Quantitative Characterization and microCT Mineral Mapping of Brown Spot Enamel Lesions

Objectives: Our aim was to characterize the mineral distribution pattern of naturally arrested proximal brown spot enamel lesions(PBSEL) and to quantify structural parameters and mineral density of these lesions in comparison to proximal white spot enamel lesions(PWSEL).
Methods: Human teeth with non-cavitated proximal white and brown spot enamel lesions were collected and assessed by two experienced clinicians. Eighteen PBSEL, twenty PWSEL (ICDAS I, II) and twenty sound proximal areas (ICDAS 0) where chosen as study and control groups. Imaging was undertaken using a high resolution micro-computed-tomography(Microct) system. A calibration equation was used to transform grey-level values into true mineral density values. Each lesion was color coded based on grey-level values using colormapeditor command in MATLAB to provide the mineral map of the lesion. The value of lesion parameters including mineral density and the thickness of the lesion surface layer were extracted from mineral density profiles plotted in FIJI and the visualized mineral maps in MATLAB. The statistical analysis was performed using GraphPadPrism.
Results: PBSELs exhibited different mineral distribution pattern compared to PWSELs. Despite PWSELs which had regular conical shape with the tip towards the DEJ, a non-regular demineralization pattern with scattered areas of high mineral density within the lesion were observed in PBSELs. A reverse triangular or trapezoid pattern with the tip towards the external surface was common in PBSELs. The quantitative analysis of the lesions indicated significantly thicker surface layer and higher mineral density in the surface layer and body of PBSELs(P-value<0.05).
Conclusions: MicroCT and proposed visualization method provided an efficient high-resolution method for non-destructive evaluation of proximal lesions. The findings of this study which also corroborate the clinical observation of re-hardening of PBSELs, suggests extensive degree of subsurface remineralization in the majority of naturally arrested PBSELs and highlights the importance of PBSELs as natural models of caries remineralisation for future remineralization research.