Rotated teeth in LO: problems and solutions

Geron S.,  D.M.D, M.Sc., Israel

www.lingualnews.com, Volume 1, Number 1 - November 2002

In comparison to labial orthodontics, rotational movement in the occlusal plane is difficult to achieve in lingual orthodontics. The main reasons for this are the small size of the arch and the short inter-bracket distance. These problems are especially relevant in the anterior region of the dental arch.(1)

During rotational movement, teeth are moved lingually into a smaller diameter arch, with less space for movement (Fig 1). The short inter-bracket distance necessarily means that any moment produced across a given bracket will be small due to the shortness of the lever-arm about the center of rotation. This is most pronounced In the mandibular dental arch, being that it is more constricted than the maxillary and the incisor mesio-distal width is less than the maxillary incisors.

Fig 1: Labial and Lingual arch perimeter

The use of brackets designed with a horizontal slot to accept the arch wire is also a hindering factor. This is because the rotation to be corrected is in the plane of the bracket arch wire slot. Therefore, the arch wire may slide out of the slot if it is held in place by the ligature only. (2)

Different ideas and solutions have been offered to overcome this problem. However, only a few of them have been reported in our professional literature. More often, these have been offered-up as a caveat during an oral presentation made by one of the many resourceful and astute clinicians experienced in the lingual orthodontic technique. This article is an attempt to formally present the spectrum of solutions available to reconcile dental rotations while treating with the Lingual Orthodontic Technique.

The first, and most important, step in rotational movement is the creation of space mesial and distal to the tooth being (de)rotated. Without this prerequisite the desired rotational movement will not occur. The creation of the space(s) needed for rotation can be achieved in several ways:

1. Retraction of posterior teeth into an extraction space or inter-proximal reduction space. (Fig 2)
2. Stripping the mesial and distal surfaces of the teeth adjacent to that being rotated.
3. Expansion and proclination, using an advancement arch or an oversize arch (Fig 3)
4. Expansion and proclination with coil spring (Fig 4)

Fig 2: Creating space by retraction

Fig 3: Expansion with oversized arch

Fig 4: Expansion with coil spring

Having opened the necessary space adjacent to the tooth needing rotation, the actual rotation can be affected with different mechanics, according to the severity of rotation, the position of the tooth and the stage of treatment.

1. Full engagement of the arch wire with steel double-over tie ligation. Mild rotations may be resolved in this way.(2) The best option for this technique is the use of copper-nickel titanium arch wires.

2. Rotation bends in the wire. However, this technique can be used if only small rotations are needed. It is best applied during finishing the early stages of alignment. The bend must be done on resilient wires like 0.016 inch TMA. The wire must be tied with metal, rather than elastic, overtie. It must be kept in mind that the aspect of the rotation bend directed lingually must be as far from the bracket being rotated. This is so that the ligature of this bracket will not slide outside the rotation bend, which would not permit full insertion of the wire into the bracket slot (Fig 5).

 
Fig 5: Rotation bends

3. Reciprocal rotation. If two neighboring teeth require rotation in opposite directions, and there exists adequate space for bonding both brackets, it is possible to solve severe rotations of both teeth together by using an elastic chain tied to the hooks of both teeth in a reciprocal rotation (Fig 6).

4. One by one rotation. If the brackets approximate each other due to the severity of the dental rotations, it is advised not to bond all the rotated teeth simultaneously. Rather, it is recommended that the teeth be bonded according to the severity of their rotations. This allows a longer lever arm to facilitate the rotation, along with better rotational control than if all the teeth had been bonded at once. After the rotation of an individual tooth, it is tied with steel ligature and the next most rotated tooth may be bonded and rotated (Fig 7).

Fig 6: Reciprocal rotation

Fig 7: One by One rotation

5. Rotation off of an anchorage unit. The rotated tooth is tied with an elastic chain to an anchorage unit composed of several teeth co-ligated by figure 8 ligation. A stiff wire is required for this rotation (Fig 8 ).

6. Rotation off of a crimpable hook (Fig 9) This is an efficient and aesthetic method for rotations, although it may be done on rectangular wires only. The use of a crimpable hook as an aid in LO treatment was described by Rummel and Wiechmann, although they did not mention the possibility to use it for rotations.(3). Here, the same mechanism is employed as in option number 5, however, the elastic chain is connected from the bracket/tooth to be rotated, to the hook crimped onto the arch wire.

Fig 8: Rotation to an anchoragr unit

Fig 9: Rotation to a crimpable hook

7. Anti-rotation elastics. If unwanted rotations occur during space closure, a clear elastic chain may be attached to the hook of one of the rotated tooth, passed along its labial surface to the labial surface of the second tooth and then to its lingual hook. These elastics may be used during the retraction phase of treatment, to avoid or to correct unwanted rotations of molars or canines which can occur as an unwanted side-effect during space close and anterior tooth retraction (Fig 10).

8. Rotation Tie. A clear elastic chain is threaded onto the arch wire prior to insertion. It is stretched from the side of the tooth needing rotation across its labial surface and passed interproximaly and hooked onto the lingual hook of said tooth. This is a very efficient method for rotations. Unfortunately, it does not receive wide patient acceptance, especially in the anterior region, because of yellowing of the elastic chain. In addition, the chain has the propensity to slide gingivally or incisally depending on the tooth contour. This problem can be avoided by placing a composite button on the labial surface of the tooth in question (Fig 11).

Fig 10: Antirotation elastics

Fig 11: Rotation tie

9. Half a rotation tie. A clear plastic button is bonded strategically onto the labial tooth surface of the rotated tooth, and an elastic chain threaded onto the arch wire as for the (full) rotation tie. The chain is stretched from the wire and hooked onto the button. This is also a very efficient method for rotation, but suffers the same drawback of the previous method: esthetics. However, the clear button is much less conspicuous than the rotation tie, and the chain is almost invisible and it cannot slide from its place. Of most significance is the fact that this is the quickest and most recommended method to (de)rotate a tooth. That is, so long as the patient does not object to the bonding of the labial plastic buttons (Fig 12).

Fig 12: Half a rotation tie

Readers of the electronic Lingual Orthodontics Journal LINGUALNEWS are invited to submit their ideas for solving the rotation problem in LO. Please email: info@lingualcourse.com

The next "Clinical problems and Solutions" will focus on the rebonding problem.
Readers are invited to contribute their solutions for different rebonding situations, as well as a new subject to be discussed in the following issue.

References

1. Kurz C., Bennett R., :Extraction cases and the Lingual appliance: J. Amer.Ling Orth Aassoc (JALOA) 1;3 1-13, 1988

2.Alexander C.M. et al : Lingual Orthodontics: A Status Report Part 5 Lingual Mechanotherapy JCO Feb 99-108, 1983

3. Rummel V., Wiechmann D., : The Crimpable Hook: An Aid in Lingual Orthodontic Treatment J. Lingual Orthod 1;1 1-3, 1999

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Adult and Lingual Orthodontics
EDITORS:
Dr. Silvia Geron D.M.D., M.Sc
Dr. Rafi Romano D.M.D., M.Sc
Dr. Pablo Echarri D.M.D., M.Sc