ABSTRACT
The aim of this study was to measure the degree of conversion [DC] of three types of composite resins [micro-hybrid, nano-hybrid and Ormocer] with different light curing units [LED LCU and QTH LCU] in two depths. Three commercially available dental resin composites were used in this study: [Tetric Ceram, Ivoclar Vivadent, Liechtenstein-A2 shade], [Tetric Evoceram, Ivoclar Vivadent, Liechtenstein-A2 shade], [Ceram X, Dentsply, Germany-M[2] shade]. Specimens were divided into two groups, 5 specimens were photo-activated by QTH unit [Coltolux 75-Colten] and the other five specimens were cured by LED [Demi-Kerr]. Then each specimen was sectioned at the top surface and at 2-mm depth. The DC was measured by FT-IR [Bruker-tensor 27]. The data were analyzed by 3-way ANOVA test. There was significant difference between tested composite resins [P<0.001]. The results of top surfaces were significantly different from those observed at 2-mm depth [P<0.001]. The type of curing unit affected the polymerization of Ceram X resin composite. This study showed a significant difference in the degree of conversion in different thicknesses within three groups of resin composites