## 4 Discussion
### Torque  
The working wires of the straight wire technique are not full-dimension archives, leading to a lack of intimate contact between the bracket and the wire. The dimensional difference between the wire and the slot is called the torsional play or the engagement angle [8]. The torsional play of a 0.019 \(\times\) 0.025 in. archive in a bracket slot with nominal dimensions of 0.022 in. could theoretically be estimated at approximately 7\({}^{\circ}\) to 10\({}^{\circ}\)[11]. Most authors have focused only on torsional play to assess the efficiency of the appliance in torque expression. [PERSON] et al. (2020) found a torsional play ranging from 11.42 \(\pm\) 0.29 to 15.84\({}^{\circ}\)\(\pm\) 0.68\({}^{\circ}\) in the three systems analyzed in their study which engaged a 0.019 \(\times\) 0.025 in. archive in a bracket slot of 0.022 in. [16]. [PERSON] et al. (2014) found a torsional play ranging from 13.80\({}^{\circ}\)\(\pm\) 0.12\({}^{\circ}\) to 28.68\({}^{\circ}\)\(\pm\) 0.48\({}^{\circ}\) while engaging a 0.019 \(\times\) 0.025 in. archive in a 0.022 in. bracket slot [17]. It is in fact clear how torsional play affects clinical torque expression; however, if the inbuilt torque value is not assessed, it is not possible to know if torque expression is affected by an oversized slot height or by an inaccuracy in the inbuilt torque information. Torque play can nullify the amount of torque informationbuilt into the bracket slot. The amount of torque play in any direction is a cumulative value that does not specify the causing factors, such as an inaccuracy of slot height, a lack of slot parallelism, or an anomalous slot geometry [8; 18]. According to our results, only seven of the twelve analyzed systems had brackets respecting the tolerance limits of the torque information in the bracket base, while the information was defective in four of them. The torque values in the study group varied between \(-3.85^{\circ}\) and \(+2.52^{\circ}\) from the declared value. The inaccuracy of the torque information built into the bracket can thus worsen the defective torque expression to a great extent due to the torsional play highlighted in previous studies. [PERSON] et al. (2010) analyzed 120 MBT prescription, maxillary canine brackets and 120 MBT prescription, mandibular canine brackets from six different manufacturers, and found their mean torque values were significantly different from those declared in four bracket series from three different manufacturers [6]. The authors concluded that for only one manufacturer was the torque value deviation high enough to be clinically significant. [PERSON] et al. (2019) evaluated the incorporated torque of 360 Roth prescription, upper and lower brackets from six different manufacturers, and found the mean torque value was significantly different from the declared value in two bracket series from two different manufacturers. The authors concluded that, despite the mean value not being statistically different in many bracket series, the standard deviation in the study sample was high enough to highlight a clear manufacturing inaccuracy or a defective quality check [19]. [PERSON] et al. (2002) assessed 220 MBT prescription, maxillary central incisors from four different manufacturers and found a torque significantly different from the declared value in two bracket series from two different manufacturers with a value range of \(13.17^{\circ}\) to \(19.43^{\circ}\), very similar to the one of the current study [2]. It should be underlined that, despite the non-significant difference of the mean value from the declared value, a range of torque variation of \(5^{\circ}\) was observed in a third manufacturer.