Long-term stability of dental arch widths after extraction and nonextraction orthodontic treatment: A retrospective cohort study.

Background: Dental arch width is considered biologically determined and is associated with a balanced occlusion. However, it is often actively altered during orthodontic treatment and these modifications are associated with postorthodontic relapse. The purpose of this study was to assess the long-term dental arch width changes among patients treated orthodontically with fixed appliances and assess the effect of dental extractions.

Methods: Young (<18 years) patients with malocclusion, who had been treated orthodontically with 0.018"-slot edgewise fixed appliances, were included in this retrospective longitudinal study. The maxillary/mandibular intercanine, interpremolar, and intermolar widths were digitally measured before treatment (T1), at debond (T2), and an average of 7 years post-debond (T3). Data was analyzed statistically at 5% with regression modeling, while a subsample of borderline patients was analyzed to assess the effect of extractions on long-term stability.

Results: A total of 104 patients were included (59.6% female; 11.5-year-old at T1), 39.4% (41/104) of which were treated with premolar extractions. All dental arch widths were increased during fixed appliance treatment, with considerable differences between extraction and nonextraction cases (P < 0.05 in all cases). On average 7 years post-debond, nonextraction cases showed significant relapse in intermolar width, while intercanine and interpremolar widths remained stable. After baseline matching of extraction/nonextraction cases, tooth extractions were not associated with post-treatment relapse (P > 0.05). Treatment-related (T1-T2) increases in all three dental arch widths were associated with post-treatment (T2-T3) relapse for both jaws, with 0.20-0.34 mm T2-T3 relapse for each additional 1 mm of width increase during T1-T2.

Conclusions: Modest dental arch width increases during fixed appliance treatment showed satisfactory stability in the long term, while greater archwire expansion was associated with increased relapse.