Dental Research Management Centre (DRMC), Faculty of Dentistry with HIR/MoHE/Dent/11
Invites you to:


Everything You Always Wanted to Know About Shrinkage Stress But Were Afraid to Ask
Part 1 – Work of the Devil

The famous physicist Wolfgang Pauli once commented, ‘God created matter, surfaces were the work of the Devil.’ For the dentist and their patients, dental material scientists created resin composite restorations, but the Devil made them debond through the creation of polymerization shrinkage stress. Shrinkage or debonding of composite restorations can lead to post-operative sensitivity, microleakage, marginal staining and, above all, recurrent caries. The study of polymerization shrinkage, shrinkage stress and bond strength of resin composites therefore forms an essential part in the design of such restorative systems. In this talk, some latest developments in the measurement of shrinkage stress and strain and their effect on the interfacial integrity of composite restorations will be discussed. It will be shown that, through the use of state-of-the-art equipment such as micro-CT and acoustic emission, it is now possible to not only see but also hear the work of the Devil.

Bio-Sketch –

Professor Dr. Alex Fok
BEng (Manchester), BA (UK), MSc (Oxford), Ph.D (Manchester)

Dr Fok obtained his BEng and PhD, both in Mechanical Engineering, from the University of Manchester, UK. He has expertise in structural and stress analysis, having spent 4 years working as a structural analyst in the nuclear industry after gaining his PhD. Prior to moving to Minnesota, he was Senior Lecturer in Mechanical Engineering at the University of Manchester.

Dr Fok’s research activities cover a range of topics in solid mechanics, nuclear graphite technology and biomechanics, both at a fundamental level and related to practical applications. These include statistical analysis of brittle failure, fractal finite elements, micro-structural modeling of materials, material characterization using full-field strain measurement and inverse methods, multiple fracture from dynamic stresses, buckling of thin embedded shells and the biomechanics of dental restorations. The finite element method forms the main tool of his research.

In 2007, Dr Fok accepted the invitation of the University of Minnesota School of Dentistry to become Director of the Minnesota Dental Research Center for Biomaterials and Biomechanics (MDRCBB). Established as an industry-academic collaboration with funding from the 3M Foundation and 3M Dental Products Division, the MDRCBB works closely with the industry on the development of new dental products and biomaterials.

Dr Fok’s current research activities include shape optimization of dental restorations, shrinkage strain measurement using digital image correlation, nondestructive examination of interfacial debonding using acoustic emission and development of alternative bond tests for dental materials. Together with colleagues from the Dental School, he has recently been awarded an NIH grant looking at the possible effect of bacterial activities on the degradation of composite restorations. He has also been successful in securing two grants from the DOE, one with colleagues from the Department of Civil Engineering, to continue his work on nuclear.