In dentistry, setting contraction means shrinkage during the hardening of impression materials and resins.
In dentistry, setting contraction refers to the property of materials to reduce their volume, i.e. shrink, during the course of a hardening process. This property of a material is rather unfavourable in dentistry, as it causes an inaccurate marginal fit (marginal gap). For example, plastics show a setting contraction (polymerisation shrinkage) during the curing process.
The opposite of the setting contraction is called setting expansion. The term "setting expansion" describes the behaviour of materials during the setting process to increase their volume. This applies especially to amalgam fillings or plasters. The setting expansion of model plasters is standardised and must not exceed certain values.