# Nanotomographic Analysis of Orthodontic Molar Tubes for Direct Bonding
## 2 Materials and Methods  
The material consisted of 100 commercially available orthodontic 0.022 inch non-convertible molar tubes for the upper right first molar tooth, from five different manufacturers (20 tubes each), e.g., Accent (Ormco, Brea, CA, USA), Bond Sing N/Conv (Adenta, Gilching, Germany), Ortho Cast M-Series (Dentaurum, Ispringen, Germany), Victory Series (3M, Plymouth, MA, USA), L LP (GC Corporation, Tokyo, Japan). The tubes were ordered form the providers by the first author and used in sequence. Initially, each of the tubes was subjected to three-dimensional scanning in a high-resolution computed tomography device (Waygate Technologies, Wunstorf, Germany), using the system GE v | tome| x s with a lamp of 240 kV (320 W), open. A handle for the brackets was designed for the purpose of the present study and made of extruded polystyrene (Styrodur, BASF, Ludwigshafen, Germany), chosen and used due to its low density. The appropriate resolution of the scanning was set by changing the geometric magnification, i.e., displacing the tested component between the lamp and the detector--the closer to the lamp, the greater the \"shadow\" and thus the resolution. Then, geometric calibration of the system was performed using a certified standard made of ruby balls connected by a carbon fiber. Appropriate scanning parameters were selected to ensure the appropriate permeability of the X-ray beam: voltage: 180 kV, current intensity: 45 \(\upmu\)A. After setting the scanning parameters, the detector calibration was performed, divided into two steps: offset: with radiation off, all scintillators are extinguished (\"tared\"); and gain: with the radiation on, all scintillators equalized to make the image as homogeneous as possible (the beam is conical, so in the center it has the highest energy, and the further from the center, the lower the energy--to eliminate this phenomenon, gain is performed). Then, the scanning procedure was started: the device took 1200 photos rotating in steps, and the detector performed a gentle side-to-side movement between individual photos in order to avoid ring artifacts from the hardware--without additional software processing. Reconstruction was performed using u GE datos | x reconstruction workstation and software: BHC (beam hardening correction) filtering was used to eliminate the hardening effect of the beam (correct for the beam hardening artifacts that can occur when lower energy photons are absorbed more than higher energy photons as an X-ray beam passes through an object) to improve the quality of the CT images, reconstruction was performed, i.e., overlaying photos obtained by scanning on one another for full digitization. Volume Graphics Studio MAX software was used for data processing in the following steps:  
* import of volumetric data to the software
* definition (by the software) of the border between the material and the air, based on the gray scale histogram
* data saving to the STL (Standard Triangulation Language) triangle mesh format  
The reliability of the measurements was ensured by high precision and a proper calibration of the equipment used. All measurements were performed by one experienced operating engineer. The heights of each tube channel were measured in millimeters, according to the method described in the study by [PERSON] et al. (2012), as presented in Table 1.  
Subsequently, each tube channel was analyzed, referring to the angle between horizontal walls (reflecting wall parallelism) and angles between the perpendicular inner walls, as presented in Table 2.  
Moreover, it was searched for any imperfections (manufacturing defects) on the inner walls of the channels and any defects in the structure of the metal of the tube. The authors used as many samples as possible. However, for the linear measurements, with the standard deviation of maximum 0.01, assuming a 95% confidence level, the standard deviation = 0.01 and the clinical significance = 0.01 mm, the sample size yielded 6.