Effects on the dental arch form using a preadjusted appliance with premolar extraction in Class I crowding

To determine the dental arch form effects of treatment with a preadjusted appliance (0.022'' slot) performed concomitantly with extraction of premolars in Class I crowding.

Twenty-six patients (20.17 +/- 12.15 years) with Class I crowding who attained a favorable occlusion after treatment were divided into nonextraction and extraction groups. The three-dimensional coordinates of the FA point of each tooth were determined. The dental arch form was expressed as a quartic polynomial expression with log F value used to represent the dental arch form and calculated using the quadratic and quartic coefficients. Changes in the dental arch form before and after treatment were compared between the groups.

In the extraction group, log F value was significantly higher after treatment, and the upper dental arch became more tapered. The U1-APo was significantly lower after treatment. No change was observed in U1-FH. The anterior teeth demonstrated posterior movement due to sliding mechanics, and torque was controlled. The anterior length of the dental arch became significantly longer after treatment for the maxilla and mandible in both groups. Results demonstrated that the upper dental arch might become tapered after treatment used concomitantly with premolar extraction, as a result of the increase in anterior length while maintaining intercanine width for dealing with crowding of the anterior teeth.

It is necessary to anticipate that the upper dental arch form will become tapered during extraction treatment for Class I crowding and to select an appropriate arch form.