气孔缺陷对磨牙双层全瓷冠力学性能影响的有限元研究

目的研究饰瓷气孔缺陷对磨牙二硅酸锂（LDG）及氧化锆（Y-TZP）双层全瓷冠力学性能的影响。 方法制作上颌第一磨牙LDG双层全瓷冠，使用显微CT扫描并三维重建分析饰瓷内气孔缺陷的尺寸及分布。分别构建上颌第一磨牙LDG及Y-TZP双层全瓷冠三维有限元模型，根据CT数据于饰瓷内添加气孔缺陷并进行加载；A组为对颌牙以200 N加载于牙冠模拟牙尖交错位时的垂直向受力；B组为以200 N与牙长轴呈45°加载于牙冠近、远中舌尖颊斜面，模拟侧方受力；C组为压头垂直位移1 mm加载于牙冠中央窝，模拟体外实验中的加载；计算最大主应力并分析气孔缺陷对其数值的影响。 结果LDG与Y-TZP在各载荷条件下的应力分布近似；垂直向加载时牙尖接触区应力集中，最大应力分别为51.683、50.084 MPa，存在气孔时，应力集中于牙尖接触应力区的气孔缺陷，最大应力上升至290.72、285.92 MPa；45°斜向加载时拉应力集中于核瓷颈部，气孔缺陷无应力集中，最大应力不变；体外加载时中央窝、沟及加载点应力集中，最大应力为107.3、125.41 MPa，存在气孔时，应力集中于拉应力区的气孔缺陷，最大应力上升至359.93、322.39 MPa。 结论饰瓷气孔缺陷对双层全瓷冠应力分布的影响与受载方式有关，位于拉应力集中区的气孔缺陷是导致冠失效的因素。

Influence of veneer pore defects on fracture behavior of bilayered all-ceramic crowns: a finite element analysis

ObjectiveTo evaluate the influence of veneer pore defects on fracture behavior of bilayered lithium dislicate glass-ceramic (LDG) and zirconia (Y-TZP) molar crowns. MethodsBilayered lithium dislicate glass-ceramic maxillary first molar crown was fabricated and scanned by micro CT to reconstruct the size and distribution of pore defects in veneering porcelain. After importing the pores in veneer according to the CT data, finite element analysis (FEA) models of bilayered LDG and Y-TZP crowns were constructed for mechanics simulation. For Group A, 200 N of Static loads were applied vertically to the occlusal surfaces of models to simulate the intercusping bite force. For Group B, 200 N loads were applied to functional inclinations at a 45° angle to imitate masticatory force. For Group C, indenter with 1 mm of vertical displacement was imposed on models to simulate the condition of in-vitro test. Maximum principle stress was calculated and analyzed accordingly. ResultsLDG and Y-TZP had similar stress distribution under the same loading protocol. For intercusping bite, stress was concentrated in the contact region and the maximum tensile stress was 51.683 MPa and 50.084 MPa, respectively. While the maximum stress raised to 290.72 MPa and 285.92 MPa when pore defects were existed at cusp contact area. For oblique loading, pore defects were free from stress concentration. Under displacement loading, pores were detrimental to veneer integrity only in regions of tensile stress located at grooves, fissures as well as contact region, the maximum stress was concentrated in pores and raised from 107.3 MPa and 125.41 MPa to 359.93 MPa and 322.39 MPa. ConclusionsThe influence of veneer pore defects was related to loading pattern and the pores located at tensile stress area of veneering porcelain would jeopardize the structure and mechanical integrity of bilayered all-ceramic crowns.