Study On Connection Stability And Fatigue Performance Of Dental Implants

The stability of dental implants is the key to improving the service life of dental implants.In dental implant system,abutment is the key structure to achieve anti-rotation and antiloosening between the upper crown and the lower implant.Because abutment-implant connection often suffers from torsion during daily mastication,and there is a requirement of torque in implant operation,the abutment-implant connection needs to ensure enough antitorsion and deformation ability to be more stable and durable.The connection structure has an important impact on the overall stability of the implant system.Besides,mechanical complications such as loosening and breaking will occur in the implant system after enduring long-term chewing force.It is very meaningful to explore the inherent law of fatigue performance of the implant system and to predict fatigue life.In this paper,finite element simulation,experimental methods and theoretical analysis were used to study the stability and fatigue properties of dental implant connections.First,according to the general rules of finite element analysis(GB/T 33582-2017),the anti-rotation and deformation performance of implants with different abutment-implant connection structures are simulated by finite element method,and the force analysis is combined,to study the effect of different connective structures on implant stability and determine which is a relatively stable internal connective structure.Then,according to the dynamic fatigue test standard of implant(BS EN ISO 14801:2016),the worst fatigue loading condition of implant was defined,and the finite element simulation analysis of the implant system with the connection structure was carried out.The results of static load,sinusoidal alternating load and random dynamic load were compared and analyzed to evaluate the mechanical properties of the implant system more comprehensively.Finally,two groups of fatigue tests were designed and carried out.Through the test results and fracture morphology analysis,a comprehensive study of the fatigue performance and failure law of the implant system and a fatigue prediction scheme were proposed.The main conclusions are as follows:(1)High levels of stress are concentrated in very small areas,which are prone to plastic deformation and damage.Plastic deformation can lead to permanent deformation and shorten service life.According to stress analysis,the torque of Torx is obviously higher than that of four angle and six corner structure.Deformation analysis showed that Torx had the lowest degree of plastic deformation.Force analysis shows that the radial force of Torx is small,and Torx is surface contact,which enlarges the contact surface and reduces wear and deformation.Torx can better transmit torque,higher torsion strength and smaller plastic deformation.Therefore,the combination of Torx and micro-cone structure has good sealing performance,anti-rotation and anti-loosening performance,so it is a relatively stable internal connection structure.(2)By simulating static load,sinusoidal alternating load and random dynamic load of the implant system,the stress concentration area and the maximum stress point of each component of the implant system are located at the contact surface.They are located at the compression side contact surface of implant and embedding interface,the compression side contact surface of implant and abutment,and the first and second threads of the tension side connection between implant and connecting screw.Static load:stress analysis and fatigue analysis determine less than 550N within acceptable range.Sinusoidal alternating load:The stress fluctuation of the system has the same trend as that of the sinusoidal load.According to the yield limit of the material,60～600N is the critical value of the sinusoidal load durability of the implant system.Random dynamic load:There is a strong correlation between the stress and load of the system.According to the yield limit of materials,the durability limit of the implant system is determined to be 600N in 50s and 100s time series.By comparing and analyzing three types of load,it is judged that the critical load of the implant system is between 550-600N.(3)The fatigue test results show that there is a certain relationship between the bending fatigue limit τ-1 and the tension-compression fatigue limitσ-1 of the implant system:τ-1=(0.35～0.55)σ-1.The fatigue performance of dental implant system was evaluated,and a series of empirical formulas related to static load,dynamic load,cycle number,displacement and deformation were obtained to predict fatigue life.According to the fracture morphology,the fatigue failure mechanism was obtained,the source of fatigue defects and the direction of crack propagation were revealed,and the relationship between the fracture morphology and different dynamic loads and the difference of fatigue failure process were found.