The left structure is showing the natural tooth in its gypsum mold, the middle structure is the artificial tooth (sintered but not yet polymer infiltrated). The model on the right has been sintered and polymer infiltrated. It is embedded in a “puck” to enable polishing and coated with Platinum to prevent charging in the electron microscope. (Photo: Tobias Niebel/ETH Zurich)
Our teeth have an interesting internal material structure that’s similar to how seashells are built, providing them strength rarely seen in the natural world. They are built from layers of stiff micro-platelets, each layer having its own alignment and orientation. It’s this layering that gives hermit crab peace of mind and lets us enjoy beef jerky. Researchers at ETH Zurich have now mimicked this structure and created a technique for building biologically-compatible materials of extreme strength.
Their method is called “magnetically assisted slip casting” (MASC) and it involves pouring a suspension of magnetized aluminum oxide platelets into a mold. As the mold is filled layer by layer, a magnetic field is switched to point in different directions. The vector of the magnetic field aligns the platelets in one direction and it’s oriented in a different direction once a new layer is built. Once a layer cools, the platelets within maintain the orientation of the magnetic field.
Cross section of the artificial tooth under an electron microscope (false colour): Ceramic platelets in the enamel are orientated vertically. In the dentin, they are aligned horizontally. (Photo: Hortense Le Ferrand/ETH Zürich)
The researchers produced an artificial tooth using the MASC method, resulting in a very similar material to that within natural teeth.
From ETH Zurich:
The surface of the artificial tooth is as hard and structurally complex as a real tooth enamel, while the layer beneath is tough, just like the dentine of the natural model.
The co-lead author of the study, doctoral student Hortense Le Ferrand, and her colleagues began by creating a plaster cast of a human wisdom tooth. They then filled this mould with a suspension containing aluminium oxide platelets and glass nanoparticles as mortar. Using a magnet, they aligned the platelets perpendicular to the surface of the object. Once the first layer was dry, the scientists poured a second suspension into the same mould. This suspension, however, did not contain glass particles. The aluminium oxide platelets in the second layer were aligned horizontally to the surface of the tooth using the magnet.
This double-layered structure was then ‘fired’ at 1,600 degrees to densify and harden the material: the term sintering is used for this process. Finally, the researchers filled the pores that remained after the sintering with a synthetic monomer used in dentistry, which subsequently polymerised.
Study in Nature Materials: Magnetically assisted slip casting of bioinspired heterogeneous composites…
Source: ETH Zürich…
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