Ausiello Pietro, Ciaramella Stefano, Garcia-Godoy Franklin, Martorelli Massimo, Sorrentino Roberto, Gloria Antonio
School of Dentistry, University of Naples Federico II, Naples, Italy.
Department of Industrial Engineering, Fraunhofer JL IDEAS, University of Naples Federico II, Naples, Italy.
Am J Dent. 2017 Aug;30(4):227-232.
To study the influence of the resin bonding layer thickness and the bulk filling material stiffness in adhesive class II mesio-occlusal-distal (MOD) restorations using numerical finite element analysis (FEA).
Four 3D-FE models of teeth restored with different filling material stiffness and resin bonding layer thickness were built-up and analyzed. The 3D model of a sound lower molar was also analyzed and compared with restored ones. The tooth tissues (enamel, dentin), dental restoration and bolus on the occlusal surface, was divided into 3D solid CTETRA elements with four grid points. The adhesive bonding around the dental restoration was modeled with shell elements. Polymerization shrinkage was simulated with a thermal expansion approach. Mechanical behavior of restored models in terms of stress and displacement distributions, under the combination effects of polymerization shrinkage and occlusal load (600 N), was analyzed. All the materials were assumed to behave as elastic materials throughout the entire deformation.
Numerical results show that the mechanical response of the restored models was very different compared to the sound tooth ones, where the stress was uniformly distributed from enamel to dentin with no critical stress concentration. In the restored models, the highest stress values were detected in the enamel, near the enamel-dentin interface and in the bulk restorative material. Tooth preparations A and B showed lower gradient stresses than corresponding C and D. The value of the vertical displacement components in models A and B were higher than corresponding C and D. The maximum displacement values were mainly located around the groove and were higher by an order of magnitude than the sound models. The results showed better mechanical response with models A and B compared to C and D. It is also evident that resin bonding thickness slightly affected the stress level of the restored teeth.
Class II MOD direct bulk resin composite restorations showed a high susceptibility to damage at the marginal and internal tissue interfaces depending on their own stiffness. The use of resin-based bulk filling materials is not recommended for large class II MOD adhesive restorations due to mechanical behavior failure risk.
运用数值有限元分析（FEA）研究树脂粘结层厚度和大块充填材料刚度对Ⅱ类近中-牙合-远中（MOD）粘结修复体的影响。
构建并分析了四个用不同充填材料刚度和树脂粘结层厚度修复牙齿的三维有限元模型。还分析了一颗完好的下颌磨牙的三维模型，并与修复后的模型进行比较。牙齿组织（釉质、牙本质）、牙齿修复体以及咬合面上的团块，被划分为具有四个网格点的三维实体CTETRA单元。牙齿修复体周围的粘结用壳单元进行模拟。采用热膨胀法模拟聚合收缩。分析了在聚合收缩和咬合负荷（600 N）联合作用下，修复模型在应力和位移分布方面的力学行为。假定所有材料在整个变形过程中均表现为弹性材料。
数值结果表明，与完好牙齿相比，修复模型的力学响应有很大不同，完好牙齿的应力从釉质到牙本质均匀分布，无临界应力集中。在修复模型中，最高应力值出现在釉质、釉质-牙本质界面附近以及大块修复材料中。牙齿预备A和B的应力梯度低于相应的C和D。模型A和B中的垂直位移分量值高于相应的C和D。最大位移值主要位于沟周围，比完好模型高一个数量级。结果表明，与C和D相比，模型A和B具有更好的力学响应。同样明显的是，树脂粘结厚度对修复后牙齿的应力水平有轻微影响。
Ⅱ类MOD直接大块树脂复合修复体在边缘和内部组织界面处显示出较高的易损性，这取决于其自身的刚度。由于存在力学行为失效风险，不建议在大型Ⅱ类MOD粘结修复中使用树脂基大块充填材料。
