Synchrotron X-Ray Microtomographic Investigation of Mineral Concentrations at Micrometre Scale in Sound and Carious Enamel

Abstract

Synchrotron X-ray microtomography (XMT) was used to measure the linear attenuation coefficient (LAC) for 1.9-µm sidelength voxels within approximal brown spot lesions and sound human enamel. XMT demonstrated three-dimensional features, notably sheets with ∼30 µm periodicity having low LAC, identified as regions of demineralization corresponding to Retzius lines. Quantitative three-dimensional measurements of mineral concentration, derived from LAC with assumption of a single model composition, were consistent with previous measurements of sound and carious enamel from microradiographic projections. The uncertainty in measurements of mineral concentration and mineral fraction volume was investigated by modelling enamel with a range of composition and component densities. This analysis showed that, although mineral concentration can be determined from LAC with an error of <0.2 g cm^–3, the variation in pore fraction volume within caries lesions cannot be reliably determined from X-ray attenuation measurements alone.

State of the Art of Micro‐CT Applications in Dental Research

“…Another investigation of mineral concentrations at the micron scale in sound and carious enamel indicated that, quantitative measurements of mineral concentration derived from linear attenuation coefficient (LAC) were consistent with previous measurements of sound and carious enamel from microradiographic projections. However, though mineral concentration could be determined from LAC with an error of <0.2 g⋅cm -3 , the variation in pore fraction volume within caries lesions could not be reliably determined from X-ray attenuation measurements alone (Dowker et al, 2004). Using the non-destructive characteristics of Micro-CT, they quantitatively showed how much mineral was lost after demineralization in the enamel of a tooth rod, and how much mineral was regained after remineralization (in the same position of the same rod) (Gao, 1993).…”

Theory of X-ray microcomputed tomography in dental research: application for the caries research

“…There have been several reports, including Dowker et al, that utilize a synchrotron XMT. [39][40][41] Today, commercially available desktop XMT systems make use of polychromatic X-ray sources, which unfortunately introduce scanning artifacts such as beam hardening and loss of information due to energy averaging ( Figure 1). 42,43 Beam-hardening artifacts arise from polychromatic sources because the attenuation of the incident X-ray beam is not exponentially related to the thickness of the object, as predicted by Beer' s law.…”

“…Since the minerals in dental tissues (mainly hydroxyapatite) are responsible for most of the X-ray attenuation observed in caries studies, and normal variations in the chemical composition of enamel minerals have little effect on the LAC, a variation in the LAC for enamel is proportional to its mineral density. 16,19,40,41,49,51 Dentin is composed of approximately 35% organic substances by weight, mainly collagen. Collagen' s contribution to the total X-ray attenuation coefficient in dentin is around 5% at an energy of 25 keV.…”

“…54 The reported densities of sound enamel range between 2.65 and 2.89 g/cm 3 . 16,32,40,41,[58][59][60] The densities of dentin have been estimated to be between 1.46 g/cm 3 for incisors and 1.62 g/cm 3 for molars, 18,58 with circumpulpal dentin having a lower density (1.3 g/cm 3 ) than peripheral dentin (1.5 g/cm 3 ). The average mineral concentration of sound human dentin has been measured at 1.29 g/cm 3 , with demineralized dentin being only 0.55 g/cm 3 .…”

Microtomography of the human tooth-alveolar bone complex

“…Actually, SRµCT is so specific that not only different types of tissues with various degrees of mineralization can be separately identified, but also minor changes in the mineralization patterns within the same type of tissue can be detected. [7][8][9][10][11][12] The various dentoalveolar calcified tissues, like bone, dentine, enamel and cementum, display a wide range in degrees of mineralization (from 60 to 98 percent). The forte of SRµCT-scans would therefore be to better distinguish between these different tissues, as due to the size of the excised segments, it was understood from the beginning that the spatial resolution for the SRµCT-scans would not be significantly better than what can be achieved with a µCT-scanner with a conventional X-ray source.…”