Do the Microshear Test Variables Affect the Bond Strength Values?

摘要

Little is known about the effect of specimen preparation and testing protocols on the micro-shear bond strength (muSBS) results. To evaluate whether variations in polyethylene rod use affect (muSBS)). Human dentin disks were randomly distributed into six groups (n = 5): polyethylene tube (3 levels) and adhesive system (2 levels). In Group 1, polyethylene tubes filled with polymerized composite) were placed on adhesive covered surfaces. Tubes were removed 24 h after water storage, leaving the rods only. In Group 2, the same procedure was performed; however, tubes were kept in place during testing. In Group 3, composite rods without tubes were placed on adhesive covered dentin. In all groups, adhesives were photoactivated after positioning filled tubes/rods on adhesive covered surfaces. Specimens were tested under shear mode and the data subjected to a two-way ANOVA and Tukey's tests. Groups 1 and 2 resulted in statistically similar mean muSBS (P > 0.05); however, a greater number of pretest failures were observed for Group 1. Higher muSBS values were detected for Group 3, irrespective of adhesive system used (P < 0.05). Removing the polyethylene tube before composite rod is placed on dentin affects muSBS values. Bond strength measurement is one of the most common methods for evaluating the adhesive properties of restorative materials. Various mechanical methods, such as tensile, microtensile, flexural, shear, and in-plane shear tests have been used to assess bond to dental substrate . Compared with conventional tensile and shear tests both microtensile and microshear tests allow standard tooth regions to be selected, thus preserving the uniformity of the testing area . The simple test protocol of the microshear test allows for straightforward specimen preparation. It also permits regional mapping of substrate surfaces and depth profiling of the substrate . This means that the test could have additional advantages over the test, because it is performed without the need for sectioning procedures, which may induce early microcracking, to obtain specimens . Although sequential sectioning is unnecessary to obtain specimens for microshear testing , a polyethylene tube is used as a mold for composite placement. However, similar to data reported for the macro-shear test, this can lead to the introduction of flaws and different stress concentrations under shear loading . Moreover, in the majority of studies, the polyethylene tubes are removed with a scalpel blade before testing , which may lead to stress at the adhesive interface and result in premature failures.