Altonbary GY¹; Azer SS²; Hegazy SA³; Habib.AA⁴. ¹Assistant lecturer of Removable Prosthodontics, Faculty of Dentistry, Mansoura University, Egypt. ²Associate Professor Division of Restorative Science and Prosthodontics, College of Dentistry, The Ohio state University, USA. ³Assistant Professor of Removable Prosthodontics, Faculty of Dentistry, Mansoura University, Egypt. ⁴Professor of Removable Prosthodontics, Faculty of Dentistry, Mansoura University, Egypt. Abstract: Objectives:study the effect of different impression transfer techniques for four implants on the passive fit of multiple bars used to retain\support mandibular implant assisted overdenture, Methods:Six patients already received four mandibular implant supported overdentures (multiple bars connecting the four implants) were selected. Pick up impression for the bar framework will be done and poured as a control cast. Three different impression techniques were done for each patient; Technique 1: short transfer impression copings were used for a closed tray impression. Technique 2: long transfer impression copings were used for open tray pick up impression. Technique 3: long transfer impression copings splinted with prefabricated acrylic resin bars were used for open tray pick up impression Evaluation:the passivity of each framework was evaluated 1) clinically: by one screw test 2) laboratory: by recording a pick up impression for the bar framework and pouring a control cast, the positional changes of the implant analogs after each impression transfer technique was measured by a digital scanning approach. Results:highly statistical significant difference (P<0.005) was found for the degree of deviation of the scan bodies between the three impression transfer techniques. Conclusions:the splinted open tray technique produced more accurate casts compared to either open tray or closed tray impression techniques. Keywordsimpression, overdenture, digital scanning