It may still surprise people that dentin, and not the femur, is the hardest structure in the human body. This is the layer just under the white enamel that protects the pulp of the tooth. But while everyone accepts the strength of dentin, scientists were never quite sure of what makes the material so durable against the stresses it faces every day.
The Benefits of Internal Stress
A group of Edinburgh Dental Specialists explains that the small size of dentin makes it difficult for researchers to gather samples large enough for study through conventional means. But a collection of interdisciplinary scientists may have been finally able to crack the code of dentin. Teams of researchers from Germany and France analysed the structure of teeth, finding out that the mineral composition is precompressed to form internal stresses.
Engineers often use internal stresses when strengthening specific materials for technical purposes –safety glass being the most recognisable example. Internal stresses works by manipulating the materials through non-physical means in order to concentrate the internal material where engineers need them to be.
The human anatomy seems to already know this trick and applies its principles to teeth. Unlike the other bones in the skeletal system, which are made of a combination of living cells, dentin is made of mineral nanoparticles embedded in collagen protein fibres.
When the collagen fibres shrink, the mineral particles go with it and compress together, making the structure stronger where it matters. The compressed state of the nanoparticles prevents the dentin from forming cracks from developing during the prolonged use. Even if cracks do occur on the enamel surface, the dentin will keep it from progressing towards the sensitive pulp of the tooth.
Another similarity the researchers found between internal stresses and dentin nanoparticles is that temperature plays a vital role in its behaviour. When the teams exposed the dentin sample to heat, they found that the bonds between the particles weakened, making them more vulnerable to cracks and damage.
Finding the role of proteins in strengthening teeth is a significant finding as it may help future studies determine new treatments for oral conditions, and create toothpaste that is more effective.