Effects of Restorative Polymerization Stress on Composite Matrix

Objective: To demonstrate failures of restorations using flowable dental restoratives with different polymerization stress and shrinkage in composite matrix. Methods: A prefabricated cylindrical dental composite (10mm x 20mm) with a cavity of 6mm deep x 6mm diameter in the center as the matrix. Flowable dental restoratives were bulk-placed (6mm deep x 6mm diameter, C factor = 5.0) and cured with ordinary bonding agents per DFU. Matrix specimens were thermocycled 5-50°C (500-1000 cycles) Samples were examined at 30-40x magnification before and after thermocycling. Results: Restoratives having high polymerization shrinkage-stress (greater than 3MPa per NIST beam deflection tensometer, C factor = 1.3) exhibited classic stress-related failures: restorative failure, matrix failure, adhesive failure. Restoratives with lower polymerization stress numbers did not show restoration failures. The volume shrinkage had little effect on the restoration failures. Conclusions: In the dental composite matrix model, the polymerization stress of restoratives demonstrates direct effect on restoration failures.