A physico-chemical explanation of the post-polymerization shrinkage in dental resins

The proposed explanation is that, as photopolymerization of dental resins is very fast, a large excess of free volume is trapped in non-equilibrated samples. As they have no time to return to an equilibrium state, free volume should decrease below Tg and samples do physically shrink during the first 24 h. As a consequence, free radicals can come into 'contact' and undergo limited propagation but significant termination justifying the decrease in overall radical concentration.