# Nanotomographic Analysis of Orthodontic Molar Tubes for Direct Bonding
## 4 Discussion
Oversized bracket slots may result in a more pronounced tipping during space closure and imperfect finishing. Subsequently, bracket rebonding with overcorrection or wire bending may be required. The results of the present study, obtained for molar tubes, are in the range of 4-14% for height measurements. The manufacturers of the molar tubes evaluated in the present study do not specify how they are produced; thus, the authors have no reliable information regarding what methods were used for the manufacturing. It seems possible that the differences in dimensions of the molar tubes reported in the present study and the occurrence of artifacts are due to differences in the production methods of the evaluated molar tubes. The present study is the first investigation analyzing the dimensions of orthodontic molar tubes. For all the tubes, upper right molars were chosen in order to ensure a uniformity of the investigation, as the authors intended to compare the quality of different molar tubes. The ideal size of the tube channel should be as declared by the manufacturer, e.g., height of 0.018 inches (0.4572 mm) or 0.022 inches (0.5588 mm). The present findings revealed that 0.022-inch orthodontic molar tubes are characterized by increased heights comparing to the declared values, similarly as most orthodontic brackets. In an ideal situation, the upper and lower inner walls of the bracket slots and molar tubes should be parallel in order to host a rectangular wire and allow for proper expression of the torque, i.e., proper orientation of the roots referring to the vestibular and palatal or lingual cortical bone. A twisted archive providing torsional torquing moments exerts a pressure with its corners on the parallel inner walls of the molar tube. A divergent bracket or tube is thus characterized by increased slot play (free movement of the loose archwire in the slot or tube without exerting force on the tooth) reducing torque expression. No studies that could be used for comparison and discussion, referring to the parallelism of the opposing inner walls of orthodontic molar tubes, could be found in the available scientific literature. It is evident that a hypodivergent bracket or molar tube may increase friction and hinder the movement of the bracket along the archwire, creating an obstacle for sliding mechanics or even completely blocking sliding of the archwire within the fixed appliance. Referring to the literature on the parallelism of the inner walls of orthodontic brackets, some brackets were hypodivergent [13; 17] and some were hyperdivergent [13; 21; 22]. Similarly, according to the present study, the inner walls of the molar tubes are not perfectly parallel. The results of the present investigations show that the opposite upper and lower walls \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \\ \hline \hline \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: _Cont._of the molar tubes are slightly hyperdivergent. This geometric feature may potentially reduce torque expression, thus enhancing buccal molar tipping during dental expansion or hindering perfect torque adjustment of posterior teeth to reach ideal occlusion. In an ideal situation, a perfect geometry of the molar tube should be associated with 90 degree angles between the adjacent perpendicular walls. No previous studies have been found referring to the geometry of molar tubes, which could be used for comparison and discussion. The literature on orthodontic brackets reveals various ranges of deviation from the ideal 90 degrees. Conversely, the results of the present investigation referring to 6 angles measured between the adjacent inner walls of the tubes indicate an acceptable precision, as revealed deviations ranged from reduction of an angle by a maximum 1% to its increase by a maximum 4.5%. The range of variation in buccal tube dimensions was therefore found to be similar to that characterizing orthodontic brackets.