Living organisms possess a unique capability to form complex bio-minerals with very diverse compositions and structures. Organic matrix and crystalline constituents are closely linked together in unique material constructions that are formed under conditions of moderate temperature, pressure and pH value. Many of these bio-minerals show excellent physical and mechanical properties [1, 2] that cannot be reproduced in the laboratory.
Rodents have long opposing pairs of continuously growing incisors that are worn down by gnawing. The front surface of the incisors is enamel consisting of 96 wt% of inorganic material; the inner part is softer dentine that forms the bulk of the teeth . The surfaces of incisors of different rodent species show a characteristic orange-brown color and are identified with the presence of iron .
In our study, the microstructure and the chemical composition of continuously growing incisors from the coypu (Myocastor coypus Molina) were investigated in detail using energy-dispersive X-ray spectroscopy (EDX) and electron energy-loss spectroscopy (EELS) combined with scanning transmission electron microscopy (STEM) imaging at high spatial as well as high energy resolution. VG HB501UX, Zeiss SESAM and Jeol ARM200F microscopes were used and the resulting data were combined with knowledge obtained from mechanical testing experiments.
A layer with variable thickness, which has not been observed before, was detected on the outer surface of the incisors as marked on the optical micrograph image (Fig. 1). An annular dark field (ADF)-STEM image of a cross-sectional view showing the interface between the Fe-rich surface layer (Fe-SL) and Fe-rich enamel (Fe-E) is shown in Figure 2a. Analytical investigations of this surface layer showed much higher amounts of iron compared to the concentration values reported in the literature up to now. Within the iron-rich surface layer we surprisingly detected multiple iron containing varieties where iron is present in predominantly the 3+ valence state, as revealed by studies of electronic structure. O-K fine structural features suggest the presence of different intermixing levels of Fe phosphate and Fe oxide/hydroxide (Fig. 2b).
The present discoveries will greatly enhance the understanding of the function of the incorporation of iron at the nanoscale level and its effect on the microstructural properties.
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To cite this abstract:Vesna Srot, Ute Salzberger, Birgit Bussmann, Julia Deuschle, Masashi Watanabe, Bostjan Pokorny, Ida Jelenko Turinek, Alison F. Mark, Peter A. van Aken; Unusually high iron enrichment in hard dental tissues of coypu. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/unusually-high-iron-enrichment-in-hard-dental-tissues-of-coypu/. Accessed: September 20, 2021
EMC Abstracts - https://emc-proceedings.com/abstract/unusually-high-iron-enrichment-in-hard-dental-tissues-of-coypu/