Objective: The aim of this study was to evaluate the effects of preform arch wires used in fixed orthodontic treatments on the lower and upper dental arch-forms with three-dimensional (3D) model analysis.Materials and Method: This study consisted of pre-treatment (T0) and post-treatment (T1) dental models of 46 patients who had minimal anterior crowding (approximately 3 mm) on the lower and upper arch, and treated in Gazi University, Faculty of Dentistry, Department of Orthodontics. Dental models were scanned using 3Shape R700 3D Scanner and the data was imported into the 3Shape ortho analyzer software program in the form of STL image files. Upper and lower inter-canine, inter-1. bicuspid, inter-2. bicuspid, inter-molar distances, canine and molar depth measurements were performed. Calculation of the area for maxilla was measured between the mucogingival junction of all teeth and the distal points of the 1st molar teeth. Kolmogorov-Smirnov test was used to check the normality. Descriptive statistics were presented as means and standard deviations. Paired t-test was used to compare two dependent groups. The level of significance was taken as 0.05.Results: Significant increases were observed in all parameters except canine depth in the maxilla and inter-canine width during treatment. The highest increase in the maxilla was observed in the inter-1. bicuspid with a value of 2.6 mm (p<0.001). On the other hand, the highest increase in the mandible was observed in the inter-2. bicuspid dimension with a value of 2.45 mm (p<0.001). The increase in maxillary area was significant with an average of 81.69 mm2 (p<0.001). The increase in molar depth was determined as 0.5 mm for both maxilla and mandible (p<0.001).Conclusion: Ni-Ti leveling arches, which are selected in accordance with the pre-treatment arch form of the patients, cause significant increases in the transversal direction in both the maxilla and mandible.