| Objective:Based on the three-dimensional finite element analysis,we evaluated the effect on the stress distribution of different restoration materials and tooth margin preparation on the remaining tooth tissue of mandibular first molars after root canal treatment after mesial-occlusal-distal(MOD)cavity onlay restoration.The influence of different restoration materials and tooth edge preparation formed on the stress of the remaining tooth tissue and provided a mechanical basis for the selection of onlay edge preparation methods and restoration materials in clinical work.Methods:A female patient with complete dentition and standard occlusal relationship was selected.Used cone beam CT to scan,and then imported the scanned file into Mimics 19.0 software in DICOM format,readed the tomographic image data,completed the file format conversion and modeled in Mimics 19.0 software,and Geomagic wrap software was used to remove the Sharp edges and corners on the surface to made the surface smoother.Then,Unigraghics NX software was used to cut the model,and the solid model of the tooth preparation of the first mandibular molar on the left was obtained,which was meshed with Ansys software.MOD type onlays with different edge designs were produced.Group A was "MOD hole type+functional tip wrapping+non-functional tip flat smoothing",and group B was "MOD hole type+functional tip and non-functional tip both wrapped Winding",Group C was "MOD hole type+functional tip and non-functional tip were evenly grounded".The onlays were repaired with lithium disilicate glass ceramics(IPS e.max press),resin infiltrated matrix glass ceramics(Vita Enamic)and leucite-reinforced glass ceramics(IPS Empress).Under static loading,a vertical force of 200 N and a 45° oblique lingual force were applied,respectively.Under these two loading methods,the restorations,dental tissues and adhesives of the onlays with three edge designs were analyzed.The magnitude and distribution of the maximum principal stress and the Von Mises stress of the layer.Results:1.From the perspective of the restoration,under vertical loading,under the same restoration material,the Von Mises stress values of the three groups of onlays were not much different;the maximum principal stress values were also not much different,but the C group onlays are slightly smaller than group A,which is slightly smaller than group B.Under the same repair form,the stress value of Vita Enamic was generally smaller than that of IPS Empress and IPS e.max press.Under oblique loads,the Von Mises stress values of the three groups of onlays were not much different,group C was slightly larger than group B and greater than group A;the maximum principal stress valued of the three groups,group C were greater than group A and group B,group A was not much different from the maximum principal stress value of group B.Under the same repair form,the maximum principal stress value of IPS e.max press was slightly smaller than that of Vita Enamic and IPS Empress.Under vertical loading and oblique loading,the stress areas of the three groups of restoration layers Von Mises stress and maximum principal stress were all located at the loading point.2.For the remaining tooth tissue,when loaded vertically and when the same restoration material was used for restoration,the Von Mises stress that values of the three groups of onlays were not much different,and group C was slightly smaller than group A and B;The maximum principal stress value was also little difference,but the onlay in group A was slightly smaller than that in group C and smaller than in group B;when loaded vertically,the stress of the Von Mises stress of the remaining teeth of the three groups were distributed at the 1/3 of the mesial root and buccal root,and the largest dominant the stress was mainly distributed at the root bifurcation,and there was no obvious stress concentration in the tooth tissue of the crown.Under the oblique load,the Von Mises stress values of the three groups of onlays,which are not much different when the same repair material was repaired.The equivalent stress of the A group was slightly smaller than that of the B and C groups;the maximum principal stress value was also not much different.Group C was slightly smaller than Group A and Group B.When the load was obliquely loaded,the stresses of the maximum principal stress of the three groups and the Von Mises stress of the remaining teeth were all distributed on the buccal tooth neck.3.From the perspective of the adhesive layer,The maximum value of the maximum principal stress appeared at the floor of the pulp chamber and the buccal edge of the pulp chamber wall of the IPS e.max press onlay(group C),and the maximum Von Mises stress appeared in the IPS e.max press onlay(group B)at the buccal margin of the pulp chamber floor and pulp chamber wall and the loading point area of the adhesive layer.Under the vertical load and the oblique load,the maximum principal stress of the three edge designs of the onlay from large to small was:IPS e.max press was greater than IPS Empress and Vita Enamic,and there was little difference between different materials.Under the two loads,the maximum principal stress of the adhesive layer was mainly distributed in the pulp chamber floor and the buccal edge of the pulp chamber wall.4.The Von Mises stress and the maximum principal stress of the restoration were larger than those under vertical loading.5.The greater the elastic modulus of the onlay repair material,the Von Mises force value of dentin and adhesive also increased gradually,and the Von Mises force value of the restoration layer also increased gradually,the maximum principal stress value of the cement also increased gradually,and the maximum principal stress value of the restoration and the dentin layer did not change with the increase of the elastic modulus of the restoration material.Conclusion:1.This experiment uses cone beam CT scan,Mimics 19.0 conversion file format,Geomagic wrap to remove sharp edges and corners on the surface,and smooth the surface.Unigraghics NX software model segmentation and finite element software ansys are used for analysis to establish the mandibular first molar.The onlay finite element model of the MOD hole type provides a reference for future modeling.2.In terms of restorative form,in clinical work,the buccal wrapping lingual side unwrapped onlay can be selected,which can make the remaining dental tissue and restoration relatively less stressed.3.In terms of restoration materials,among the three materials of IPS e.max press,IPS Empress,and Vita Enamic,it is recommended to use Vita Enamic onlays to repair MOD holes in clinical work,this material can make the remaining dental tissue relatively less stressed.4.The prosthesis is subjected to large lateral forces,so when onlays are used to repair MOD cavity tooth defects,in the process of clinical trial fitting of the prosthesis,we should try to reduce the occlusal contact points on the side and reduce occlusal force on the medial side of the mouth.5.From the point of view of the prosthesis falling off after the adhesive is damaged,it is better to choose the buccal wrapping lingual non-wrap onlay and Vita Enamic material. |
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