Investigation of traumatic forces in atrophic mandible treated with All-On-4 concept by finite element analysis

Tooth loss causes the person to encounter functional problems such as chewing, nourishment and speaking, and to experience social and even emotional problems. With the increase in the functional and aesthetic expectations of the patients, the use of dental implants has become a frequently applied treatment worldwide for the treatment of patients. In 2003, Dr. Paulo Malo et al. He defined the 'All-On-4' concept, which allows implant application in atrophic jaws without further surgical procedures. According to this concept, a total of 4 implants are sufficient for the fixed or temporary rehabilitation of edentulous jaws, 2 axial implants anteriorly and 2 distally inclined posteriorly to the premolar tooth region. No detailed researches have been found on how the 'All-On-4' concept affects the fragility of the manibula, which has increased fragility due to resorption and atrophy, against traumatic forces. In this study, it is aimed to determine the most suitable option by comparing the implants that we placed in different positions and lengths in the All-On-4 concept applied to the atrophic mandible against traumatic forces during the period until the prosthesis stage. In our study, a 3D model of the atrophic edentulous mandible was created in the computer environment and implants in accordance with the 'All-On-4' concept were placed as monocortical, bicortical and long bicortical. Provided that the position of the distal inclined implants is kept constant, the positions of the anterior axial implants are positioned as the lateral and canine region, and 2000 N frontal traumatic force from the symphysis region and 2000 N lateral traumatic force from the premolar region are applied to 6 models. According to the anatomical regions of the mandible, Pmax and Pmin stress values in cortical bone and cancellous bone, and Von Mises stress values formed on the bone around the implant and on the implant were measured by three-dimensional finite element analysis. In all study models in which frontal and lateral traumatic force were applied, it was determined that the stresses in the cortical bone were higher than the stresses in the cancellous bone. It was observed that the Pmax and Pmin stress values were concentrated in the highest condyle region and the stress accumulation in the condyle region increased as the implant length increased. It was determined that Von Mises stress values formed around the implant and in the cortical and cancellous bone around the implant in models with frontal force applied were higher in implants placed in the lateral region, and these values increased as the implant length increased. When the models with lateral force are examined, as the implant length increases, the stress on the cortical bone around the posterior implant on the same side as the force decreases while the stress increases in cortical bone surrounding other implants. As a result of our study, we think that the placement of anterior implants in the canine region and monocortical in the 'All-On-4' concept applied in the atrophic mandible may reduce the risk of fracture.