ultrastructural and Chemical Analysis of Carious Enamel by Scanning Microscopy and Tomographic Imaging

Caries, a major global disease associated with dentalenamel demineralization,remains insufficiently understood to devise effective prevention orminimally invasive treatment. Understanding the ultrastructural changesin enamel is hampered by a lack of nanoscale characterization of thechemical spatial distributions within the dental tissue. This leadsto the requirement to develop techniques based on various characterizationmethods. The purpose of the present study is to demonstrate the strengthof analytic methods using a correlative technique on a single sampleof human dental enamel as a specific case study to test the accuracyof techniques to compare regions in enamel. The science of the differenttechniques is integrated to genuinely study the enamel. The hierarchicalstructures within carious tissue were mapped using the combinationof focused ion beam scanning electron microscopy with synchrotronX-ray tomography. The chemical changes were studied using scanningX-ray fluorescence (XRF) and X-ray wide-angle and small-angle scatteringusing a beam size below 80 nm for angstro''m and nanometerlength scales. The analysis of XRF intensity gradients revealed subtlevariations of Ca intensity in carious samples in comparison with thoseof normal mature enamel. In addition, the pathways for enamel roddemineralization were studied using X-ray ptychography. The resultsshow the chemical and structural modification in carious enamel withdiffering locations. These results reinforce the need for multi-modalapproaches to nanoscale analysis in complex hierarchically structuredmaterials to interpret the changes of materials. The approach establishesa meticulous correlative characterization platform for the analysisof biomineralized tissues at the nanoscale, which adds confidencein the interpretation of the results and time-saving imaging techniques.The protocol demonstrated here using the dental tissue sample canbe applied to other samples for statistical study and the investigationof nanoscale structural changes. The information gathered from thecombination of methods could not be obtained with traditional individualtechniques.

Automated summary

Insufficient understanding of dental caries hinders effective prevention or minimally invasive treatment. This study demonstrates the strength of analytical methods using a correlative technique to compare regions in dental enamel, providing insights into the chemical and structural modifications in carious enamel.