Effects of orthodontic extraction on mesiodistal angulation of lower second molars in patients with early permanent dentition correction.

Objective This study aimed to explore the relationship between the spontaneous changes of mesiodistal angulation of lower second molars (L2M) and individual clinical characteristics in patients with early permanent dentition correction. Methods A total of 44 patients with a total of 88 mandibular second molars were included in this study after screening. Based on the frequency distribution histogram of the initial angle of inclination (L2M initial angle) of the L2M crown before treatment, it was divided into three groups: Group A: small angle group, L2M initial angle is 0° ~ 17.5°; Group B: medium angle group, L2M initial angle is 17.5° ~ 42.5°; Group C: large angle group, L2M initial angle is 42.5° ~ 60°. According to whether L2M has erupted and exposed most of the crown, it was divided into erupted group and unerupted group. According to the mandibular plane angle, it can be divided into high angle, low angle, and average angle. CBCT reconstructed panoramic images were used to measure the mesiodistal inclination of L2M and analyze the relationship between each group and the change in mesiodistal inclination angles of L2M. Results After treatment, L2M mesiodistal angulation in the small angle, large angle, non-eruption, and high angle groups became more significant. The angle in the middle angle group was significantly smaller. The L2M mesiodistal angulation in the eruption and average angle group did not change significantly.The angles of ANB, Y-axis, and mandibular plane have no correlation with the initial angle of L2M. Conclusion The L2M in patients with large and high angles is more likely to topple during a correction. During the correction, the L2M tends to approach the normal axial inclination. [ABSTRACT FROM AUTHOR]