Quantitative analysis of the mineral content of sound and carious primary dentine using BSE imaging.

Backscattered electron-scanning electron microscope (BSE-SEM) imaging has been recommended as a reliable tool to quantify the mineralisation state of calcified tissues and is commonly used in bone studies. The aim of this study is to investigate the use of BSE imaging to quantitatively analyse the mineral content of sound and carious dentine. Eight primary molars with untreated carious dentine were embedded in resin, axially sectioned and fine polished for this study. The BSE images were from a solid-state detector in an SEM operating at 1.5Torr gas pressure. BSE images of a number of different elements and compounds with atomic number ranged from 4 to 26 were analysed prior to the test to calibrate the experimental conditions and an enamel-carbon block. The mineral analysis was based on the change in BSE intensity (measured in graylevels). The results showed that variation in graylevels accurately represented difference in the atomic number and BSE coefficient of the test materials. The mineral content of sound primary dentine in the most regions was 59.3+/-5.5 wt.%, but it decreased gradually to be just 41.82+/-6.74 wt.% adjacent to the pulp. The carious dentine showed a marked reduction in mineral content which proceeded progressively toward the cavity floor, in which the minimum value of less than 10 wt.% was normally found in the outer layer of the lesion. The results show that BSE imaging is a simple and reliable technique that can be used to quantify the mineral content of sound and carious dentine. More importantly the variable pressure SEM offers an approach to minimize the impact of dehydration on carious dentine specimens.