Ghassemieh Elaheh
Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
Dent Mater. 2008 Apr;24(4):536-47. doi: 10.1016/j.dental.2007.06.022. Epub 2007 Aug 13.
The aim of this research is to use finite element analysis (FEA) to quantify the effect of the sample shape and the imperfections induced during the manufacturing process of samples on the bond strength and modes of failure of dental adhesive systems through microtensile test. Using the FEA prediction for individual parameters effect, estimation of expected variation and spread of the microtensile bond strength results for different sample geometries is made.
The estimated stress distributions for three different sample shapes, hourglass, stick and dumbbell predicted by FEA are used to predict the strength for different fracture modes. Parameters such as the adhesive thickness, uneven interface of the adhesive and composite and dentin, misalignment of axis of loading, the existence of flaws such as induced cracks during shaping the samples or bubbles created during application of the adhesive are considered. Microtensile experiments are performed simultaneously to measure bond strength and modes of failure. These are compared with the FEA results.
The relative bonding strength and its standard deviation for the specimens with different geometries measured through the microtensile tests confirm the findings of the FEA. The hourglass shape samples show lower tensile bond strength and standard deviation compared to the stick and dumbbell shape samples. ANOVA analysis confirms no significant difference between dumbbell and stick geometry results, and major differences of these two geometries compared to hourglass shape measured values. Induced flaws in the adhesive and misalignment of the angle of application of load have significant effect on the microtensile bond strength. Using adhesive with higher modulus the differences between the bond strength of the three sample geometries increase.
The result of the research clarifies the importance of the sample geometry chosen in measuring the bond strength. It quantifies the effect of the imperfections on the bond strength for each of the sample geometries through a systematic and all embracing study. The results explain the reasons of the large spread of the microtensile test results reported by various researchers working in different labs and the need for standardization of the test method and sample shape used in evaluation of the dentin-adhesive bonding system.
本研究旨在通过微拉伸试验，运用有限元分析（FEA）来量化样本形状以及样本制造过程中产生的缺陷对牙科粘结系统的粘结强度和失效模式的影响。利用FEA对各个参数影响的预测，估算不同样本几何形状下微拉伸粘结强度结果的预期变化和离散程度。
FEA预测的三种不同样本形状（沙漏形、棒形和哑铃形）的估计应力分布，用于预测不同断裂模式下的强度。考虑了诸如粘结剂厚度、粘结剂与复合材料及牙本质的界面不平整、加载轴的不对准、样本成型过程中产生的诱导裂纹或粘结剂施加过程中产生的气泡等缺陷参数。同时进行微拉伸实验以测量粘结强度和失效模式。将这些结果与FEA结果进行比较。
通过微拉伸试验测得的不同几何形状样本的相对粘结强度及其标准偏差证实了FEA的结果。与棒形和哑铃形样本相比，沙漏形样本的拉伸粘结强度和标准偏差较低。方差分析证实哑铃形和棒形几何形状结果之间无显著差异，且这两种几何形状与沙漏形测量值相比存在主要差异。粘结剂中的诱导缺陷和加载角度的不对准对微拉伸粘结强度有显著影响。使用模量较高的粘结剂时，三种样本几何形状的粘结强度差异增大。
研究结果阐明了在测量粘结强度时选择样本几何形状的重要性。通过系统全面的研究，量化了每种样本几何形状下缺陷对粘结强度的影响。结果解释了不同实验室的研究人员报告的微拉伸试验结果差异较大的原因，以及评估牙本质 - 粘结剂粘结系统时测试方法和样本形状标准化的必要性。
