Objectives: The purpose of this study was to develop and evaluate a dynamic light scattering-based method for monitoring the polymerization reaction of a light activated dental composite.
Methods: Laser light back-scattered from thin disk-shaped composite samples was used to study the curing reaction kinetics. Samples were irradiated simultaneously on opposite surfaces with a 633 nm laser beam and a halogen curing lamp (320, 160, or 100 mW/cm(2)). Dynamic laser speckle patterns were imaged onto a CCD camera at a rate of 32 frames/s for 2 min. The intensity decorrelation rate calculated from sequential speckle patterns was used to assess the rate of motion within the samples during the reaction.
Results: Motion within the composite increased immediately upon the onset of light exposure for all trials. This was followed by a brief period characterized by a relatively constant high rate of motion. Finally the rate of motion decreased exponentially. The reaction acceleration, deceleration, and maximum rate were dependent upon the irradiance of the curing light source.
Significance: This method monitors reaction rate and the change in reaction rate at high temporal resolution without contact. Reaction kinetics was shown to begin immediately after light exposure suggesting limited opportunity for viscous flow and stress relief.
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