Sixty identical zirconia specimens (Yeti-Dental, Digital Line, Germany) were fabricated using computer-aided design/computer-aided manufacturing technology (Wieland Dental, Zenotec Select, Germany). The specimens were designed to be identical to a natural-size crown and to simulate the contour of the buccal surface of the lower second premolar with a stump base. The specimens underwent sintering for 9 h in a zirconia-sintering furnace (Programat S1, Ivoclar Vivadent), with temperature reaching 1500°C, for 2 h. A glaze layer (Glasur, Degudent) was applied to all the specimens and fired for 15 min in a ceramic furnace (ProFire 2 Press, Degudent). One specimen was mounted in a stone base, simulating its position in the oral cavity, and three industrial silicon molds (Catasil 21; Vertex, Switzerland) were made for this specimen. Each specimen was placed in its proper indentation in the mold, and chemical-cured acrylic resin (Meliodent, Heraeus Kulzer, Germany) was then poured to fill the mold. This procedure was repeated to obtain 60 identical specimens. All the specimens were bonded with stainless steel Discovery brackets #790-123-00 (Dentaurum GmbH, Ispringen, Germany) for a lower second premolar with a laser-structured base. The average surface area of the bonded bracket was 13.42 mm2.[15 (link)]