Longitudinal Assessment of Dynamic Caries Process with Microfocus Computed Tomography

Objective: Evaluate the usefulness of Microfocus Computed Tomography (µ-CT) for longitudinal caries-process assessment using a demineralization (demin) / remineralization (remin) model. Methods: 12 ground/polished 1×2×0.5-mm human enamel specimens were chemically demineralized for 48h or 96h, then remineralized with 1100 ppm F as NaF for 6 or 12 days. µ-CT images of sound, demineralized and remineralized enamel were acquired (Skyscan1172, Aartselaer, Belgium). 67 µ-CT cross-sections for the middle portion of each specimen were used for the µ-CT analyses. The region of interest (ROI) was equally divided into three zones (Zone 1: outer 1/3, Zone 2: middle 1/3, Zone 3: inner 1/3). Mineral content volumes [MC (µm³×10⁶)] were determined [100–91 (Vol_100–91) and 91–0 (Vol_91–0) wt%]. MC change from sound [MCC (µm³×10⁶)] was calculated: MCC=MC_{Subsequent-period}–MC_Sound. Results: Vol_100–91 MC decreased through 96h-demin then increased through remin phase. For comparison, at the end of each treatment period, three specimens were removed for TMR analysis. Integrated mineral loss and MCC at Vol_100–91 and Vol_91–0 were correlated strongest within Zone 2 (Zone 1: r=-0.27 and 0.47 for Vol_100–91 and Vol_91–0, Zone 2: r=-0.80 and 0.80, Zone 3: r=-0.64 and 0.71). Comparisons were unable to distinguish between 48h-demin and 12d-remin using the entire ROI or within Zones 2 or 3, but were significant for Zone 1. After 48h-demin Vol_91–0 MCC was higher in Zone 1 than Zone 2, while at 96h-demin and 6d-remin Vol_91–0 MCC was higher in Zone 2 than Zone 1; Zone 3 had the lowest Vol_91–0 MCC regardless of time. Conclusion: The µ-CT shows promise for non-destructive longitudinal assessment of the caries process.