Researchers have charted the first complete atlas of single cells that make up human teeth: a molecular map unfolding new stem cells, and tissue generation dental approaches.
Tooth enamel.
This outermost layer of human teeth, is a complex, hierarchically structured biocomposite.
It’s a structure that’s important: both in human health contexts – from understanding the progression of tooth decay – to understanding the process of amelogenesis. Amelogenisis is the four defined stages of enamel development: presecretory, secretory, transition, maturation and its related developmental defects.
Tooth enamel is primarily composed of long, nanoscale crystallites of hydroxyapatite, bundled in the thousands, to form micron-scale rods. Studies with transmission electron microscopy have shown the relationship between small groups of crystallites, but the direct measurement of variations in crystallographic structures across and between enamel rods, has been absent.
These methods represent a step forward in the characterisation of human enamel and will elucidate the variation of the crystallographic structure across and between enamel rods for the first time.
Mineralised biological materials are an important record for archaeology. The most common are bones, teeth, mollusc shells, eggshells, otoliths, and plant phytoliths – the microscopic structures made of silica, found in some plant tissues after decomposition. The fact that they are mineralised greatly increases the chance of embedded information.
Biomineralisation common in archaeological sites are part of a much larger group of materials produced by a variety of organisms, ranging from bacteria to man. More than 65 minerals are known to be biologically produced. These include minerals that, at the atomic level, are highly disordered, such as opal, amorphous calcium carbonate, and amorphous calcium phosphate. Most biogenic minerals at the atomic level are relatively ordered; and are thus crystalline.
The mineralisation process, like all biological processes, is orchestrated by cells.
In contrast to the process of calcareous biocrystallisation, for which different interpretations are still being scientifically currently debated, questions concerning the state of the mineral phase on the one hand in bones and teeth, and on the other in siliceous structures, are not particularly controversial on comparable scale. Thin sections under the optical microscope in polarised light has established the crystal organisation of phosphatic material in bones and teeth, as well as the amorphous state of the silica in sponge spicules.
Surprisingly, the questions that do arise concern the more precise characterisation of these two very different mineral phases because they are so incredibly comparable.
In bones and teeth, crystals are so small that, until electron microscopy, then atomic force microscopy, direct observation was impossible. Yet bones and teeth are by far the most studied of all mineralised biological structures in medical and dental research. The situation concerning the mechanisms right up to the highest resolution of instrumentation, leading to this striking paradox in every case, morphology is seen to be controlled – first demonstrated in the spectacular drawings of microscopic observations of radiolarians made by German naturalist and eugenicist Ernst Haeckel in the nineteenth century, and completely confirmed by scanning electron microscopy.
The team of material and structure engineers and dentists from the University of Sydney produced 3D maps using a relatively new microscopy technique called atom probe tomography. Described in a paper published in Science Advances, it suggests it could help improve oral hygiene and prevent tooth decay.
According to the World Health Organisation (WHO) 60-90% of school children, and nearly 35% of the global population is affected by untreated tooth decay – which of course is the progressive dissolution of dental enamel: the hardest tissue in the body.
Scientists have already established that the mechanical strength and resistance to fatigue of dental enamel, comes from its complex, hierarchical structure of periodically arranged bundles of hydroxyapatite (HAP) nanowires.
The new study gives detailed information about important trace ions in its tough structure.
Interestingly, rates of tooth decay have fallen significantly in the United States over the last four decades, but in young children there has been a recent rise.
Human tooth enamel is extremely intricate. While we have known that magnesium carbonate, and fluoride ions are its basic properties, science has never been able to capture its structure at a high enough resolution or definition.
Now there is the first direct evidence that the amorphous magnesium-rich, calcium phosphate phase plays an essential role in the behaviour of teeth. It is a phase that had been proposed before, but without evidence.
An important discovery was the “nanoscale clumps” of organic material able to be seen in the 3D structure.
This suggests that proteins and peptides occur in unequal patterns throughout the enamel, rather than all along the nanorod interfaces, as was previously assumed. This new understanding of how enamel forms also helps tooth remineralisation research.
The mapping of the human tooth gives intricate understanding to its cells: the key to understanding the exact biology of its health, and process of disease. It opens conceivable treatments for protection against the ending of this specific amorphous phase, meaning that cavities could not possibly develop. It expands our understanding of how cells differ across each organ, and even how many cell types there are.
This research is the difference between driving through the outback in a roadworthy ute with a printed map, and using GPS on an iPad Pro 12.9, mounted on the dash of a Toyota Land Cruiser.
This, is how we’re now able to find our way around the human body.
