University of São Paulo School of Dentistry, Dept. of Dental Materials, Av. Prof. Lineu Prestes, 2227, São Paulo, SP 05508-000, Brazil.
Dent Mater. 2010 Feb;26(2):e38-49. doi: 10.1016/j.dental.2009.11.150. Epub 2009 Dec 11.
Bond strength between adhesive systems and the tooth structure is influenced by a large number of variables, which makes the comparison among studies virtually impossible. Also, failure often times propagates into the dental substrate or the composite, deeming the results questionable at best. In spite of the increased popularity gained by micro-tensile and micro-shear tests, in vitro evaluations using specimens with relatively large bonding areas remain frequent. This review focuses on aspects related to specimen geometry and test mechanics of "macro" shear and tensile bond strength tests.
Besides information drawn from the literature, the effect of some parameters on stress distribution at the bonded interface was assessed using finite element analysis (FEA).
Bond strength tends to increase with smaller bonding areas and with the use of high elastic modulus composites. Stress concentration at the bonded interface is much more severe in shear compared to tension. Among shear methods, the use of the chisel shows the highest stress concentration. Within the limits suggested by the ISO/TS 11405, crosshead speed does not seem to influence bond strength values. Pooled data from currently available adhesives tested in either shear or tension showed 44% of adhesive failures, 31% mixed and 25% cohesive in the substrate (tooth or composite). A comparative bond strength study involving three adhesive systems revealed similarities between "macro" and "micro" counterparts regarding material ranking, whereas "macro" tests presented a higher incidence of cohesive failures.
Simplicity warrants "macro" bond strength tests an enduring popularity, in spite of their evident limitations. From a mechanical standpoint, knowing the stress distribution at the bonded interface and how it is affected by the materials and loading method used is key to explain the results.
黏结系统与牙齿结构之间的黏结强度受大量变量的影响，这使得研究之间的比较几乎不可能。此外，失效往往会扩展到牙本质或复合层，使得结果充其量是可疑的。尽管微拉伸和微剪切测试的普及度有所提高，但使用具有相对较大黏结面积的标本进行体外评估仍然很常见。本综述重点介绍了“宏观”剪切和拉伸黏结强度测试的试件几何形状和测试力学相关方面。
除了从文献中获取的信息外，还使用有限元分析（FEA）评估了一些参数对黏合界面应力分布的影响。
黏结强度随着黏结面积的减小和使用高弹性模量复合材料而增加。与拉伸相比，剪切时黏合界面的应力集中更为严重。在剪切方法中，使用凿子会导致最高的应力集中。在 ISO/TS 11405 建议的范围内，十字头速度似乎不会影响黏结强度值。目前可用于剪切或拉伸测试的各种黏结剂的汇总数据显示，44%的黏结失败是黏结剂破坏，31%是混合破坏，25%是基底层（牙或复合层）破坏。一项涉及三种黏结系统的比较黏结强度研究表明，“宏观”和“微观”对应物在材料分级方面具有相似性，而“宏观”测试的黏结破坏发生率更高。
尽管存在明显的局限性，但由于其简单性，“宏观”黏结强度测试仍然受到广泛应用。从力学角度来看，了解黏合界面的应力分布以及材料和加载方法如何影响其分布对于解释结果至关重要。
