Investigation of the effect of the replacement of implants in different angles and extending their length on the stress that would occur in the bone, the implant and the superstructure using the finite element stress analysis

At the present time, implant-supported denture prostheses are significant treatment options due to superior functional performance of lives partial denture and performance problems in removable prosthesis, and anatomical changes caused by complete lose teeth. However, anatomical limitations such as insufficient height for the implant or osseointegration problems may cause implant failures. Thus, in recent years, the inclined replacement of implants in areas where bone height is insufficient, has been frequently used and achieved successful results. The purpose of the present dissertation is to assess the stress that occurs in the bone under functional loading using implants placed with different angles and using different superstructures, and the effect of inclıned implant placement and extending implant length on stress distribution using three dimensional finite elements stress analysis. In the present dissertation, three implants with the same diameter and length (4 mm × 8 mm), were replaced in the mandibular canine, second premolar and second molar tooth regions, and in a separate model, implants with 10 mm length were used. The implants were first replaced perpendicular to the axial line and then inclined in the distal direction preserving their parallelism increasing 6 ° at each step, forming 7 different study models. In the 8th study model, the implant angles were kept constant and 10 mm long implants were used. The effect of restorations conducted with different superstructure material on the stress distribution was also investigated. Cr-Co, zirconium, titanium and polyetheretherketone (PEEK) material were used to prepare the superstructures. Oblique forces were applied to the superstructures at certain points. Study findings demonstrated that the inclined implant replacement did not significantly increase the stress and compressive forces on the bone, and the stress on the bone around the the implant decreased as the inclination angle increased. On the other hand, in the model where the implant length was increased, it was observed that stress was concentrated in one region st the bone, besides it decreased at the other regions and displayed more homogeneous distribution. The implant's von Mises values decreased. The difference in the superstructure material did not result in significant changes in von Mises stress at bone and the implants. Analysis of material's von Mises stresses demonstrated that the stress magnitude and density were similar for Cr-Co and Zr. Stress concentrations were lower in the titanium material and lowest stress concentrations was observed with the PEEK material. This was due to the fact that each material has different elastic modulus and respond differently under force.