OBJECTIVE To evaluate the biomechanical behavior of different types of PEEK as implant materials for mandibular implant-retained overdentures. METHODS Virtual models of mandibular overdentures retained by two interforaminal implants were simulated. In each model, one implant material was assumed resulting in four models; titanium, carbon-reinforced PEEK, ceramic-filled PEEK and unfilled PEEK models. Unilateral vertical and oblique loads were applied separately. Von-Mises stresses and maximum equivalent strain values were computed. RESULTS All PEEK implant models induced higher stresses in the cervical portion of peri-implant bone compared to the titanium model. A more homogenous stress distribution pattern along the whole length of the titanium implants was observed compared to PEEK implants. The highest amount of strain values was recorded in the unfilled PEEK implants. CONCLUSIONS Titanium remains to be the most optimum material for dental implants. Unfilled and ceramic filled PEEK might not be recommended as a dental implant material due to the high stresses generated within the implant bodies and cervical part of peri-implant bone under oblique load which might contribute to an increased probability of implant body fracture and marginal bone loss.