Assessment of polymerization contraction stress of three composite resins

Objectives The purpose of this study was to measure the development of contraction stress of three composite resin restorative materials during photo-polymerization: a micro-hybrid composite (Filtek Z250, 3M ESPE, St. Paul, MN, USA); a nano-filled composite (Filtek Supreme, 3M ESPE, St. Paul, MN, USA); and a low-shrinkage composite (Ælite LS, Bisco Inc., Schaumburg, IL, USA). Methods Curing shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen-curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40 s. The contraction force (N) generated during polymerization was continuously recorded for 150 s after photo-initiation. Contraction stress (MPa) was calculated at 20, 40, 60 and 150 s. Data were statistically analyzed. Results The low-shrinkage composite Ælite LS exhibited the lowest stress values compared to other materials (p < 0.05). Statistical analysis did not show significant differences between Filtek Z250 and Filtek Supreme. Significance The low-shrinkage composite showed lower contraction stress than micro-hybrid and nano-filled composite. Ideally, non-shrinking resins would represent the ultimate solution to overcome polymerization contraction and stress-related problems.