Three-Dimensional Finite Element Stress Analysis Of Mandibular Unilateral Distal-Extension With Extra Coronal Precision Attachment

The denture defect is the common disease of the prosthodontics dentistry, and the distal-extension absence is frequent in denture defect. The denture defect can influence the masticatory function and pronunciation; cause the periodontal diseases, temporomandibular disorders. Denture retained by attachment is the third kind of denture clinically besides removable partial denture and telescope denture, which is widely used in distal-extension removable partial denture. It has a biology principle and designs vivid, can increase the retention and the stabilization, give the abutment more protection, decrease the alveolar absorbability, eliminate the clasp exposure, and improve the appearance. The study of the attachment is one of the important topics in prosthodontics dentistry.Considering the Kennedy II defect, from alveolar bone and the complete dentition CT images, a three-dimensional nonlinear finite element model of mandibular unilateral distal-extension with extra coronal precision attachment was established. The model also includes the porcelain crown and periodontal membrane. The contact elements are used between the denture and alveolar bone. This study focuses on the stress distribution of the periodontal tissue with the different number of abutments, the different loss of the periodontal tissue and the different loading conditions.The result is that, with the full periodontal tissue, there is a stress concentration area in the distal area of the distal abutment neck. The stress in the second premolar and periodontal tissue decreased obviously as the second abutment was added. However, the stress difference was unapparent as the third abutment was added. Considering various facts, the attachment with two abutments was suggested to be used. With the decrease of the periodontal tissue, the stress in the periodontal tissue of the second premolar increased, however the stress in the tooth changed slightly. The stress in the periodontal tissue of the second premolar decreased effectively when the third abutment was added, as the tooth root was sorbed by 50%. In this situation, the extra coronal precision attachment can also be used. The stress in the abutments and the periodontal tissue increased when the ligual-buccal oblique force and the buccal-ligual oblique force are loaded. When the ligual-buccal oblique force is loaded, the stresses are maximum, however when the veritical force is loaded, the stresses are minimum. So the stress distribution in the periodontal tissue is closely related with the direction of the occlusion force. The oblique force, especially the ligual-buccal oblique force should be avoided.