The influence of the methodological variables on the shear bond strength

Objectives: Evaluate the influence of several methodological variables on the shear bondstrength of in vitro studies.
Methods: 105 bovine incisors were sectioned at the cervical level.The coronary portion was included in PVC rings, fulfilled with auto polymerized acrylic resin,with its labial surfaces positioned upward. All the samples were prepared for bonding, cleanedand acid etched on the central area of the crowns. In this area, central incisors’ Morelli™brackets were bonded with Concise™ (3M/Unitek). Three testing groups were established,according to the studied variable: Group 1—storage previous to bonding (a- thymol 0.1%;b- distilled water; c- freezing); Group 2—crosshead speed of the universal testing machine(a- 0.5 mm/min; b- 1.0 mm/min; c- 2.00 mm/min) and Group 3—commercial brand of 37%phosphoric acid (a- 3M/Unitek; b- Acid Gel; c- Attack Tek). The shear bond strength test wasperformed at the Emic DL2000™ universal testing machine. Data was analyzed through theStudent’s t test for independent samples. Results: In Group 1, the freezing group showed thehigher values of shear bond strength when compared to the others, although no statisticaldifference was observed (p > 0.05). For Group 2, the higher the crosshead speed, the lowerthe shear bond strength, with no statistical difference. In Group 3, the 3M/Unitek brandshowed the highest average of shear bond strength in MPa, but also no statistical differencewas shown. Conclusions: The variable analyzed in this research had not presented enoughinfluence to determine significant differences between the results.