| Objective: To analyze the effect of different restoration methods on the tooth defects after root canal treatment by three dimensional finite element method.A finite element model with only maxillofacial defect and complete four walls was created.Two loading directions were set,vertical and oblique.To investigate the stress size and distribution of the residual tooth tissue and the prosthesis,so as to provide mechanics basis for the repair of dental defects in clinical practice,so as to select an optimal restoration method for clinical practice.Methods: 1.Establish a normal mandibular molar model An isolated third lower left molar with complete shape and no caries was selected as the research object.CBCT scanning and Mimics,Geomagic,Soild Works,Ansys Workbench software were used for modeling,and stress analysis was conducted.2.Six groups of repair mode models were established On the basis of normal mandibular first molar model,six models of direct resin filling(group A),inlay(group B),hyperinlay(group C),reinforcement for maxillary veneer(group D),half crown(group E),and full crown(group F)were established.3.Experimental loading conditions: 3.1 Loading site and force value: Vertical loading: maxillofacial central fossa,proximal and distal marginal crest,proximal and distal buccal tip and buccal plane are five sites,and the force value at each point was 40 N.Oblique loading: there were two points on the buccal inclined plane of the tip of the tongue near and far,and the force value at each point was 50 N,which is 45° with the tooth length axis.3.2 Analysis indexes: the distribution of equivalent stress(VM)and maximum principal stress(S1)of the remaining tooth tissue and the prosthesis.Results: 1.Three-dimensional finite element models of normal mandibular molars and 6 groups of different restoration methods were established.2.Stress distribution results of normal molar: 2.1 Under vertical and oblique loading of enamel,the stress distribution law was similar: The stress of VM was mainly distributed in the loading area.The S1 stress was mainly distributed in and around the loading area and the tooth neck.2.2 Under vertical and oblique loading of dentin,the stress distribution was different: Vertical loading: The VM stress was mainly distributed in the loading area,the mesial surface and the root of the buccal side.The S1 stress was mainly distributed in the tooth neck and pulp chamber floor.Oblique loading: The VM stress was mainly distributed in the middle and upper 2/3 of the root surface of the buccal lingual side and the neck of teeth.The S1 stress was mainly distributed in the middle and upper 2/3 of the buccal root surface.3.6 Stress results of repair methods: 1)Under vertical loading: Enamel VM peak: A > B > E > D > C;S1 peak :A > B > D> E> C.Dentine VM peak: A > D > C > B > E > F;S1 peak: D > C > E > A > B > F.Restoration VM peak: A > B > E> F > D > C;S1 peak:A > B > E> F > C > D.2)Under oblique loading: Enamel VM peak: E > A > B > C> D;S1 peak: A > B > C >E > D.Dentin VM peak: E > D > A > C > B > F;S1 peak: C > E > D > F > A> B.Restoration VM peak: D > E > C> F > B > A;S1 peak: C > B >D > E > F > A.Conclusion: 1.The stress value of resin direct filling and inlays group was higher than that of other groups,so it was not suitable for the restoration of tooth defects after root canal therapy.2.The stress distribution of the maxillary veneer strengthening position was uniform and the force value of the tooth tissue was relatively small.When the root canal needs secondary treatment,it was easier to remove than the onlay,so the maxillary veneer strengthening position was more suitable for clinical repair.3.The stress distribution of the full crown and the semi-crown was similar,and the half crown was more suitable for clinical restoration in terms of preserving residual tooth tissue and periodontium.4.The force distribution in the tooth neck and pulp chamber floor area was relatively concentrated,which should be protected during root canal treatment and tooth preparation. |
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