| Background: Due to the existence of buccal canine fossa in maxillary premolar area,direct axial implantation tends to cause bone fenestration and dehiscence on the implant buccal site.In order to avoid unnecessary ridge augmentation surgery,some doctors advocate inclining implantation on the palatal side at a certain angle to avoid canine fossa area.However,there is still no theoretical basis for the specific scheme of inclining implantation in maxillary premolar area.Objective :The objective of this experiment is to study the stress distribution of surrounding bone tissue under the static load condition of vertical occlusal surface when two common length implants with different angles of palatal inclined implant combined with angle abutment are repaired under the condition of tooth loss in maxillary premolar area with bone types of class III bone and class IV bone respectively by the threedimensional finite element method.It can provide some theoretical references for the selection of inclined implant in maxillary premolar area.Methods: The CBCT data of a volunteer with normal height and weight without systemic diseases and jaw diseases and the basic specification parameters of SPI system implant were selected as a reference.The forward modeling and accurate assembly of jaw block,implant,abutment and crown in maxillary premolar area were carried out in UG.Twenty groups of implant repair models were established,in which 9.5mm and 11 mm long implants were used for axial implantation and palatal tilt implantation respectively,combined with 0 °,5 °,10 °,15 ° and 20 °abutments.The pre-processing operations were carried out in Hyper Mesh software,including meshing Material parameter assignment,boundary constraint and load setting.Finite element calculation and analysis of the processed model in ABAQUS,which can obtain the stress distribution nephogram of surrounding bone tissue and record the maximum equivalent stress value(σVM,unit:MPa)of each part.Results: 20 groups of three-dimensional finite element models of two length implants combined with five angled abutments in maxillary premolar area under two kinds of bone mineral density were successfully established in this experiment.From the stress nephogram,it can be seen that the abutments with angles greater than 15 ° tend to cause the stress concentration of the surrounding bone tissue.Meanwhile,the bone tissueσv M surrounding implant in each model was obtained.Cancellous boneσv Ms were all within the corresponding yield strength range,but cortical bone σv M did not exceed its yield strength only when the abutment with angle less than 10 ° applied in class III bone.With the abutment angle increasing,the cortical bone σv M shows an increasing trend as a whole.When abutments within 15 ° were applied,cancellous bone σv M decreased,while the angle abutment above 15 ° resulted in the increase of cancellous bone σv M.The effect of implant length shows as followed: When using straight abutment,the increase of implant length leads to the decrease of bone tissue σv M.But when angled abutments were applied,the increase of implant length made no difference.Bone type also affects bone tissue σv M:each group in class IV showed higher stress values than the counterparts in class III bone.Conclusion: Based on the three-dimensional finite element analysis results of this experiment,the following conclusions can be drawn:1.The lower the bone density,the weaker the effect of jaw on resisting the stress of bone tissue around implant;2.The maxillary premolar area with class III bone condition can be tilted palatally within 10 °;3.The maxillary premolar area of class IV bone is not suitable for palatal oblique implantation;4.Under the bone condition of maxillary premolar area,the increase of implant length has no obvious effect on resisting the stress caused by angled abutment. |
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