Strong but brittle like glass, the enamel forms the outer coating of the human tooth, which can last a lifetime without cracking. For years, scientists have wondered how a strong yet brittle outing layer do not fall apart or crack despite its daily activities.
A research team led by Brian Lawn from the National Institute of Standards and Technology put teeth samples from humans and animals to the ultimate biting test. The study, sponsored by the George Washington University Research Endowment Fund, worked with Lawn to finally crack the mystery of the tooth enamel.
Lawn and his team found that the enamel's microscopic 'basket weave-like' structure keeps cracks at bay. Tooth cracking does happen but the enamel's microstructure keeps them from spreading and breaking the tooth. The 'basket weave-like' is made up of layers upon layers where micro-platelets are 'weaved' together, creating a very strong structure with identical orientation.
The study findings made its first crack publicly in the Proceedings of the National Academy of Sciences journal published on April 13, 2015. This breakthrough explains why teeth of older people remain intact despite the various microscopic cracks.
Lawn and his team also studied various teeth samples from animals. They found that the tooth size and enamel thickness dictate how long they last despite the daily grind. Gorillas have larger teeth and thicker enamel. Gorillas are mostly vegetarians but stronger and thicker enamel allow them to crack fruits using their teeth alone and chomp on raw bamboo shoots.
The researchers believe that the findings will not just help anthropologists map out the dental evolution of early humans and animals but also materials engineers to come up with more advanced and stronger dentures.
"Currently, the crowns used to replace bad teeth "look nothing like the microstructure of an actual tooth," said Lawn. If engineers can come up with teeth replacement bearing a similar 'basket weave-like' microstructure, it could better benefit the entire dental industry.
A Bite of Old and New
A team led by Complex Materials Professor, André Studart, from ETH University in Zürich, Switzerland, took a crack at this potentials of this new discovery and succeeded.
Stuart's team was able to re-create the complex 'basket weave-like' microstructure of the tooth enamel using artificial materials. They called the procedure MASC which stands for Magnetically Assisted Slip Casting.
"The wonderful thing about our new procedure is that it builds on a 100-year-old technique and combines it with modern material research," said Tobias Niebel, doctoral student at ETH Zurich University. Niebel co-authored the study which debut in the Nature Materials journal.
First, the team created a spongy plaster mold. A liquid substance filled with magnetized ceramic platelets was poured onto the plaster mold. Since the plaster mold is permeable, it slowly absorbs the ceramic platelets, allowing it to settle. During the casting process, the scientists used a magnetic field to tweak the alignment of the platelets while still in its liquid state. To create the weave-like pattern, they changed the orientation of the platelets at various intervals. The process enabled them to create materials with microscopic complex structures. When sintered, the platelets retain their orientation in the final solidified form.
With a plaster mold of the human wisdom tooth, the team used aluminium oxide platelets and glass nanoparticles to mimic the mortar. The double layer formed a weave-like pattern and was sintered at 1,600 degrees. A dental synthetic monomer was used to fill the remaining 'pores'. The result was as close as you can get to an actual human tooth. The outer layer (artificial enamel) was hard while the inner layer (artificial dentin) was a softer. The finished product bears the natural model's complex microstructure.
Studart expressed that MASC is still in its early stages. Further studies and fine-tuning are needed before it can be used for dental prosthetics.