A REVIEW OF POLYMERIZATION SHRINKAGE STRESS: CURRENT TECHNIQUES FOR POSTERIOR DIRECT RESIN RESTORATIONS

It is generally accepted that resin-based composites are not yet able to guarantee excellent results when used in posterior tooth restorations. This is due to polymerization shrinkage, which can still be regarded as the main drawback of composite resins. Firstly, all of the factors which contribute to the polymerization process, polymerization shrinkage and resin composite polymerization shrinkage stress have been examined by means of an overall review of available literature. Secondly, several studies aimed at suggesting a judicious selection and an appropriate use of modern dental materials, layering techniques, and polymerization strategies for a better control of shrinkage stress were reviewed. Several factors which are responsible for the polymerization process may negatively affect the integrity of the tooth-restoration complex. There is no straightforward way of handling adhesive restorative materials, that would guarantee the reliability of a restoration. At present the practitioner has to coexist with the problem of polymerization shrinkage and destructive shrinkage stress. However, evolving improvements associated with resin-based composite materials, dental adhesives, filling and light curing techniques have improved the predictability of restorations. This critical review paper is meant to be a useful contribution to the recognition and understanding of problems related to polymerization shrinkage and to provide clinicians with the opportunity to improve the quality of their restorations.