# Nanotomographic Analysis of Orthodontic Molar Tubes for Direct Bonding
## 4 Discussion  
Contemporary orthodontic treatment, despite proper diagnostics and treatment planning, requires knowledge of the quality requirements for elements of the fixed appliance, in order to enhance the proper selection of orthodontic materials, especially brackets, tubes, and wires, providing orthodontic forces which are transferred to the teeth. A high quality of orthodontic materials might have an important influence on the results of fixed orthodontic treatment. Orthodontic brackets and tubes should allow us to achieve smooth sliding mechanics for a perfect dental alignment and ideal occlusion. Thus, they should be characterized by a precise geometry, perfect dimensions, and a smooth surface. An important quality issue is how orthodontic brackets are manufactured. In this regard, significant progress has been made over the past few decades, from casting and milling techniques to the metal injection moulding (MIM) method [12; 22; 25]. The MIM method was developed in the United States in the early 1980s and has been applied to the production of small parts [23]. The molding technique uses pre-prepared molds that are poured with a liquid metal alloy. Milling involves machining a metal rail, while the injection molding (MIM) method involves introducing metal powders mixed with an organic binder into a prepared mold under pressure, using an injection molding machine. Then, in the baking process, the polymer is burned away and the metal is fused together. The recipient of the product, i.e., the doctor, is not in a position to assess the precision of the bracket's manufacture. However, the treatment obtained may influence the choice of supplier for the future consecutively treated patients. However, it should be remembered that this evaluation is subjective, as many other factors influence the treatment effect [26; 27]. Manufacturers of orthodontic brackets are reluctant to provide any information on how and what the manufacturing process is, while they spend huge amounts of money on promoting their products, claiming that they are selling the highest quality brackets. The body of an orthodontic molar tube contains the tube channel for the archwire and a hook protruding from its wall towards the gingival margin of the molar tooth. The base of the tube serves for bonding the tube to the tooth buccal surface. From Table 5, it is apparent that in most cases, the body and the base are manufactured separately and then soldered together, as the soldering can be visually identified. Interestingly, in most tubes, the hook consists of two halves which are joined together in apparently imperfect way. This finding might potentially have an influence on the bending strength and breaking susceptibility. Figure 1: A Bond Sing tube with four metallurgic imperfections. \begin{table}
\begin{tabular}{c c} \hline \hline  & \multicolumn{1}{c}{Accent (Ormco)} \\ \hline  & \multicolumn{1}{c}{Bond Sing (Adenta)} \\ \hline  & \multicolumn{1}{c}{Ortho Cast M (Dentaurum)} \\ \hline  & \multicolumn{1}{c}{Victory Series (3M)} \\ \hline  & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Molar tubes inspected—examples of typical appearance of molar tubes inspected. However, a recent review of the literature has confirmed that orthodontic brackets are characterized by different manufacturing imperfections that may occur in a single bracket, a specific set, or in a whole series of orthodontic brackets [28]. Referring to orthodontic brackets, numerous studies assessing accordance to perfect slot dimensions have been found [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 23]. It was revealed that orthodontic bracket slots were usually oversized, referring to the declared heights of 0.018 or 0.022 inches. According to the literature, the heights of the slots of orthodontic brackets differed by 0.5% to 30%, referring to values declared by the manufacturers. In absolute values, the differences ranged from 0.008 inches to 0.01 inches [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23].