The effect of the loading method and cross-head speed on resin–dentin microshear bond strength Miguel Angel Muñoz a,b,n , Rafael Baggio a , Yasmine Bitencourt Emilio Mendes a , Giovana Mongruel Gomes a , Issis Luque-Martinez a , Alessandro D. Loguercio a , Alessandra Reis a a State University of Ponta Grossa, Department of Restorative Dentistry, Carlos Cavalcanti Street 4748, Bloco M, sala 64A, Uvaranas, Ponta Grossa, Paraná (PR), Brazil b Universidad de Valparaíso, Facultad de Odontología, Cátedra de Operatoria Dental, Calle Leopoldo Carvallo 211, Playa Ancha, Valparaíso, V Región, Chile article info Article history: Accepted 12 December 2013 Available online 25 January 2014 Keywords: Adhesive Microshear bond strength Loading methods Cross-head speed abstract This study compared the effect of different loading methods and crosshead speeds on resin–dentin microshear bond strength (μSBS) using two etchandrinse adhesive systems. Sixty molar teeth had their dentin surfaces exposed and were randomly distributed into 12 groups (n ¼5), according to a combination of the factors: loading methods (orthodontic-looped wire and chisel systems), cross-head speed (0.5, 1.0 and 5.0 mm/min) and adhesive system (Adper Single Bond 2 and XP Bond). Five tygon tubes were positioned over each sample, filled with composite resin and photoactivated. After 24 h, they were tested. The data were analyzed with a two-way ANOVA and Tukey test (α ¼0.05). The mSBS of the adhesives was higher with the chisel methods, compared to the orthodontic-looped wire (p o0.05). The cross-head speed was only significant for the chisel (p o0.05). The evaluated test variables affect the mSBS for both adhesives and therefore should be standardized; however the loading method proved to have the most effect on μSBS values. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Bonding tests have been extensively employed by different authors to investigate the performance of adhesive systems and techniques [1,2]. The rationale is that the stronger the adhesion between the tooth and a biomaterial, the better it will resist the stress imposed by resin polymerization and oral function. The shear bond strength test was the most commonly used [1,2] among the available bond strength tests. Improvements in dentin bonding, however, have made this test inappropriate for screening materials and techniques [3]. Cohesive failures in the substrates have been more frequently observed with the newest adhesives [1,3–6]. By using this conventional bonding test, researchers rapidly approached the point where product improve- ments were not distinguishable as dentin cohesive failures, rather than interfacial failures [1,3–6]. This limitation of the shear test led to the development of the microtensile test [7,8], which relies on the application of tensile stresses to areas with reduced bonds. The smaller the area, the higher the bond strength value and the higher the sensitivity of the test in detecting subtle differences among groups [8,9]. This new test was claimed to have a better stress distribution, while preventing cohesive failures within the substrates [5,7,8]. Based on the same rationale, some authors have advocated a new test method using specimens with reduced dimensions, as a substitute for the conventional shear test: the so-called micro- shear test [4,10]. This permits regional mapping or depth profiling of different substrates. In addition, multiple specimens from the same tooth can be prepared, as in the microtensile test, but without the need for sectioning procedures that might, by them- selves, induce early cracking [11], mainly when bonded to brittle substrates. Despite all the advantages of microshear [4], there is a lack of methodological standardization among the different studies. For this reason, analyses of the same adhesive system unavoidably produce different data on the bonding resistance [12]. Although the need for standardization has been widely recognized [13], few efforts have been made towards this end. Two common sources of variation are loading methods and crosshead speed used for testing [14,15]. Authors have employed crosshead speeds of 0.5 mm/min [4,16–18] and 1.0 mm/min [19–23]. This small varia- tion was shown to significantly affect conventional shear testing [14]; however, whether this variable has any impact on microshear Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijadhadh International Journal of Adhesion & Adhesives 0143-7496/$ -see front matter & 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijadhadh.2014.01.024 n Corresponding author at: Universidad de Valparaíso, Facultad de Odontología, Subida Leopoldo Carvallo 211, Playa Ancha, Valparaíso, V Región, Chile. Tel.: þ56 32 250 8531. E-mail address: drmunozperez@gmail.com (M.A. Muñoz). International Journal of Adhesion & Adhesives 50 (2014) 136–141