Mapping tooth microcracks by combining X-ray tomography and photoluminescence

Although teeth microcracks (MCs) were recently characterized in three-dimensions (3D), it is still unknown whether there are changes in the tooth material within the MC compared to the uncracked enamel. Thus, spectral analysis of the cracked area could provide information on the composition of the material along the crack line. However, this is followed by the major methodological challenge – to find the same MC using different methods. Therefore, the aim of this study was to identify the same crack-affected and pristine tooth regions by combining X-ray µCT with photoluminescence (PL) and to assess the structural integrity of the extracted human teeth along the very same MC. The samples were first examined using an X-ray µCT. Secondly, buccal and palatal surfaces with visible cracks and pristine areas were used to obtain fluorescence spectra excited at 325 nm. In total 192 PL spectra were detected for each sample: 96 from visible MCs from the buccal and palatal surfaces and 96 from the pristine regions on the adjacent areas. The X-ray µCT technique allowed the accurate identification of the cracks that were analysed by PL using the 3D mesh structure developed. The 3D mesh structure created to overlap the outer enamel surface of the tooth served as a link between the 3D X-ray and spectral images to identify the same crack locality and to qualitatively assess the structural integrity along the crack line, using two complimentary techniques. This is opening a clinically viable spectro-spatial identification of the location of the damaged tooth material.