In pursuit of the perfect fit
Germany: Researchers from the Fraunhofer Institute for Mechanics of Materials (IWM) in Freiburg have discovered a way to simulate the tension created by shrinkage after curing of filling material in dental restorations. Research assistant, Dr Christof Koplin explains: “Until now, it has not been possible to establish a theoretical model of the hardening process. The tension occurring in the material always depends on the shape of the cavity, and can vary widely by a factor of up to ten, particularly at the edges.”
According to Dr Koplin, the two main challenges of the study were to find a combined model that integrates all the important influences (11 model parameter had to be estimated) and to find an experimental methodology that can be used to characterize a process that is completed in three minutes and the related material changes from a paste-like sticky behaviour to a stiff form and consistency. “Our solution is based on the experiences of many and the detailed documentation by individuals in dental research, polymer science, material science and numerical methodology,” he explains.
With this method, dentists can now draw on the results of the IWM to select the best material which will create the least amount of tension for each cavity shape. At the same time, manufacturers can use the simulations to optimize their products. Koplin feels this methodology will be of great benefit to dentists. “When doing a restoration a dentist has to tailor his process to each individual patient and select his tools from an arsenal of different materials and devices. Dentists may have experience with several materials but there are always more to choose from. Anything that will help them select the right material in the shortest amount of time is a valuable asset to any practice,” he says.
In the near future, Koplin and his team will test various filling materials that are commercially available. It is hoped that manufacturers will publish their results of this unbiased method as an aid to dentists. “The results between filling materials are sometimes surprisingly similar but differences occur in the maximal internal stress with a factor >2 for state-of-the-art composites,” he says.
Moving forward, the team aims to further explore the underlying and distributed stress in fillings as a starting point to understand degradation and how it can be deal with. “The great field of adhesive research is based on the challenge of adhesive strength overcoming internal and loading stresses despite of chemical and biological attack,” he concludes.