Profile changes following extraction vs. nonextraction orthodontic treatment in a pair of identical twins.

A pair of 11.5-year-old monozygotic twin boys--with a class I occlusion, deep bite and crowding in the lower arch--was presented for orthodontic treatment. One of them was treated in combination with extraction of 4 premolars while in the other the treatment was carried out without extractions. The superimposition of the pretreatment cephalometric tracings on the N-Pog line displayed minimal differences in the sagittal position of the incisors and no differences in the soft tissue profile. As a result of protrusion of the incisors in the nonextraction case and retrusion in the extraction case, a sagittal difference of 7.0 mm for the incision superius and 5.5 mm for the incision inferius was registered between the twins in relation to the N-Pog line at the end of treatment. However, the corresponding soft tissue differences were only 2.0 mm for the labrale superius and 3.2 mm for the labrale inferius and seemed to be reduced 1 year later.