Influence Of Post-core Material,cement Material And Thickness On Stress Of Post-core System Under Ultrasonic Vibration: A Three Dimensional Finite Element Analysis

Objective: This study was conducted to analyze the impact of post-core material,cement material and thickness on the stress of post-core systems under ultrasonic vibration at different frequencies and amplitudes using three-dimensional finite element analysis.The findings would provide a theoretical guidance for clinical removal of casted post-cores under different conditions and cemented with different cements using ultrasonic vibration.Methods: Eight three-dimensional finite element models of central maxillary incisor with reconstructed post-cores were established by Computer Aided Design(CAD)software.They were assigned with two post-core materials(Au and Ni-Cr alloys),two cements(Glass ionomer(GI)cement and Zinc phosphate(ZP)cement)and two cement layer thicknesses(50 and 150μm).Vibration loads were applied near the neck on the lip side at the frequencies of 10,20,30,40 k Hz and the amplitudes of 10,20,30,40,50μm.The maximum shear stress of cement layer and the maximum principal stress of abutment and their distributions were investigated.Results:3D FEA models of the central maxillary incisor with reconstructed post-cores were constructed efficiently and accurately.The stress of cements and abutment increased with the increase of frequency and amplitude of vibration load and elastic modulus of cements,and decreased with increasing cement layer thickness and elastic modulus of post-core.The maximum value of the cement stress appeared in the contralateral neck of the loading side;the maximum value of the abutment stress concentrated on the ferrule where the load was applied.Conclusions: 1.When ultrasound instrument is used to remove post-core,high frequency and large amplitude should be used when elastic modulus of post-core is large and elastic module of cements is small and cement layer is thick.2.If the elastic modulus of post-core is small,the elastic modulus of cement is large with small thickness,low frequency and small amplitude may be used.3.The position of ultrasonic working tip may be changed or use two tips in the same time to improve efficiency as well.The ferrule near the tip may be protected by reducing the amplitude and increasing the frequency.