Resolution of mandibular arch crowding in growing patients with Class I malocclusions treated nonextraction

The purpose of this study was to determine the manner in which mandibular arch crowding was resolved in Class I growing patients who were treated nonextraction. A retrospective study was completed with 30 patients from a postgraduate orthodontic clinic, treated with a variety of treatment modalities. Eight study models and six cephalometric parameters were examined before treatment and at the end of active treatment (posttreatment). The results showed that statistically significant increases in arch width occurred at the canine (0.9 mm), first premolar (1.6 mm), second premolar (1.8 mm), and first molar (1.2 mm). The incisors were advanced an average of 2.1 mm and proclined 6.1 degrees. The molars showed no anteroposterior movement. Arch perimeter increased 2.3 mm and arch depth increased 1.6 mm. Multiple linear regression analysis revealed that 52% of the variance in crowding resolution was accounted for by an increase in arch perimeter. It was concluded that the resolution of crowding, in this group of patients with Class I malocclusions, was achieved by generalized expansion of the buccal segments, along with advancement of the lower incisors. In some cases, these changes may be consistent with treatment objectives; in others, they may be undesirable. It is therefore important for practitioners to carefully evaluate treatment outcome irrespective of the treatment modality, to determine whether treatment objectives are being met.