Effect of First Premolars Extraction with Maximum Retraction on Airway and Hyoid Bone Position in Class I Bimaxillary Dentoalveolar Protrusion Cases

Background: The aim was to determine the effect of first premolars extraction with maximum incisor retraction on airway magnitude and hyoid bone position in cases with bimaxillary dentoalveolar protrusion. Methods: Lateral cephalograms of patients with Class I skeletal and dental relationships were retrospectively recruited. Inclusion criteria were 15-30 years old patients having bimaxillary proclination who had undergone all first premolar extractions with maximum incisor retraction. Patients with dentofacial anomalies, chronic mouth breathing and those who had undergone tonsillectomy or adenoidectomy were excluded. Pre-and post-treatment lateral cephalograms were digitally analyzed for airway measurements and hyoid bone position. Paired samples T-test was used for statistical analysis. P-value<0.05 was considered statistically significant. Results: A total of 33 patients, comprising 22 females and 11 males, with a mean age of 24.39 ± 6.92 years were included. Statistically significant differences were found in airway dimensions from pre-treatment to post-treatment; upper airway size between soft palate and posterior pharyngeal wall (SPP-SPPW) was reduced by 1.91mm (12.78%), at uvula & middle posterior wall (U-MPW) by 2.51mm (20.60%), at tongue base to posterior-inferior point on middle pharyngeal wall (TB-TPPW) by 3.39mm (24.26%) and vallecular to lower pharyngeal wall by 1.51mm (9.94%). The vertical position of hyoid bone also significantly reduced as indicated by inferior movement of hyoidale (H) by 4mm (3.8%). There was no significant changes in the horizontal position of the hyoid bone. Conclusion: Premolar extraction with maximum retraction in bimaxillary protrusion cases can decrease the airway dimension and increase vertical position of hyoid bone.