The polymerization shrinkage of a range of chemical and photopolymerized resin‐based restorative materials available in Australia was investigated using a previously reported volumetric shrinkage measuring method. The method proved easy to use, reproducible, independent of specimen size, and capable of use in both chemically and photo‐initiated systems. The values obtained for the polymerization shrinkages ranged from 1.67 to 5.68 per cent with most materials being in the 2 to 3 per cent range and the overall average result being 2.81 per cent. It was observed that powder‐liquid systems seemed to have the highest shrinkage and light‐activated materials the least with the paste‐paste materials having intermediate results. An experiment carried out to examine the effect of voids incorporated upon mixing showed that increased void content caused a greater shrinkage of material per unit mass. This, together with other factors such as amount and size of reacting monomer, is seen to partially explain the observed order of polymerization shrinkages.
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Michaël Goldman (1983) studied this question.