The effects of curve of spee in skeletal class II patients treated with combined orthodontics and surgery
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Purpose: To perform a retrospective study with the question: Is there a significant correlation between pre-surgical Curve of Spee (COS) and skeletal changes from mandibular bilateral sagittal split osteotomy (BSSO) advancement surgery? Furthermore, in skeletal Class II patients, does initial mandibular plane angle (MPA) make a difference? Methods: The sample was made up of a group of patients who underwent a single surgical procedure of mandibular BSSO advancement and divided into three groups by mandibular plane angle (MPA). Pre-surgical Curve of Spee (COS) was measured on digital dental models and correlated with skeletal changes from pre-surgical and post-surgical cephalograms using Spearman rank-order analysis. Paired T-test was utilized to identify statistical significance. Regression analysis was performed to estimate the cephalometric change per unit of pre-surgical COS. P-value was set at 0.05. Results: The sample was composed of 90 subjects; divided into 3 groups: (1) high-MPA (MPA 34.10 ± 3.23°; aged 26.28 ± 17.66 years; n = 30) (2) medium-MPA (MPA 27.85 ± 1.61°; aged 22.04 ± 11.40 years; n = 30) (3) low-MPA (MPA 20.91 ± 3.20°; aged 26.84 ± 15.58; n = 30). Statistical significance was found between pre-surgical Curve of Spee (COS) and both linear and percentage changes of lower face height (LFH) in the low-MPA group (p < 0.001). The estimated relationship between COS and LFH was that for each 1mm pre-surgical COS, there was an increase in LFH of 1.629 mm from the surgical procedure (p = 0.000). Conclusion: Pre-surgical Curve of Spee is significantly correlated with surgical changes in lower face height in low-MPA subjects. The quantified ratio between them could be applied in simulating surgical outcome clinically.