Calculation of contraction rates due to shrinkage in light-cured composites

Objective. To calculate the contraction rate that results from polymerization shrinkage in photo-cured resins. Method. Fourteen materials were irradiated in a previously developed instrument. This instrument uses measurements of deflection using a 'bonded cisk' method. Six measurements were made on each material at 20 2 degreesC and 70 +/- 10% RH. Means and standard deviations were analyzed. Results. Shrinkage-strain and contraction rate are reported. Total shrinkage-strain for photo-polymerized resins (packable and flowable composites) varies between 1.65 and 4.16%. Both are ormocers. The contraction rate for photo-polymerized resins varies between 55.71 and 167.00 mum/min. Packable resins present a Lower contraction rate than flowable resins. Significance. The distance-time graph is linear. The slope of this Line is the average velocity. This concept was used to calculate the average contraction rate. The monomer percentage affects the contraction rate, because higher contraction rate means higher percentage of monomer. We can infer that contraction rate bears some relation to polymerization shrinkage. (C) 2003 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.