Background and Aim: Unilateral extractions have been proposed as potential treatment options to correct Class II subdivision malocclusion, suggesting that most side effects associated with asymmetrical mechanics can be avoided, however the post-treatment arch form may not be symmetrical. Therefore, the aim of this study was to determine the post-treatment effects of unilateral premolar extraction on the maxillary dental arch in Class II subdivision malocclusions.
Material and Methods: Thirty-four patients with Class II subdivision malocclusion were treated for tooth extraction were selected. Patients were divided into two groups treated with unilateral and bilateral extractions in the maxilla.  Dental arch symmetry was assessed using maxillary digital 3D casts and anterior-posterior, vertical and transverse changes of upper dental arch was calculated. The amount of displacement of the molars and canines were recorded and the changes in inclination of incisors was also measured on lateral cephalography. The T-test and k^2 test was used for each index with normal distribution and Mann-u Whitney test was used for specific data with abnormal distribution
Results: The amount of molars asymmetry in the unilateral extraction group in the transverse dimension was 0.15 mm and in anterior-posterior dimension 4.55 mm more than bilateral extraction group which was statistically significant (p≤0.001).  However, in the vertical plane, the molars showed statistically insignificant differences.   The amount of canines’ asymmetry in the unilateral extraction group in the transverse, vertical and anterior-posterior dimension was 0.18 mm, 0.58 mm and in 0.60 mm respectively, when compared with bilateral extraction group which was statistically significant (p≤0.0001). The difference in the inclination of the upper anterior teeth at the end of treatment was also statistically significant.
Conclusion: The effect of unilateral premolars extraction on the symmetry of the dental arch form is significantly different from bilateral premolars extraction.  Unilateral extration leading to more narrow arch and  posterior displacement of molars.