Physical Properties of New Dual-Cured Composite Restorative Materials

Objective: To compare the physical properties of new dual-cure, bulk-fill restorative composites (Injectafil DC, Apex; Hyperfill, Parkell) to a hybrid composite material (Filtek Z250, 3M/ESPE). Method: Depth of cure, volumetric shrinkage, fracture toughness, porosity, and microleakage were examined.  For depth of cure, a cylindrical mold (4x14mm long) was filled with composite and light-cured for 20 secs (40 secs for Hyperfill) at 1200 mW/cm² (Bluephase G2, Ivoclar) or allowed to self-cure (n=5).  Uncured composite was removed and remaining polymerized composite was measured and divided by two.  For volumetric shrinkage, composite was placed in a video-imaging device (AcuVol, Bisco) and light-cured or allowed to self-cure.  Shrinkage was recorded continuously for ten minutes (n=10). For fracture toughness, single-edge notched-beam specimens were created in a mold (2.5x5x25mm), light-cured or allowed to self-cure, stored for 24-hours at 37^oC in water, and tested in 3-point flexure (n=10).  For porosity, specimens were created in a proximal slot preparation in an extracted human third molar. Composite was incrementally placed and light-cured (Z250) or placed in bulk (Hyperfill, Injectafil) and light-cured or allowed to self-cure.  The teeth were scanned with a microtomographic unit (Bruker) for porosity formation, then thermocycled, placed in dye, sectioned, and analyzed for microleakage using Image J software (NIH).  Dye penetration was expressed as a percentage of the length of microleakage divided by the length of the restorative interface (n=10). A mean and standard deviation were determined per group.  Data was analyzed with ANOVA/Tukey’s test per property (alpha=0.05).  Percent porosity was evaluated with a Kruskal-Wallis/Mann-Whitney U test (alpha=0.005). Result:  Significant differences were found between groups per property. See table. Conclusion: Compared to the incrementally placed composite (Filtek Z250), the new dual-cure, bulk-fill restorative composites (Hyperfill, Injectafil) in self-cure mode had complete depth of cure, similar fracture toughness and porosity formation, but greater polymerization shrinkage and microleakage.