下颌第一磨牙全瓷冠强度可靠性的三维有限元分析

Analysis of reliability of the strength of all-ceramic crown on mandibular first molar

目的对随机载荷作用下全瓷冠强度的可靠性进行三维有限元分析，探讨不同加载模式对全瓷冠强度可靠性的影响。方法建立用于下颌第一磨牙全瓷冠可靠性分析的三维有限元模型，通过概率统计方法处理获得3～300N区间内的随机载荷，确定3种加载模式：异常[牙合]接触加载：随机载荷分别单独加载于颊尖尖部、颊尖舌斜面和中央窝，加载面积均为0．4mm2；咀嚼[牙合]接触加载：随机载荷加载位置同异常[牙合]接触加载，加载面积为1．5mm2；广泛[牙合]接触加载：随机载荷广泛加载于牙尖交错位时的[牙合]接触面，加载面积为12．6mm2。根据可靠度计算公式计算全瓷冠强度的可靠度。结果异常[牙合]接触加载时，全瓷冠颊尖尖部、颊尖舌斜面、中央窝强度的可靠度分别为97％、99％、100％；咀嚼[牙合]接触加载时，全瓷冠颊尖尖部、颊尖舌斜面、中央窝强度的可靠度分别为99％、100％、100％；广泛[牙合]接触加载时，全瓷冠[牙合]面强度的可靠度为100％。结论随机载荷作用下，早接触、过锐牙尖及咀嚼过硬食物造成的局部小面积集中载荷可显著降低全瓷冠强度的可靠度。

Objective To analyze the reliability of all-ceramic crown on mandibular first molar under randomized biting force, and to explore the failure possibility of all-ceramic crown. Methods Finite element（FE） models of all-ceramic crown on mandibular first molar were established using the Algor FE software. All-ceramic crown was loaded at different occlusal areas and positions with random variables of biting force, and the reliability of all-ceramic crown was analyzed. Results The occlusal contact positions were located on the fossa,inclined surface and dental cusp. When the oeclusal contact area was 0.4 mm2, The reliability of all-ceramic crown on mandibular first molar were 100% （fossa）, 99% （inclined surfacee）, and 97% （cusp） respectively. When the occlusal contact area was 1.5 mm2, the reliabilities of all-ceramic crown on mandibular first molar were 100% （fossa） , 100% （inclined surfacee ）, and 99% （cusp） respectively. When the occlusal contact area was increased to 12. 6 mm2, the reliability of all-ceramic crown was 100%. Conclusions Premature occlusal contact and steep cusp inclination on all-ceramic crown on mandibular first molar will result in stress concentration and the crown will exhibit high failure probabilities. Chewing hard food is another contributing factor to the failure of all-ceramic crowns.