Replica technique remain most commonly used technique for measuring the marginal fit in the medical literature, the silicone rubber addition is considered most accurate and least changing dimensions. Aim of study to compare the accuracy and simplicity of traditional replica technique and modified replica technique to measure marginal fit of zirconium posterior bridges manufactured by CAD\CAM. After removal of first lower molar from TYPODENT (Frasco, Tettnang, Germany), the second lower molar and premolar neighboring were prepared commensurate with full ceramic restoration. Final impression of this bridge was taken by silicone rubber addition (Zhermack Elite HD+) with the aid of custom tray. The impression was condensed with amalgam to make the main metal cast. Fifteen custom acrylic resin trays were used for fabricate fifteen impressions of main metal cast that were used for fabricate 15 zirconium bridges by CAD\CAM technique According to the manufacturer's instructions. Tow rubber thicknesses were taken for the marginal fit of each bridge over its cast gypsum by used light silicone rubber addition. Then the first rubber thickness was treated by developed replica technique to form the Group (A) of the study and the second rubber thickness was treated by replica technique to form the group (B) of the study. Depending on T-test, no significant difference between two techniques was detected. We conclude that developed replica technique reliable technique to study and measure the marginal gap of bridge and crown, and it is statistically more accurate than the traditional technique.