First 3D atomic map of enamel


Rebecca Pool

Thursday, September 8, 2016 - 21:30
Image: Magnesium in enamel at atomic scale [Tom Hartley/University of Sydney].
Using atom probe tomography, Australia-based materials engineers have mapped the exact composition and structure of tooth enamel at the atomic scale.
Working with dentists and bioengineers, Professor Julie Cairney from the Faculty of Engineering and Information Technologies, University of Sydney, and colleagues, produced the first-ever 3D maps showing the positions of atoms critical in the decay process.
The new knowledge on atom composition at the nanolevel has the potential to aid oral health hygiene and caries prevention.
"Dental professionals have known that certain trace ions are important in the tough structure of tooth enamel but until now it had been impossible to map the ions in detail," says Cairney.
"The structure of human tooth enamel is extremely intricate and while we have known that magnesium, carbonate and fluoride ions influence enamel properties, scientists have never been able to capture its structure at a high enough resolution or definition," she adds.
Given this, Cairney and colleagues turned to atom probe tomography, using a Cameca LEAP 4000× Si atom probe equipped with a picosecond-pulsed ultraviolet laser.
Here, individual atoms or small molecules from a 100 nm diameter needle-shape tip were field-evaporated by picosecond laser pulses whilst applying a high voltage to the tip.
A detector recorded the position of each atom, with the mass/charge ratio determined by time-of-flight mass spectrometry.
As a result, a 3D reconstruction of the field-evaporated volume - typically millions of atoms - was obtained. 
"We have found magnesium-rich regions between the hydroxyapatite nanorods that make up the enamel," explains Cairney. "This means we have the first direct evidence of the existence of a proposed amorphous magnesium-rich calcium phosphate phase that plays an essential role in governing the behaviour of teeth."
As co-researcher, Dr Alexandre La Fontaine from the University's Australian Centre for Microscopy and Microanalysis, adds: "We were also able to see nanoscale 'clumps' of organic material, which indicates that proteins and peptides are heterogeneously distributed within the enamel rather than present along all the nanorod interfaces, which was what was previously suggested."
"The mapping has the potential for new treatments designed around protecting against the dissolution of this specific amorphous phase," he says. "The new understanding of how enamel forms will also help in tooth remineralisation research."
Research published in Science Advances.
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