# Nanotomographic Analysis of Orthodontic Molar Tubes for Direct Bonding
###### Abstract  
(1) Background: The most important part of an orthodontic attachment (bracket or tube) is the tube or slot for the insertion of the orthodontic wire. Aligning teeth along the archive according to angular values preadjusted in the bracket slots (or tubes) requires a very precise size accordance between the archives and slots. The aim of this study was to perform a nanotomographic analysis of the geometric features of molar tubes for direct bonding in terms of their dimensions and angles of their inner walls and analyze the presence of metallurgical imperfections. (2) Methods: Orthodontic tubes (n = 100) for upper right first molars from five different manufacturers (3M-Victory Series, Adenta-Bond Sing, Dentaurum-Ortho Cast M, GC-L LP, and ORMCO-Accent), 20 tubes each, were subjected to nanotomographic analysis. Measurements of the inner channel of the tubes, angles between the walls, and analysis of metallurgical imperfections were performed using high-resolution computed tomography. (3) Results: height measurements differed by 4-14% from ideal values declared by manufacturers, whereas the angles ranged from reducing by a maximum 1% comparing to values declared (hypodivergent walls) to increasing by a maximum 4.5% (divergent walls). (4) Conclusions: 1. The sizes of channels measured were slightly larger than those declared by manufacturers. 2. Slight deviations in wall parallelism and angles between the walls were found. 3. Some tubes were characterized by manufacturing defects of the metal. 4. Efforts should be made to further improve the production process of orthodontic attachments. orthodontics; molar tubes; precision; CT; measurement; size +
Footnote †: journal: Medical  
The use of bands was associated with the fact that they have to be bought in different sizes, require trying on to find the proper size, and then must be pre-cleaned and sterilized [6]. Moreover, the cement distribution is uneven, with space between band and enamel surface not completely filled by the cement [7], and microleakage occurs between the cement-enamel interface [8], increasing susceptibility to caries and gingival inflammation. Oral hygiene is difficult with orthodontic bands [9], and thus, a more prolonged shift in subgingival microbiota comparing to bonded brackets is found [10]. The molar tubes available on the orthodontic market have usually a single tube, a base to be bonded directly to the enamel, and a hook for elastics. The rectangular molar tube channel hosts subsequently inserted (initially round and later rectangular) wires of increasing dimensions. Molar tubes are commercially available in two standard sizes (heights), 0.018- and 0.022-inch, which are chosen depending on the clinical preferences of the orthodontist. Various bondable molar tubes from different manufacturers are available on the market. During orthodontic treatment with a fixed appliance, insertion of a rectangular archive into a precise rectangular tube of the proper shape, orientation, and dimensions allows us to transfer orthodontic forces and force moments from the archives to the periodontitis in order to align the molars in three dimensions of space in the leveling phase at the initiation of the treatment. Subsequently, during space closure, as teeth are moved along the archive, a proper accordance between the dimensions of the archive and of the tube provides anti-tipping force moments, allowing for control of the dental tipping in order to achieve a more bodily tooth movement despite the force application point (to the tube) which is outside of the center of resistance of the tooth. Nevertheless, [PERSON] and [PERSON] [11], creating an algorithm based on the dimensions of archives and brackets, showed that a minimal discordance between the two elements is a factor that has a significant impact on the sliding mechanics (e.g., the displacement of the archive in the tube channel).