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.

A cytoplasmic role of Wnt/β-catenin transcriptional cofactors Bcl9, Bcl9l, and Pygopus in tooth enamel formation

“…It is mainly composed of minerals (97%), water, residual organic molecules, and small amounts of substituting ions that strongly affect its properties (21). In rodent incisors in particular, iron (Fe 2+ ) deposition is linked to the yellow pigmentation of the outermost layer of enamel and strongly increases its hardness (16). Moreover, iron provides additional resistance to bacterial toxins and acids that prevent pathological tooth alterations such as caries (16).…”

“…2E, F to 2G, H). The white and glossy appearance of the incisors in K14-Bcl9/9l-flox mutants additionally suggests lack of iron, an element that increases the hardness of enamel in rodents (16). We used energy-dispersive X-ray spectroscopy (EDS) to quantify the relative abundance of iron and other enamel-composing elements such as magnesium (Mg 2+ ) and calcium (Ca 2+ ).…”

Atom Probe Tomography of Human Tooth Enamel and the Accurate Identification of Magnesium and Carbon in the Mass Spectrum

“…Laser-assisted atom probe tomography (APT) provides position and identity of atoms with sub-nanometer resolution [4]. APT was recently used to reveal nano-structures in apatites [5,6] and rodent tooth enamel [7,8]. Inspired by this work, we examined human dental enamel using APT [9] and found Mg-rich ACP nanolayers between the HAP nanowires that make up the enamel.…”

Chemical Imaging of Interfaces and in Interphases in Tooth Enamel

“…[3][4][5] We report here on our recent discovery, by APT and correlative techniques, of a Mg-rich amorphous intergranular phase in regular enamel, and of iron-rich intergranular phases in pigmented rodent enamel (Figure 1), and the dramatic influence that these intergranular phases have on enamel mechanical properties and its resistance to acid corrosion. [6] We further discuss the localization of residual organic macromolecules, carbonate, and water in the intergranular phases and discuss the differentiation between organic and inorganic carbon (Figure 2). [7] and Energy at Northwestern (ISEN), the Petroleum Research Fund of the ACS.…”