| ObjectiveIn clinical practice,there were many ways to increase the retention of the crown of natural teeth and reduce the shedding rate.In this study,the abutments with different upper shapes were designed according to the methods of reducing the total crown shedding rate by increasing the adhesive area and broadening the shoulder,and the three-dimensional finite element method was used to establish the single crown models of posterior implants with different shape of abutments.The loading was carried out according to the characteristics of posterior teeth masticatory cycle.The stress of bone tissue,implant,abutment,adhesive and crown around implant were compared between custom abutments and original abutment in dynamic loading process to observe whether the stress distribution of implant and prosthesis was affected by the design of abutment with different upper shape,so as to provide theoretical basis for the selection of abutment from the perspective of biomechanics.Materials and MethodsIn this study,finite element analysis was used to compare the stress and stress distribution on bone tissue,implants,abutments,adhesives and crowns around the implants during dynamic loading.1.Three-dimensional finite element model establishingA patient with missing mandibular posterior teeth was selected from the Stomatological Hospital of Shandong University for CT of the head and neck.The three-dimensional finite element model of the mandibular and implant-restoration was established by using Mimics19.0,Geomagic Studio 2012 and CATIAV5R 19 software.The model consisted of mandibular,implants,abutments,adhesives and crowns.Three experimental groups were established by different designs of abutment:traditional titanium abutment with 1.0mm width shoulder(A),custom abutment with 1.0mm width shoulder(B),traditional titanium abutment with 1.0mm width shoulder(C).2.Stress analysisThe three groups of experimental models were imported into ANSYSL8.0 software to divide the mesh and set the parameters.The load was set at 250N,and the cycle time was 0.875s.The loading method was dynamic loading,and the stress point was located at the implant crown.The loading process was divided into five stages according to the masticatory cycle.The Von Mises stress and maximum principal stress of the dental crown,adhesive layer,abutment,implant and surrounding bone tissue of each group were selected as the analysis indexes.Results1.The Von Mises stress and the maximum principal stress values of the bone tissue,implant,abutment,adhesives and crown around the implants of the three groups of models were analyzed during dynamic loading.The stress values of the three groups of models reached the maximum at 0.260-0.300 seconds in the fourth stage when tongue to buccal loading.2.The stress distribution of the three models was similar.The stress concentration area of bone tissue was located at the junction between the neck of the implant and the surrounding cortical bone.The implant stress concentration area was located in the neck of the implant.The abutment stress concentration area was located at the junction of implant and abutment.The stress of each group of adhesives was concentrated at the neck edge of abutment.The stress of the crown was concentrated at the loading site and the crown edge.3.Compared group A and group B models.The Von Mises stress peak value and the maximum principal stress value of bone tissue,implant and abutment in group B were higher than those in group A.The peak Von Mises stress of group B was 86.07MPa,which was 11%higher than that of group A.The maximum principal stress of group B was 103.9MPa,which was 5.8%higher than that of group A.The peak value of Von Mises stress in group B was 342.05MPa,0.3%higher than that in group A,and the maximum principal stress in group B was 334.977MPa,7.1%higher than that in group A.The peak value of Von Mises stress in group B was 357.05MPa.The peak value of Von Mises stress in group B was 5 8.76MPa,and that in group A was 73.95MPa.The peak value of Von Mises stress in group B was 20%lower than that in group A.The maximum value of Von Mises stress in group B was 48.73MPa.The peak value of tooth crown stress in group B was lower than that in group A.The peak value of Von Mises stress in group B was 70.08MPa,and that in group A was 82.7 MPa.The maximum principal stress in group B was 82.714MPa,and that in group A was 74.55MPa.4.Compared group A and group C models.The peak value of Von Mises stress in group C was higher than that in group A during dynamic loading.The peak value of Von Mises stress in group C was 80.93MPa,4.6%higher than that in group A.The peak value of Von Mises stress in group C was 80.93MPa.The maximum principal stress of group C is lower than that of group A,but there is no significant difference between the two groups.Implant stress was concentrated in buccal neck of the implant.During dynamic loading,there was no significant difference between the peak Von Mises stress and the maximum principal stress in each stage of group A and C.The stress value of group C abutment during loading is greater than that of group A.The Von Mises stress peak of group C is 364.93MPa,which is 14%higher than that of group A.The maximum principal stress of group C is 408.668MPa,which is 1.7%lower than that of group A.The peak value of Von Mises stress in group C was 65 MPa,which was 12.1%lower than that in group A.ConclusionIn this study,three groups of implant and prosthesis models were established according to different abutments by using three-dimensional finite element method.The models were relativity similar to clinical models,and the following conclusions can be drawn:1.Lateral force is more harmful to the implant than axial force.2.Compared with the custom abutments,the abutment with the predental shape is more likely to form stress on the abutment and the cortical bone margin around the implant.3.Widening the shoulder will increase the neck stress of abutment. |
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