Evaluation of Demineralization in Root Dentin Using in-air Micro-PIXE/PIGE

Objectives: The aim of this study was to evaluate the demineralization in human root dentin using in-air micro-PIXE/PIGE (proton induced X-ray/gamma-ray emission) measurement system at WERC (Wakasa, Japan).
Methods: A total of 16 human third molars free from caries were used. Three root dentin blocks were obtained from each tooth. Exposed dentin surfaces were covered with fluoride containing materials (FCMs); Fuji VII (G-F7) and MI Varnish (G-MI); while dentin without FCMs was served as control (G-Con). Specimens were immersed in saline at 37°C for 1 or 3months. After removing the FCMs, blocks were cut parallel to the longitudinal axis and perpendicular to the exposed surfaces to make a 500µm section. A copper foil was set on the edge of their cutting plane in order to make a reference point. Specimens were immersed in 10ml of demineralizing solution (pH5.0, 37°C) for 3days. Before and after the demineralization, Ca and F concentration were measured using the PIGE/PIXE system. The results obtained from same specimens before and after the demineralization were compared on the basis of a reference point designated by the cupper foil (Kruskal-Wallis and Scheffe tests, α=0.05).
Results: After 3months, G-F7 and G-MI showed significantly higher integrated F concentration (median (interquartile range); G-F7=6273(5024-7126)ppmF･µm, G-MI=14844(11640-21180)ppmF･µm) and lower amount of Ca loss (G-F7=128(28-189)wet%･µm, G-MI=59(35-76)wet%･µm) than G-Con (F concentration=1(1-13)ppmF･µm, Ca loss=416(231-538)wet%･µm). The F uptake before and after the demineralization showed significant negative correlations with the Ca loss and the lesion depth.
Conclusions: Demineralization in root dentin was successfully evaluated by using in-air micro-PIXE/PIGE. The FCMs were effective to prevent demineralization of root dentin. This study was supported by Grants-in-Aid for Scientific Research (25293387, 26462879) from the JSPS.