Four-dimensional µCT Analysis of Remineralization in Enamel and Root Caries

Objective: We previously reported µCT reconstruction of subsurface carious lesions developed around coronal fissures. In the present longitudinal remineralization study of carious lesions at occlusal, fissure and root regions, we aimed at extending the µCT-3D reconstruction technology to non-invasively visualize and monitor site-specific changes in mineral density. Materials and methods: Tooth blocks were prepared from the coronal and root region of human extracted molars including fissure-, smooth surface-, and root-caries. Remineralization solutions used were Ca 2 mM, total P 1.2 mM, NaCl 100 mM, and pH7.3, with the addition of Xylitol gum extracts. All µCT data were acquired from individual tooth blocks submerged in the solution using Nittetsu ELE-SCAN apparatus. To facilitate superimposition of 3D reconstructs made at various times, silver paste was adhered to four corner points of the tooth rectangular block as position references. Mineral density of sound tooth and carious lesions was assessed using a mixture of hydroxyapatite resin composite as standard. Reconstruction and visualization was conducted using RATOC 3D-BON software. Results: To date, 12 enamel caries lesions and 2 root dentin caries were monitored over remineralization periods for 28 days. For individual demineralized lesions, 3D reconstructs with the identical contour and volume were achieved reproducibly at various time points of remineralization treatment. The average increase in mineral density of the 12 enamel lesions was 13.3(±5.0) % at the end of remineralization treatment. The mineral density of two root carious lesions also increased 12.1 and 13.1% during the same period. Inspection of the reconstructed carious lesions in 4D motion views proved the advancing mineralization at multi-foci including peripheral and central portions of the originally demineralized lesion. Conclusion: The overall results indicate that the computer-assisted µCT reconstruction of enamel and root caries is useful in visualization and assessment of remineralization inside the demineralized lesions.