Shear Bond Strength of Orthodontic Brackets

Ten bovine teeth per group were fixed in self-curing acrylic resin blocks. The tooth surface was polished in the order of 300, 600, 1000, and 1200 grit silicon carbide (SiC) paper, treated with 37% phosphoric acid (Scotchbond™ Universal Etchant, 3M ESPE, Seefeld, Germany) for 60 s, washed with water for 30 s, and dried with air flow for 30 s [1 (link),19 (link)]. Primer (Transbond™ XT primer, 3M Unitek, Monrovia, CA, USA) was applied to the tooth surface by lightly blowing air, and then the bracket (Micro-arch Appliances Formula-R; Roth Type, Tomy Intl Inc., Tokyo, Japan) was attached to the tooth with a load of 450.14 g using adhesive (Transbond™ XT Adhesive, 3M Unitek, Monrovia, CA, USA) in the center of the tooth. Excessive adhesive around the bracket was removed, and light was irradiated for 20 s each in the distal and mesial directions. Teeth were stored in distilled water at 37 °C for one day. The shear bond strength was measured using a universal testing machine (Instron 5942, Instron, Norwood, MA, USA). The edge of the blade rod and the tooth-to-bracket adhesive were positioned parallel to each other. A load was applied using a 1 kN load cell at a crosshead speed of 1.0 mm/min, and the result was recorded as N (newton) and converted to MPa (megapascal) as the surface area of the bracket (9.1 mm²). The following formula was applied: MPa = N/(9.1 mm²)