Three-dimensional Finite Element Analysis Of Different Implant Sites And Angles In The Posterior Region

Objective: With the continuous development of science and technology,implant restorations have become a common treatment for tooth loss.Due to the local anatomical constraints of the posterior region and the patient’s restricted mouth opening,implants are not placed in the ideal position to achieve the desired restorative effect in clinical work,thus affecting the long-term retention of the implant.The integration of the implant-bone interface is the theoretical cornerstone for the survival and function of the implant denture,which requires good biomechanical properties in addition to the necessary biological adaptability.In this paper,the stress distribution in the bone tissue around the implant is analysed by means of finite element simulations at different sites and angles,in order to support the rationalisation of clinical implant design solutions.Methods:1.Establishment of a finite element modelAn adult male patient with complete crown morphology,no defective teeth,normal occlusal relationship,good soft tissue condition and no obvious defects in the alveolar bone was selected and,with the patient’s consent,cone beam CT was taken to obtain mandibular bone data and saved in DICOM format.Solid Works 2022 3D software was used to construct the solid model,including the local mandibular cortical bone,cancellous bone,implant,angled abutment and zirconia all-ceramic crown.The initial position of the implant was used as the base,and the position was moved by 2 mm in0.5 mm steps in each of the four directions of buccolingual and distal,for a total of 17 different implant positions;each position was considered to be 2°,4°,6°,8°and 10° off the original position and each of the four directions of buccolingual and distal,for a total of 21 different implant angles.2.Three-dimensional finite element stress analysis was carried outThe 3D models of the above experimental categories were imported into the finite element analysis software ANSYS Workbench 19.0,which automatically meshed them,set the experimental conditions,boundary constraints and mechanical parameters,and referred to the normal occlusal force statistics,mean occlusal force,and normal masticatory cycle(the average time required was 0.875S)of healthy adult males in oral anatomy and physiology,and applied forces on the restorations.The Von Mises equivalent force peaks and their distribution in each component of the 3D finite element model developed during the masticatory cycle were recorded and analysed.Results:1.The maximum equivalent forces in the mandible(cortical and cancellous bone) fluctuated with increasing variables in the site offset and tilt angle experiments.The maximum equivalent forces in cortical bone were concentrated in the area of contact between the implant and the roof of the alveolar ridge,while the peak equivalent forces in cancellous bone tended to occur at the cervical or root side of the implant.2.the peak stresses in cancellous bone are much lower than those in cortical bone;the peak stresses on all surfaces are often greater under an oblique 45° load than under a vertical load.3.Compared to the smooth trend of the stress distribution on the implant surface under site-shift,the trend of the stress on the implant surface changes more significantly with increasing tilt angle.Conclusion:1.Both the position offset and the angular tilt of the implant can change the stress distribution in the bone tissue around the implant to varying degrees,and the stresses at the bone interface are at risk of increasing.2.The peak stresses generated by oblique loading are greater than the effect of vertical loading.Therefore,a comprehensive decision should be made in the clinical formulation of the implant restoration plan according to the patient’s local anatomical conditions and occlusal characteristics to avoid or reduce the occurrence of oblique forces and cantilever beams as much as possible.