Document Type : Original Articles

Abstract

Introduction: Incomplete polymerization of composite resins has unfavorable effects on the clinical function and the esthetics of the restoration. The aim of this study was to determine the relationship between the light intensity of light-curing units in the Department of Operative Dentistry of Isfahan Faculty of Dentistry and the curing depth according to ISO 4049 standards and also to compare the primary and final light densities of the units.Materials and Methods: In this in vitro study, first the light intensities of 9 light-curing units of the Department of Operative Dentistry were measured by a radiometer. According to ISO 4049 if the intensity of the light-curing unit was higher than 200 mW/cm2, the unit was used to cure five samples of Z100 composite resin. A total of 7 units were used to cure 35 specimens. The exposure time of the units with 200-300 mW/cm2 light intensity was twice those of units with over 300 mW/cm2. The uncured composite resins were removed by scraping and half of the least remaining composite resin thickness was recorded as the curing depth. Finally the light intensity of each unit was measured again. Data was analyzed with SPSS using t-test and correlation coefficient (α = 0.05).Results: The light intensity of light-curing units was 40‒620 mW/cm2: four units with above 300 mW/cm2; three with 200-300 mW/cm2 and two with less than 200 mW/cm2. Only two light-curing units exhibited significant differences between primary and final light intensities (p value < 0.001). The correlation coefficient between the light intensity and curing depth was 0.58. All the curing depths were within the ranges of ISO 4049 standards regardless of duration of exposure.Conclusion: All the light-curing units with a light intensity of more than 200 mW/cm2 had achieved the necessary curing depth specified by ISO 4049 and there was a positive correlation between light intensity and curing depth. Key words: Light curing unit, Light intensity, Composite resin, Polymerization.