Longitudinal evaluation of mineral loss at the earliest stage of enamel demineralization using micro-computed tomography

Abstract

As the prevalence of dental caries decreases, the diagnosis and treatment of initial mineral loss resulting in white spot lesions have been getting more and more important. Since dental CT provides computed tomography images of a tooth with radiation exposure similar to panoramic radiography, it will become possible in the near future to evaluate the enamel mineral density using CT in the same way as measurement of the bone mineral density. Such computed tomography images enable dentists to perform longitudinal, three-dimensional, and precise evaluation of the enamel mineral density before a demineralized lesion becomes detectable by any other traditional means. Despite their advantage, there are not enough reports on evalu- ation of the enamel mineral density using CT. This study evaluated the serial changes in mineral density in the earliest stage of enamel demineralization. Eight bovine enamel specimens were coated with nail varnish. On each specimen, 4 square windows measuring 1 mm2 were created. The specimens were incubated in lactic acid solution at 38?C. During incubation, the windows were covered by nail varnish one by one at 30, 60, and 90 minutes, respectively. At 120 minutes, the specimens were removed from the solution. After the nail varnish was removed, X-ray microradiography was performed using SKYSCAN1172 at settings of 100 kV and 100 μA. The mean Hounsfield unit values (HUV) of enamel in a non-window area and those in the window areas were calculated every 180 μm over a depth of 0 - 900 μm and analyzed by two-way ANOVA. Data were affected by the incubation time and depth from the enamel surface, and there was not interaction between the two factors. Considering the incubation time, HUV of the whole measured enamel (0 - 900 μm) in the non-window group was significantly higher than that of the other incubated groups. Considering the depth, HUV was decreased at 721 - 900 μm compared with that at 0 - 180 μm in the 30-minute-incubated group, and the decrease spread to 361 - 900 μm in the 60- and 90- minutes-incubated groups. HUV was additionally calculated at increments of 18 μm and compared within the 60-minute-incubated group, and changes in the mineral density at the boundary of the earliest demineralized lesion could be observed. This study demonstrated detailed mineral density changes in the earliest period of demineralization.