| Clinical dentists are confronted with the problem oftooth-missing restoration when bone quantity and bone quality inposterior maxillary area are not ideal. With the development offunctional surgery, functional restitution, implant technique andbiomedical material concerned, applying zygomatic implant dentureis clinically a good method in the treatment of the severely resorbedmaxilla and maxilla after resection because of carcinoma.Zygomatic implant denture is that implant is inserted intozygoma directly or through maxilla after cutting maxillary softtissue, and then that superstructure is fabricated for the sake ofrestoring facial defect concerned and missing tooth.By now, some foreign scholars had undertaken some clinicalstudies about zygomatic implant denture, but there is nonedomestically. There is no systemic study about the influence ofzygomatic-implant-denture cantilever on stress distribution andabout interfacial stress distribution condition around zygomaticimplant. Excessive stress and little stress of residual alveolar ridgeand bone tissue around zygomatic implant can cause respectivelycompressive bone absorption and waste bone atrophy, which willresult in restoration failure. So, how to produce the stressphysiologically, and avoid stress concentration of bone aroundzygomatic implant as possible as we can is the key tozygomatic-implant-denture success.According to these above, three-dimensional finite elementmodel for maxillary posterior-tooth area, maxillary sinus andzygoma was established biomechanically in this study by spiral CTtechnique and FEA software technique, and zygomatic implant issimulated into the model in the first-maxillary-molar region.Combined with clinical parameters of bone altitude and normalimplant diameter, three kinds of maxillary altitudes aredesigned—8mm, 6mm and 4mm, and three kinds of implantdiameters are designed—3.5mm, 4.0mm and 5.0mm. By simulatingmasticatory condition, vertical loading, buccal (30°) loading andlingual (30°) loading are designed, 100N. According to threevariables above, three groups of load cases are formed, loaded,calculated and analyzed. Overall stress distribution of bone aroundzygomatic implant can be obtained. By comparing stress peak valueof implant-bone interface, the biomechanical influence of variousload cases of zygomatic implant denture on bone tissue aroundzygomatic implant can be revealed. So structural design, clinicaldesign and indication selection of zygomatic implant denture can beoptimized.Experimental results demonstrate that:Three-dimensional finite element model for maxillaryposterior-tooth area, maxillary sinus, and zygoma can be establishedprecisely. The model can be observed from any angle, and has goodgeometric similarity compared with CT image. The model can bemoved, rotated, magnified and shrunk freely, and can be sectionedfrom any direction so as to be observed. All kinds of load cases canbe well stimulated by designing models with various materialsparameters, installing zygomatic implant and exerting various kindsof loading.Stress concentrates mainly in the area of the implant-boneinterface. The larger the distance between implant and bone is, thesmaller the stress of bone is. Under vertical loading or obliqueloading, stress peak value always appears in the area of maxillaryalveolar ridge. In the maxillary area, the stress of implant-boneinterface near maxillary sinus floor is relatively larger. In thezygomatic area, the stress of implant-bone interface near maxillarysinus roof is relatively larger.The stress of implant-bone interface in the maxillary alveolarridge is significantly larger than that of implant-bone interface in thezygomatic area. Compressive stress peak value is larger than tensivestress peak value. When implant, 3.5mm in diameter, is verticallyloaded, the compressive and tensive stress peak values ofimplant-bone interface in the maxillary-alveolar-ridge area and thezygomatic area near maxillary sinus roof increase gradually as themaxillary altitude decreases. When the maxillary altitude is 4mmand vertical loading is applied, the compressive and tensive stresspeak values of implant-bone interface in the maxillary alveolar ridgeand the zygomatic area near maxillary sinus roof decrease graduallyas the implant diameter increases. When the maxillary altitude is4mm and the implant diameter is 3.5mm,the stress resulting fromoblique loading is significantly larger than that resulting fromvertical loading in the area of maxillary alveolar ridge, but there isno remarkable change tendency relatively in the zygomatic area.Within the limitation of this investigation, the conclusions canbe drawn as follows:1,The method to develop three-dimensional finite elementmodel for maxillary posterior-tooth area, maxillary sinus, zygomaand zygomatic implant by spiral CT scanning and Altair hypermeshsoftware is feasible.2,As far as zygomatic implant denture is concerned, stressconcentrates mainly in the area of the implant-bone interface. Thelarger the distance between implant and bone is, the smaller thestress of bone is.3,As far as zygomatic implant denture is concerned, the stressof implant-bone interface in the maxillary alveolar ridge issignificantly larger than that of implant-bone interface in thezygomatic area. And so the possibility of bone absorption andinterface separation in maxilla is larger.4 , The compressive and tensive stress peak values ofimplant-bone interface in the maxillary-alveolar-ridge area and thezygomatic area near maxillary sinus roof increase gradually as themaxillary altitude decreases. Pay attention to select the patient casewhose maxillary altitude is larger in consideration of indicationselection.5,The stress peak value of implant-bone interface decreasesgradually as the implant diameter increases. Select wider-diameterimplant as possible as the residual bone permits clinically.6,The stress resulting from oblique loading is significantlylarger than that resulting from vertical loading in the area ofmaxillary alveolar ridge. Stress can be lessened by minishing contactangle or decreasing the tooth-cusp inclination.
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