Arch Width Control

Along with good bracket positioning, good arch width control is one of the most important parts of quality orthodontic treatment. Proper arch width control starts with a good diagnosis. Does the patient require arch expansion, arch contraction, or maintenance of the existing arch form? Once this question is answered, some simple steps performed throughout treatment allow the practitioner to reach the treatment goals.

I alter all stainless steel archwires to help give the patient the desired arch form. If no expansion is desired, here is how I co-ordinate archwires.

1. Draw a line on the lower pretreatment model from the buccal cusps of the posterior teeth through the incisal edges of the anterior teeth

2. Co-ordinate the lower wire so it is 3mm wider than this line throughout

the circumference of the wire.

3. Co-ordinate the upper wire with the lower. If no expansion is desired, make the upper wire 3mm wider than the lower.

4. About 6mm of expansion (3mm per side)can be obtained with archwires alone. Simply expand each stainless steel wire used to the desired amount of expansion. If expansion in only one arch is needed (for example, correction of a narrow upper arch), just expand the archwires for that particular arch.

5. Any cases requiring more than 5-6mm of expansion need an expansion appliance (RPE,quad helix, or Schwarz plate). This should be determined during the initial diagnosis.

6. Molar area expansion is much less reliable than is bicuspid area expansion when using only archwires. A future posting will describe techniques for expanding the molar area with archwire bends.

7. Use a hollow chop pliers (or finger pressure) when forming the wires. The hollow chop is shown here.

Good arch width control techniques result in good interdigitation of teeth as the treatment progresses. Less elaborate finishing techniques and faster treatment will be the end result if these techniques are used.