Long term stability of treatment outcome after fixed orthodontic treatment with or without premolar extraction

Purpose: To evaluate and compare the long term stability of treatment outcome in patients treated with fixed orthodontic treatment with and without premolar extractions. Material and methods: Fifty five debonded patients (35 females and 20 males) with complete pre-treatment (T0) and post-treatment (T1) records with at least 3 years of post-retention (T2) were included in the study. These patients were divided into two groups; Extraction group comprising of 30 patients who had undergone 4 premolar extractions and non-extraction group had 25 patients. Long term stability of post-treatment occlusion was assessed with Little's irregularity index, intercanine width and ABO model grading system. Results: The incisor irregularity score increased in both extraction and non-extraction groups from post-treatment (T1) to post-retention (T2) and the mean changes were statistically significant. The results of Mann-Whitney test for Little's irregularity index and intercanine width showed no statistically significant differences between the extraction and the non-extraction groups at T1 to T2. The overall mean changes in the ABO variables showed no statistically significant differences (P>0.05) from post-treatment (T1) to post-retention phase (T2) in extraction and non-extraction groups except interproximal contacts, which showed a statistically significant difference. Conclusion: There was significant relapse in the alignment of maxillary and mandibular anterior teeth with a change in Little's irregularity score, intercanine width and ABO scores from post-treatment to post-retention. The comparison of relapse in extraction and non-extraction groups did not show significant differences from T1 to T2. Therefore, similar relapse may be expected irrespective of treatment plan. (C) 2019 Published by Elsevier Ltd and The Japanese Orthodontic Society.