اثر تابش نور بر روند پلیمریزاسیون سیمان های رزینی

Indirect esthetic restorations have recently gained popularity, and choosing suitable cement is an important concern in this regard. A wide variety of resin cements with different curing models:(chemical, light, dual), have been introduced to the profession, and among them the dual systems are claimed to be able to continue polymerization after stopping the light. In order to study and compare the polymerization process of different curing systems, this research was performed.The present study measured the degree of conversion (DC) of three types of resin cements: a self cured,a light cured and a dual cured cement. The samples were prepared as follows:1-The self cured samples were made according to the manufacturer.2-The light cured samples were exposed to the curing light for 60 seconds, through a 2 mm thick waferof porcelain.3- The dual cured samples were divided into 2 groups. The first was lighted similar to the light cured samples, and the second did not receive any light.The degree of polymerization was measured by FTIR at time levels of 5, 10,20,30,45,60 minutes and 24 hours post mixing. The infrared spectrum of the samples were recorded and degree of conversion were determined. The results demonstrated an increase in mean DC of all groups at post mixing time, but this was significant only in the lighted dual cured cement (PO.05). The light cure resin showed high DC at the base line time (5min). At the end of 60 minutes, the self cure resin had the most DC. The unlighted dual cement had a very low DC and didn't improve in polymerization during the post mixing controls.The lighted dual cement had a significant improve in curing at post mixing times, and it was significantly different from unlighted dual cement. So the dual cure cement needs to receive sufficient light energy to initiate the curing process and the chemical component of this cement could not improve the DC completely.After 24 hours migration of unpolymerized monomers, seams to decrease the DC at the surfaces and removing the most superficial layer, showed that the underlying parts, had improved DC. It seems that in order to be sure of what happens at the restoration-tooth interface, it is appropriate to use self cure cements with improved flow and film thickness.