Excerpt from Abstract

Purpose: This study investigated the leaching of monomers from bulk-fill composites, as well as physical properties of the materials

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Conclusion: The leaching of monomers increased dramatically when a distance from the light tip to the material was introduced. This indicated that a  prolonged curing time, relative to that given by the manufacturer, may be necessary in clinical situations in order to retain an optimal performance of the material

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Reference
Leaching of monomers from bulk-fill composites
Kopperud HBM, Kleven IJS, Knarvang T, Wellendorf H.
Dental Materials 2014; 30: e46.