FEM analysis of stresses on implant, surrounding bone and superstructure with different implant number and position for implant supported fixed prothesis in different crown heights

İmplant-supported fixed partial prosthesis have become a predictable, reliable and biocompatible restoration procedure for partial edentulous patients. However, crown height is a critical factor against achieving the optimal treatment result. Because an increase in biomechanical forces in directly relationship to the increase in crown height, the treatment plan should be carefully considered. The aim of our study to investigate and compare the effect of crown height on the surrounding bone, implant and superstructure under functional forces by placing dental implants in different numbers and positions. In our study, three planning models supported by dental implants of the same diameter and length (4.1 mm×10 mm) were simulated in posterior mandibula. In these models, the vertical and oblique forces applied to three-unit fixed dental prostheses with two different crown heights were evaluated by finite element stress analysis. The principal stress values for cortical and trabecular bones, the Von Mises stress values for all structures and implant were compared. While the increase in crown height did not show a significant impact in the stress values in the models under vertical forces, it increased the stress values in all models under oblique forces. The highest stress values in the models occurred when oblique forces were applied to implant-supported fixed dental prostheses with a crown height of 14 mm. It was concluded that to prevent cortical bone resorption especially in cases of increase of crown height should be one implant for each lost tooth. In cases where one implant for each lost tooth is not possible and anatomical structure prevent from to place the implants in an optimal position, placing two implants at an angle of 30 degrees was found more appropriate than placing two implants straight.