Crystallographic and Physicochemical Analysis of Bovine and Human Teeth Using X-ray Diffraction and Solid-State Nuclear Magnetic Resonance

Abstract

Dental research often uses bovine teeth as a substitute for human teeth. The aim of this study was to evaluate differences in the crystalline nanostructures of enamel and dentin between bovine and human teeth, using X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (NMR). The crystallite size (crystallinity) and microstrains were analyzed using XRD with the Rietveld refinement technique and the Halder-Wagner method. The ³¹P and ¹H NMR chemical environments were analyzed by two-dimensional (2D) ¹H-³¹P heteronuclear-correlation (HETCOR) magic-angle spinning (MAS) NMR spectroscopy. Enamel had a greater crystallite size and fewer microstrains than dentin for both bovine and human teeth. When compared between the species, the bovine apatite had a smaller crystallite size with more microstrains than the human apatite for both dentin and enamel. The 2D HETCOR spectra demonstrated that a water-rich layer and inorganic HPO₄^- ions were abundant in dentin; meanwhile, the hydroxyl group in the lattice site was more dominant in enamel. A greater intensity of the hydroxyl group was detected in human than in bovine for both dentin and enamel. For ³¹P projections, bovine dentin and bovine enamel have wider linewidths than human dentin and human enamel, respectively. There are differences in the crystallite profile between human and bovine. The results of dental research should be interpreted with caution when bovine teeth are substituted for human teeth.

Keywords: X-ray diffraction; apatites; dentin; enamel; heteronuclear; solid-state nuclear magnetic resonance.

Figure 1

The results of the Rietveld refinement of (a) bovine dentin, (b) bovine enamel, (c) human dentin, and (d) human enamel. The calculated pattern (solid light blue) and observed diffraction (doted red line) profiles are shown, as well as the difference line obtained after the final refinement. The small trace in the difference line indicates the good agreement between the calculated and measured diffraction profile. Rwp, weighted profile R-factor; Rp, unweighted profile R factor; Re, expected R factor; and GOF, goodness-of-fit factor. Based on the Rwp values, the Rietveld refinement fittings of the X-ray data were good for all the samples. The lower trace is the difference between observed and calculated patterns, and the vertical lines mark the positions of the calculated Bragg peaks.

Figure 2

The polyhedral model using three-dimensional visualization program VESTA. Note: the representations of Ca (blue), P (black), O (red).

Figure 3

Two-dimensional ¹H-³¹P HETCOR of (A) dentin and (B) enamel. The summation projection to the ³¹P axis is on the upper side of the HETCOR spectrum, and the summation projection to the ¹H axis is on the right. On the ³¹P axis, the ³¹P spectra are normalized to maximum intensities. On the ¹H axis, the ¹H spectra are normalized to the intensities of the up-field shift at around 0.5 ppm.