Polymerization shrinkage of composite resins: consequences and control

Bonding strategies associated with the aesthetic and conservative properties of resin materials have increased their popularity in restorative dentistry. Direct composite restorations are one of the most prevalent medical interventions on the human body, with millions of composite restorations placed each year around the world. The optimal performance of these restorations depends on the proper polymerization of the resin component, which is characterized by the transformation of monomers into polymers, accompanied by volumetric reduction of the material. Despite several improvements in new restorative materials in recent years, the disadvantages related to polymerization shrinkage of resin composites remain a clinical problem. The aim of this study is to explore, through an integrative literature review, the causes of polymerization shrinkage of composite resins, as well as their risks and how to control them, in order to obtain long-lasting restorations. A consequence of shrinkage stress can be related to the detachment along the restoration/tooth interface or restoration margins, resulting in internal and marginal gaps, microcracks of one or both restorative material and tooth structure, marginal stain, and cusp deflection.