Quantitative micro‐XRF combined with X‐ray imaging reveals correlations between Zn concentration and dentin tubule porosity across entire teeth

Abstract Bony materials are biogenic composites of protein fibers and mineral that create hierarchical structures. In the case of teeth, dentin is the main component and similar to other bones, it contains porosity at multiple length scales. It is traversed by micron‐sized hollow channels known as dentinal tubules, essential for temperature and pain sensation. Tubule density and thus porosity vary throughout the macroscopic three‐dimensional (3D) structure, with porosity increasing toward the pulp. The different densities in teeth are easily revealed non‐destructively in 3D by X‐ray imaging using computer tomography (CT). Yet elemental composition analysis is more difficult to obtain from within the centimeter‐sized heterogeneous bulk material. We describe an approach of merging CT measurements of healthy, intact bovine teeth with micro‐X‐ray fluorescence (micro‐XRF) images of matching serially sectioned slices. Through the combination of multi‐resolution quantitative CT measurements with elemental mass fraction derivation, gradients in density and element distributions such as calcium (Ca), phosphorus (P), and zinc (Zn) are revealed across entire teeth in 3D. While the main constituents (Ca and P) are homogeneously distributed in the matrix, Zn concentration increases significantly and exponentially toward the pulp. We find an inverse association between dentin tissue density and Zn concentration localizing this element in or around tubules. Our data serve as a quantitative reference for density and Zn mass fractions in healthy, neither carious nor hypermineralized dentin, as a basis for comparisons across species in health and disease states.