الفهرس 
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Abstract
The purpose of this investigation was to study the effect of the degree of conversion on some mechanical properties (Diametral tensile strength and Vickers hardness) of different shades (A1, A2 and A4) of two composite resin restorative materials [Heliomolar (Microfilled) and Tetric Ceram (microhybrid)]. For each shade of composites, three experimental tests (degree of conversion, diametral tensile strength and Vickers hardness) were performed. The degree of conversion (DC) was measured for the uncured and cured six shades of both types of composite resin using Fourier transformation infrared spectroscopy (FTIR). The uncured pastes of all shades were smeared on potassium bromide disks. The absorbance peaks of infrared rays by the aliphatic C=C and aromatic C<U+2026>C double bonds of the monomer were determined. For cured conditions, diskshaped specimen (10 mm diameter and 1 mm in thickness) were prepared in stainless steal mold and cured according to the manufacturer<U+2019>s instructions. The specimens were ground into fine powder and mixed with KBr powder. The absorbance peaks of infrared rays by the aliphatic C=C and the aromatic C<U+2026>C were determined. Based on the results of this investigation the following conclusions can be made: 1. Shade A1 in both Heliomolar and Tetric Ceram composite resin restorative materials showed the highest values of the degree of conversion (%), diametral tensile strength and Vickers hardness number. 2. Shade A4 in both Heliomoalr and Tetric Ceram composite resin restorative materials exhibited lowest values of the degree of conversion (%), diametral tensile strength and Vickers hardness number.