| Objective:Using the finite element method,according to the different degrees of wedge-shaped defects,a three-dimensional finite element model of the maxillary first premolars was constructed,and various types of wedge-shaped defects of the maxillary first premolars with different restoration methods were analyzed from the perspective of tissue biomechanics.Under loading,the size and distribution of stress in the remaining teeth and restorations provide a biomechanical reference for the selection of the restoration methods of maxillary first premolars with different degrees of penetrating wedge-shaped defects after clinical root canal treatment.Methods:Use CBCT to scan the upper and lower jaws of the volunteers,and import the images into Mimics19.0 and other related software to extract the relevant structures and construct the maxillary first premolars and periodontal tissue models required by the target.Refer to Professor Tan Jianguo The classification method of penetrating wedge-shaped defect based on the degree of defect.Analyze the internal stress distribution of the remaining teeth and restorations of the maxillary first premolars with different degrees of penetrating wedge-shaped defects under the action of vertical and lateral jaw forces.The experiment was carried out in two parts.The first part: the establishment of three-dimensional finite element models of maxillary first premolars with different degrees of penetrating wedge-shaped defects.According to the degree of wedge-shaped defects,they are divided into three groups: Group A: the wedge-shaped defect does not exceed the adjacent buccal axis angle.Take 1/3 of the crown width as an example;Group B: The wedge-shaped defect spans the adjacent buccal axis angle and does not reach 1/2 of the mesial and distal wall.Take 2/3 of the crown width as an example;Group C: The wedge-shaped defect spans more than 1 /2 mesio-distal adjacent wall,taking 1/2 crown thickness as an example;the second part: on the basis of the previous part,different restoration methods are used to simulate the oral force form for vertical and lateral jaw force loading,total 26 working conditions,and finally record and analyze the equivalent stress,maximum principal stress and stress distribution inside the tooth and restoration in each working condition,and record the equivalent stress peak value of the tooth and restoration(Von-Mises peak sress,v M)And the maximum principal stress peak(max principle peak elastic strain,max)and compare and analyze.Results:1.A total of 13 sets of three-dimensional finite element models were established according to the degree of wedge-shaped defect and different repair methods;2.When the jaw force is loaded,the Von mises stress and maximum principal stress distribution cloud diagrams of the three groups of A1,B1,C1 are basically the same: the stress peak concentration area appears at the tip of the wedge-shaped defect,and the crown surface and the inside of the tooth root The force is uniform and the stress value is low;3.The scope of the wedge-shaped defect has a certain influence on the force of the remaining tooth tissue,that is,under the load of jaw force,the Von mises stress peak and the maximum principal stress peak of the remaining dentin in groups A1,B1,and C1 are all higher than those of the blank control group.Group,and O<A1<B1<C1 group,that is,as the degree of wedge-shaped defect increases,the peak stress at the tip of the defect increases sharply;4.When the degree of wedge-shaped defect is greater than 1/3 of the crown width and does not reach the adjacent buccal axis angle,the Von mise stress peak and the maximum principal stress peak of the remaining dentin in group A2 are smaller than those in groups A3 and A4,and the stress distribution on the surface of the tooth and enamel is even And the value is small;5.When the degree of wedge-shaped defect exceeds the adjacent buccal axis angle and does not reach 1/2 of the mesio-distal adjacent wall,the Von mise stress peak and the maximum principal stress peak of the remaining dentin of group B2 are both smaller than those of groups B3 and B4,and the overhanging tooth is removed In tissue(group B3),the peak stress of the remaining tooth is larger than that in group B2 and the stress is mainly concentrated on the tooth neck;6.When the degree of wedge-shaped defect reaches 1/2 the mesial and distal adjacent wall,the Von mise stress peak and the maximum principal stress peak of the remaining dentin in group C4 are both smaller than those in groups C3 and C4,and the stress on the crown surface and the remaining tooth is evenly distributed.After the overhang was removed(group C3),the stress was mainly concentrated in the full crown and jaw force loading area and the weak tooth neck.Conclusion:1.After a wedge-shaped defect occurs in the maxillary first premolar,the stress is mainly concentrated at the tip of the wedge-shaped defect area,and as the degree of the defect increases,the stress in the defect area increases sharply;2.When the range of the penetrating wedge-shaped defect does not exceed the adjacent buccal axis angle,the overall stress distribution in group A2 is uniform,and the peak stress peak of the defect tip decreases sharply.It is recommended to choose fiber post and resin filling to repair;3.When the range of the penetrating wedge-shaped defect exceeds the adjacent buccal axis angle but does not reach 1/2 of the mesio-distal adjacent wall,the overall stress distribution of group B2 is uniform and the peak stress peak of the defect tip decreases sharply.It is recommended to choose fiber post and all-ceramic crown to repair;4.When the piercing wedge-shaped defect reaches 1/2 the mesial and far adjacent wall,the overall stress distribution in group C4 is uniform and the peak stress at the tip of the defect decreases sharply,prompting the clinical choice of metal post-core crown repair;5.For fiber post and all-ceramic crown restoration,retaining the overhanging tooth tissue can reduce the internal stress peak of the remaining dentin,suggesting that the wedge-shaped defected maxillary overhanging tooth tissue should be preserved as much as possible in the clinical tooth preparation. |
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