The Optimizing Designs And Mechanics Analyses Of Implants Location For The Edentulous Mandibular Overdenture Which Be Retained By Four Implants And Telescopic Crowns

Objective:To establish a mathematic model of edentulous mandible in which four implants were inserted. The stresses loading and mechanical analyses for different location combined designs of four implants were carried out by the means of three-dimensional finite element,which to simulate the stresses distribution of mandibular implant overdentures that were supported by 4 implants and retained by different locations telescopic crown attachments. The stress distribution on the cortical bone in peri-implants were analyzed qualitatively and compared quantitively; At the same time, the associated applying designs of telescopic crown and bar clasp with regard to the different implants location designs were analyzed, thereby the optimum designs were determined concerning of telescopic crows retentive locations and bar clasp connected modes for four implants supported mandibular overdentures, which providing determinate theory gist and practical applying reference for clinical implanting treatment of edentulous jaws patients.Methods: The DICOM database of edentulous mandible were built by advanced CT scanning the suitable edentulous mandible sample. The modeling software of CATIA were used to manage and analyse on the data of edentulous mandibular CT scanning images of which slice thickness was 1mm. Combining 3-D finite element software of ABAQUS the finite element mandible models which with four standard ITI implants (4.1×10mm) were built. Moreover,four implants were inserted symmetrically into each model. According to different implant locations, I-VII models were established. These models were loaded with vertical and static loading to simulate the stress status of implant overdenture which retained by telescopic crown attachment. Moreover, for the models of I-VII, two mesial implants were attached with bar clasp constrained condition by setting up corresponding parameters,then the models also were loaded by same methods and simulated stress distribution on the cortical bone in peri-implants of the designs in which telescopic crown and bar clasp attachment were applied together. The stress distribution of each model was analyzed qualitatively and compared quantitively. Thereby the optimum designs were determined concerning of implant location and bar clasp connection.Results: According to different implant locations, model of I-VII were built. After mechanical loading test, the result showed that the established models had the qualities of accurate and non-invasive. Moreover, the acquired images, figures and data may be analyzed tautologically. The structure of finite element models had good similarity with real mandible. The models may simulate stress distribution of mandibular overdenture which be supported by 4 implants according to different study purpose. In this study, with respect to every model, a base plate that connected four implant as integer was simulated which was as loading surface. The elastic modulus of loading surface was equal to which of base plane. Moreover,constrained condition may be attached between implants according to experiment design. After applying the vertical static loading of 100N for every model, the stress distribution on the bone around every implant were analyzed by using finite element software. The result showed :①To analyse different implant location,the model VI(3-6 design) showed better stress distribution,and stress status seemed to be uniformity. The models of I(2-4design) and V (3-5design) were secondary. For the rest models, stress distribution seemed to be malconformation. There were great difference between stress values around the bone of peri-implant, especially for the models in which the distance between mesial and distal implant were larger.②The model designs in which telescopic crown and bar clasp attachment were simulated to applied together, in other words the constrained condition of bar clasp were attached between two mesial implants, the stress distribution of 3-6 design and 2-4 design were more equilibrate. For the rest models, the stress values had increasing tendency. With distance increasing between mesial and distal implant, the tendency were more obviously.Conclusion:①The applying of CT scanning and modeling software, it may provide the accurate and compact method for establishing the three dimen- sional finite element models of edentulous mandible with 4 implants. The models can be applied to the correlative study of biomechanics.②For the implant overdenture which be supported by four implants, the designs that inserting implants in the molar areas should be considered, especially for the 3-6 design. Because the stress distribution seemed to be more balanced and reasonable in 3-6design, the 2-4 design and 3-5 design were secondary.③When the distance between the distal and mesial implant was overlong , the stress peak values on the cortical bone around implants were represented increased , especially the mesial region of distal implants and the distal region of mesial implants.④The designs that telescopic crown and bar clasp attachment were applied together should be considered. But the distance between mesial and distal implants should be concerned. Because of adding bar clasp connection, it may be lead to increase stress distribution on the distal and lingual cortical bone around distal implants.