Oropharyngeal 3-dimensional changes after maxillary expansion with 2 different orthodontic approaches


The objective of this research was to compare the oropharyngeal volume and minimal cross-sectional area (MCA) changes after maxillary expansion using either the Damon system or Hyrax appliances as assessed through cone-beam computed tomography (CBCT) imaging.


Patients aged between 11 and 17 years with skeletal maxillary transverse discrepancy in need of maxillary expansion were included and allocated randomly into 1 of the 2 treatment groups, Damon or Hyrax. Patients underwent CBCT imaging at 2 time points: T1, after initial clinical evaluation before treatment, and T2, after completion of full orthodontic treatment. The CBCT data were assessed using Dolphin software (Dolphin Imaging & Management Solutions, Chatsworth, Calif). In addition, a qualitative assessment of breathing function was done using the modified Nasal Obstruction and Septoplasty Effectiveness Scale questionnaire.


A statistically significant increase in the oropharyngeal volume (2.23 mL; P = 0.005) and MCA (29.72 mm 2 ; P = 0.007) after the completion of treatment (T2 – T1) for the Hyrax group was suggested. No statistically significant difference was found in the Damon group for volume (1 mL; P = 0.311) and for MCA (7.32 mm 2 ; P = 0.643). In addition, no statistically significant difference was found in the breathing function in both treatment groups ( P >0.05).


Hyrax expansion followed by fixed appliances produced more dimensional upper airway changes at the oropharyngeal level than the Damon system approach. No breathing functional changes were noted in either samples.


  • The oropharynx is prone to collapsibility.

  • Maxillary expansion carried out using hyrax can help increase oropharynx dimensions.

  • More studies are necessary to verify the real effect of maxillary expansion on breathing effort.

The etiology of breathing-related sleep problems varies largely. A possible contributing factor may be due to an atypical orofacial growing pattern that can lead to a diminished size of the upper respiratory tract. This volumetric reduction may be one of the causes of obstructive-related sleep-disordered breathing in children. An atypical orofacial growing pattern may be manifested by a constricted maxilla, usually leading to posterior crossbites and teeth crowding. The earlier the diagnostic and related management is facilitated, the better the possibilities of normalizing the craniofacial development. ,

Maxillary expansion is used to correct posterior crossbites and constricted maxilla, increasing the dental arch perimeter. Indirectly, it has the potential to alter some of the upper airway supporting structures. It can be achieved by using either orthopedic approaches or orthodontic appliances or performing maxillofacial surgery. Rapid maxillary expansion (RME) is a common technique used to manage the constricted maxilla using orthopedic appliances. , The most common RME appliances are fixed (banded or bonded) and have an expansion screw to separate the midpalate suture, increasing the maxillary arch transversal dimensions between 3 and 10 mm. , The activation phase takes approximately a month, and the retention phase, 3-6 months, is required to allow the recalcification of the palatal suture. Hyrax is one of the orthopedic appliances frequently used to manage maxillary dental and/or skeletal constriction through RME. , Moreover, it is the one mostly used in studies evaluating maxillary expansion.

The Damon self-ligating system was first proposed in the 1990s. It is an orthodontic philosophy that is also suggested to manage transversal discrepancies. This treatment approach is based on light archwire-generated forces, which allegedly facilitate faster treatment results, under the assumption of operating through the concept of stimulating cellular activity without damaging the vascular net of the periodontium. Damon system-related expansion is facilitated through a combination of expanded archwires and crossbite elastics. According to Damon’s supporters, considerable expansion can be achieved in the buccal segments, producing a broader arch form. , Only a few studies have evaluated the Damon system results in regard to maxillary expansion, and they suggest increased interpremolar and molar widths after treatment when compared with other conventional self-ligating bracket approaches. , , Although, some argue that those differences could be more related to dental tipping buccally rather than a true skeletal maxillary expansion.

Orthopedic treatments, such as maxillary protraction and maxillary expansion, have been related to increases in the upper airway volume and minimal cross-sectional area (MCA). , However, there is no published scientific evidence regarding what degree of related changes could be produced through the Damon philosophical approach. Following the claim from Damon proponents that the therapeutic effect after its use in the narrowed maxilla is a broader dental arch related to alveolar bone remodeling, we speculate that the upper airway volume and MCA could also be increased. Therefore, the goals of the study were 2-fold: (1) to compare the volume and MCA changes in the oropharyngeal space after maxillary expansion using the Damon system and hyrax appliances, as assessed through cone-beam computed tomography (CBCT) imaging and (2) to compare the subjective patients’ perceived breathing capacity before and after treatment using a modified Nasal Obstruction and Septoplasty Effectiveness (NOSE) questionnaire.

Material and methods

This project was derived from an original study approved by the Health Research Ethics Board of University of Alberta, number Pro00013379. All patients signed informed consent allowing the use of their records for research. The Consolidated Standards of Reporting Trials statement was used to report its methods and results.

Patients aged from 11 to 17 years with skeletal maxillary transverse discrepancy in need of maxillary expansion were included. Patients with unilateral or bilateral posterior crossbites were allocated randomly into 1 of 2 treatment groups, hyrax or Damon approaches, at the orthodontic clinic at the University of Alberta.

Patients in the Hyrax group had the appliance cemented with bands and nonself-ligating brackets were placed on the maxillary teeth from canine to canine and on the mandibular teeth from first molar to first molar. The Hyrax appliance was banded on the maxillary first permanent molars and first premolars. The expansion screw was activated twice a day, 0.25 mm per turn, (0.50 mm per day) until 20% overcorrection was achieved. After correction was achieved, the appliance was left passively for 6 months as a retention period. After this period, the Hyrax was removed and the maxillary first premolars and the first molars were bracketed with nonself-ligating brackets.

The Damon group had full braces installed using Damon Q braces. Buttons were fixed on the lingual surface of the upper first molars and first pre-molars, this way crossbite elastics (3/16 inch, 2-ounce force) were used against lower first molars and first pre-molars brackets/tubes. The elastics were used the entire time until 20% overcorrection was achieved. At the time when overcorrection was achieved, the patients were instructed to wear the elastics at night for 6 months. The archwire sequence used in the first 6 months of treatment was 0.014, 0.016, and 0.018 nickel-titanium wires and by the end of the 6 months had 16 × 22 nickel-titanium wires.

The 20% overcorrection was obtained by overexpanding or expanding until palatal cusps of the maxillary molars were at level of the buccal cusps of mandibular molars. The amount itself was determined by measuring the interpalatal cusp distance of the upper first molars and the interfossa distance of the lower 6s, and the difference would be the expansion needed, and 20% extra was calculated on that.

CBCT scans were acquired with I-Cat (Imaging Sciences International, Hatfield, Pa) at 120 kVp; 18.54 mA; scan time, 8.9 seconds; 0.3-mm voxel size; and field of view 16 × 13 cm. Patients underwent a CBCT scan at 2 time points: T1, before treatment and after clinical evaluation to further investigate the dental and craniofacial orthodontic discrepancies and skeletal crossbite, and T2, after completion of full treatment. The mean time for the second CBCT was 22 months. All images were acquired following the standardized protocol for this study. The patients were instructed to stay still with a natural head position and Frankfort plane parallel to the horizontal plane. The patients’ heads were stabilized with a strip to standardize the head and neck position and to prevent movements. The patients were instructed to maintain the tongue right behind the maxillary central incisors and in maximum intercuspation. The reconstructed images were stored as Digital Imaging and Communications in Medicine files and made anonymous by the dental assistant (C.Z) for blinding purposes. All the CBCTs analyses were made without knowledge of patients’ data.

The CBCT reconstructed data were assessed through the Dolphin software (Dolphin Imaging & Management Solutions, Chatsworth, Calif) ( Fig ). The slice in the midpalatal plane was chosen to insert the boundaries of the landmark to allow the software to evaluate the airway using the sinus/airway tool. The protocol using Dolphin was to select the boundaries as described in Table I and populate the selected area with “seed points.” Thereafter, the area was automatically filled out in pink by the software giving the volume in milliliters. The MCA tool was then enabled to permit the software to calculate it; 2 limiting lines were offered by the software to be placed in the desired area, then the software automatically produced the yellow cut representing the MCA in millimeters. Patients’ data were anonymized by the radiologic technician to avoid bias.

Oropharyngeal volume selected: A, frontal view with seed point and selected oropharynx region; B, sagittal view with boundaries described in Table I and seed point indicating oropharynx region; C, axial view showing seed point and oropharynx area selected.

Table I
Oropharynx boundaries
Region of interest Anterior boundary Posterior boundary Superior boundary Inferior boundary
Oropharynx Line extending from the PNS to the tip of the hyoid bone Line extending from the basion to the inferior border of CV3 Line extending from the PNS to the basion Line extending from the inferior border of CV3 to the superior/posterior tip of the hyoid bone

PNS , posterior nasal spine; CV , cervical vertebrae.

A qualitative assessment of breathing capability was done using the NOSE questionnaire modified from the validated one designed for adult and children populations, the NOSE Scale 2003 by the American Academy of Otolaryngology-Head and Neck Surgery Foundation. , The NOSE questionnaire comprises 5 statements regarding nasal congestion or stuffiness, nasal blockage or obstruction, trouble breathing through the nose, trouble sleeping, unable to get enough air through the nose during exercise or exertion. For each statement, a Likert scale consisting of 5 points ranging from 0 to 4 was used. The patients were instructed on how to fill out the questionnaire and the importance of accurate answers. The question “Over the past month, how much of a problem were the following conditions for you?” was valid for the 5 statements. The 5 possible answers were not a problem, very mild problem, moderate problem, fairly bad problem, and severe problem. The questionnaire was applied at T1 and T2 ( Supplementary material ).

The available pool of CBCTs from patients with transverse deficiency, aged between 11 and 17 years, was considered. To evaluate the sampling capability, we checked the post-hoc power analysis, at a significant level of 0.05. Therefore, 31 patients were allocated in the Damon group and 29 patients were allocated in the hyrax group.

To ensure the same position of images, thus minimizing errors while limiting the landmarks and calculating the volume and the MCA, a standardized protocol was used to reposition the reconstructed Digital Imaging and Communications in Medicines according to the head position as described in a previous study. The Figure shows the oropharynx area selected in the Dolphin software.

Inter- and intrarater reliability for all the measures were performed using part of the sample (n = 24), 12 hyrax and 12 Damon. For the reliability, the recommendations by Walter et al for the sample size calculation and optimal parameters for reliability studies were used following the parameters: α = 0.05, β = 0.2 (implying a power test of 80%), n = 3 (number of replicates − number of repetitions), p 0 = 0.7 (minimum acceptable level of reliability) and p 1 = 0.9 (expected level of reliability). For those parameters, the sample size required for the reliability was 12 subjects.

Statistical analysis

A pilot study tested the reliability of the evaluators using intraclass correlations. Repeated measures multivariate analysis of variance and Bonferroni post-hoc tests were used to analyze the differences between the treatment groups at each time point and each software. A paired-samples t test was applied to verify whether the changes were statistically significant. All the statistical analysis was made at a 5% significance level (95% CI) using SPSS (version 25; IBM, Armonk, NY). Descriptive statistics were used to assess the NOSE questionnaire scores. Analysis of variance test was applied to analyze NOSE data between the groups.


For the reliability test, a total of 144 measures were made from examiner 1 and 96 measures from examiner 2; all results showed an excellent agreement (intraclass correlation >0.93).

A total of 60 patients with unilateral or bilateral posterior crossbites who received treatment at the orthodontic clinics of the University of Alberta were allocated randomly into 1 of 2 groups: group 1 treated with a Hyrax (n = 29) and group 2 treated with Damon approach (n = 31). Table II shows age, sex, vertical skeletal pattern, type of crossbite, and molar width in both groups.

Feb 28, 2021 | Posted by in Orthodontics | Comments Off on Oropharyngeal 3-dimensional changes after maxillary expansion with 2 different orthodontic approaches
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