Determination of Polymerization Shrinkage Stress in Low Shrinkage Resin Composites

Objective: The aim of the study was to examine the polymerization shrinkage stress of new and experimental low shrinkage resin composites (Venus Diamond/Heraeus, Clearfil Majesty posterior/Kuraray, SDR/DENTSPLY and an Ormocer/VOCO) in comparison to established low shrinkage resin composites (els/Saremco, Filtek Silorane/3M ESPE) and a control composite (Filtek Supreme XT/3M ESPE). Methods: Cylindrical cavities (Ø 4mm) in Araldit B epoxide resin plades (40 x 40 x 4 mm) were pretreated with the Rocatec system to ensure a bonding of the resin composites. The resin composite specimens (n = 10) were exposed for 60 s with a QTH curing device (Translux Energy, Heraeus Kulzer, Germany) from both sides. The samples were stored dark and dry (23°C). Polymerization shrinkage stress data [MPa] 4 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 = 0.005, Bonferroni adjustment). Results: For all materials, polymerization stress values increased from 4 h to 24 h (p < 0.005). After 24 h the following mean stress values were obtained: Venus Diamond 3.4 ± 0.3, Clearfil Majesty Posterior 5.6 ± 0.3 MPa, SDR 3.4 ± 0.2 MPa, exp. Ormocer 4.0 ± 0.2 MPa, els 2.5 ± 0.1 MPa, Filtek Silorane 2.8 ± 0.2 MPa, and Filtek Supreme XT 6.0 ± 0.2 MPa. Conclusion: All differences in the shrinkage stress data obtained after 24 h from the investigated resin composites were of statistical significance (p < 0.005). Clearfil Majesty Posterior showed shrinkage stress data more comparable to the control, while Venus Diamond, els, and SDR, showed shrinkage stress data more equivalent to Filtek Silorane.