Changes of pharyngeal airway size and hyoid bone position following orthodontic treatment of Class I bimaxillary protrusion

Abstract

Objectives: To test the hypothesis that the sagittal position of the anterior teeth has no effect on pharyngeal airway dimension or hyoid bone position and to investigate the influence of orthodontic retraction of the anterior teeth on each section of pharynx and hyoid position. Materials and Methods: Forty-four Class I bimaxillary protrusion adults, treated with preadjusted appliances and maximum anchorage after extraction of four premolars, were divided into two groups according to their vertical craniofacial skeletal patterns. Pretreatment and posttreatment variables were compared using paired t-test, and the relationship between pharyngeal airway size and dentofacial variables was analyzed using Pearson correlation coefficient. The changes of pharyngeal airway size and hyoid position after treatment were compared between two groups using independent t-test. Results: Upon retraction of the incisors, the upper and lower lips were retracted by 2.60 mm and 3.87 mm, respectively. The tip of upper incisor was retracted by 6.84 mm and lower incisor retracted by 4.95 mm. There was significant decrease in SPP-SPPW, U-MPW, TB-TPPW, V-LPW, VAL, C3H, and SH (P , .05). No statistically significant different changes were observed in the dentofacial structures, pharyngeal airway, and hyoid position between the two groups after the treatment. There was a significant correlation between the retraction distance of lower incisor and the airway behind the soft palate, uvula, and tongue. Conclusions: The pharyngeal airway size became narrower after the treatment. Extraction of four premolars with retraction of incisors did affect velopharyngeal, glossopharyngeal, hypopharyngeal, and hyoid position in bimaxillary protrusive adult patients. (Angle Orthod. 2012;82:115-121.)

Effect of retraction of anterior teeth on pharyngeal airway and hyoid bone position in Class I bimaxillary dentoalveolar protrusion

“…This confirms that maximal retraction of the anterior teeth did influence the pharyngeal airway posterior to the level of soft palate, uvula, and tongue in adults. The hyoid bone in the present study moved posteriorly similar to the finding by Wang et al 9 ; however, it did not move inferiorly. According to Wang et al, 9 hyoid bone moved both posteriorly and inferiorly.…”

“…The hyoid bone in the present study moved posteriorly similar to the finding by Wang et al 9 ; however, it did not move inferiorly. According to Wang et al, 9 hyoid bone moved both posteriorly and inferiorly. In the present study, there were significant changes in the velopharynx and glossopharynx but no changes were observed in the nasopharynx and hypopharynx due to the fact that the nasopharynx and hypopharynx are not easy to deform because of supportive bone and cartilage, while the antetheca of the velopharynx and glossopharynx is made up of the soft palate and tongue, which were easily affected by the change in the surrounding tissue.…”

“…2) with extraction of four first premolars, similar to the findings by Wang et al 9 and Germec-Cakan et al 11 According to Wang et al, 9 there is a significant decrease in SPP-SPPW, U-MPW, TB-TPPW, V-LPW, VAL, C3H, and SH and no significant changes in PNS-R, PNS-Ad1, HRGN, and HH1; but in our study, the only differences from the above mentioned study were significant changes in HRGN and no significant decrease in V-LPW, VAL, C3H, and SH. This confirms that maximal retraction of the anterior teeth did influence the pharyngeal airway posterior to the level of soft palate, uvula, and tongue in adults.…”

“…6 The correlation between craniofacial growth pattern and pharyngeal airway was found to be doubtful. 7,8 Limited evidence-based research 9,10 is available on the correlation of the retraction of anterior teeth in bimaxillary protrusion patients undergoing extraction of four premolars and the pharyngeal airway. A recent study 9 showed that the orthodontic treatment with extraction of four premolars did influence oropharyngeal airway space in adults.…”

“…7,8 Limited evidence-based research 9,10 is available on the correlation of the retraction of anterior teeth in bimaxillary protrusion patients undergoing extraction of four premolars and the pharyngeal airway. A recent study 9 showed that the orthodontic treatment with extraction of four premolars did influence oropharyngeal airway space in adults. Another study 10 showed that the same orthodontic treatment did not influence oropharyngeal airway in adolescents.…”