title: Dental materials. Amorphous intergranular phases control the properties of rodent tooth enamel.
abstract: 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 Mg(2+), F(-), and CO3(2-). 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, Mg(2+) 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.
authors: Northwestern University, Materials Science and Engineering, 2220 Campus Drive, Evanston, IL 60208, USA.
authors: Lyle M
authors: LM
authors: Gordon
authors: Northwestern University, Materials Science and Engineering, 2220 Campus Drive, Evanston, IL 60208, USA.
authors: Michael J
authors: MJ
authors: Cohen
authors: Northwestern University, Quantitative Bioelemental Imaging Center (QBIC), 2170 Campus Drive, Evanston, IL 60208, USA.
authors: Keith W
authors: KW
authors: MacRenaris
authors: Washington University, Department of Earth and Planetary Sciences, Campus Box 1169, St. Louis, MO 63130, USA.
authors: Jill D
authors: JD
authors: Pasteris
authors: Western Washington University, Department of Physics and Astronomy, Bellingham, WA 98225, USA.
authors: Takele
authors: T
authors: Seda
authors: Northwestern University, Materials Science and Engineering, 2220 Campus Drive, Evanston, IL 60208, USA. d-joester@northwestern.edu.
authors: Derk
authors: D
authors: Joester
mesh_terms: D000818:Animals; D002130:Calcium Phosphates / Q000737:chemistry*; D003743:Dental Enamel / Q000737:chemistry* / Q000648:ultrastructure*; D007180:Incisor / Q000737:chemistry / Q000648:ultrastructure; D051379:Mice; D008855:Microscopy, Electron, Scanning; D056928:X-Ray Absorption Spectroscopy
chemical_list: D002130:Calcium Phosphates