الفهرس 
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Abstract
Aim: To evaluate the effect of pre-cure heating of a nanohybrid composite (Tetric N-Ceram) on its degree of conversion, polymerization shrinkage, flexural strength and flow. Methodology : A total number of 130 specimens were prepared for this study. The specimens were divided into three groups (control group cured at RT and the other two groups were pre-cure heated to 39 o C and 54 o C, respectively).The degree of conversion (DC) was measured using Fourier Transformation Infrared Spectroscopy (FTIR). The specimens were mixed with potassium bromide (KBr) powder and pressed in the form of a disk. The absorbance peaks of infrared rays by the aliphatic C=C and aromatic C=C double bond of were determined. Percent of DC was calculated for each specimen. The percentage of polymerization shrinkage was calculated by measuring specific gravity differences between uncured and cured composite specimens using a modified version of ASTM method D792 “specific gravity and density of plastics by displacement”.The flexural strengths were calculated using the three point bending test carried out by Lloyd instron universal testing machine. The flow test was conducted using American Dental Association (ADA) no. 57 and International Standards Organization (ISO)-6876, where the specimens were packed into stainless steel ring, thenthe ring was removed and a glass slide was placed over the uncured material and a weight of 1.2 kg was applied on the specimen for 120 seconds. The flattened composite discs were curedand their diameters were measured. Mean values of degree of conversion, polymerization shrinkage, flexural strength and flow were calculated. The results were analyzed and compared using one way ANOVA and least significant difference (LSD). Results: The results of this study showed that there were no significant differences in degree of conversion and flexural strength between the control group (cured at room temperature) and the pre-cure heated groups (to 39 o C and 54 o C, respectively) (P>0.05). On the other hand, the pre-cure heated groups showed higher polymerization shrinkage and flow values than the control group cured at room temperature (P=0.0001). Conclusion: Pre-cure heating of composite resin greatly increased the flow of the material which would enhance its adaptation to cavity walls in clinical situation. Also it increases the material volumetric shrinkage. However, pre-cure heating didn’t improve the degree of conversion as well as the flexural strength in comparison to its curing at room temperature.