Altohami Mohamed M Sharrada¹, Mohammed M Fouad², Ibrahim Mohammed Elewa³, Radwa .M. K. Emera^{4 1}B.D.S, Colleague of Master Degree, Faculty of Dentistry, Mansoura University, Mansoura, Egypt. ²Professor of Removable Prosthodontics and Chairman of Prosthodontic Department ,Faculty of Dentistry, Mansoura University, Mansoura, Egypt. ³Professor of Industrial Production Engineering, Faculty of Engineering, Mansoura University, Mansoura, Egypt. ⁴ Assistant Prof. of removable prosthodontics, Faculty of Dentistry, Mansoura University, Mansoura, Egypt. Abstract: Objectives:This in vitro study was aimed to compare between different designs of attachments regarding stress transmitted to bone around four implants assisting mandibular complete overdenture. These attachments were bilateral posterior bars, four balls and four magnetic attachments. Methods:Four implants were anchored in a mandibular model made of resin, and a removable overdenture was fabricated. The surface of the model was covered with a layer of silicone soft liner material to simulate oral mucosa. Three groups of attachments were used: Group I: bilateral posterior bars. Group II: four ball attachments. Group III: four magnetic attachments. A vertical force was applied to the central point on occlusal acrylic stent with metal plate and gradually increased from 0 to 70 N in 5-N steps. The resultant stress distribution around implants was measured with each attachment group. Results:When comparing between the means of peri-implants stresses around all implants in the three groups, insignificant difference between groups was found. Comparing between the means of peri-implants stresses around canine implants in all groups, showing insignificant difference between groups I and II.The difference between group III and other two groups was found to be significant. Bar attachments (group I) recorded the highest stresses followed by ball attachments (group II) and magnetic attachments (group III) recorded the lowest stresses. Comparing between the means of peri-implant stresses around first molar implants in all groups, showing insignificant difference between groups I and II. The difference between group III and other two groups was found to be significant. Magnetic attachments (group III) recorded the highest stresses followed by bar attachments (group I) and ball attachments (group II) recorded the lowest stresses. Conclusions:This in vitro study concluded that although the insignificant difference between stresses transmitted around four implants assisting mandibular complete overdenture. Magnetic attachment recorded the lowest stresses followed by ball attachments and the bar attachments recorded the highest stresses. Regarding the peri-implant stresses for each implant location (canine and first molar), for canine implants the magnetic attachments are preferred, while for first molar implants ball and socket attachment are preferred as these attachments were associated with the least peri-implant stresses. Keywords:Overdenture, Mandibular complete overdenture, and Implant assisted complete overdenture.