A method for mapping submicron-scale crystallographic order/disorder applied to human tooth enamel

Abstract

Tooth enamel, the outermost layer of human teeth, is a complex, hierarchically structured biocomposite. The details of this structure are important in multiple human health contexts, from understanding the progression of dental caries (tooth decay) to understanding the process of amelogenesis and related developmental defects. Enamel is composed primarily of long, nanoscale crystallites of hydroxyapatite that are bundled by the thousands to form micron-scale rods. Studies with transmission electron microscopy show the relationships between small groups of crystallites and X-ray diffraction characterize averages over many rods, but the direct measurement of variations in local crystallographic structure across and between enamel rods has been missing. Here, we describe a synchrotron X-ray-based experimental approach and a novel analysis method developed to address this gap in knowledge. A ~500-nm-wide beam of monochromatic X-rays in conjunction with a sample section only 1 μm in thickness enables 2D diffraction patterns to be collected from small well-separated volumes within the enamel microstructure but still probes enough crystallites (~300 per pattern) to extract population-level statistics on crystallographic features like lattice parameter, crystallite size, and orientation distributions. Furthermore, the development of a quantitative metric to characterize relative order and disorder based on the azimuthal autocorrelation of diffracted intensity enables these crystallographic measurements to be correlated with their location within the enamel microstructure (e.g., between rod and interrod regions). These methods represent a step forward in the characterization of human enamel and will elucidate the variation of the crystallographic structure across and between enamel rods for the first time.

Combination of Two Synchrotron Radiation-Based Techniques and Chemometrics to Study an Enhanced Natural Remineralization of Enamel

“…51 Diffraction spots in Figure 4a,b are concentrated in distinct arcs, both in the enamel and in the layers, which means that the crystals are ordered. 54 The strongest texture (the most extreme intensity variation) for both kinds of samples (NMTD treatment with or without amelogenin) was found in the reflection (002), as can be appreciated in Figure 4a,b. The lattice plane reflection (002) does not overlap with other reflections and has the greatest intensity variation with maxima normal to the c-axis.…”

“…The intensity variations around the diffraction rings are indicative of tooth enamel texture . Diffraction spots in Figure a,b are concentrated in distinct arcs, both in the enamel and in the layers, which means that the crystals are ordered . The strongest texture (the most extreme intensity variation) for both kinds of samples (NMTD treatment with or without amelogenin) was found in the reflection (002), as can be appreciated in Figure a,b.…”

Microstructure and energy dispersive diffraction reconstruction of 3D patterns of crystallographic texture in a shark centrum

“… 6 Analogous preferred orientation of bioapatite axes exists in other collagen-based mineralized tissues including bone, 14 dentin, 21 and cementum. 17 Although the individual diffraction peaks within the unresolved quadruplet reflection exhibit crystallographic texture, as can be seen in enamel, 22 the very broad diffraction 21.1, 11.2, 13.0, and 20.2 peaks (from very small crystallites) of bone, dentin, and cementum produce a combined peak which does not exhibit strong texture. In addition to the relatively strong 00.2 and quadruplet peaks, Fig.…”

Bioapatite in shark centra studied by wide-angle and by small-angle X-ray scattering

“…The quadruplet peaks in the pattern from shark mineralized cartilage and that from bone (figure 3 c ) cannot be resolved, a common observation for mineralized, bioapatite-containing tissue except tooth enamel, e.g. [15,24]. Note that instrumental broadening differed between the patterns of figure 3 c and the 00.2 peak widths cannot be compared by inspection.…”