Shrinkage strain of bulk-fill dental composites with novel strain-gauge model

Objectives: Bulk-fill composites allow a 4 mm depth of cure, however, it is crucial to measure the polymerization shrinkage strain in order to determine if bulk placement is clinically feasible. The objective is to assess the polymerization shrinkage strain of 5 bulk fill composite resins.
Methods: Teflon molds with standardized Class I (2 mm × 4 mm × 4 mm) cavity preparations were used to fabricate composite blocks to serve as tooth analogs. A strain gauge was secured to the simulated buccal surface of each block and oriented in an incisal-cervical direction. The cavity preparations were treated with CoJet particle-abrasion and light-cured adhesive. One low viscosity and four high-viscosity bulk fill composite materials (n=8) were placed into the preparation in bulk and light cured according the manufacturer’s instructions with a Bluephase 20i light (output=1010 mW/cm²). Shrinkage strain was continuously recorded from 10 seconds prior to light polymerization to 15 minutes following the final light cure. Data were analyzed with 1-way ANOVA and Tukey’s test (α=.05).
Results: Comparison of the shrinkage strain exhibited by each material revealed the only significant difference in shrinkage strain between Surefil SDR and Sonicfil.
Conclusions: Within the limitations of this in vitro study, all bulk fill composites showed similar shrinkage strain values with the exception of the only significant difference between Surefil SDR (lowest recorded strain) and Sonicfil (highest recorded strain).