Arch Width Changes During Orthodontic Treatment of Class II Malocclusions

Objective: To evaluate arch width changes during treatment and retention of Class II division 1 (II-1) malocclusions with and without premolar extractions and Class II division 2 (II-2) non-extraction malocclusions.

Method: Maxillary and mandibular intercanine and intermolar widths were measured from orthodontic models of 123 Caucasian adolescent patients: 78 II-1 non-extraction cases (38 females/40 males), 23 II-1 extraction cases (13 females/10 males), and 22 II-2 non-extraction cases (12 females/10 males). An electronic Boley gauge was used (± 0.01 mm) at pre-treatment, post-treatment, and retention examinations with 57 patients evaluated 1-2 years in retention.

Result: Maxillary intermolar widths increased a mean value 2.0 mm (1.8 II-1, 2.2 II-2) during treatment for non-extraction cases but decreased an average of 1.0 mm in extraction cases. Mandibular intermolar widths increased a mean value 0.8 mm (1.1 II-1, 0.6 II-2) during non-extraction treatment but decreased 1.0 mm in extraction cases. All values were higher for males than females. Maxillary intercanine widths increased a mean value 1.6 mm (1.3 II-1, 1.9 II-2) during non-extraction treatment, while mandibular intercanine widths increased a mean value 1.3 mm for both non-extraction groups. Maxillary and mandibular intercanine widths increased an average 1.9 mm during extraction treatment. In the selected retention groups, two circumstances demonstrated greater loss relative to intermolar widths: II-2 non-extraction cases in both arches and II-1 extraction cases in the mandible, which were over 1.0 mm. The intercanine width changes after treatment had a mean loss 0.5 mm except for the mandibular II-1 extraction cases at 1.0 mm.

Conclusion: Intermolar widths slightly increased in non-extraction cases, more in the maxilla and more in males. However, all slightly decreased in retention. Intercanine widths increased in all three groups during treatment and maintained most of it in retention. All these changes were considered clinically not significant.