Atom Probe of Apatites - from Single Crystals to Interphases in Tooth Enamel

Lyle M. Gordon, Karen A Derocher, Michael J. Cohen, Derk Joester

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Tooth enamel is the hardest tissue in vertebrates. Optimized to withstand the forces of mastication, it is
composed of hydroxylapatite nanowires, thousands of which are bundled into rods that are organized in
a three-dimensional weave. The outstanding fracture resistance of ename l and its long fatigue life are the
consequence of this hierarchical architecture. Tooth enamel is also the target of the most prevalent
infectious disease in humans: dental caries. It is an infectious disease that has extremely high morbidity,
with 60-90% of children and nearly 100% of adults worldwide having or having had caries.
[1] Caries, simply put, is the destruction of tooth biominerals by dissolution and commonly begins with the
demineralization of enamel by acids produced in plaque biofilms. It has long been known that the
susceptibility of enamel to acid dissolution is greatly dependent on the presence of
magnesium, carbonate, and fluoride ions. A major bottleneck in understanding formation, structural evolution, and
degradation of enamel under normal conditions and during tooth decay has been that
imaging the distribution of these impurities in enamel has remained a great challenge.

Others and we have recently shown that UV laser-pulsed atom-probe tomography (APT), in
combination with correlative techniques, enables unprecedented insight into the nano-structure and
chemistry of apatitic biominerals. [2-4] This required developing a work flow for sample preparation, data
collection, and data analysis tailored for apatites (Ca5(PO4)3X, X=F, Cl, OH), wide band gap (~5.3 eV) insulators
[5] that had never before been investigated by atom probe. We approached this by first
performing a comprehensive analysis of synthetic and geologic single crystals of apatite end members.
[2] This was the basis for a second step, in which we analysed biogenic nanocomposites,
including cortical bone and dentin.[2] Our approach culminated in the recent discovery of amorphous interphases in tooth
enamel and their importance in controlling mechanical properties and resistance to acid corrosion.[6,7]

We report here on the optimization of sample preparation conditions using FIB, the dependence of
spectral quality and stoichiometry on atom probe operational parameters (Fig. 1), an analysis of multihit
events in single-crystalline apatites (Fig. 2), and the differentiation of organic and inorganic carbon in
enamel samples (Fig. 3). Finally, we will discuss preliminary results from atom probe of human enamel.
Original languageEnglish (US)
Title of host publicationProceedings of Microscopy & Microanalysis 2015
Number of pages2
StatePublished - 2015


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