Quantitative high contrast X-ray microtomography for dental research.

OBJECTIVES X-ray microtomography (XMT or micro-CT) is a miniaturized version of medical CT and has been used extensively for in vitro dental research. The technique allows three-dimensional analyses of both structure and density (or concentration), the latter requiring some a priori knowledge of composition. The aim of this paper is to demonstrate the capabilities of an XMT scanner specifically designed for dental research, especially that requiring high contrast resolution or accurate mineral concentration quantification. METHODS The MuCAT scanners designed at Queen Mary, University of London, use high dynamic range CCD cameras with time-delay integration readout to provide high quality tomographic images. Accuracy in mineral concentration quantification is achieved using a modelling approach to beam hardening correction with automatic calibration following every scan. Accuracy was tested by measuring the density of a hydroxyapatite disc, and the utility of the high contrast and high accuracy capabilities are demonstrated in three applications from ongoing dental research projects. RESULTS Quantification accuracy in the hydroxyapatite disc density was better than 1%. In dental applications, slight differences in mineral concentration allowed features such as dead tracts to be visualized and ion transport from a glass-ionomer cement into demineralized dentine to be observed. CONCLUSION The improved accuracy and contrast sensitivity, together with the non-destructive nature of XMT in general, facilitates precise studies of dynamic processes in teeth. The ability to differentiate subtle differences in mineral concentration allows dead tracts to be traced in three dimensions, linking external pathology in teeth to reactive processes from the pulp. CLINICAL SIGNIFICANCE The MuCAT scanners have been optimized for quantification of mineral concentration and are particularly useful for in vitro studies of de- and re-mineralization, excavation and other treatment methodologies, and for gaining further insight into tooth morphology and pathology. Results from such studies will inform development of clinical treatment and management.