| Objective: In this study,by establishing a digital models of missing left maxillary lateral incisor tooth,three-dimensional finite element analysis(FEA)was used to analyze the stress of the prosthesis,abutment,periodontal ligament,alveolar bone,adhesive layer and the displacement of abutment teeth and prosthesis during functional and parafunctional movement.In order to provide reference for selection of the ideal retainer position of the all-porcelain single-retainer bonding bridges with the maxillary lateral incisor tooth missing.Methods: Cone Beam Computed Tomography(CBCT)was used in this study,to scan isolated teeth embedded in silicone rubber.The CBCT data were processed by software of Mimics,Solidework,Geomagic Studio and Ansys Workbench to obtain the dentition defect model(including abutment,periodontal ligament and simple alveolar bone)of the left maxillary lateral incisor.According to the position of the retainer(labial or lingual side of the central incisor and labial or lingual side of the canine),four groups of digital models were established.Group A:maxillary central incisor labial veneer single-retainer bonding bridge.Group B:maxillary central incisor lingual wing single-retainer bonding bridge;Group C:maxillary canine veneer single-retainer bonding bridge;Group D: maxillary canine lingual wing single-retainer bonding bridge.Three-dimensional finite element method was used to analyze the digital models.In the case of functional movement(the load was applied at the junction of the lingual incisor 1/3 and the middle 1/3 of the bridge and abutment,30°,50 N or50N loading was applied perpendicular to lingual incisor 1/3)and in the case of parafunctional movement(the load was applied at the junction of the lingual incisor 1/3 and the middle 1/3 of the bridge,30°,50 N or 100 N loading was was applied perpendicular to lingual incisor 1/3).The stress on the prosthesis,abutment,periodontal ligament,alveolar bone,and adhesive layer,and the displacement of abutment and prosthesis in each group were calculated.Results:1 The Von-Mises stress was mainly concentrated at the edge of abutment,guide plane,the connector,the labial side of alveolar bone and periodontal ligament near the neck and the edge of the adhesive.2 Under vertical load,Von-Mises stress of abutment,prosthesis,alveolar bone,periodontal ligament and adhesive in group A,B,C and D were 66.27-327.54 MPa,and the minimum of displacement peak value was 146.33μm.Under vertical load,the stresses of abutment,prosthesis,alveolar bone,periodontal ligament and adhesive were46.94-292.80 MPa.The maximum of displacement peak value is 127.45μm.3 Under the same load and the same movement,the stress ranges of abutment teeth and prosthesis with central incisor as abutment teeth were 58.22-166.13 MPa and112.00-327.54 MPa,the displacement ranges of abutment teeth and prosthesis are68.59-269.86μm.In group with canine as abutment,the stress range of the abutment teeth and the prosthesis was 46.94-98.24 MPa,80.83-204.46 MPa,and the displacement range of the abutment teeth and the prosthesis is 57.46-211.51μm.4 Under the same abutment and the same motion state,the equivalent stress of the abutment teeth in group A was 58.22-97.57 MPa and the equivalent stress of the prosthesis was 149.23-292.80 MPa.The equivalent stress of the abutment in group B was58.40-106.94 MPa and the equivalent stress of the prosthesis was 112.00-223.70 MPa.The equivalent stresses of the abutment teeth in groups C and D were 46.94-98.24 MPa and47.37-87.87 MPa,respectively.The equivalent stress of the cement in group C was23-71 MPa lower than that in group D.Under vertical loading,the equivalent stress of the abutment and prosthesis in group C was not more than 20 MPa higher than group D.The equivalent stress of the abutment and prosthesis in group C was similar to that in group D.Under vertical loading,the equivalent stress of the abutment and prosthesis in group C was not more than 20 MPa higher than group D.5 During functional movement,the equivalent stress of abutments ranged from 46.94 MPa to 92.15 MPa,the equivalent stress of restorations ranged from 80.83 MPa to159.92 MPa,and the maximum stress of adhesives ranged from 35.54 MPa to 99.86 MPa.The displacement of abutment and restoration was 180.03μm and 207.29μm,respectively.Under the parafunctional movement,the stress range of the abutment teeth was 77.84-166.13 MPa,the stress range of the prosthesis was 156.71-327.54 MPa,and the stress range of the adhesive was 63.69-198.72 MPa.The peak value of displacement of the abutment teeth and the prosthesis was 190.80μm and 269.86μm.Conclusions:1 The edge of abutment,adhesive,and the connector of the restoration are the weak links.Attention should be paid to avoid sharp line angles and ensure the strength of the connector.2 For patients with maxillofacial parafunction,resin-bonded bridges should be carefully selected.3 The occlusal contact between the prosthesis and the opposing teeth should be avoided during forward extension and lateral occlusion.4 The canine as the abutment is more in accordance with the biomechanical principles than the central incisor.5 The design of labial and lingual retainer has little effect on periodontal supporting tissue,mainly due to the difference in stress between the adhesive and the prosthesis,but the difference is small,and the maximum stress does not reach the fracture strength.IPS e.max Press can be applied to the bonding bridges of anterior teeth,the occlusal relationship of the patient and the actual situation of the abutment should be taken into account in the clinical design.If there is a lack of lingual restoration space or the adjacent teeth need to improve the appearance,the labial veneer retainer design can be selected. |
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