Optimum Design And Lifetime Prediction Of All-ceramic Bridge Based On Probabilistic Reliability Analysis

Bioceramics have been increasingly used in prosthetic dentistry to fabricate a wide variety of restorations. The growing demand for ceramic materials in prosthodontics can be attributed to their enhanced biocompatibility, wear resistance,outstanding mechanical strength and esthetics in comparison with traditional metal-based restorations. However, it cannot achieve a satisfied outcome in the clinical practice when oral prosthesis is under maximal biting force and cyclic normal biting force. The failure of oral ceramic restoration is determined by uncertain factors, and it is a random and probabilistic incident. Structural reliability theory is a systematic method which is based on the probability statistics and numerical calculation, and it has been widely used in the field of engineering and mechanical design. In reliability analysis, the reliability can be calculated with respect to uncertain factors under certain circumstance after the probabilistic distribution of random variables are determined. This study tends to make optimum design and lifetime prediction of all-ceramic bridge based on structural reliability analysis and the optimization design module of ANSYS Workbench, which will lay a foundation of parametric optimization of oral prosthesis. To construct a reliability analysis model of mandible 3-unit all-ceramic bridge by using reverse techniques combined with software such as Geomagic Studio, UG NX 6.0 and ANSYS Workbench. To study the effect of continuous change parameters of all-ceramic bridge (pontic length, connector area, vertical height and bucco-lingual length of connector, gingival and occulsal curvature of connector, Occlusal thickness of retainer, alveolar height of abutment ) to maximum principal stress and maximum total deformation based on the function of bidirectional parameters transmitting of UG NX and ANSYS Workbench. To obtain random parameters in the ultimate strength and fatigue strength reliability analysis and calculate the ultimate strength and fatigue strength reliability based on stress-strength inference theory. To observe the principle of the changes of fatigue limit and fatigue reliability with respect to time and make the optimization design by using the module of GDO based on reliability analysis. The results are summarized as follows:1. The finite element models of mandible 3-unit all-ceramic bridge were constructed by using 3DSS combined with Geomagic Studio. The parametric models were obtained based on self-adapting assembled program of UG NX 6.0. Finite element models with 25924 elements and 14465 nodes were constructed in ANSYS Workbench after Meshing.2. The tangent slope rate of OBJ response curves indicated that the optimal interval of vertical height and bucco-lingual length of connector are H₁≥2.45mm, W₁≥2.16mm, H₂≥1.77mm, and W₂≥1.6mm. The sensitivity of MPS to design variables H₁, W₁, H₂ and W₂ were 12%, 3%, 23%, 62%.3. The tangent slope rate of OBJ response curves indicated that the optimal interval of connector area are S₁≥8.5mm², S₂≥7mm². The sensitivity of MPS to design variables S₁,S₂,P were 46%,34%,20%. 4. The tangent slope rate of OBJ response curves indicated that the optimal interval of vertical height and bucco-lingual length of connector are O₁≤1.18mm, G₁≤1.55mm, O₂≤1.1mm or≥0.25mm, G₂≤1.73mm or≥0.72mm. The sensitivity of MPS to design variables O₁, G₁, O₂ and G₂ were 9%,3%,22%,68%.5. The tangent slope rate of OBJ response curves indicated that the optimal interval of Occlusal thickness of retainer are T₁≤2.3mm, T₂≤2.13mm. The sensitivity of MPS to design variables T₁,T₂ were 76% and 24%.6. The tangent slope rate of OBJ response curves indicated that the optimal intervals of alveolar height of abutment are A₁≤4.5mm, A₂≤6mm. The sensitivity of MPS to design variables T₁,T₂ were 56% and 44%.7. Under maximal biting force, the reliability of Empress-2, In-Ceram Alumina, Zirconia TZP all-ceramic bridge are all 99.99% when the loading area is 25 mm²; The reliability of Empress-2, In-Ceram Alumina, Zirconia TZP all-ceramic bridge are 74.51%,88.30%,99.99% respectively when the loading area is 1 mm².8. Based on the curve fitting of SPSS software, the formula of strength-life curve of Empress-2 is ln (Strength) =ln (684.056)-0.041*lgN; the formula of strength-life curve of In-Ceram Alumina is ln (Strength) =5.995- 0.1896*lgN; the formula of strength-life curve of Zirconia TZP is ln (Strength) = 6.9431-0.0076(lgN)³+0.1012(lgN)²-0.4635lgN.9. Under normal chewing force, reliability of Empress-2 all-ceramic bridge in 1 year, 5 years, 10 years, 15 years, 20 years are respectively 94.30%,82.64%,75.17%,70.54%,67.00%; Reliability of In-Ceram Alumina and Zirconia TZP all-ceramic bridge in 1 year, 5 years, 10 years, 15 years, 20 years are all 99.99%. To assume the predicting reliability of all-ceramic bridge in 1 year, 5 years, 10 years, 15 years, 20 years are respectively 99%,97%,95%,90%,85%, the connector area of In-Ceram Alumina all-ceramic bridge should be designed as: S₁≥17.98mm² and S₂≥13.86mm²; the connector area of Zirconia TZP all-ceramic bridge should be designed as: S₁≥4.15mm² and S₂≥4.11mm²To conclude, according to the effect of MPS and MTD to design variables, pontic length, connector area on molar side, connector area on premolar side are three top key factors; alveolar height of premolar abutment, alveolar height of molar abutment, vertical height and bucco-lingual length of connector on molar side, vertical height and bucco-lingual length of connector on premolar side are secondary factors; Occlusal thickness of premolar and molar retainer are less important factors. Empress-2 is not suitable for all-ceramic bridge. To fulfill the demand of all-ceramic bridge based on reliability theory, the connector area of In-Ceram Alumina all-ceramic bridge should be designed as: S₁≥17.98mm² and S₂≥13.86mm²; the connector area of Zirconia TZP all-ceramic bridge should be designed as: S₁≥4.15mm² and S₂≥4.11mm². Optimization design of all-ceramic bridge based on ANSYS Workbench and probabilistic analysis will lay the foundation for the application of reliability analysis in other oral prosthesis.