Three Dimensional Finite Element Analysis Of Four-implants Supported Mandibular Overdentures Using Two Different Attachments

Background:Conventional complete dentures often cannot obtain satisfactory retention,especially mandibular complete dentures.Implant-retained overdenture has became an effective way to improve the retention of traditional complete denture.The long-term stability of implant overdenture is closely related to its biomechanical compatibility.Excessive loading will result in bone resorption around implants.Many scholars have analyzed the biomechanical properties of mandibular implant overdentures which are repaired by different kinds of attachments.Three-dimensional finite element analysis is a common method to study the biomechanical properties of implants at home and abroad.Purposes:In this experiment,three-dimensional finite element analysis method was used to establish models of mandibular overdentures with four implants repaired by two kinds of attachments,to analyze the stress distributions of mandibular overdentures supported by two different kinds of attachments under different mechanical loads.The biomechanical characteristics of mandibular overdentures supported by different types of attachments were evaluated to provide a certain mechanical reference for clinical attachments selection and application.Methods:After the jawbone was scanned by CBCT,two different models of mandibular overdentures supported by Locator attachment and bar-clip attachment were established respectively by using Mimics 17,Geomagic Studio 2012,UG NX 10.Each model was subjected to five different mechanical loading conditions:100N vertical loading in central incisor,100N vertical loading and oblique loading in canine,100N vertical and oblique loading in posterior teeth.The stress distributions of implants,peri-implant bone and mucosa were recorded under the above five conditions to evaluate the effects of different attachments on the biomechanical properties of implant-supported mandibular overdentures.Results:1.Regardless of loading conditions and types of attachments,the stress concentration of implants were located in the neck of implants,and the stress concentration of peri-implant bone was located in the cortical bone.The stress values of mucosa were always much smaller than those of implants and cortical bone.2.Regardless of loading on anterior or posterior teeth,when the overdenture was subjected to lateral force,the maximum Von-Mise stress values of implants and cortical bone were much higher than those of vertical force.3.Under various loading conditions,the stress values of implants and cortical bone of the overdenture using Locator attachment were smaller than those of bar-clip attachment while the pressure of mucosa was slightly larger than that of the bar-clip attachment.Conclusion:1.When the two overdentures were subjected to different mechanical loadings,the Von-Mise stress of implants were concentrated on the neck of implants,and the Von-Mise stress of bone was concentrated on the cortical bone around the implants.2.The stress concentration of implants and surrounding cortical bone were more obvious when the overdenture was subjected to lateral force than vertical force.In clinical practice,the lateral force to the implant-retained overdenture should be minimized to avoid complications caused by pathological loads.3.Under the same loading condition,the stress values of implants and surrounding cortical bone repaired by bar-clip attachment were greater than those of Locator attachment,while the pressures of mucosa were slightly little than that of Locator attachment.The results suggested that the stress distributions of overdenture using Locator attachment are more dispersed,which is more conducive to long-term stability of implants.