On the mineral in collagen of human crown dentine

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.