# Compressive Strength Comparison of Different Orthodontic Metal Bracket Systems
## 2 Materials and Methods  
This study received approval from the Kocaeli University Non-Interventional Clinical Research Ethics Committee on 21 September 2023, with approval number KU GOKAEK-2023/15.20. Our research was designed as an in vitro experimental study modeling the application of compression forces and orthodontic debonding methods in living tissues. Samples for our study were collected from patients who applied to the Department of Oral and Maxillofacial Surgery at Kocaeli University Faculty of Dentistry for treatment purposes. A total of 85 upper central incisors were used, with 17 teeth in each group. Inclusion criteria for teeth in the study were as follows:  
* No cracks or fractures in the enamel
* No fillings or restorations on the teeth
* Teeth should not have undergone root canal treatment
* No discoloration due to reasons such as medication usage
* Teeth should not exhibit major deformations  
After extraction, organic debris was removed from the teeth, and they were washed, dried, and stored in a surgical specimen container in a dark and cool environment with a 0.1% thymol solution for up to 4 weeks. A total of 85 brackets were used in our study, with 17 brackets from each bracket model. These brackets were: BioQuick(r) Forestadent, Pforzheim, Germany), Damon Q (Ormco Corp., Orange, CA, USA), Experience M (GC, Breckerfeld, Germany), Mini Diamond (Ormco Corp., Orange, CA, USA), and Mini Sprint(r)II Forestadent, Pforzheim, Germany) brackets (Figure 1). The base areas of the brackets were measured and recorded as follows:  
Mini Diamond: 11.73 mm\({}^{2}\), Damon Q: 10.51 mm\({}^{2}\), BioQuick: 11.13 mm\({}^{2}\), Experience: 10.40 mm\({}^{2}\), Mini Sprint II: 9.61 mm\({}^{2}\). The sample size was calculated using G*Power Software (version 3.1.9.7), with an effect size of 0.4, \"\(\alpha\)\" = 0.05, and power of 0.80 for a priori power analysis. Accordingly, the basic sample size for 5 study groups was calculated to be at least 80 (16 \(\times\) 5). Considering the possibility of losing a sample during procedures, 17 samples were included in each group. After being removed from the thymol solution, the collected central incisors were rinsed and dried. The vestibular surfaces of the teeth were cleaned using a low-speed polishing cup with a fluoride-free water-pumice mixture for 15 s, followed by rinsing and drying with oil-free air. A 37% phosphoric acid gel was applied to the buccal surfaces of the dried teeth for 30 s. Subsequently, the teeth were rinsed with water for 30 s and dried with oil-free air for 10 s. Once an opaque white surface was observed, a thin layer of TransbondTM XT Light Cure Adhesive Primer (3M Unitek, Monrovia, CA, USA) was applied to the tooth surface. Individual brackets were then removed from their storage containers. TransbondTM XT adhesive resin was placed on the base of each bracket and positioned on the buccal surface of the tooth. The brackets were aligned on the tooth surface and gently pressed into place (Figure 2). Figure 1: Brackets used in our study. The brackets were light-cured for thirty seconds using the Light-Emitting Diode (LED) curing unit, model Elipar S10, manufactured by 3M ESPE (3M ESPE, Seefeld, Germany), with a light intensity capacity of 1200 mW/cm\({}^{2}\). The intensity of the light-curing unit was measured using the built-in radiometer in the EliparTM S10 LED Curing Light's charging station. This ensures that measurements are taken before each curing session, confirming that the light intensity levels remain consistent. Subsequently, the teeth were stored in distilled water at 37 \({}^{\circ}\)C in specimen containers for one week to allow for the final polymerization of the adhesive resin. Prior to the experiment, the specimens were removed from the specimen containers and lined up (Figure 3). The compression process of the brackets was conducted using a Universal Testing Machine (Shimadzu AG-X, Kyoto, Japan) with a Weingart plier (Dentaurum, Ispringen, Germany). A specially designed apparatus held the Weingart plier in the testing machine.