Influence Of Supplementary Retention Form For Stress Distribution On Crown Preparation

caries, bruxism and wear are not infrequent. The retention of such teeth has always been a nodus for restorative dentists in treating fixed prosthodontic. The research in the field of biomedical faces a specific problem due to the fact that the research on live subjects is restricted by the great expense and the doubt in ethnics. To reduce the costs and risks involved in live experiments, building virtual models to process emulational calculation becomes quite significant. Finite Element Method is commonly used in the mechanical analysis. It evaluates various factors and guides the practice by doing numerical calculation on the 3D finite element model, which is got in reconstruction of the computer. Nowadays, Finite Element Analysis Method has been widely used in dental biomechanics.In this study, a 3D-FEA model of mandibular first molar crown and corresponding preparation with lower occlusogingival distance are constructed by using Micro-CT technology combined with the Mimics, Geomagic, Pro/E and ABAQUS software. Preliminary analysis is carried out and the validation of the model has been proved. Then modify the model's parameters on this basic and we get several kinds of 3D-FEA models of mandibular molar crown and corresponding preparation with 3 kind of common supplementary retention forms. We get the models we need by changing the length of each retention form. By adding a load of normal chewing pressure to each model, analyzing the stress and strain distributions by using the ABAQUS software, observing the strains associated with von Mises equivalent stress at three different directions, such as in parallel with the tooth long axis (vertical), at the angle of 45o partial buccal (buccal oblique) and at the angle of 45o partial tongue (tongue oblique), we draw the conclusions as follows:1. The method used to construct the models is convenient, fast and effective. The softwares used in the experiment are efficient and easy to operate. And the exactness and accuracy of the constructed model can meet the needs of biomechanical analysis.2. As for crown preparation with groove retention form, stress distribution on all the three models is almost consistent. It is similar with the crown model. Average maximum von Mises equivalent stress in different directions is decreasing with the increase of groove's length. The 2.5 mm-long groove retention form is better than the other two models.3. As for crown preparation with pin hole retention form, stress distribution on all the three models is almost consistent. Unlike the crown preparation, there is a stress concentration region at the bottom of pin hole crown preparation. Stress distribution on the 2mm-deep hole crown preparation is better than the other two models.4. As for crown preparation with inlay retention form, stress distribution on all the three models is almost consistent. There is a stress concentration region at the bottom of inlay crown preparation. As for crown preparation with inlay retention form, average maximum von Mises equivalent stress in different directions is decreasing with the increase of inlay's depth. Stress distribution on the 3mm-deep inlay crown preparation is better than the other two models.5. Among the three kinds of model analysed in this experiment, stress distribution on the crown preparation with groove retention form is the best. So this form is recommended in clinical design for molar tooth with lower occlusogingival distance .