Extraction Orthodontic Treatment Changes On Upper Airway Dimension And Hyoid Bone Position In Adolescents With Classâ…¡ Malocclusion

Objective:To analyze the changes of the upper airway dimension and the hyoid bone position in adolescents with skeletal class â…¡ malocclusion after extraction or nonextraction orthodontic treatment, and to investigate the relationships between the changes in the dentofacial structure and the upper airway dimension and the hyoid bone position.Methods:40adolescents with skeletal class â…¡ malocclusion and normally vertical growth pattern were selected,20patients with four premolars extraction for study group and20patients without extraction for control group. Cephalometric analysis of the dentofacial structure, upper airway dimension and hyoid bone position was performed before and after treatment. The data were analyzed by paired sample t-test, independent sample t-test and linear correlation analysis.Results:After treatment, SNA angle and ANB angle significantly decreased, and the upper and lower incisors were significantly retracted in the extraction group (P<0.01). While in the nonextraction group, changes in the craniofacial measurements were not statistically different (P>0.05) except the lower incisors were significantly labial inclined. Of all the upper airway demensions only the skeletal nasopharyngeal dimensions increased in nonextraction group (PNS-Ba, P<0.05). The hyoid bone moved down within two groups (AH-FH, AH-SN, AH-PP, P <0.01), and the hyoid bone moved backward in extraction group (AH-RGn, AH-NP, P<0.05). In linear correlation analysis, the changes of U-MPW and PAS were positively correlated with the changes of SNB angle in extraction group (P<0.05), while the changes of SPP-SPPW were negatively correlated with the changes of ANB angle in nonextraction group (P<0.05). The changes of AH-Or were positively correlated with the changes of Y axis angle within two groups (P<0.01).Conclusion:Whether the adolescents with skeletal class â…¡ malocclusion and normally vertical growth pattern are treated by extraction or nonextraction orthodontic treatment, their craniofacial growth patterns have smaller changes. The oropharyngeal airway dimension can not be changed obviously by extraction orthodontic treatment, however extraction treatment will affect the nasopharyngeal airway dimension and the hyoid bone level position. The changes of jaw bone, especially the size and position of the mandible have more effects than the displacement of teeth on the oropharyngeal airway dimension and the hyoid bone level position.