Changes in pharyngeal airway dimensions and hyoid bone position after maxillary protraction with different alternate rapid maxillary expansion and construction protocols: A prospective clinical study

Abstract

Objective: To evaluate the changes in pharyngeal airway dimensions and the position of the hyoid bone after maxillary protraction with different alternate rapid maxillary expansion and construction (Alt-RAMEC) protocols in patients with skeletal class III malocclusion as a result of maxillary retrusion.

Material and methods: The patients with skeletal class III malocclusions were consecutively divided into two groups. Group 1 consisted of 17 patients (11 boys and 6 girls, mean age 11.31 ± 1.71 years) who had the Alt-RAMEC protocol for 5 weeks, and group 2 consisted of 17 patients (10 boys and 7 girls, mean age 11.64 ± 1.24 years) who had the Alt-RAMEC procedure for 9 weeks. In this study, 4 angular and 13 linear measurements were performed to evaluate the skeletal and pharyngeal airway changes that occurred after maxillary protraction.

Results: A significant increase in the maxillary growth, inhabitation of mandibular growth, and clockwise rotation of the mandible caused the improvement of the maxillo-mandibular relationship in both groups. Those changes caused a significant increase in the upper pharyngeal airway dimension (P < .01) and affected the vertical position of the hyoid bone in both groups (P < .05 and P < .01, respectively). However, changes that occurred in both groups were found to be similar for all airway variables (P > .05).

Conclusion: Upper pharyngeal dimension and vertical position of the hyoid bone were affected by the maxillary protraction with different Alt-RAMEC protocols. There were no statistically significant differences between the groups.

Keywords: Alt-RAMEC; Maxillary protraction; Pharyngeal airway.

Figure 1.

Full coverage maxillary expander.

Figure 2.

Petit type maxillary protraction appliance.

Figure 3.

Cephalometric angular measurements: (1) SNA°, (2) SNB°, (3) ANB°, (4) SN-MP°.

Figure 4.

Pharyngeal airway dimensions: (1) PNS-AD1, the distance from posterior nasal spina (PNS) to posterior pharyngeal wall along the line from PNS to basion (Ba); (2) AD1-Ba, the distance from Ba to adenoid (AD1) along the line from PNS to Ba; (3) PNS-AD2, the distance from PNS to the adenoid tissue (AD2) along the line from PNS to Hormion (H, the point located at the intersection between the perpendicular line to Sella-Ba and the cranial base); (4) AD2-H, the distance from AD2 to H; (5) PNS-Ba, the distance from PNS to Ba (6) Ptm-Ba, the distance from pterygomaxillare (Ptm) to Ba (7) PNS-H, the distance from PNS to H; (8) McNamara's upper pharyngeal dimension, minimum distance from the soft palate to the nearest point of the posterior pharyngeal wall; (9) McNamara's lower pharyngeal dimension, minimum distance from the point where the posterior tongue contour crosses the mandible to the nearest point on the pharyngeal wall; (10) lower pharyngeal dimension, the distance between the anterior and posterior pharyngeal wall through the line between the Cv3ai and Cv3pi points.

Figure 5.

Variables evaluating the position of the hyoid bone: (1) the distance from hyoid (hy) to the horizontal reference line (HRL, the line passing through the tuberculum sella [T] and wing [W] points); (2) the distance from hy point to vertical reference line (VRL, perpendicular line passing through the T point); (3) the distance from hy to Cv3ai.