Hyper‐spectral Raman imaging correlating chemical substitution and crystallinity in biogenic hydroxyapatite: Dentin and enamel in normal and hypoplastic human teeth

Abstract

Micro‐Raman imaging and spectroscopy has become an established technique for the characterization of biogenic hydroxyapatite as, for example, the primary constituent of human teeth. However, few studies have yet gone beyond a qualitative analysis of the Raman response providing only limited insight into spatial heterogeneity of composition, structure, and degree of crystallinity. Here, we show how correlative electron microprobe and extended hyperspectral Raman imaging with high spatial and spectral resolution, with peak position and linewidth analysis, and from the μm to mm scale, provides insight into structural characteristics in dentin and enamel. From comparison of healthy and hypoplastic teeth as a representative tooth disease example, we determine variations in degree of crystallinity, both locally across the dentin–enamel junction, and with distinct long‐range spatial variations. We identify a correlation of spectral peak position and linewidth as a measure of crystal lattice disorder across tubules, dentin, dentin–enamel junction, and enamel. This correlative Raman imaging and analysis approach may help to provide a better understanding of apatite geochemistry and biomineralization.

Application of low‐wavenumber Raman spectroscopy to the analysis of human teeth

“…Also, FWHM gradually increases towards the pulp region within samples. For dentine, the spectral broadening of the band can be attributed to the carbonate substitution (b‐type) for the ions, which is believed to cause a loss of long‐range structural order . However, integral ratio maps (Fig.…”

“…Interestingly, higher FWHM values are also characteristic to caries lesions, in addition to blueshifted position and distorted (nonsymmetrical) line shape for the particular band . It is reported that peak position of generally increases towards inner subcomponents (from enamel to dentine) . Typical hydroxyapatite constituents such as fluoride and strontium can also affect the peak position of this band .…”

“…The chemical composition and structural attributes of teeth can be probed by Raman spectroscopy . The spectral data from the midwavenumber region (350‐4,000 cm ‐1 ) have been utilized to monitor transformations of artificial dental caries lesions, as well as to map naturally formed ones .…”

“…The spectral data from the midwavenumber region (350‐4,000 cm ‐1 ) have been utilized to monitor transformations of artificial dental caries lesions, as well as to map naturally formed ones . Recently, spatio‐chemical and structural heterogeneity in healthy and hypoplastic teeth was studied using Raman microimaging . The interface boundaries between different subcomponents have also been investigated .…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIII

“…The results obtained were supported by vibrational analysis and indicate that IR and confocal Raman spectroscopy are important, useful, and fast tools to identify changes in the proteins' secondary structure in normal tissues, goiter, and follicular and papillary thyroid carcinomas . Wang et al implemented hyper‐spectral Raman imaging to correlate chemical substitution and crystallinity in biogenic hydroxyapatite for dentin and enamel in normal and hypoplastic human teeth . Zhao and Cai reported early detection of zinc deficit using confocal Raman spectroscopy.…”