The neutron physics of teeth

We all have, or know someone who has, cavities. But, sadly, the notion of going to the dentist is associated with something unsettling. My hope is that we can avoid some of this discomfort by improving a material.

In my research we are developing a material that can be used in many types of restorative needs. Like all cements, the material used in tooth fillings won’t last forever, but we believe that we can make a material that can last longer, so we won’t have to change the filling very often.

It would be advantageous if there were one type of dental cement for all clinical situations. Ideally, such a cement would be easily mixed and follow a setting reaction governed by the cementation case.

One dental cement for all

Key to developing such a material is controlling hydration. My role is to understand how solvent mobility evolves during the cement hardening process.

I am trying to understand the hydration process of these cements to develop a new material.

My field is not only exciting physics, but it is also is of benefit to society. I get the chance to combine something as ‘down to earth’ as tooth fillings with a branch of physics that is not so commonly known to the public. I think that is special.

Glass Ionomer Cements

Dentists use Glass Ionomer Cements (GIC) to pre-form fillings because these materials possess very interesting biocompatible properties. Different types of GIC show different strength and durability. This is directly linked to the hydration process during the hardening.

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We are currently investigating two types of GIC that show different characteristics in strength and durability. Our group’s aim is to improve the quantification of the properties that govern quality and durability of GIC. So far our findings suggest that the lower mechanical strength results from the increased hydrogen mobility within the material.

Recently our group has also shown that on the nano-second (ns) time-scale, the immobile protons bind faster to the microstructure in one type of cement, while if we look at picosecond (ps) time-scale the protons bind faster to the microstructure in the other cement.

To further this work, my task is to correlate the different setting processes of the two materials with the diffusivity of the liquid solvent used to mix the GIC.

Technically speaking, I will combine quasi-elastic neutron scattering (QENS) and molecular dynamics simulations (MD) to study the confined liquid. Understanding hydration routes in these two materials will provide unique insight for future development of dental cements.

Building a scientific network

In this research, collaboration is important. I can learn a lot from other people around me. We collaborate a lot with some researchers from the UK, who know a lot about water dynamics. We also collaborate with our Danish colleagues at Glass and Time at Roskilde University and scientists at the ESS.

Moreover, this is an interdisciplinary PhD thesis and I work with scientists from the Department of Odontology at the University of Copenhagen (dentistry).

Denmark has invested a lot of money in the big international ESS project, that will be the new generation of Neutron Science; this will facilitate the investigation of all sorts of materials not only dental cements for Denmark.

Travel and research

When working with neutron scattering you are required to travel to the large facilities with experimental halls. At these facilities we encounter the best researchers in the field, and get a first hand idea of what is going on beyond our own projects. It is an exciting world.

This year I have been to Brazil on a conference on materials to broaden collaboration between the two countries. Within the last four months I have been to England and Norway. In addition, I am going to France on experiment and Spain to present my exiting results in summer.

It is always exciting to go on experiments, especially on the neutron scattering facilities. They are really big and it requires a lot of planning to perform a good experiment. Fortunately, with the European Spallation Source in Lund, I will still need to travel but it will not be far away for long periods.

There are many interesting aspects that will not be a part of my project directly, e.g. the structural understanding of the different cements are currently being investigated by Casper Madsen, a master’s student in our group.

If we want a profound understanding of water dynamics on a molecular level we also need to do simulations replicating the dynamics in the cement. This combination of simulation and experimental results needs to be compatible, and so, further development of existing software is needed.

This project is relatively new, so if a new result arises that cannot be included in my project we see it as an opportunity to extend it by finding new interested master of science students that can develop the ideas. We already had three students that worked in this project.

Always room for improvement

In the area of water dynamics, and especially in porous material, there are still a lot of unanswered questions. We cannot couple the micro dynamics with the macro scale dynamics.

We do not understand exactly why some types of cements harden faster than others. In the field of neutron scattering we need some new innovative instruments so we can measure at smaller time scales or with higher energies. This will be a possibility when ESS is up and running.

In the area of molecular dynamics faster and more powerful computers would make a difference. Furthermore, a broad collaboration between experimentalist computer theorists is really a necessity.

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