3-Dimensional Finite Element Analysis Of Mandibular Bilateral Distal-Extension Removable Partial Denture With Intracoronal Attachment

The distal-extension absence is frequent in denture defect, and it is always difficult to restore it. The RPI system has been the mainly retention technique. Now, the precision attachment, which is widely used in Europe and America, especially in distal-extension removable partial denture, gives the abutment more protection, increases the retention and stabilization, decreases the alveolar absorbability, eliminates the clasp exposure, and improves the appearance et al. The occlusal forces of the distal-extension removable partial denture are mainly on both the abutment and the alveolar of edentulous space. It is commonly considered, that increasing the number of the abutments could make the occlusal forces disperse and even, decrease the press on alveolar, and diminish the alveolar absorbability. But in using of the removable partial denture with the precision attachment, more tooth tissue must be abraded for increasing the abutments, and it always causes gum irritated and increases the expenses. This paper focus on stress distribution of the removable partial denture, retained with McCollum attachment in three different numbers of the splinted abutments. The method we used is 3-dimensional finite element analysis (3DFEA).Kennedy I defect model was made with one adult mandibula specimen, a removable partial denture was made on the model. The mandible with restoration was scanned using helix computer tomography, and then we got the data of the margin of the mandible with restoration in digital instrument. We wrote ANSYS program files using these data. Three models were created, meshed, analyzed in computer. The results is below: the distal abutment has disto-clination, there was a stress concentration area in the distal area of the distal abutment neck, when 300 Newton each false teeth was loaded on occlusal surface, the maximum of the stress on root and periodontal membrane of the distal abutment, dense alveolar and spongiosa alveolar around the distal abutment and mucous membrane under the4base is 14.215MPa, 2.153MPa, 15.925MPa, 3.277MPa and 0.667MPa in two abutments; in three abutments, the maximum of the stress on the above five positions is 18.402MPa, 2.091MPa, 16.413MPa, 2.876MPa and 0.665MPa; in one abutments, the maximum of the stress on the above five positions is 16.006MPa, 2.181MPa, 13.449MPa, 2.794MPa and 0.677 MPa. When 100 Newton each false teeth was loaded on occlusal surface(one side is on buccocclussal, the other side on linguo-occlusal), at working side, the maximum of the stress on the above five positions is 15.477MPa, 2.351MPa, 14.516MPa, 1.482MPa and 0.466MPa in one abutments; 14.551MPa, 2.424MPa, 12.418MPa, 1.680MPa and 0.545MPa in two abutments; 15.843MPa, 2.500MPa, 13.817MPa, 2.091MPa and 0.55IMPa in three abutments. At balancing side, the maximum of the stress on the above five positions is 16.575MPa, 30194MPa, 16.126MPa, 1.731MPa and 0.541MPa in one abutments; 15.038MPa, 3.016MPa, 12.308MPa, 1.537MPa and 0.565MPa in two abutments; 15.364MPa, 3.171MPa, 12.421MPa, 2.169MPa and 0.590MPa in three abutments.Conclusively, while designing the attachment-retained mandibula bilateral distal extension removable partial denture, the splinted-abutment span should not be too long. The number selection of abutments should be decided by different situations of the periodontal condition of distal abutment and the edentulous alveolar crest.