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Researchers use snowflakes to explain tooth enamel formation

HELSINKI, Finland: Researchers from the University of Helsinki and Aalto University in Finland have used the snowflake formation process as a way to explain how tooth enamel is distributed over the crown during growth. The newly published study provides a theoretical basis for the developmental regulation of enamel formation and helps to uncover why even closely related species, such as humans and orangutans, have distinct dental features.

The enamel matrix is soft when freshly laid down. However, it starts to harden immediately, and once mature, it is the most mineralised and the hardest part of the mammalian body. The hardness of the enamel makes teeth more durable and damage-resistant. It cannot be repaired or remodelled, making the growth of the enamel matrix a critical step in tooth formation. The researchers suggested that differences in enamel thickness are regulated by the nutrient diffusion rate needed to form the enamel.

Starting from a model that is used to simulate snowflake formation, the researchers built a new model that, instead of ice, mimicked the formation of the enamel matrix. “Whereas enamel is not obviously as intriguingly shaped as snowflakes, it is interesting that the same physical principles can account for the increase in complexity in both systems,” explained first author Dr Teemu Häkkinen, a researcher at Aalto University in Finland.

The new model can be used to investigate both differences in evolutionary species and medical defects in enamel formation. Starting from a CT image of real teeth from which enamel was digitally removed, the scientists reloaded the enamel matrix on the underlying dentinal surfaces by computer simulation. When matrix secretion was simulated as a diffusion-limited process, this produced the subtle enamel features found on a molar.

According to the study, in contrast to human molars, orangutan molars have complex ridges and grooves that could be simulated by lowering the diffusion rate of enamel-forming nutrients even further. Thus, orangutans, which also eat hard foods such as unripe fruits and bark, may have evolved their wrinkly enamel with a relatively simple developmental change. “There are huge amounts of different data available on enamel, and now we have the tools of physicists to make testable predictions,” explained co-author Dr Jukka Jernvall, Academy Professor at the Institute of Biotechnology at the University of Helsinki.

The study, titled “Modeling enamel matrix secretion in mammalian teeth”, was published online on 29 May 2019 in PLOS Computational Biology.

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