The buildup of shrinkage stress in composite restorations depends on the amount of polymerization shrinkage and the rate at which it happens. The aim of this study was to measure in real time the full-field polymerization shrinkage in dental resin composites using a novel technique based on digital image correlation (DIC).
Polymerization shrinkage in commercially available resin composite (Z100, 3M ESPE) was measured as a function of both time and position using DIC. The experimental setup included an external shutter inversely synchronized with a CCD camera and a 550nm long-pass optical filter to block off the remaining light that passed through the shutter during its closing/opening. The resin composite samples (2mm×4mm×6mm) were irradiated for 40 seconds at an intensity of 1200mW/cm2. Image acquisition occurred at 15fps, during which the external shutter temporarily obstructed the curing light at the same rate. The acquired images were then processed using proprietary software to obtain the full-field strain maps as a function of time.
Result: The DIC outputs were able to show the extent of polymerization shrinkage at different stages of the cure. The samples showed greater shrinkage in the y-direction (-0.65±0.24%) than the x-direction (-0.53±0.12%). Furthermore, shrinkage was greatest near the curing light and decreased with the distance away from the curing light. The initial rate at which the material polymerized was estimated to be about 7.36%/s.
Conclusion: The new DIC method using an inversely synchronized shutter provided real-time results that could aid in assessing the level and rate of shrinkage stress buildup.
Keywords: Composites, Digital image analysis, Polymerization and Stress
See more of: Dental Materials 7: Polymer-based Materials-Physical Properties and Performance