The effect of bruxism and temporary prosthetic materials on stress distribution in ALL-ON-FOUR immediate loading protocol for edentulous maxilla: Finite element analysis

The aim of this study is to evaluate the effect of temporary prosthetic materials and bruksism on stress distribution in cortical and cancellous bone around the implants in the immediate loaded all-on-four prosthetic design for an edentulous maxilla. Implant supported fixed restorations are preferred in dentistry today in order to solve the limitations and problems caused by the conventional complete dentures under function for edentulous jaws. The all-on-four concept has been developed in order to avoid advanced surgical procedures in patients with insufficient bone volume, to reduce the stress caused by the cantilever distance and to reduce cost. It is a common procedure to fabricate a temporary fixed prosthetic restoration immediately after implantation for use until the permanent restoration's loading time. The literature review revealed that there was no comprehensive study about the use of monoblock reinforced polymers for immediate all-on-four prosthesis. In addition to this, there is no study found on the effect of increased chewing and parafunctional forces on immediat loaded all-on-four prosthesis in bruxist patients. Hence, three different polymers for temporary prosthesis on immediatly loaded all-on-four implants was evaluated in the presented study under static and dynamic loading. According to the all-on-four concept, two implants have been placed perpendicular to the lateral area and two implants 45 degrees inclined to the second premolar area. Monoblock prostheses was fabricated from three different polymers: polimethylmethacrylate (PMMA), polyetheretherketone (PEEK), polyetherketonketone (PEKK). The worst scenario was applied considering the opposite arch as natural dentition. Predicting the presence of bruxism, two different angles of force was created: an increased vertical force to imitate the clenching activity and an oblique force to imitate the grinding activity.The forces was applied as a dynamic loading in the form of a 10-seconds bruxism attack. Stress analysis was examined on 6 models with 3 materials and 2 different force scenarios in a single case design. Among the stress analysis methods, three dimensional SEA(Finite Element Analysis) method, which works in computer environment and gives the most detailed numerical values, was used. In the study, the von Mises stress values obtained on the implants and abutments were observed below the fracture strength. The maximum principal stress values obtained in spongious and cortical bone were measured below the values reported to initiate bone resorption. The stress values obtained under static loading conditions were higher than the dynamic loading values. In the model fabricated with PEKK, the amount of displacement in the prosthesis, the stress values measured in the implant, abutment and cortical bone were found to be lower than the models fabricated with PEEK and PMMA. The result of this study is aimed to guide the selection of temporary prosthetic material for immediate prothesis applications, especially in bruxist patients. Keywords: all-on-four, immediate loading, finite element analysis This study was approved by Baskent University Institutional Review Board(Project No: DDA21/01) and supported by Baskent University Research Fund.