Abstract
Background: In this study, we aimed to determine the changes in mandibular incisor proclination and mandibular arch widths after leveling the curve of Spee (COS). Methods: Patients included in this quasi-experimental study were scheduled for fixed orthodontic treatment with a non-extraction therapy in the mandibular arch, no posterior crowding, eruption of all mandibular teeth except third molars, no spacing and Little’s irregularity index greater than 2. The COS depth and mandibular arch widths (inter-canine and inter-molar widths) were measured on plaster casts and recorded in millimeters. Mandibular incisors inclinations were measured on a cephalometric radiograph according to the incisor mandibular plane angel (IMPA) and lower incisor to NB (L1) angle. The pre-treatment and post-treatment values were compared using paired sample T-test. Pearson correlation was used to analyze the association between COS changes and other variables. P-value <0.05 was considered statistically significant. Results: A total of 58 subjects with an average age of 25.10±6.81 years participated in this study. COS depth values significantly reduced after treatment (2.34±0.78mm vs 1.75±0.56mm), (P<0.001). Average IMPA and L1-NB values significantly increased following COS flattening (P<0.001). Mandibular inter-canine and inter-molar widths also showed significant increase after treatment (P<0.001). Pearson’s correlation revealed a significant and inverse correlation between COS changes and mandibular arch width and mandibular incisor proclination values (P<0.001 for both). Patient’s age and gender did not have a significant effect on COS depth. Conclusion: Flattening of COS leads to an increase in lower incisor proclination and mandibular arch width.
Published Version
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