Abstract
Tooth enamel is the hardest tissue in vertebrates. Optimized to withstand the forces of mastication, it is
composed of hydroxylapatite (OHAp) nanowires, thousands of which are bundled into rods that are
organized in a three-dimensional weave. During tooth development, a preformed organic matrix is
thought to be integral to the biological control over the precipitation of an amorphous precursor phase,
its transformation into hydroxylapatite, and the growth of individual OHAp nanowires in enamel. This
matrix is degraded during enamel maturation, but a small amount of organics remains in the final
biocomposite, where its presence and that of water affect the mechanical properties. Once the tooth has
erupted, enamel is affected by caries (tooth decay), a chronic infectious disease that affects nearly 100%
of adults worldwide.[1] Caries commonly begins with the demineralization of enamel by acids produced
in plaque biofilms. It has long been known that the susceptibility of enamel to dissolution is greatly
dependent on the presence of magnesium, carbonate, and fluoride ions. However, mapping the
distribution of organic and inorganic ‘trace’ constituents is very challenging due to the complex 3D
architecture, the importance of primarily low atomic number (Z) constituents, and the sensitivity of the
sample to beam damage.
Laser-pulsed atom probe tomography (APT), an imaging mass spectrometry technique of unrivalled
spatial resolution (< 0.2 nm) and chemical sensitivity, allowed us to dramatically improve our
understanding of the complex chemistry and structure of nano-scale organic/inorganic interfaces.[2]
Others and we have recently expanded the use of APT to apatitic biominerals.[3-5] We report here on our
recent discovery, by APT and correlative techniques, of a Mg-rich amorphous intergranular phase in
regular enamel, and of iron-rich intergranular phases in pigmented rodent enamel (Figure 1), and the
dramatic influence that these intergranular phases have on enamel mechanical properties and its
resistance to acid corrosion. [6] We further discuss the localization of residual organic macromolecules,
carbonate, and water in the intergranular phases and discuss the differentiation between organic and
inorganic carbon (Figure 2). [7]
Original language | English (US) |
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Title of host publication | Proceedings of Microscopy & Microanalysis 2015 |
Pages | 2293-2294 |
Number of pages | 2 |
Volume | 21 |
Edition | S3 |
State | Published - 2015 |