Three-dimensional Finite Element Study Of Different Restorative Methods For Ultra-short Implants

Objective:To compare and analyze the effects of different restorative methods on the implant and surrounding bone tissue after implantation of ultrashort implants in the first and second molar areas with severe alveolar bone resorption(insufficient distance from the mandibular nerve).The results were used to provide further reference for the clinical application of ultrashort implants and the choice of restorative methods.Methods:Cone beam CT images of a patient with implant restoration in the first and second mandibular molar area were selected from the database and met the Class II bone quality classification of the jaw.Two TSIII Φ5.0×5mm ultra-short implants of the OSSTEM system were used for the implants.Using finite element software,the mandibular bone model was first established using Mimics Research 21.0 software,and then the mandibular bone model was imported into SOLIDWORKS 2018 software to construct a joint-crown restoration model or two single-crown restoration models for the implants in the lower first and second molar areas.In ANSYS Workbench 2021 software,the vertical occlusion and lateral occlusion were simulated in the oral cavity on the models of different restorations of the upper part of the two ultra-short implants,respectively,and a force perpendicular to the long axis of the dentition with the long axis of the dentition was applied in the first and second molar areas at 45° obliquely(the points of action were located on the fossa of the dentition-andbuccal occlusal half surface,respectively)with a loading force of 300 N.The stress distribution in the different restorative methods and in the internal structures and bone tissues of the implant was analyzed for the 2 different loading directions.Results:when ultra-short implants were used in different crown restorations in the mandibular posterior region,(1)when the vertical force was applied,the peak stress of the implant with combined crown restorations was lower than that with single crown restorations;When the force is 45 ° oblique to the long axis of the tooth,the peak stress of the implant with the combined crown is significantly greater than that of the single crown,and the stress distribution of the bone tissue is slightly smaller than that of the single crown.(2)When the same type of restoration is loaded in different directions,the long axis of the tooth is inclined at 45 °,which is significantly greater than the vertical force.Conclusion:In clinical work,personalized design of ultra-short implants is required.After comprehensive consideration,the short-term and long-term complications of ultra-short implants can be better reduced.In this experiment,we found that if the patient only considers the stress distribution area and stress peak of cortical bone,when the bite force is large,the combined crown repair method can be preferred,and either of the two repair methods can be selected anyway.If considering the factors of prosthesis and in order to reduce the linkage reaction caused by the failure of a single implant during the combined crown repair due to retrograde peri-implant inflammation,porcelain collapse or loosening or breaking of the central screw in the later stage,the single crown repair method can be selected.