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Contraction stresses of composite resin filling materials.

The polymerization shrinkage of composite resin filling materials and the tensile stresses developed when the shrinkage is restrained were measured in an in vitro experiment. This allows an estimation to be made of the forces exerted upon the enamel walls of cavities filled with the resin in the acid etch technique. The results indicate that the stresses acting on the enamel are low compared to the tensile strength of the enamel.