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.

BACKGROUND: In the treatment with dental implant prosthesis, the stress distribution of marginal bone and implant-bone interface Is affected by the factors of restoration and occlusion. The Internal structure and the stress distribution of Implant-bone Interface determine the long-term life of the implant and the stability of the marginal bone. OBJECTIVE: To analyze the effects of zirconia-based all-ceramic crown and Co-Cr alloy porcelain ceramic crown on the stress distribution of implant-bone interface, implant, prosthesis abutment, retention screw, and the inner structure in three occlusal relationships. METHODS: Using Mimics 17.0 software, the implant model of maxillary central incisor was established based on the cone beam CT of a patient undergoing prosthesis implantation Into the maxillary central incisor. Two kinds of three-dimensional finite element models of zirconia-based all-ceramic crown and Co-Cr alloy porcelain ceramic crown were constructed. The edge to edge occlusion, normal occlusion and deep overbite were simulated to analyze the stress distribution of Implant structure and the Implant-bone Interface in the three occlusal relationships. RESULTS AND CONCLUSION: (1) In the Co-Cr alloy porcelain ceramic crown group, when the occlusal relationship changed from the edge-to-edge occlusion to the normal occlusion and deep overbite relationships, the stress at the occlusal point of the prosthesis increased correspondingly, and the stress at the abutment, Implant and the Implant-bone Interface decreased. In the normal occlusal relationship, the stress at the retention screw was more concentrated than that in the other two occlusal relationships, and its peak value of the equivalent stress was higher. (2) In the zirconia-based all-ceramic crown group, when the occlusal relationship changed from edge-to-edge occlusion to the normal and deep overbite relationships, the stress peaks of the abutment, implant and implant-bone interface decreased gradually. In the normal occlusal relationship, the stress peaks of the occlusal point and the retention screw were higher than those in the other two occlusal relationships. (3) In the edge-to-edge occlusion relationship, the peak of equivalent stress at the occlusal point of the implant prosthesis in the Co-Cr alloy porcelain ceramic crown group was slightly higher than that in the zirconia-based all-ceramic crown group. The peaks of equivalent stress of the abutment, retention screw, Implant, and Implant-bone Interface in the Co-Cr alloy porcelain ceramic crown group were slightly lower than those in the zirconia-based all-ceramic crown group. In the normal occlusal relationship, the peak of equivalent stress at the neck of the implant in the Co-Cr alloy porcelain ceramic crown group was slightly higher than that in the zirconia-based all-ceramic crown group. In the deep overbite relationship, the peaks of the equivalent stress at the occlusal site of the implant prosthesis and the neck of the implant in the Co-Cr alloy porcelain ceramic crown group were higher than those in the zirconia-based all-ceramic crown group. The peaks of equivalent stress of the abutment, retention screw, and implant-bone interface In the Co-Cr alloy porcelain ceramic crown group were slightly lower than those in the zirconia-based all-ceramic crown group. (4) These results showed that different occlusal relationships and different upper structures of the implant prosthesis affected the stress distribution in each part of the implant and at the implant-bone interface. This finding may provide a reference for the prediction of long-term complications of implant prosthesis.