Abstract: PURPOSE: To study the upper canine's self-adjustment after the first premolar extraction and the effect of casting Nance arch in the sustainment of the upper first molar position. METHODS: Twenty severely crowded adolescents whose upper canines were in labial malposition were chosen. After the treatment plan was made, the upper first premolars were removed, the individually made casting Nance arches were fixed on the upper first molars. The measurement and fixed orthodontic treatment began 6 months later. Graphpad Prism 6.0 software was used for data analysis. RESULTS: The average movement of the malpositioned canines was (3.6±0.1)mm (P＜0.01); while the forward movement of the first molars was (0.2±0.16)mm (P＞0.05). CONCLUSIONS: Extraction of the first premolars is beneficial to the canine's self-adjustment in adolescents and the casting Nance arch could help keeping the first molar's positions.

Key words: Crowding, Auto-adjustment, Casting Nance arch