Polymerization Shrinkage in Resin-Based Composites: Mechanisms, Clinical Impact, and Evidence-Based Management – A Systematic Review with the Grading of Recommendations Assessment, Development, and Evaluation Assessment
Shivkumar P. Mantri, Sneha S. MantriAbstract
Background:
Polymerization shrinkage limits the performance of resin-based composite restorations, often resulting in marginal gaps, microleakage, postoperative sensitivity, and restoration failure. Although many material modifications and restorative techniques aim to reduce shrinkage stress, the evidence supporting this remains unclear.
Objectives:
To systematically review polymerization shrinkage mechanisms, clinical effects, and how material changes or techniques reduce stress in resin-based composites, while assessing evidence certainty using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE).
Methods:
A systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines. Electronic searches, conducted in PubMed/MEDLINE, Scopus, and Web of Science, identified randomized controlled trials, non-randomized clinical studies, laboratory investigations, and evidence syntheses evaluating polymerization shrinkage and management strategies. Risk of bias was assessed using the risk of bias 2 and ROBINS-I tools. Due to substantial heterogeneity across studies, findings were synthesized narratively, and certainty of evidence was assessed using the GRADE framework.
Results:
Thirty-one studies met eligibility criteria and were included in the qualitative synthesis. Polymerization shrinkage was consistently linked with marginal adaptation defects, microleakage, postoperative sensitivity, and restoration longevity. Notably, low-shrinkage resin systems, nanohybrid composites, and modified bulk-fill materials exhibited lower shrinkage than conventional methacrylate-based composites. Importantly, incremental layering reduced shrinkage stress in high C-factor cavities. Bulk-fill composites appear to provide comparable clinical performance based on moderate-certainty evidence. In addition, intermediate liners and modified curing protocols improved marginal adaptation and reduced microleakage. Overall, evidence certainty ranged from low to moderate.
Conclusion:
Polymerization shrinkage remains a clinical challenge, despite advances in restorative materials and techniques. However, modern low-shrinkage materials and evidence-based protocols can reduce complications and improve outcomes. Notably, bulk-fill composites offer efficiency while performing similarly to incremental layering. To further refine recommendations, more robust multicenter randomized trials with standardized outcomes and long-term follow-up are needed to strengthen the evidence base.