Atomic-scale compositional mapping reveals Mg-rich amorphous calcium phosphate in human dental enamel.
Human dental enamel, the hardest tissue in the body, plays a vital role in protecting teeth from wear as a result of daily grinding and chewing as well as from chemical attack. It is well established that the mechanical strength and fatigue resistance of dental enamel are derived from its hierarchical structure, which consists of periodically arranged bundles of hydroxyapatite (HAP) nanowires. However, we do not yet have a full understanding of the in vivo HAP crystallization process that leads to this structure. Mg(2+) ions, which are present in many biological systems, regulate HAP crystallization by stabilizing its precursor, amorphous calcium phosphate (ACP), but their atomic-scale distribution within HAP is unknown. We use atom probe tomography to provide the first direct observations of an intergranular Mg-rich ACP phase between the HAP nanowires in mature human dental enamel. We also observe Mg-rich elongated precipitates and pockets of organic material among the HAP nanowires. These observations support the postclassical theory of amelogenesis (that is, enamel formation) and suggest that decay occurs via dissolution of the intergranular phase. This information is also useful for the development of more accurate models to describe the mechanical behavior of teeth.
School of Aerospace, Mechanical, and Mechatronic Engineering, University of Sydney, Sydney, New South Wales 2006, Australia.; Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, New South Wales 2006, Australia.
Alexandre
A
La Fontaine
Faculty of Dentistry, University of Sydney, Sydney, New South Wales 2006, Australia.; Institute of Dental Research, Westmead Centre for Oral Health, Sydney, New South Wales 2145, Australia.
Alexander
A
Zavgorodniy
Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, New South Wales 2006, Australia.
Howgwei
H
Liu
School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia.
Rongkun
R
Zheng
Faculty of Dentistry, University of Sydney, Sydney, New South Wales 2006, Australia.; Faculty of Dentistry, Kuwait University, P. O. Box 24923, Safat 13110, Kuwait.
Michael
M
Swain
School of Aerospace, Mechanical, and Mechatronic Engineering, University of Sydney, Sydney, New South Wales 2006, Australia.; Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, New South Wales 2006, Australia.
Julie
J
Cairney
D000566:Amelogenesis / Q000502:physiology*; D002118:Calcium / Q000737:chemistry; D002130:Calcium Phosphates / Q000737:chemistry*; D003460:Crystallization / Q000379:methods; D003743:Dental Enamel / Q000737:chemistry*; D017886:Durapatite / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000737:chemistry* / Q000302:isolation & purification; D053770:Nanowires / Q000737:chemistry
D002130:Calcium Phosphates; C519480:amorphous calcium phosphate; D017886:Durapatite; D008274:Magnesium; D002118:Calcium
Human dental enamel; Mg-rich amorphous phase; atom probe tomography; tooth decay