| Optimization design and lifetime prediction has always been the main topic in the field of prosthodontics. With respect to single factor, some deterministic computational methods (such as the measurement of rapture limit by testing standard test block) are presented in the former research. However, the failure of oral prosthesis is determined by uncertain factors (such as oral environment, cyclic biting force, shape and characteristic of certain material). Furthermore, it is a random and probabilistic incident. The theory of reliability analysis is a systematic method, which is based on the probability statistics and numerical calculation. It has already been applied in the field of architecture, electronic fields, aeronautics and astronautics, and so on. With respect to the uncertain nature of the factors in oral environment, to apply the theory of reliability analysis in the optimization design and life-time prediction of oral prosthesis will make the analysis more close to clinical practice.All-ceramic prosthesis exhibit outstanding esthetics, the nature of translucency, age resistance and wear resistance and excellent biocompatibility. With the improvement of aesthetic requirement, more and more people choose all-ceramic prosthesis. However due to the cyclic chewing, all-ceramic prosthesis cannot exhibit a long-term effect in the clinical practice.Therefore, to construct reliability analysis model of all-ceramic crowns with respect to the randomness of physical parameters and loading state. To make a probe study in the fatigue reliability analysis by using stress-strength inference theory; To explore a way for the further study of mechanical strength in the study of reliability analysis, and to lay a foundation for the application of reliability analysis in other oral prosthesis.To construct a reliability analysis model of mandible first molar all-ceramic crown by using reverse techniques combined with software such as Geomagic Studio, CATIA V5 and ALGOR V19. To determine the part which is more prone to have fracture and exfoliation and safety factor of every node with the aid of Fatigue Wizard analysis module. To acquire some random parameters in the reliability analysis (such as load spectrum of routine biting force, S-N curve of Shofu Vintage Porcelain, fatigue limit curve of Shofu Vintage Porcelain) by reviewing literatures and probability statistics. In this study, to calculate the reliability by using stress-strength inference theory based on normal-normal distribution probabilistic model. To summary the law of the changes of fatigue limits with respect to time, and make an analysis of its mechanism. The results are as follows:1. It is an accurate and safe way to acquire point clouds file, which has high resolution and similar external physical characteristic of first molar. The solid model constructed by CATIA V5 is with good characteristics, distinct structures and good geometric similarity, which more get close to clinical practice and lay a basis for the further study of reliability analysis.2. To construct a three-dimensional finite element model with 119924 nodes and 184986 cells after meshing.3. Static analysis shows that loading surfaces are prone to have exfoliation and fracture. The value of maximal principle stress is 32.25MPa. It also means that with the cyclic biting force the loading surfaces (occlusal surfaces), and stress concentration also takes on in the mesio-buccal cervical parts.4. The minimum safety factor is 1.41, which can be acquired by the Fatigue Wizard module of ALGOR, and to set predicted lifetime (10E+7) in advance; to get 200 nodes which have the lowest lifetime and the minimum safety factor. It can be concluded that 60 nodes have the lifetime under 10E+7. The node 753 have the minimum safety factor, and it is value without correction, Goodman correction value are respectively 2.05,1.41。5. Based on the S-N curve of Shofu Vintage porcelain, the formula of stress-life curve is ln (load) =ln (684.056)-0.041*lnN through the curve fitting. Based on fatigue limit curve and Hertzian contact theory, the 95% confidence interval of fatigue limit strength of 1 year, 5 years, 10 years, 15 years, 20 years are respectively 46.941MPa～58.886MPa, 45.021MPa～56.619MPa, 44.191 MPa～55.629MPa, 43.726MPa～55.096MPa, 43.443MPa～54.657MPa.6. Reliability index of the fatigue limit strength of all-ceramic crown in 1 year, 5 years, 10 years, 15 years, 20 years are respectively 2.29, 2.06, 1.96, 1.91, 1.87; Corresponding reliability are respectively 98.89%, 98.03%, 97.50%, 97.13%, 96.93%. The fatigue limit strength of porcelain and all-ceramic crown decreases with respect to the change of time, but it maintains a high level somehow.To conclude based on results: 1. To construct a reliability analysis model of mandible first molar all-ceramic crown by using reverse techniques, 3DSS laser scanning system, combined with software such as Geomagic Studio, CATIA V5 and ALGOR V19. To determine the part which is more prone to have fracture and exfoliation and safety factor of every node with the aid of Fatigue Wizard fatigue analysis module under cyclic routine biting force. The results show that the design can fulfill the clinical requirements, but there are still some dangerous parts in all-ceramic crown of mandible first molar. It indicates that the loading surfaces are prone to have exfoliation and fracture. To seek a novel way for the further study of mechanical strength in reliability analysis and lay a basis for the use of reliability analysis in other oral prosthesis.2.Through the static and analysis of alternated load and fatigue resistance strength, to calculate the fatigue reliability of all-ceramic crown by stress-strength inference theory in mechanical and structural field. The fatigue limit strength of porcelain and all-ceramic crown decrease with respect to the change of time, but it maintains a high level somehow. To apply the theory of reliability based on the probability theory and numerical statistics in the prosthodontics. It is a probe study and may explore a new way for the application of reliability analysis in other prosthesis.
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