The evaluation of asymmetrical premolar extraction treatment on arch symmetry and occlusion

The aim of our study is to retrospectively evaluate the effects of different extraction protocols (asymmetric, unilateral, bilateral) on arch form and symmetry. 86 patients with a mean age of 14,6 ± 2,3 years were included in our study. Of the 86 patients, 115 models were used in our study. Our study groups are as follows; asymmetrical (1st premolar on one side and the 2nd premolar extraction on other side), unilateral (one-sided 1st premolar extraction), and bilateral (1st premolar on both sides) extraction. All measurements were performed digitally. The symmetry between the two sides of the arch was compared between T0 (pre-treatment) and T1 (post-treatment) periods, and the comparisons between the groups were performed over T1-T0 difference. In addition, cephalometric analyzes of the patients included in our study were also made, and dentoalveolar and soft tissue measurements were compared. Bilateral extraction protocol resulted in a statistically significant decrease in the transversal direction asymmetry in the anterior region of the lower jaw (p <0.05). As a result of unilateral extraction, an increase of the anteroposterior asymmetry was observed in the posterior region of the upper jaw, whereas in the lower jaw, asymmetry was decreased for the same parameter (p <0.05). Asymmetric and bilateral extraction protocols reduced the asymmetry of the arch length in the upper jaw. However, as an expected result of unilateral extraction, both the upper and the lower jaw arch length asymmetry was found to be increased significantly (p <0.05). The effects of asymmetric and bilateral extraction protocols on arch asymmetry were found to be similar. Unilateral extraction protocol has an increasing effect on the arch length asymmetry as expected. Unilateral extraction protocol increased the anteroposterior asymmetry in the posterior region of the maxilla but its effect in the lower jaw was the opposite.