Objective To investigate the effect of orthodontic tooth extraction and non-extraction on dental arch width and esthetical smile. Methods 100 patients treated without extraction and 100 patients treated by 4 first-premolars extraction were selected. The study models of the patients were measured before and after the treatment and compared statistically. Measurements were made in the maxillary and mandibular canine regions from the most labial aspect of the buccal axial surfaces of the canine roots. Results Before treatment, maxillary and mandibular arch widths were the same between both groups (P＞0.05). In non-extraction group, mandibular arch width of posttreatment was 0.88 mm larger than that of pretreatment (P＜0.001), and maxillary arch width of posttreatment was 0.84 mm large (P＜0.001). In extraction group, mandibular arch width of posttreatment was 1.64 mm larger than that of pretreatment (P＜0.001), and maxillary arch width of posttreatment was 1.50 mm large (P＜0.001). After treatment, the width of mandibular arch in the extraction group was 0.59 mm larger than that in the non-extraction group (P>0.05), while the width of maxillary arch in the extraction group was 0.10 mm less (P>0.05).Conclusion Both extraction treatment and non-extraction treatment do not result in narrower dental arch, but wider. The view that orthodontic extraction results in narrower arch widths and unaesthetic smiling is untenable.