口腔冠修复模型构建及有限元分析应用

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烤瓷贴面氧化锆牙冠残余应力的粘弹性有限元分析

Viscoelastic finite element analysis of residual stresses in porcelain-veneered zirconia dental crowns.

Kim, Jeongho et al. “Viscoelastic finite element analysis of residual stresses in porcelain-veneered zirconia dental crowns.” Journal of the mechanical behavior of biomedical materials vol. 82 (2018): 202-209. doi:10.1016/j.jmbbm.2018.03.020

Abstract

The main problem of porcelain-veneered zirconia (PVZ) dental restorations is chipping and delamination of veneering porcelain owing to the development of deleterious residual stresses during the cooling phase of veneer firing. The aim of this study is to elucidate the effects of cooling rate, thermal contraction coefficient and elastic modulus on residual stresses developed in PVZ dental crowns using viscoelastic finite element methods (VFEM). A three-dimensional VFEM model has been developed to predict residual stresses in PVZ structures using ABAQUS finite element software and user subroutines. First, the newly established model was validated with experimentally measured residual stress profiles using Vickers indentation on flat PVZ specimens. An excellent agreement between the model prediction and experimental data was found. Then, the model was used to predict residual stresses in more complex anatomically-correct crown systems. Two PVZ crown systems with different thermal contraction coefficients and porcelain moduli were studied: VM9/Y-TZP and LAVA/Y-TZP. A sequential dual-step finite element analysis was performed: heat transfer analysis and viscoelastic stress analysis. Controlled and bench convection cooling rates were simulated by applying different convective heat transfer coefficients 1.7E-5 W/mm(2) °C (controlled cooling) and 0.6E-4 W/mm(2) °C (bench cooling) on the crown surfaces exposed to the air. Rigorous viscoelastic finite element analysis revealed that controlled cooling results in lower maximum stresses in both veneer and core layers for the two PVZ systems relative to bench cooling. Better compatibility of thermal contraction coefficients between porcelain and zirconia and a lower porcelain modulus reduce residual stresses in both layers.

摘要瓷贴面氧化锆（PVZ）牙科修复体的主要问题是由于在贴面烧制的冷却阶段产生有害的残余应力而导致贴面瓷的碎裂和分层。本研究的目的是阐明冷却速率，热收缩系数和弹性模量对使用粘弹性有限元方法（VFEM）在PVZ牙冠中产生的残余应力的影响。已经开发了三维VFEM模型来使用ABAQUS有限元软件和用户子程序来预测PVZ结构中的残余应力。首先，使用维氏压痕在平坦PVZ试样上通过实验测量的残余应力分布验证新建立的模型。发现模型预测和实验数据之间的极好一致性。然后，该模型用于预测更复杂的解剖学正确的冠系统中的残余应力。研究了两种具有不同热收缩系数和瓷模量的PVZ冠系统：VM9/Y-TZP和LAVA/Y-TZP。进行顺序双步有限元分析：传热分析和粘弹性应力分析。通过应用不同的对流传热系数1.7E-5模拟受控和台式对流冷却速率 W/mm（2）℃（控制冷却）和0.6E-4 暴露在空气中的冠面上的W/mm（2）℃（台式冷却）。严格的粘弹性有限元分析表明，控制冷却导致较低的最大应力在单板和核心层的两个PVZ系统相对于工作台冷却。瓷和氧化锆之间的热收缩系数的更好兼容性和较低的瓷模量降低了两层中的残余应力。