| The retention of oral and maxillofacial prostheses is essential to successful prostheses . So applying attachment to solve the retention of prostheses is the important developing trend of prosthodontics. It is considered the third kind of attachment system afterwards simple attachment and precise attachment because magnetic attachments possess prominent virtue that other mechanical attachments don't have. In recent years, the base of magnetic attachment's development has been established along with appearance of magnetic field's optimizing design and analysis theory and new type of super intensity's magnetic materials as well as the development of laser procedure controlling welded technique. In this study, we established the finite element analysis model of the cup yoke type magnetic attachment in two-dimensional magnetic field on the basis of the progress and analyzed the influence factors of the retentive force and optimized the design of magnetic attachment. According to design results, using screened high performance magnetic materials and laser procedure controlling welded technique, we finally manufactured magnetic attachment series that could provide about 700gf retentive force including Z-2 type (the directly cemented keeper), Z-3 type (the incorporated keeper) and 7.-A type (removable keeper) to meet the clinical requirements and to continue to keep our country's predominance in this domain.1. Establishing the two-dimensional finite element analysis model of the cup yoke type magnetic attachment in magnetic fieldIn this study we established the two-dimensional finite element analysis model of the cup yoke type magnetic attachment in magnetic field through computer to optimize magnetic circuit design by calculating and comparing the maximal retentive force of magnetic attachment of different dimension. This method can save time, labor and material. Meanwhile, it can precisely calculate the distribution of flux to make magnet and soft magnetic alloy reach the best matching and to exert its maximal effect and to realize the maximal retentive force in the minimal volume and the best combination. Compared with traditional fact measure screening method, it notably improves efficiency.Procedure's elements include magnetic material, non-line magnetic material and non-magnetic space factor. Magnetic material is NdFeB magnet, its (BH)max=334~366KJ/m3, Br=1.33~1.38T; soft magnetic alloy is Fe-Cr-Mo system its BS=1.6T, moreover, magnetization curve is initially obtained by experiment method; peripheral space factor drawn up is 4~5 times bigger than magnetic attachment's.In order to evaluate the correctness of procedure, author compared the results that increasing height of magnet and clearance between magnet and keeper influenced retentiveforce by using this procedure to measure with that of fact measure and found that the retentive force was well-distributed and was 10% smaller than that of fact measure. Moreover, the results of procedure calculating method primely reflected the changing trend of retentive force that fact measure obtained. So it was considered that this procedure factually reflected the trend that changing all elements of magnetic attachment influenced retentive force and could be used to optimize design of the cup yoke type magnetic attachment whose retentive force need be corrected, which the calculating formula is: rectify virtue=procedure result X 110%. 2. Optimizing design of the cup yoke type magnetic attachmentBecause the retentive force of magnetic attachment closely correlated with material characteristics and shape of its all parts, author discussed that dimension of all parts influenced on the retentive force by using the two-dimensional finite element analysis model of the cupyoke type magnetic attachment in magnetic field. And the following conclusions was drawn:2.1 Along with increasing the height of magnet, the retentive force submitted slowly increasing trend, when its height was 0.8mm, the retentive force reached peak value. But consid...
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