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Abstract
Dentine, the main material of mammalian teeth, contains mineral platelets that are
embedded in a collagen fiber mesh. These particles entail stiffness and longevity,
which is important for human teeth because these organs do not remodel. By means of
small angle X-ray scattering, we mapped 2D and 3D variations in mineral particle characteristics
in molar crowns. Our results show that the mean mineral-platelet thickness of 3.2
nm decreases to 2.6 nm within the shallow 300 microm beneath the dentin-enamel junction
(DEJ), and that these platelets become still thinner albeit moderately in deep dentine
surrounding the pulp. The mineral volume fraction in crown dentine is mostly 50% except
for a 250 microm layer beneath the DEJ. Most of the mineral particles are randomly
orientated, with about 20% having a preferred orientation that is parallel to the
plane of the DEJ. Beneath the cusps and close to the margins of enamel, higher co-alignment
is found: 40% of the particles reveal orientations that match expected load trajectories
that are imposed on teeth during mastication in the general cusp-root direction. This
suggests that variations in mineral platelet arrangements help to locally tune dentine
anisotropy and stiffness. The serendipitous finding of incipient caries suggests that
at least in early stages of pathological destruction, mineral particle thickness and
orientation resemble those of the intact tissue.