Shrinkage stress of new experimental low shrinkage resin composites

Objective: Low shrinkage resin composites are in the focus of research in posterior resin composite restoratives. The aim of this study was to examine the polymerization shrinkage stress of experimental low shrinkage resin composites (K0152/Dentsply, NEUN/Heraeus, Hermes/3M ESPE) in comparison to new and established low shrinkage resin composites (Tetric EvoCeram/Ivoclar Vivadent, QuiXfil/DENTSPLY, Xtrafil/VOCO). Method: Cylindrical cavities (Ø 5mm) in Araldit B epoxide resin plates (40x40x3mm) were pretreated with the Rocatec system to ensure a bonding of the resin composites. The resin composite specimens (n=10) were exposed for 60s with a QTH curing device (Translux Energy, Heraeus Kulzer, Germany). The samples were stored dark and dry (23°C). Polymerization shrinkage stress data [MPa] 5 min and 24 h post exposure were calculated based on the diameter of the isochromatic curves of first order, obtained from the Araldit-plates. Statistical analysis was carried out with the Wilcoxon-test (p = 0.002, Bonferroni adjustment). Results: After 24h the following mean stress values were obtained: 3.7 ± 0.08 MPa for Tetric EvoCeram , 4.7 ± 0.2 MPa for Quixfil, 4.6 ± 0.1 MPa for Xtrafil, 3.8 ± 0.1 MPa for K0152, 3.7 ± 0.05 MPa for NEUN and 2.9 ± 0.3 MPa for Hermes. After 24 h, due to post-exposure shrinkage, significantly higher polymerization stress values (p < 0.001) were recorded for all materials, except for Hermes. After 24 h, significant differences (p < 0.001, Bonferroni correction) were found between Hermes and all other composits while K0152 and NEUN showed significantly less shrinkage stress compared to QuiXfil and Xtrafil. Conclusion: New low shrinkage resin composite formulations are able to show a significantly reduced shrinkage stress compared to most of the conventional resin composites investigated. After 24h, the experimental silorane restorative Hermes showed the lowest polymerization shrinkage stress. This study was supported by DENTSPLY/Konstanz and Heraeus/Hanau.