| Edentulous is a clinical common oral disease in dental restoration, impacting onappeatance, pronunciation, masticatory function and social contact. Complete dentures is theconventional restoration treatment method for edentulous, while the lack of abutment teethresults in the absorption of alveolar bone and soft tissue thinning, which leads to theretention stability of the complete dentures being poor, masticatory efficiency being less, andit often causes mucosal pressure ulcers, so restoration result is not that satisfied. With thedevelopment of the oral cavity implanting technology, the application of implant greatlyimproves the retention and stability of the complete dentures, and it has achieved highmasticatory efficiency and satisfactory effect on the patients. However, for some patientswith severe atrophy of edentulous alveolar ridge, often face the problem of shortage of bonemass on implant restoration. To this, in order to reduce complications, some scholars putforward All-on-4implanting method. This method is to put4implants which include2mesial straight implants and2distal tilting implants in edentulous, to support a fixedprosthesis. This method applies the posterior tilting implants to avoid the maxillary sinus or inferior alveolar nerve, and reduce cantilever length and increase the contact area of implantand bone. In All-on-4, how to choose the suitable angle of inclination of posterior implant,the cantilever length of the superstructure and the length of posterior implant, to reduce thestress of peri-implant bone and increase the long-term retention rate of implant and denture,is a problem that is worthy of study and discussion.Objective: To investigate the distribution in peri-implant bone with All-on-4implantwith the angle of inclination of distal implant, the cantilever length of the superstructure andthe length of distal implant by three-dimensional finite element method, to providetheoretical reference for clinical therapy.Methods: To obtain the3D data of the edentulous mandible using the CT scanner, usingMimcs, Geomagic and Unigraphics software to establish the3D model of the edentulousmandible. To mesh by HyperMesh software, then establish three-dimensional finite elementmodel of edentulous mandible.Establishing the finite element models of All-on-4implant restoration with inclinationangles of distal implants are0°,15°,30°and45°, corresponding to the length of thecantilever are19.5mm,17.2mm,13.3mm and9.8mm, respectively. Assigning the propertiesof model and boundary constraints. A150N vertical static load was applied on the right endof the cantilever. To observe the equivalent stress peak value and equivalent stressdistribution of peri-implant bone.Establishing the finite element models of All-on-4implant restoration with inclinationangle of distal implants is45°, corresponding to the length of the distal implants are13mm,15mm,17mm and19mm, respectively. Assigning the properties of model and boundaryconstraints. A150N vertical static load was applied on the right end of the cantilever. Toobserve the equivalent stress peak value and equivalent stress distribution of peri-implantbone.Establishing the finite element models of All-on-4implant restoration with distalimplants tilting0°corresponding to the length of the cantilever is19.5mm, and distalimplants tilting45°corresponding to the length of the cantilever is9.8mm.The verticalstatic load was applied on the unilateral distal-extension of superstructure, the region of unilateral distal implant corresponding to superstructure, the anterior teeth area ofsuperstructure, bilateral distal-extension of superstructure, the region of bilateral distalimplant corresponding to superstructure, bilateral distal-extension and anterior teeth area ofsuperstructure, the region of bilateral distal implant corresponding to superstructure andanterior teeth. Each load is150N, to observe the equivalent stress peak value and equivalentstress distribution of peri-implant bone.Results:1. Establishing the edentulous mandibular finite element model,25mm height and8mmwidth, the distance between the mental foramen is53mm and the vertical distance betweenthe superior border of mental foramen and alveolar ridge top is8mm, the thickness ofcortical bone in all directions is2mm.2. In the study on the influence of inclination angle of distal implant and the length of thecantilever on stress distribution in peri-implant with All-on-4, increasing inclination angle ofdistal implant and decreasing the length of the cantilever, the stress of peri-implant bonehave been reduced.3. In the study on the influence of length of distal implant on stress distribution inperi-implant with All-on-4, increasing the length of distal implant, the stress of cortical boneand cancellous bone are reduced, but the change is not obvious.4. In the study on the influence of loading positions on stress distribution in peri-implantwith All-on-4, when the load was applied on the unilateral distal-extension of superstructure,the region of unilateral distal implant corresponding to superstructure, the anterior teeth areaof superstructure, bilateral distal-extension of superstructure, bilateral distal-extension andanterior teeth area of superstructure, the stress of peri-implant bone in the model of distalimplant tilting45°is lower than the model of distal implant tilting0°. When the load wasapplied on the bilateral distal-extension of superstructure, the region of bilateral distalimplant corresponding to superstructure and anterior teeth, the stress of peri-implant bone inthe model of distal implant tilting45°is slightly higher than the model of distal implanttilting0°. It shows that All-on-4distal implant with large inclination angle and shortcantilever will reduce the stress of peri-implant bone, when the load was applied on the unilateral and bilateral distal-extension of superstructure, the anterior teeth area ofsuperstructure.5. From the result of the stress distribution, no matter where the loading positions wereapplied on the superstructure, the equivalent stress of cortical bone and cancellous bone aremainly concentrated in the neck of implant.Conclusion: The experimental results show that the influence of the cantilever length onstress distribution in peri-implant with All-on-4is greater than the influence of theinclination angle. Increasing the length of distal implant is not significantly reduced thestress of peri-implant bone. When the load was applied on the distal-extension ofsuperstructure, the distal tilting implant will provide the length of the longer safe chewingteeth and lower stress of implant-bone interface than distal straight implant. |
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