4 Trends ORTHO TRIBUNE | NOv./DEC. 2009 f OT page 3 action and jacking position of a labial or a lingual arch wire, the position of the bracket slot has different consequences. The horizontal slot makes fewer problems in labial, as in lingual, technique. Today, the majority of the lingual brackets in the market offer horizontal slots. With this particular orientation of the slot, only the ligature contains the arch. Thus, the points of the applying forces are not firm when elastic ligature is used, even with steel ligation and full engagement of the arch wire in the bracket slot. Even slight rotations of the tooth are difficult to be solved completely in this way with stainless steel ligature. The use of copper-nickel titanium arch wires will slightly increase the effectiveness because the arch has a tendency of sliding out of the lingual slot. What is the solution? For derotation, the slot needs to be close to force direction (Fig. 6). In principle, a tube would solve all problems. However, to use tubes on all teeth makes it impossible to insert the wire. When the leveling stage requires de-rotation of a single tooth, the vertical slot is an alternative. During de-rotation, the arch wire is in contact with the bracket body or metallic framework (Figs. 6, 7 and 9). Therefore, the power from the arch wire will transfer completely to the tooth. However, a vertical slot instead of a horizontal slot is also not enough because some of the movements in this stage (leveling) might be affected, and it may not be very efficient with this orientation of the slot. For example, any vertical movements, especially intrusion movements, are difficult with a vertical slot. In principle, this is the same problem with a horizontal slot and de-rotation as described. Fig. 7: Magic brackets provide a vertical slot for the posterior teeth. (Photo/Dentaurum) Fig. 5: With an open lingual horizontal slot, the arch wire can slip off the bracket. Fig. 8: Magic brackets provide a vertical entrance for the anterior teeth. (Photo/Dentaurum) the insertion of the arch wire is vertical.8 When the arch wire is in position, it is held into the horizontal slot and cannot slide in the direction of the force because the metal wall of the bracket body does not allow it (Fig. 9). This special design will achieve most of the movements that derotation requires and is effective in realizing the necessary vertical, in–out and angulations movements that leveling requires. In the posterior teeth, the situation is identical because of the vertical slot design of the brackets (Fig. 7). These are the advantages of a vertical slot (not only for lingual brackets): better torque control, rotation and “en-masse” retraction (Fig. 10). Additionally the arch wire is easy to insert because there is a direct view into the slot. Effective control with rotation and torque require brackets with a long mesial-distal distance (Fig. 11).9 Naturally, the issues of a short inter-bracket distance can be solved or minimized with the use of memory-shaped arch wires and, especially, super elastic arches. In order to accomplish those movements effectively, it is important to consider indirect bonding to place and position lingual brackets. Indirect bonding significantly reduces rotation deviation with irregular proximal contact points.10 Fig. 6: The closed lingual horizontal slot with a vertical entrance provides excellent rotational control. (Photo/Dentaurum) The clever solution To find a satisfactory reply for the outlined problems, an ideal lingual bracket would need a vertical and a horizontal slot. This is a technical challenge because, on one hand, lingual brackets need to be small in all directions.7 On the other hand, they should have many features. A good compromise is the magic® lingual bracket system.* For front teeth, magic brackets have a horizontal slot (Fig. 8), but AD Fig. 9a Fig. 9b Conclusion In comparison to labial orthodontics, rotational movement is difficult to achieve in lingual orthodontics. There are many reasons for this, but one of the most important is the use of brackets designed with a horizontal slot. Figs. 9a, 9b: The arch wire cannot slip off during tooth rotation. (Photos/Dentaurum)