Drop the drill – exploring Nature’s potential for the prevention or reversal of tooth decay. By Alexander Korsunsky
Professor Alexander Korsunsky has an established track record in gaining insights into the strains and stresses in complex natural and engineered materials, from advanced metallic aerospace alloys to polymers, ceramics, and composites. Several years ago he turned his attention to human dental tissues, enamel and dentine. Together with his team of researchers working at University of Oxford and Diamond Light Source (Harwell, Oxfordshire), he has been able to shed some light on the way in which these hierarchically structured materials respond to mechanical and thermal loading.
Now part-way through a project funded by the Engineering and Physical Sciences Research Council (EPSRC), their focus is set on the process of demineralization and remineralization during caries. The team hope to figure out whether it is possible to prevent or reverse decay by relying on the natural ability of our bodies for self-repair.
Prof Korsunsky’s initial interest in studying dental tissues arose from his wish to explore the mechanics of these materials – starting with how enamel and dentine respond to chewing forces. He was also keen to understand their structure and composition, and how they enable these tissues to perform a complex range of demanding functions under extreme conditions in the oral cavity for decades on end.
Enamel is an example of a hierarchically structured material built by nature from a brittle ceramic component (hydroxyapatite) in the form of nanoparticles of various shapes and orientations that are glued together with organic matter into micron-sized features, ultimately forming a tissue with fascinating overall properties. Early studies of mineralized dental tissues showed that they are remarkably resilient and resistant to failure, unless afflicted with construction flaws caused by genetic disorders, or attacked by acids in the course of caries. In fact, it was the recognition of the tremendous destructive impact of caries that led Prof Korsunsky to embark on this project.
It quickly became apparent that nanoscale events during the damage evolution process were difficult to visualise and understand using traditional dental techniques such as X-ray radiography and surface examination, but they could be elucidated by advanced microscopy and synchrotron X-ray techniques. To study the evolution of caries at all levels, the Oxford team are collaborating with the School of Dentistry at the University of Birmingham. “We were particularly eager to link our research with practical dentistry, so that our findings made at finer scales had a good chance of being passed on into practice,” Prof Korsunsky explained. “We wanted to be fully aware of the practicalities and the range of tools available to dentists in a surgery, in order to ensure that our work is transferable. Now we are able to cross-correlate our findings with the data obtained using well-trusted and established techniques, such as histology and laboratory X-ray tomography. One of our aims is to see if we can learn to read the signs of caries progression with conventional dental methods.”
When a caries lesion first forms on the surface and propagates sub-surface into the enamel, hydroxyapatite is dissolved and the mineral density is reduced. “Human saliva contains calcium and phosphate ions needed to re-build hydroxyapatite, so the saliva-facing surface of the enamel gets remineralized – but it is not structured in the same way as the original surface,” warned Prof Korsunsky. “Once a surface is repaired in this way, the sub-surface layers of the lesion become harder to reach for the ions and remain compromised, until eventually the lesion collapses to expose a cavity. We wanted to know if we could intervene in this process to help remineralization from the bottom up, instead of top down.”
Now a quarter of the way through this long-term project, Prof Korsunsky and his team have already made some headway. Initially, they built a computer model of the dissolution (erosion) of dental tissues by caries to explain the connection between structural changes and mechanics. Simulating the process in this way suggested that it may be possible to slow down or even reverse the process.
Some of the key experimental studies were conducted at the synchrotron facility in Oxfordshire called Diamond Light Source. The synchrotron acts like a giant microscope, firing electrons at almost the speed of light around a large ring, and utilising powerful light emitted by them as they travel. Prof Korsunsky described the importance of this advanced research tool: “Synchrotron light has the advantage that it allows one to perform most complex in vitro experiments. We can adjust the resolution, going from fractions of a millimetre down to sub-micron beams to probe what is happening across the scales. The beam brings out a variety of information pertaining to the structure and mechanics of the tissue, so we can look at the changes in the crystal size, orientation, and composition of the mineral and organic fractions over time. We are particularly lucky to receive great support from colleagues at beamline B16 and the Optics and Metrology group at Diamond, which allows us to continue trying out new experimental configurations and obtaining fresh insights.”
So far, Prof Korsunsky’s team found correlations between the acidity levels and the rate of lesion progression into the tissue, and how the concentration and type of acid affect the reformation of enamel. The team are now working towards setting up an ‘artificial mouth’, a device that can reproduce the bacterial, chemical and mechanical effects to mimic the process of caries.
“We will carry out experiments that attempt to control remineralization. Our ultimate goal is to understand at the microbial, chemical and nano-mechanical levels how we can guide remineralization so that caries lesions are repaired by natural processes. By understanding the conditions needed to reverse caries, we hope to figure out ultimately how to make this happen in vivo,” clarified Prof Korsunsky.
The work at Diamond is already helping us improve our understanding of tooth decay. With the input from dentistry specialists, favourable conditions will be sought that can to stave off decay, or even reverse it. Could the dentist’s drill become a thing of the past if nature’s inclination to repair can be encouraged?
