Amorphous intergranular phases control the properties of rodent tooth enamel

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Science  13 Feb 2015:
Vol. 347, Issue 6223, pp. 746-750
DOI: 10.1126/science.1258950

Key trace minerals greatly strengthen teeth

The outer layers of teeth are made up of nanowires of enamel that are prone to decay. Gordon et al. analyzed the composition of tooth enamel from a variety of rodents at the nanometer scale (see the Perspective by Politi). In regular and pigmented enamel, which contain different trace elements at varying boundary regions, two intergranular phases—magnesium amorphous calcium phosphate or a mixed-phase iron oxide—control the rates of enamel demineralization. This suggests that there may be alternative options to fluoridation for strengthening teeth against decay.

Science, this issue p. 746; see also p. 712


Dental enamel, a hierarchical material composed primarily of hydroxylapatite nanowires, is susceptible to degradation by plaque biofilm–derived acids. The solubility of enamel strongly depends on the presence of Mg2+, F, and CO32–. However, determining the distribution of these minor ions is challenging. We show—using atom probe tomography, x-ray absorption spectroscopy, and correlative techniques—that in unpigmented rodent enamel, Mg2+ is predominantly present at grain boundaries as an intergranular phase of Mg-substituted amorphous calcium phosphate (Mg-ACP). In the pigmented enamel, a mixture of ferrihydrite and amorphous iron-calcium phosphate replaces the more soluble Mg-ACP, rendering it both harder and more resistant to acid attack. These results demonstrate the presence of enduring amorphous phases with a dramatic influence on the physical and chemical properties of the mature mineralized tissue.

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