【作者】 刘丹丹；

【导师】 刘晓秋；

【作者基本信息】 吉林大学 ， 口腔医学（专业学位）， 2020， 硕士

【摘要】 研究目的:利用有限元法探讨在垂直向与斜向载荷作用下,初期隐裂对全冠修复后下颌第一磨牙牙体组织应力分布的影响,为隐裂牙临床治疗方案的选择及预后判断提供一定理论依据。材料方法:1.通过CBCT扫描获得牙列图像,利用逆向工程软件构建牙齿三维模型,将不含隐裂纹的氧化锆全冠修复设为对照组。2.基于对照组,构建隐裂牙模型。根据隐裂纹位置将模型分为A(裂纹一端止于牙合面近中边缘嵴,一端越过远中边缘嵴到达远中邻面)、B(裂纹越过近远中边缘嵴到达近远中邻面)、C(裂纹一端止于牙合面中央窝,一端越过远中边缘嵴到达远中邻面)三组;根据裂纹末端位置分为1(末端位于冠边缘以上)、2(末端位于冠边缘以下)两组。最终实验组共有A1、A2、B1、B2、C1、C2六组。3.对照组及实验组网格划分后,每组模型施加三种工况。工况1以600N的力平行于牙长轴方向施加在模型牙合面,模拟最大咬合力条件下的牙齿受力情况;工况2以200N的力平行于牙长轴方向施加在模型牙合面上,模拟正常咬合力下的正中咬合运动牙齿受力情况;工况3以200N的力与牙长轴成45°方向施加于模型上,模拟侧方运动时的受力情况。观察7组模型剩余牙体组织最大主应力的大小及分布。结果:1.斜向载荷:裂纹末端在牙冠边缘以上时,釉质应力峰值较对照组略低,应力分布与对照组一致,位于近远中颈部;裂纹末端在牙冠边缘以下时,釉质应力峰值较对照组显著升高,集中在颈部裂纹末端。两种裂纹末端形式的牙本质应力峰值以及应力集中区与对照组均无明显差异。2.垂直向载荷:两种裂纹末端形式的釉质应力峰值较对照组均有所升高,应力集中区也有所不同:裂纹末端在牙冠边缘以上时,应力主要集中在牙合面裂纹边缘;裂纹末端在牙冠边缘以外时,应力集中在颈部裂纹末端。两种形式下牙本质的峰值及分布与对照组均无明显差异。结论:1.当裂纹末端完全被牙冠覆盖,斜向载荷时全冠可以对隐裂处牙体组织提供更好的保护,而垂直向载荷时牙合面裂纹边缘较其他部位会受到更大的拉应力,折断的可能性更高。2.当裂纹末端暴露在牙冠边缘外,颈部裂纹末端总是应力集中区,且斜向载荷时的应力峰值更大,即斜向载荷较垂直载荷更易导致裂纹末端的扩展。3.当修复体并未完全覆盖裂纹时,裂纹同时跨过近远中边缘嵴组裂纹附近牙体组织断裂的可能性最高,其次是一端止于中央窝一端向远中延伸组,最后是一端止于近中边缘嵴一端向远中延伸组。4.与牙釉质相比,垂直载荷与斜向载荷均对裂纹附近牙本质影响不大。更多还原

【Abstract】 Objective:Finite element analysis was used to study the stress distribution of enamel and dentin of cracked mandibular first molar with full crown restoration under vertical and oblique loads.The difference in stress distribution was also be studied when the restoration completely covered the crack or not.It is hoped that the results will provide some reference for the selection of clinical treatment options.Materials and Method:1.The dentition image was obtained by CBCT scan,and the three-dimensional model of the tooth was constructed by using reverse engineering software.The model of zirconia full crown restoration without cracked line was set as the control group.2.A cracked tooth model was constructed based on the control group.According to the location of the crack,the model was divided into A(Crack runs through the mesial and distal edges of the occlusal plane.One side ends at the mesial edge and the other end passes far distal edge,extending towards the gingival side),B(Crack extends through the mesial and distal edges of the occlusal plane and extends toward the gingival side)and C(Crack starts from the central fossa and extends far beyond the distal edge extending toward the gingival side).According to the end of the crack,it was divided into 1(The end is above the edge of the crown),2(The end is under the crown edge)two groups.The final experimental group consisted of six groups: A1,A2,B1,B2,C1 and C2.3.After the mesh was divided,a complete three-dimensional finite element model of the tooth was constructed,and three sets of working conditions wereapplied to each group of models.Condition 1: A force of 600 N was applied in the vertical direction on the central fossa to simulate the tooth stress under the condition of maximum bite force;Condition 2: The force of 200 N was applied on the occlusal surface of the model in the vertical direction on the central fossa to simulate the force of the teeth in the middle of the occlusal movement under the normal bite force;Condition 3: A force of 200 was applied to the model in the oblique direction on the buccal incline of mesial and distal buccal cusp,simulating lateral movement.Observed the size and distribution of the maximum principal stress in the remaining tooth tissue of the 7 groups of models.Results:1.Oblique 45°loading:When the end of the crack was above the crown edge,the peak stress of enamel was slightly lower than that of the control group,and the stress distribution was consistent with that of the control group,which appeared in the mesial and distal neck region.When the end of the crack was below the crown edge,the peak of enamel was significantly higher than that of the control group,concentrated at the end of the neck crack.The peak and distribution of dentin of the two forms were not significantly different from those in the control group.2.On vertical loading:The peak stress of the enamel under two forms of crack was higher than that in the control group,and the stress concentration area was also different: when the crack end was above the crown edge,the stress was mainly concentrated at the crack edge of the occlusal surface;the other was concentrated at the end of the neck crack.The peak and distribution of dentin of the two forms were not significantly different from those in the control group.Conclusion:1.When the end of the crack is completely covered by the crown,the full crown can provide better protection to the dental tissue under the oblique load,however,the crack end on the occlusal surface will be subject to greater tensile stress than other parts under vertical load,and more likely to failure.2.When the crack end is exposed outside the crown edge,the stress concentration area is always at the crack end of neck,and the stress peak is larger under the oblique load.That is,the oblique load is more likely to lead to the crack end growth than the vertical load.3.When the prosthesis do not completely cover cracks,it is most likely to fracture that the cracks will cross the mesial and distal edges at the same time,followed by one ends at the central fossa and one extends distally,and the last is that one ends at the mesial edge and one extends to the distal.4.Compared with enamel,both vertical and oblique loads have little effect on dentin near the crack.更多还原