Monitoring and Instantaneous Evaluation of Composite Resin Linear Shrinkage with Computerized Topography

Aims: To measure the linear shrinkage of composite resin by digital image analysis, to evaluate the effect of light curing type on composite resin linear shrinkage, to evaluate the effect of light curing intensity on linear shrinkage of composite resin and to evaluate the linear shrinkage of composite resin after 24 hours. Materials and method: images of composite samples were obtained before curing. The samples were cured with four types of light curing units, halogen light curing unit 420 mW/cm2, LED light curing unit 420 mW/cm2, halogen light curing 300 mW/cm2 and LED light curing unit 300 mW/cm2. the curing time was 40 seconds. After curing, the cured composite surface was exposed to the microscope allowing the attached camera to capture an image. The samples were then stored in 37 degree centigrade incubator for 24 hours and another image for each sample, was obtained. The images were analyzed via specially prepared image analysis program and the linear shrinkage was measured. Results: Regarding the type of LCUs, statistical analysis showed that composite samples cured with QTH LCUs exhibit significantly higher linear shrinkage values than those cured with LED LCUs. While regarding the intensity of the curing light, it was shown that LCUs with higher curing light intensities produce a significant higher values of linear shrinkage. Conclusion: The type and the intensity of the light curing unit play a major role in the end result linear shrinkage of the cured composite resin. Image analysis system is an excellent method to determine linear shrinkage.