Shape memory polymers: more efficient tooth correction thanks to TPU

The treatment of malocclusions can sometimes be lengthy and cost-intensive. A new corrective splint (aligner) is needed for each individual therapy step. So-called shape memory polymers can help not only to make the therapy more patient-friendly, but also to reduce material waste.

In an interview with K-MAG, Dr Thorsten Pretsch talks about a newly developed material, how the shape change of an aligner works thanks to it and where else shape memory polymers could be used in the future.

Dr Pretsch, you have developed a new material for straightening teeth. What is it about?

Dr Thorsten Pretsch: The material we have developed and tested on model tooth rims is a shape memory polymer made of thermoplastic polyurethane (TPU). Strictly speaking, it is an optically transparent polyether urethane.

You talk about shape memory polymers. What does that mean?

Pretsch: Shape memory polymers are among the intelligent materials. Objects can be made from these plastics that change their shape in a previously precisely defined way. An external stimulus such as heat triggers the shape memory effect. In the case of aligners made of shape memory polymer, the splint slowly changes its shape, opening up the possibility of moving misaligned teeth into the desired position. In our case, it is possible to trigger the shape memory effect both by heat and by soaking the polymer in body-warm water.

How does the patient benefit from aligner therapy with the new material, especially compared to conventional therapy?

Pretsch: Currently aligners are made of materials that cause unnaturally strong pressure forces. In order to correct a malpositioned tooth without damaging the adjacent tissue, many small treatment steps are therefore required. A removable, transparent splint is made for each individual therapy step. Studies recommend limiting tooth movement to a maximum of 0.2 millimetres per aligner. The individually made aligners cause high treatment costs. Depending on the degree of misalignment, an average of 30-60 aligners are needed to move the teeth into the desired position over several months. The ability of the now newly developed polymer to change its shape in pre-determined, small and controlled steps has the potential to reduce the number of stages required in orthodontic treatment compared to therapies using conventional aligner materials.

How does this contribute to more sustainability?

Pretsch: By reducing the number of orthodontic aligners in the course of a therapy, avoiding excessive material waste and reducing treatment costs. That is our declared goal.

What other possible applications could you imagine for the material?

Pretsch: There are, for example, applications in which materials are required to have very good shape recovery behaviour. The dual stimulus-responsiveness, i.e. the ability of the material to react to changes in ambient temperature and humidity with changes in shape, makes it particularly attractive for use as sensors and for applications in the field of Soft Robotics.