上颌中切牙种植盾构术中不同根盾片厚度的有限元分析

Finite element analysis of various root shield thicknesses in maxillary central incisor socket-shield technique

背景:口腔种植盾构术有效维持了唇侧软硬组织,但术后根盾片暴露、移位等并发症发生率较高,推测种植牙长期行使功能后根盾片可能受到了过大负载而导致其暴露及移位。目的:通过三维有限元法,探讨正常咬合下不同根盾片厚度对根盾片、牙周膜、种植体及周围牙槽骨应力分布、应力峰值、位移等的影响,分析不同根盾片厚度与根盾片暴露、移位及折裂发生的力学相关性。方法:在数据库中选取1例符合上颌中切牙种植盾构术适应证患者的锥形束CT资料,通过逆向建模技术构建上颌骨和根盾片模型,根据种植体相关部件参数,通过正向建模技术构建种植体相关部件模型。将各模型导入Solidworks 2022软件,根盾片厚度分别设为0.5,1.0,1.5,2.0 mm。使用ANSYS Workbench 2021软件模拟分析正常咬合情况下各模型中根盾片、牙周膜、种植体及周围牙槽骨的应力分布、应力峰值、位移情况。结果与结论:(1)各组模型中根盾片的应力集中于腭侧颈部、两侧边缘与唇侧下缘,随着根盾片厚度的增加,模型中根盾片的等效应力峰值及位移呈下降趋势,厚度0.5 mm组模型中根盾片的等效应力峰值达到176.20 MPa,超过了牙体组织屈服强度150 MPa;(2)各组模型中牙周膜应力集中于颈部边缘及上部区域,随着根盾片厚度的增加,模型中牙周膜的等效应力峰值及位移呈下降趋势;(3)各组模型中种植体应力集中于种植体颈部与种植体-修复基台连接处,唇侧均较腭侧集中,随着根盾片厚度的增加,模型中种植体的等效应力峰值呈上升趋势;(4)各组模型中皮质骨应力主要集中于种植体颈部周围和根盾片下缘周围,唇侧较腭侧集中,随着根盾片厚度增加,模型中根盾片周围骨的等效应力峰值呈降低趋势,种植体颈部周围骨的等效应力峰值呈上升趋势;模型中松质骨的应力主要集中于种植体唇侧颈部周围、螺纹顶端、根尖部和根盾片下缘周围,唇侧较腭侧集中,随着根盾片厚度增加,模型中根盾片周围骨的等效应力峰值呈降低趋势;各组模型中皮质骨的最小主应力集中于种植体颈部周围,呈扇形分布,随着根盾片厚度的增加,皮质骨的最小主应力呈上升趋势;(5)结果显示不同根盾片厚度对盾构术系统产生了不同的生物力学影响,0.5 mm厚的根盾片易出现根盾片折裂,对于骨宽度充足的患者,2.0 mm厚根盾片是一个能降低根盾片暴露、折裂、移位并发症风险的选择,同时预备过程中应注意保护牙周膜,对根盾片两侧及下缘作圆顿处理。

BACKGROUND:Socket-shield technique can effectively maintain labial soft and hard tissues,but the incidence of postoperative complications such as exposure and displacement of root shield is relatively high.It is speculated that the root shield may be exposed and displaced due to excessive load after long-term function of dental implants.OBJECTIVE:Through three-dimensional finite element analysis,we aim to study the influence of varying root shield thicknesses on the stress distribution,equivalent stress peaks,and displacement in the root shield,periodontal ligaments,implant,and surrounding alveolar bone under normal occlusal loading.We also attempt to analyze the correlation between the thickness of the root shield and occurrence of mechanical events such as root shield exposure,displacement,and fracture.METHODS:Cone-beam CT data of a patient who met the indication standard of socket-shield technique for maxillary central incisor were retrieved from database.Reverse engineering techniques were used to build models of the maxillary bone and root shield,while forward engineering was used to create models for the implant components based on their parameters.Models depicting various root shield thicknesses(0.5,1.0,1.5,and 2.0 mm)were created using Solidworks 2022 software.ANSYS Workbench 2021 software was then used to simulate and analyze the effects of varying root shield thicknesses on stress distribution,equivalent stress peaks,and displacement of the root shields,periodontal ligaments,implants,and surrounding alveolar bone under normal occlusion.RESULTS AND CONCLUSION:(1)In all root shield models,the stress was concentrated on the palatal cervical side,both sides of the edges and the lower edge of the labial side.As the thickness of the root shield increased,the equivalent stress peak and displacement showed a decreasing trend.The 0.5 mm thickness model produced a stress concentration of 176.20 MPa,which exceeded the yield strength(150 MPa)of tooth tissue.(2)The periodontal ligament stress in each group was concentrated in the neck margin and upper region.With the increase of root shield thickness,the equivalent stress peak and displacement of periodontal ligament showed a decreasing trend.(3)Implant stress in all models was concentrated in the neck of the implant and the joint of the implant-repair abutment,and the labial side was more concentrated than the palatal side.With the increase of root shield thickness,the equivalent stress peak of the implant in the model showed an increasing trend.(4)In each group of models,stress of cortical bone concentrated around the neck of the implant and the periphery of the root shield,and the labial side was more concentrated than the palatal side.With the increase of the thickness of the root shield,the equivalent stress peak around the root shield decreased;the peak value of the equivalent stress of the bone around the neck of the implant showed an increasing trend.In the model,the stress of cancellous bone was mainly concentrated around the neck of the lip of the implant,the top of the thread,the root tip and the lower margin of the root shield,and the labial side was more concentrated than the palatal side.With the increase of the thickness of the root shield,the peak value of the equivalent stress of the bone around the root shield in the model showed a decreasing trend.The minimum principal stress of cortical bone in each group of models was concentrated around the neck of the implant,exhibiting a fan-shaped distribution.As the thickness of the root shield increased,the minimum principal stress of cortical bone showed an increasing trend.(5)These results indicate that different thicknesses of the root shield have different biomechanical effects.The root shield with a thickness of 0.5 mm is easy to fracture.For patients with sufficient bone width,the root shield with a thickness of 2.0 mm is an option to reduce the risk of complications such as root shield exposure,fracture,and displacement.Meanwhile,it should be taken into account to protect the periodontal ligament in the preparation process,and rounding treatments ought to be carried out on both sides and the lower edge of the root shield.