Design And Biomechanical Analysis Of Unilateral Distal-extension Removable Partial Dentures Retained By Stress Breaking Attachments

Distal-extension absence is a common dentition defect in clinic,due to the defect located in the terminal position and the lack of abutment teeth,which RPD is also the common method of restore because other methods are limited by maxillary sinus and mandibular never tube.It was easy to produce large non-axial stress on abutment teeth when conducted traditional RPDs by distal plate go down,resulting in damage of abutment teeth and periodontal tissue and the failure of restoration.Denture retained by resilient attachment can reduce injury of supporting tissues with stress absorbing.Split connector played the role of transforming non-axial stress on abutment teeth into axial force with mechanism of stress breaking,which was benefits to keeping healthy of supporting tissue.Combined extracoronal resilient attachment(ERA)with split connector to design the repair method of stress breaking,stress distribution of different loads was determined by three dimension finite element method(3D FEM)after the establishment of three dimension digital models,in this study to find out distribution regularity of stress from the perspective of biomechanics and to explore the feasibility of unilateral distal-extension removable partial dentures retained by stress breaking attachments,aiming at providing foundation for clinical application.Methods:1.Mandibular model of volunteer with individual normal occlusion was prepared to grind 46 ?47and 48 tooth and flat pressing alveolar cavity in order to simulate the right mandibular distal-extension absence,and to design and make denture retained by attachment with stress breaking.2.Data of mandible and teeth from the same volunteer was collected to establish three-dimensional model and mesh generation in reverse engineering software to obtain three-dimensional finite element models of denture retained by attachment of split connector with ERA and ordinary ERA with denture retained by attachment.3.3D finite element model of two groups of attachment was to load axial force respectively and maximum von Mises stress and distribution of abutment teeth,periodontal tissue and free end of alveolar cavity were compared.4.Two groups of attachment was to load non-axial force(buccolingual and mesiodistal),maximum von Mises stress and distributions of supporting tissue including abutment teeth and periodontal tissue under loading different forces stress were compared.Results:1.Dentures retained by attachment with stress breaking for unilateral mandibular distal-extension absence were designed and made.2.Two groups of three-dimensional finite element model of dentures retained by attachment with ERA for repairing unilateral distal-extension absence were set up.Results showed that 473376 nodes and 238800 units were obtained from the ordinary group,while 447567 nodes and 233576 units received from the split connector group,then to perform with preliminary calculation effectively.3.Stress distribution regularity of the two groups model of dentures retained by attachment with ERA under axial loading force were in line with each other.Terminal stress of abutment was mainly on the distal cervical segments and the maximum von Mises stress was 40.236 MPa and 12.056 MPa,respectively which was reduced by range of 233% in the split connector group than the ordinary group.Stress on periodontal ligament of abutment teeth was lower in split connector group.Stress distribution of edentulous alveolar ridge was more uniform in split connector group which mesial part was higher than distance and which was little higher than that in the ordinary group.4.Stress distribution regularity of the two groups model of dentures retained by attachment with ERA under buccolingual loading force were consistent.Terminal stress of abutment was concentration on the distal cervical segments and the maximum von Mises stress was 53.568 MPa and 39.255 MPa,respectively which in the split connector group was lower obviously.Stress on periodontal tissue of abutment teeth mainly distributed on the cervical segment and stress of edentulous alveolar ridge was mainly on the mesial part,which in the split connector group were lower than that in the ordinary group.Stress distribution regularity of mesiodistal loading force on nearly,lingual segments of the two groups was different.Terminal stress of abutment of the ordinary group was focused on the distolingual side with the maximum von Mises stress of 21.323 MPa,while terminal stress of split connector group located mesiolingual cervical segment with the maximum von Mises stress of 17.926 MPa.Stress on periodontal ligament of abutment teeth mainly distributed on the distal segment,the stress distribution uniformity of the split connector group was higher than that of the ordinary group.Alveolar bone of the cervical segment of abutment teeth and mesial alveolar bone of edentulous area was the main distribution area,which in the split connector group was lower than that in the ordinary group.5.Stress of dentures retained by attachment with ERA and split connector and periodontal tissue under non-axial loading force was significantly higher than that under axial loading force,in which the buccolingual loading force was the maximum and the vertical loading force was the minimum.Conclusions1.According to design of dentures retained by attachment with stress breaking for unilateral distal-extension absence,3D finite element model was successfully established.A general modeling method to improve the model of geometric similarity and similarity mechanics,through the preliminary validation analysis to ensure the calculation accuracy.2.It has achieved the effect of stress breaking under axial loading force for dentures retained by attachment with ERA and split connector,which protect abutment teeth,be able to bear much more occlusal force while more occlusal force transferring to the alveolar ridge to reduce burden of the abutment teeth,which contribute to overall promote balance and dispersion occlusal force of the abutment tooth area and edentulous alveolar ridge.3.Dentures retained by attachment with ERA and split connector has passed through mechanism of stress breaking under the non-axial loading force,which received a degree of protection effect for the abutment and periodontal tissue,at the same time the strengthening supporting tissue increased stability of the denture,in which the buccolingual loading force influenced the supporting tissue most.4.Research results suggested that dentures retained by attachment with ERA and split connector showed benign mechanism of stress breaking and benefit to keep health of supporting tissues,which provided appropriate strategy for clinical restoration.