Institute of Materials Chemistry, School of Chemistry, Brno University of Technology, Purkynova 118, 612 00 Brno, Czech Republic.
J Mech Behav Biomed Mater. 2011 Apr;4(3):245-54. doi: 10.1016/j.jmbbm.2010.09.004. Epub 2010 Sep 19.
The adhesion tests utilized in dentistry are unable to separate the effects of adhesive composition, substrate properties, joint geometry and type of loading on the measured bond strength. This makes it difficult for the clinician to identify the most suitable adhesive for a given procedure and for the adhesive manufacturer to optimize its composition. Thus, an adhesion test protocol based on the fracture mechanics has been proposed to generate data for which separation of the effect of composition from that of the joint geometry on the shear (τ(a)) and tensile (σ(a)) bond strengths was possible for five commercial dental adhesives.
Planar 40×5×5 mm(3) sections of bovine femur were used as model adherends. The adhesive thickness (h) was varied from 15 to 500 μm. Commercial adhesives with fracture toughness (K(IC)) ranging from 0.3 to 1.6 MPa m(1/2) were used. Double lap joint (DLJ) and modified compact tension (MCT) specimens were conditioned for 24 h in 37 °C distilled water, then dried in a vacuum oven at 37 °C for 24 h prior to testing. The thickness dependence of σ(a) and τ(a) was measured at constant strain rate and analyzed using the interface corner stress intensity factor model.
Both τ(a) and σ(a) increased with increasing adhesive thickness, exhibiting a maximum bond strength at the optimum thickness (h(opt)). For h<h(opt), both τ(a) and σ(a) were proportional to h, and, above h(opt), both τ(a) and σ(a) decreased with h(-4/10) in agreement with the fracture mechanics predictions. Hence, two geometry-independent material parameters, Ψ and (H(c)/Q), were found to characterize τ(a) and σ(a) over the entire thickness interval.
The adhesion tests currently used in dentistry provide the geometry-dependent bond strength, and such data cannot be used either for prediction of clinical reliability of commercial dental adhesives or for development of new ones. The proposed test protocol allowed us to determine two composition-only dependent parameters determining τ(a) and σ(a). A simple proposed procedure can then be used to estimate the weakest point in clinically relevant joints always exhibiting varying adhesive thickness and, thus, to predict the locus of failure initiation. Moreover, this approach can also be used to analyze the clinical relevance of the fatigue tests of adhesive joints.
牙科中使用的黏附测试无法分离黏附成分、基底特性、接头几何形状和负载类型对测量黏附强度的影响。这使得临床医生难以确定特定程序最适合的黏附剂，也使得黏附剂制造商难以优化其成分。因此，提出了一种基于断裂力学的黏附测试方案，该方案为 5 种商业牙科黏附剂生成的数据，可分离成分的效果与接头几何形状对剪切（τ(a)）和拉伸（σ(a)）黏附强度的影响。
使用牛股骨的平面 40×5×5mm(3) 截面作为模型黏附物。黏附剂厚度（h）从 15 到 500μm 变化。使用断裂韧性（K(IC)）范围从 0.3 到 1.6MPa·m(1/2) 的商业黏附剂。双搭接接头（DLJ）和改良紧凑拉伸（MCT）试件在 37°C 蒸馏水中调节 24 小时，然后在 37°C 真空烘箱中干燥 24 小时，然后进行测试。在恒应变速率下测量 σ(a)和 τ(a)的厚度依赖性，并使用界面角应力强度因子模型进行分析。
τ(a)和 σ(a)均随黏附剂厚度的增加而增加，在最佳厚度（h(opt)）处表现出最大黏附强度。对于 h<h(opt)，τ(a)和 σ(a)均与 h 成正比，而在 h(opt)以上，τ(a)和 σ(a)均与 h(-4/10)成反比，这与断裂力学的预测一致。因此，发现了两个与几何形状无关的材料参数，Ψ和（H(c)/Q），用于描述整个厚度范围内的 τ(a)和 σ(a)。
牙科中目前使用的黏附测试提供了与几何形状相关的黏附强度，并且这种数据既不能用于预测商业牙科黏附剂的临床可靠性，也不能用于开发新的黏附剂。所提出的测试方案使我们能够确定决定 τ(a)和 σ(a)的两个仅与成分相关的参数。然后，可以使用一个简单的建议程序来估计在临床相关接头中始终表现出不同黏附剂厚度的最薄弱点，从而预测失效起始的位置。此外，该方法还可用于分析黏附接头疲劳试验的临床相关性。
