Department of Biomedical Engineering, National Yang-Ming University, No. 155, Section 2, Linong Street, Taipei 112, Taiwan.
J Biomech. 2011 Jan 4;44(1):134-42. doi: 10.1016/j.jbiomech.2010.08.038. Epub 2010 Sep 15.
This study investigates the micro-mechanical behavior associated with enamel damage at an enamel/adhesive interface for different bracket bases subjected to various detachment forces using 3-D finite element (FE) sub-modeling analysis. Two FE macro-models using triangular and square bracket bases subjected to shear, tensile and torsional de-bonding forces were established using μCT images. Six enamel/adhesive interface sub-models with micro- resin tag morphology and enamel rod arrangement were constructed at the corresponding stress concentrations in macro-model results. The boundary conditions for the sub-models were determined from the macro-model results and applied in sub-modeling analysis. The enamel and resin cement stress concentrations for triangular and square bases were observed at the adhesive bottom towards the occlusal surface under shear force and at the mesial and distal side planes under tensile force. The corresponding areas under torsional force were at the three corners of the adhesive for the triangular base and at the adhesive bottom toward/off the occlusal surface for the square base. In the sub-model analysis, the concentration regions were at the resin tag base and in the region around the etched holes in the enamel. These were perfectly consistent with morphological observations in a parallel in vitro bracket detachment experiment. The critical de-bonding forces damaging the enamel for the square base were lower than those of the triangular base for all detached forces. This study establishes that FE sub-modeling can be used to simulate the stress pattern at the micro-scale enamel/adhesive interface, suggesting that a square base bracket might be better than a triangular bracket. A de-bonding shear force can detach a bracket more easily than any other force with a lower risk of enamel loss.
本研究使用三维有限元（FE）子模型分析，调查了不同托槽基底在不同分离力作用下与釉质损伤相关的微机械行为。使用 μCT 图像建立了两种使用三角形和方形托槽基底的 FE 宏观模型，这些模型分别受到剪切、拉伸和扭转脱粘力的作用。在宏观模型结果中的相应应力集中处构建了六个具有微树脂标签形态和釉质杆排列的釉质/粘结剂界面子模型。子模型的边界条件由宏观模型结果确定，并应用于子模型分析中。在剪切力下，三角形和方形基底的釉质和树脂粘结剂的应力集中在粘结底部朝向咬合面的区域，在拉伸力下在近中和远中侧平面观察到。相应的扭转力区域在三角形基底的粘结剂三个角和方形基底的粘结剂底部朝向/远离咬合面的区域。在子模型分析中，集中区域在树脂标签底部和釉质中蚀刻孔周围的区域。这些与平行体外托槽分离实验中的形态观察完全一致。在所有分离力下，方形基底的临界脱粘力破坏釉质的力均低于三角形基底的临界脱粘力。本研究建立了 FE 子模型分析可以用于模拟微观尺度釉质/粘结剂界面的应力模式，表明方形基底托槽可能优于三角形基底托槽。脱粘剪切力可以比任何其他力更容易地分离托槽，而不会有更大的釉质损失风险。
