Few people enjoy the experience of going to the dentist. However, as light activated resin based polymer composites (RBCs) increasingly replace traditional dental amalgam, difficulties with these materials are being identified. The main issue is that of decreased bio-compatibility due to insufficient cure and shrinkage stress that can lead to a further restoration.

NPL's research, in collaboration with the University of Birmingham's School of Dentistry, is seeking to apply our non-invasive refractive index measurement techniques to the real-time monitoring of the extent of cure as a function of depth into RBCs.

Fig 1: Real-time low coherence refractometer for measuring curing dental composites,
developed in collaboration with the Dental School, University of Birmingham

We have successfully shown how the refractive index of an RBC is correlated with its extent of cure and measured the physical shrinkage of commercial and experimental RBC materials.

Fig 2: Group index (left) and physical thickness (right) change of a resin based dental
composite material, before, during and after illumination with a dental curing lamp

Following the success of this work we are now developing more sophisticated techniques to reconstruct three-dimensional refractive index maps of RBC samples.

Fig 3: Experimental three-dimensional refractive index measurement of curing dental composite

This work will lead to new dental materials that obviate the limitations of current restoratives. It is also anticipated that research in this area could be translated into the non-destructive evaluation of composite materials used in other sectors, such as aerospace.

Related publications

[1] P H Tomlins, W M Palin, A C Shortall, and R K Wang, 'Time-resolved simultaneous measurement of group index and physical thickness during photopolymerization of resin-based dental composite', J Biomed Opt 12, 014020 (2007).

For further information, please contact Peter Woolliams