| Objective: To establish 3-D finite element models of three-unit mandibular posterior all-ceramic fixed partial dentures with different connector design; to analyze stress distribution of three-unit mandibular posterior all-ceramic fixed partial dentures with different connector design under the maximum bite force; to predict the fatigue lifetime of three-unit mandibular posterior all-ceramic fixed partial dentures with different connector design, and to investigate the influence of different connector design to fatigue lifetime of all-ceramic fixed partial dentures.Methods: 3DSS combined with Geomagic 9.0 and MSC.MARC 2003 was used to establish 3-D finite element models of three-unit mandibular posterior all-ceramic fixed partial dentures with different connector design. MSC.MARC 2003 was then used to analyze the stress distribution of all-ceramic fixed partial dentures under the maximum bite force. The fatigue lifetime of three-unit mandibular posterior all-ceramic fixed partial dentures with different connector was predicted by means of the MSC.FATIGUE software. Result:①3-D finite element models of three-unit mandibular posterior all-ceramic fixed partial dentures with different connector design(section areas are 2×2,2.5×2.5,3×3,3.5×3.5,4×4mm2 respectively)was constructed. The model has favorable comparability.②Under the effect of loading, Von Mises peak stresses are in the connector location, and the maximum peak stresses are in gingival face of connector.③Under the effect of maximum bite force, the maximum principal peak stresses in the Emp2-Eris system all-ceramic bridges are 86.1, 83.18, 82.39, 81.83, 80.97MPa; the maximum principal peak stresses in the TZP-CerS are 116.29, 114.2, 111.2, 108.0, 104.0MPa; the maximum principal peak stresses in the Inc-VM7 are 126.3, 122.2, 118.8, 113.9, 111.1MPa. The analysis of stress distribution in the loaded ceramic bridges showed that the connector area between the bridge abutment and the pontic component is the critical part of the dental restoration. As the Yang's modulus of the core ceramics increase, the peak stress of all-ceramic fixed partial dentures increases. With the same all-ceramic material, as the connector dimensions increase, the peak stress of all-ceramic fixed partial dentures decreases.④Under the effect of daily masticatory force, stress distribution is same as it under the effect of maximum bite force, but the stress values are smaller than it under the effect of maximum bite force.⑤Under the cyclic fatigue loading, fatigue lifetime in the Emp2-Eris system all-ceramic bridges at 5% failure probability are 6.72,8.16,9.22,9.40,9.57 years, at 1% failure probability 5.45,6.98,7.77,7.80,7.81 years; in the TZP-CerS system all-ceramic bridges at 5% failure probability are 26.39,30.32,32.52,34.14,34.95 years,at 1% failure probability 21.18,23.50,26.04,28.47,29.17 years; in the Inc-VM7 system all-ceramic bridges at 5% failure probability are 25.00,28.01,29.51,30.44,30.90 years,at 1% failure probability 19.68,21.64,22.80,23.03,23.26 years. Under the cyclic fatigue loading, as the connector dimensions with the same all-ceramic material increase, the fatigue lifetime of all-ceramic fixed partial dentures increases. With the same connector dimension and failure probability, the fatigue lifetime of the three all-ceramic bridges is like this: TZP-CerS>Inc-VM7>Emp2-Eris.Conclusion:①3DSS combined with Geomagic 9.0 and MSC.MARC 2003 was used to establish 3-D finite element models of three-unit mandibular posterior all-ceramic fixed partial dentures with different connector design. By using this easy convenient method, 3-D finite element models can be constructed accurately and quickly.②All-ceramic bridges fracture mainly in the connector area, so the connector area is the critical and weak part of all-ceramic bridges.③The peak stress of all teams have greater allowable stress values than the maximum principal stresses evaluated at 600N loading in the simulation. It may not be the main reason of the failure of all-ceramic bridges to load of the maximum bite force in the short time.④It can be inferred that Emp2-Eris system is not suitable to make posterior all-ceramic bridges, and the connector dimension should be at least 2.5×2.5mm2 when Inc-VM7 and TZP-CerS system is used to make three-unit posterior all-ceramic bridges. How to design the connector dimension should be taken in further study.
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