Abstract: BACKGROUND: In the treatment of edentulous maxillary implants supported fixed repair, the selection of upper scaffold structure materials and the design of different distal implant implantation methods have a close influence on the long-term stability of the whole mouth implant repair.
OBJECTIVE: To comprehensively explore the influence of three different materials of upper scaffold and two implant fixation designs on the biomechanics of the fixed maxillary implant repair based on the three-dimensional finite element method. 
METHODS: Based on the conical beam CT data of a healthy adult with normal jaws, the Mimics software was used to separate the maxillary and maxillary dentin three-dimensional solid models, and the Geomagic Studio software was used to construct the three-dimensional finite element model of denture with denture implant and fixed maxillary arch combined with specific model parameters. According to the different designs of distal implants in the maxillary posterior region, two scheme models were established. Scheme 1 (Design 1) was designed in accordance with the “All-on-4” design used in clinical practice. Two implants were vertically implanted in the bilateral incisor region of the maxilla, and the other two implants were implanted in the bilateral second premolar region at a 30° angle. In scheme 2 (Design 2), two implants were vertically implanted in the lateral incisor region of the maxilla, and two short implants were vertically implanted in the posterior region of the maxilla in the bilateral second premolar region. Three materials (titanium, zirconia and polyether ether ketone) were used to assign values to the upper scaffold structure in the two designs, and six different models were obtained. The biomechanical effects of the implant, surrounding bone tissue and the upper scaffold structure were compared and analyzed in the oblique loading direction.
RESULTS AND CONCLUSION: (1) The maximum stress peaks of all models were distributed in the neck region around the posterior implant and the cortical bone under the two edentulous implant fixed restoration schemes, regardless of the material of the upper scaffold. (2) Compared with the alternative design of Design 2, which adopted vertical implantation of short implants, Design 1 showed a more ideal stress distribution on the maxilla. (3) The scaffold model constructed by polyether ether ketone material transferred higher stress to the implant and surrounding bone tissue close to the loading zone of the upper jaw bone, followed by titanium and zirconia. As for the support itself, the peak stress of the upper scaffold of polyether ether ketone was significantly lower than that of the zirconia and titanium scaffolds. Zirconia scaffolds were used among the three upper scaffolds to disperse the stress distribution of implant and bone tissue. (4) The results suggest that both designs can be applied to clinical practice. However, from the perspective of biomechanics, the stress distribution of the implant, surrounding bone tissue and upper scaffold in Design 1 is more rational, which is more conducive to the long-term prognosis of fixed implant repair in patients with edentulous jaws. The upper scaffold material has a certain influence on the stress distribution of the implant-bone interface. 

Key words: toothless jaw, fixed implant repair of edentulous jaw, All-on-4, tilted implantation, short implant, support material, static load, three-dimensional finite element analysis