Few structures in nature are more durable than teeth or seashells. The secret of these materials lies in their unique fine structure: They are composed of different layers in which numerous micro-platelets are joined together, aligned in identical orientation.
Now scientists have combined old and new technologies to construct artificial teeth that mimic the complex structure of natural teeth.
André Studart, a professor of complex materials at ETH Zurich, led the team that created the teeth using a technique called magnetically assisted slip casting (MASC).
“The wonderful thing about our new procedure is that it builds on a 100-year-old technique and combines it with modern material research,” says Studart’s doctoral student Tobias Niebel, coauthor of a paper describing the work published in the journal Nature Materials.
How MASC works
Researchers first create a plaster cast to serve as a mold. Into this mold, they pour a suspension containing magnetized ceramic platelets, such as aluminium oxide platelets. The pores of the plaster mold slowly absorb the liquid from the suspension, which causes the material to solidify and to harden from the outside in.
The scientists create a layer-like structure by applying a magnetic field during the casting process, changing its orientation at regular intervals. As long as the material remains liquid, the ceramic platelets align to the magnetic field. In the solidified material, the platelets retain their orientation.
“Our technique is similar to 3D printing, only 10 times faster and much more cost-effective.”
Through the composition of the suspension and the direction of the platelets, a continuous process can be used to produce multiple layers with differing material properties in a single object.
This creates complex materials that are almost perfect imitations of their natural models, such as nacre or tooth enamel.
“Our technique is similar to 3D printing, only 10 times faster and much more cost-effective,” says Florian Bouville, a postdoc with Studart and co-lead author of the study.
Plaster cast of a wisdom tooth
To demonstrate the potential of the MASC technique, Studart’s research group produced an artificial tooth with a microstructure that mimics that of a real tooth. The surface of the artificial tooth is as hard and structurally complex as a real tooth, while the layer beneath is softer, just like the dentine of the natural model.
Doctoral student Hortense Le Ferrand, the study’s co-lead author, and colleagues began by creating a plaster cast of a human wisdom tooth. They then filled this mold 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 mold. 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 compress 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 polymerized.
“The profile of hardness and toughness obtained from the artificial tooth corresponds exactly with that of a natural tooth,” says Studart, who points out the current study is just an initial proof-of-concept.
“The appearance of the material has to be significantly improved before it can be used for dental prostheses.”
Nonetheless, as Studart explains, the artificial tooth clearly shows that a degree of control over the microstructure of a composite material can be achieved, previously the sole preserve of living organisms. One part of the MASC process, the magnetization and orientation of the ceramic platelets, has already been patented.
The new production process also has other potential applications. For instance, copper platelets could be used in place of aluminium oxide platelets, which would allow the use of such materials in electronics.
Source: ETH Zurich