Evaluation of stress distribution around a dental implant with different amounts of bone by "all on four" technique applied in bilateral atrophic mandible by using finite element analysis

Implant is a very successful prosthetic rehabilitation option in the oral cavity defects. In severe posterior atrophy cases of the mandible dental implant applications due to various reasons pose difficulty and complications while the osseointegration period is prolonged. In order to be able to apply dental implants with the "All-on-four" technique to patients with severe mandible atrophy, sufficient bone must be present in the anterior mandible. In cases with insufficient bone volume, augmentation techniques have disadvantages in terms of the advanced age of these patient populations, the risk of complications, nerve damage, prolongation of the treatment process and cost. In dental implant applications, the increase in implant diameter is an important parameter in terms of stress distribution. Considering the disadvantages of augmentation techniques to use larger diameter implants in cases with insufficient bone volume, many surgeons may prefer bone reduction at the alveolar crest instead of augmentation techniques. He has to choose between using a shorter and wider implant with bone reduction or using a longer and thinner implant without bone reduction. As result of alveolar crest with bone reduction or natural resorption of alveolar bone after delayed dental implant treatments after tooth extraction the crown/implant ratio increases with vertical bone loss. Along with the decrease in the vertical bone height, the length of the implant decreases, and the destructive stresses due to the increased crown/implant ratio with the increase in the height of the prosthetic superstructure are another source of concern. In our study, a model with a length of 21 mm in the anterior mandible where dental implants will be applied and a width of 3 mm with an alveolar crest increasing towards the basal mandible was obtained with the "All-on-four" system showing bilateral posterior mandible atrophy by using computerized tomography records. In the model, 4 different models were obtained by reducing 2 millimeters of bone to each model. The aim of our study is to investigate how the stress values that occur as a result of the vertical and oblique forces applied to these models, which are obtained with different diameter, length and varying prosthetic superstructure length in different bone volumes, and the dental implants placed with the "All-on-four" technique, affect the stress accumulations and the obtained data. It is to choose the most accurate surgical planning by understanding which bone level implant applications are superior to others and giving optimal results by comparing them. In our study, group models containing 4 different bone levels were created. In the group 1 model, the anterior mandible with a length of 18 mm and a width of 5.5 mm obtained with 3 mm bone reduction from the main model was 3.5x15 mm long, and in the group 2 model obtained with a bone reduction of 5 mm from the main model, a length of 16 mm and a width of 5.8 mm. 3.8x13 mm long to anterior mandible, 14 mm long and 6.3 mm wide anterior mandible obtained by 7 mm bone reduction from the main model in the group 3 model, 4.3x11 mm to the anterior mandible, and 12 mm obtained by 9 mm bone reduction from the main model in the group 4 model 5x9 mm long dental implants were applied to the anterior mandible with a length of 7 mm and a width of 5x9 mm, perpendicular to the lateral incisor region and at an angle of 30 to the premolar region, with the "All-on-four" technique (Medentika® GmbH, Hügelsheim Gerrmany). Vertical 100 N, 150 N, 200 N and obliquely 100 N, 100 N and 150 N forces were applied bilaterally from the 2, 4, 6 numbered teeth area in the prosthetic superstructure at an angle of 30, respectively. Von Mises stress values formed in implants, abutments, abutment screws as a result of applied forces and Maximum and Minimum Principal stress values occurring in alveolar bone were investigated by Finite Element Stress analysis. According to result of our study, Von Mises stress values formed in dental implants increased with increasing bone reduction under vertical and oblique forces, and that these stresses concentrated in dental implants transmitted less to the alveolar bone ıt also showed that Maximum and Minimum Von Mises stresses formed in the alveolar bone decreased. There was no significant difference in Von Mises stresses formed in abutment and abutment screws. No significant difference was found in the stress values. Von Mises stresses formed in abutment and abutment screws no significant difference was found in the stress values. Based on the results of our study, Group 4 was found to be the most ideal planning and the most optimal stress results at different bone heights in the bilateral atrophic mandible.