Sunday, November 20, 2011

Anterior labial root torque

When upper anterior teeth, particularly lateral incisors, are in cross bite, they often need labial root torque. Normally positioned lateral incisor brackets, due to the torque built into those brackets, encourage the expression of lingual root torque. In cases where labial root torque is desired, the laterals never look quite right when normal torque expression occurs. My answer to this problem is to place the lateral incisor brackets on upside down. Flipping the brackets changes the torque expression from predominately lingual root torque to predominately labial root torque when rectangular wire is used.

Flipped upper lateral incisor bracket (top)
Normally positioned upper lateral incisor bracket (bottom)

The procedure to encourage labial root torque is as follows:

1) Create space in the arch form for the blocked out lateral incisor. This can be done on the initial arch wire by packing open coil spring between the central and canine in non-extraction cases, or by using a combination of coils and/or lacebacks in extraction cases. Remember not to pack too much coil on the initial arch wire (my coil springs are usually about 2mm longer than the space between the brackets on the adjacent teeth). This helps prevent distortion of the arch form. Be patient; use a slightly larger (about 2mm) piece of coil each month until enough space in the arch form is created to accommodate the blocked out tooth.

Blocked out upper right lateral.
Labial root torque will be needed.

Creating space with lacebacks and coil spring.

2) Once sufficient space is created, bracket the blocked out tooth (in our example, the upper lateral incisor). Place the bracket on upside down and engage the tooth. A light flexible arch wire must be used because that wire must be deflected a significant amount to engage the tooth. Often, as in the case shown here, a tandem arch wire set up is used. Additionally, in patients with deep bites, the bracket on the blocked out tooth may cause severe occlusal interferences. If this is the case, temporarily prop the bite open by bonding composite to the occlusal surface of both lower 1st molars. Remove the composite after the crossbite is corrected.

The lateral can be moved into the arch form after space is created. Note how composite is used to temporarily eliminate the occlusal interferences.

3) This set-up will result in labial movement of the crown. Because round wire is being used, no torque expression occurs as a result of torque in the bracket slot. At this stage of treatment it doesn't matter what the torque in the bracket slot is. Once the crossbite is corrected, remove the composite from the occlusal surface of the lower molars. The overbite will help retain the labial crown movement.

Crown is now in place. Note the need for labial root torque.

4)Once initial aligning is complete, begin torque expression by using a low load deflection rectangular arch wire. I often use 019x025 heat activated nickel titanium (HANT) followed by 021x025 HANT. Filling the slot encourages the expression of torque. The upside down bracket means the torque in the bracket slot encourages labial root/lingual crown torque. Because of anterior overbite, occlusion helps the crown retain its position while labial root torque occurs. Usually about 10 weeks of 021x025 HANT is necessary to achieve full torque expression. Leave the bracket on upside down for the whole treatment. That way correct torque expression is encouraged throughout the whole treatment.

Rectangular wire (021x025HANT) fills the slot. Note expression of labial root torque.

The treatment photos below (courtesy of Dr. Gerald Samson) demonstrate how much improvement in root position is possible with this technique.


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