Evaluation of stress distribution of the implant and surrounding bone against the forces on increased length of pontics supported by different length implants, using three-dimensional stress analysis

Some additional surgical procedures are required to obtain sufficient bone volume for dental implants in severely resorbed alveolar crest. Short implants are alternative treatment option for limited bone volume to avoid the risks of surgical treatment for bone reconstruction. However, its usage is controversial since it has less surface contact area with the surrounding bone than standard implants. The aim of our study to investigate and compare the effect of increased span length of short and standard length implant supported fixed partial prosthesis on the surrounding bone, implant and prosthetic structures under functional forces. The stresses which were generated under vertical and oblique forces on three and four unit fixed prosthesis supported with 6 mm and 12 mm length, 4.2 mm diameter implants were evaluated by using ANSYS 2019R2 finite element package program. The maximum principle stress and the minimum principle stress for cortical and cancellous bones, the Von Mises stress for implant and whole structures are used to compare stress. In addition, deformation images under forces were interpreted in all structures. In all models, higher stress values were observed for four-unit implant supported fixed prosthesis compared to three-unit models. The stress values for the implant body in both span lengths were higher in the short implant. Connected to increased prosthesis length greater stress value was occured in the surrounding cortical bone of short implants, while this effect was in the connection screw in the standard implant. Due to the increased prosthesis length high stress values were achieved for both the surrounding bone of short and standard implants and standard implant connection screw under oblique loads. It was concluded that oblique forces should be avoided for 4-unit implant supported fixed prosthesis.