The study aimed to evaluate the biomechanical behaviors of different prosthetic materials and posterior implant angles in All-on-4 implant-supported fixed maxillary prostheses with three-dimensional (3D) finite element analysis. The model of complete edentulous maxilla was created using the Rhinoceros and VRMesh Studio programs. Anterior vertical and 17 degrees- and 30 degrees-angled posterior implants were positioned with All-on-4 design. Straigth and angled multi-unit abutments scanned using a 3D scanner. Two different prosthetic superstructures (monolithic zirconia framework and lithium disilicate veneer (ZL) and monolithic zirconia-reinforced lithium silicate (ZLS)) were modeled. Four models designed according to the prosthetic structure and posterior implant angles. Posterior vertical bilateral loading and frontal oblique loading was performed. The principal stresses (bone tissues-Pmax and Pmin) and von Mises equivalent stresses (implant and prosthetic structures) were analyzed. In all models, the highest Pmax stress values were calculated under posterior bilateral loading in cortical bone. The highest von Mises stress levels occured in the posterior implants under posterior bilateral load (260.33 and 219.50 MPa) in the ZL-17 and ZL-30 models, respectively. Under both loads, higher stress levels in prosthetic structures were shown in the ZLS models compared with ZL models. There was no difference between posterior implant angles on stress distribution occurred in implant material and alveolar bone tissue. ZLS and ZL prosthetic structures can be reliably used in maxillary All-on-4 rehabilitation.