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Abstract:
Dentin in teeth is a bone-like nanocomposite built of carbonated hydroxyapatite (cHAP) mineral particles, protein and water that does not remodel nor heal. It is assumed to be excellently adapted for decades of mechanical function, due to the interplay between its constituents. Using samples of human origin, we combine heat treatments with synchrotron X-ray diffraction, second-harmonic generation microscopy, Raman spectroscopy, and phase contrast-enhanced nano-tomography to study the water-assisted functional coupling of the biocomposite components. Across roots we find a gradual reduction in the c-lattice parameter of the cHAP nano-crystals, from 6.894 Å externally down to 6.885 Å in deeper tooth regions. Here, approaching the pulp, tissue is formed at later stages of tooth development. In all regions, a compressive strain of ~0.3 % is observed upon drying by mild heating (125 ºC). Dehydration results in a substantial increase in the averaged microstrain fluctuations in the mineral nanoparticles. The mineral crystallite platelet lengths fall off from ~36 nm externally to ~26 nm closer to the pulp. Our results suggest that both morphology and mineral-collagen coupling allow mineral nano-particles in dentin to sustain rather large stresses of 300 MPa, far exceeding mastication stresses, and that such loads are sustained through durable collagen fibril contractions.
