Curing contraction

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.

Setting or hardening is generally the term used to describe the complex chemical solidification of materials that consist primarily of a liquid substance.

The setting contraction is the property of materials to reduce their original volume during the hardening process. Amalgam fillings have the advantage of expansion, which improves the marginal seal, in contrast to the polymerization shrinkage of dental fillings with plastic. Therefore, when the amalgam sets, cracks may appear in the tooth.

In dentistry or during dental treatment this property of setting contraction is rather unfavourable, as it causes an inaccurate marginal gap or marginal seal, which can lead to secondary caries (marginal caries). Plastics show a setting contraction or polymerisation shrinkage when hardening. For example, polyether materials have a setting contraction of about 0.1 percent due to polymerization shrinkage.