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Scientists detect new structures in tooth enamel to explain its incredible strength

Scientists detect new structures in tooth enamel to explain its incredible strength

A recent glance at the nanostructure of tooth enamel helps to explain the unbelievable resilience of the hardest substance in the human body.

The outer layer of the tooth enamel which surrounds and shields other tissue inside the tooth appears like bone but is actually living tissue. The teeth once developed has no natural capability to self-regrow or repair. Tooth enamel, a very hard substance, harder than steel is produced during the mineralization process and new investigation helps to answer the reason behind its exceptional resilience.

Pupa Gilbert, a biophysicist from the University of Wisconsin-Madison said that every time while chewing, enormous pressure is applied on tooth enamel several hundred times per day. Our enamel being unique manages to do it the whole lifetime, so the question arises how does it prevent any failure?

The answer is the “hidden structure” of tooth enamel which is a microscopic structural arrangement of the nanocrystals forming the outer layer of the teeth. These very minute crystals measuring less than one-thousandth the thickness of a human hair which is also found in the teeth of other animals are made of a kind of calcium apatite known as hydroxyapatite. The work appears in Nature Communications. 

Gilbert said that they didn’t have the methods to look at the structure of enamel before this study but they can determine and visualize the color orientation of individual nanocrystals and observe several of them at once with a method called polarisation-dependent imaging contrast (PIC) mapping.

He added that this electron microscopy method reveals the architecture of complex biominerals to the human eye. The scientists found that the hydroxyapatite nanocrystals were not oriented in the way that they had earlier assumed while using the PIC mapping technique. The crystals in enamel are grouped into structures called rods and inter-rods but the team identified misorientations of the crystal between adjacent nanocrystals ranging between 1 and 30 degrees.

The authors wrote in the paper that they have suggested that the misorientation of adjacent enamel nanocrystals provides a toughening mechanism i.e., a transverse crack can propagate across crystal interfaces if all crystals are eco-oriented whereas a crack primarily propagates along with the crystal interfaces if the crystals are misoriented.

The molecular dynamics simulations carried out by the team support the concept as testing this hypothesis in human teeth in real life is not feasible. The cracking is circulated more rapidly through crystal networks that didn’t look like human teeth misorientations (of 1 to 30 degrees) in a computer model configured to simulate the spreading of cracking through the enamel.

The team said that this range of nanocrystal misorientation may portray a sweet spot in crack deflection, selected by the long evolutionary history of the enamel. This sweet spot, crystals that are 1–30° apart may maximize the release of energy along with strengthening. The observed misorientations in enamel play a major mechanical role as crack deflection is an important toughening mechanism. They increase the toughness of enamel at the nanoscale, which is essential to withstand the powerful masticatory forces, nearing 1,000 newtons, repeated several thousand times per day.

Journal Reference: Nature Communications. 

Scientists Have Developed a Genius Method That Actually Regenerates Tooth Enamel

Researchers come up with a technique which regenerates tooth enamel

  • A properly designed material which is made of calcium phosphate ion clusters can be used to create a precursor layer for inducing the epitaxial crystal growth of enamel apatite.
  • This needed a new type of calcium phosphate ion clusters which had a diametrical measurement of 1.5 nanometres. They were stabilised in ethanol with the help of triethylamine

Tooth enamel is the hardest substance in our body. It is irreplaceable and many people all over the world suffer from tooth decay due to loss of enamel. However new studies offer hope to end this problem. 

Researchers in China have come up with a liquid solution which can help in growing back the outer surface of the damaged tooth enamel with the help of a material which mimics the mineralisation process of the protective outer layer of our teeth. The work appears in Science Advances journal

Tooth enamel is created in a biomineralisation process where cells known as ameloblasts generate proteins which harden to form the tough outer coating of our teeth. But ameloblasts are only present during the course of tooth development as a result of which the mature teeth cannot repair itself after its formation. 

Researchers have tried several approaches to coax enamel remineralisation artificially but they have mostly failed since the crystalline structure of the enamel has not been properly replicated in the laboratory. Zhaoming Liu, biomimetics and materials researcher said that in this new technique they reveal that a properly designed material which is made of calcium phosphate ion clusters can be used to create a precursor layer for inducing the epitaxial crystal growth of enamel apatite. This mimics the biomineralisation crystalline-amorphous frontier for the development of hard tissue. 

This needed a new type of calcium phosphate ion clusters which had a diametrical measurement of 1.5 nanometres. They were stabilised in ethanol with the help of triethylamine which avoided them being clumped together. They were then applied to the human teeth which were donated by the patients. The super-small clusters properly fused to form the fish scale-like structure of native enamel. This replicated the tooth coating with an equally hard layer which had a thickness of 2.8 micrometres in 48 hours. 

That is very much thinner compared to the full layer of normal tooth enamel, however, researchers feel that repeated coatings of CPIC solution could increase the thickness along with further refinements. Liu said that that generated enamel has the similar structure and properties to that of native enamel. Researchers hope to generate tooth enamel without fillings that contain entirely different materials. They are expecting to begin trials within one to two years. 

To meet the deadline, scientists have to prove that the material is safe as presently there are concerns regarding the toxicity of triethylamine, which is the stabilising compound. It evaporates during the process hence should not be of any risk. The substance is currently being tested in mice. It might take some time before it is adopted for daily use and till then the conventional advice on dental health has to be followed. Chen Haifeng, Peking University who was not part of the study thinks artificial replacement can never properly replicate the natural teeth. 

Journal Reference: Science Advances journal