Editorial Type:
Article Category: Research Article
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Online Publication Date: 04 Jun 2012

Three-dimensional airway evaluation in 387 subjects from one university orthodontic clinic using cone beam computed tomography

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Page Range: 985 – 992
DOI: 10.2319/122811-801.1
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Abstract

Objective:

To determine the linear, volumetric, and cross-sectional area measurements in a large sample of subjects seeking treatment in a university clinic of orthodontics.

Materials and Methods:

Cone-beam computed tomography (CBCT) scans from 387 patients were analyzed retrospectively. All scans were loaded into the 3dMDvultus program (Atlanta, Ga) for airway analysis using automated segmentation. Gender, age, height, weight, airway length, volume, and area of maximum constriction were collected.

Results:

The rostrocaudal length of the airway increased with age until the age of 15 years in female subjects but continued to increase in male subjects and ranged from 44 to 88 mm over the period of 8 to 18 years of age with the gender data combined. The volume of the airway increased through the entire 11-year age range from 2000 mm3 to 27,000 mm3. The rate of airway volume increased at a slower rate in female than in male subjects. The smallest cross-sectional area increased with age ranging from 20 to 250 mm2 but at a slower rate with female subjects, while male subjects demonstrated a more exponential increase after the age of 13 years.

Conclusions:

The human airway increases in length and volume during a rapid period of craniofacial growth in patients between the ages of 8 and 18 years, and the site of maximum cross-sectional area constriction can vary.

Keywords: CBCT; Airway; Humans; Three-dimensional; Volume analysis; Automated analysis

INTRODUCTION

Evaluation of the airway three-dimensionally using cone-beam computed tomography (CBCT) is rapidly becoming the standard in orthodontics and oral surgery1,2 and may eventually be the standard in early diagnostic evaluation of selected patients in otolaryngology.3 CBCT may also replace helical CT as a diagnostic standard.4 Evaluation of calibrated acrylic airway models have indicated the accuracy of CBCT in defining the shape and size.5 The application of CBCT in evaluating patients with obstructive sleep apnea has shown that this relatively low radiation, rapid scanning tool, which provides both multiple planes and three-dimensional (3D) volumetric views, can discern differences in the airway between this experimental group and normal breathing subjects similar to helical CT analysis.6–11

Some studies are now determining how mandibular and maxillary surgery can alter the airway12–14 as well as applying mandibular advancement appliances15 or rapid maxillary expansion.3 Investigators are beginning to evaluate the 3D airway in terms of growth and development, assessing different age groups using both CBCT and helical CT.16–20 Abramson et al.4 found no gender differences in airway parameters; however, airway volume, shape, compactness, and uniformity were greatly influenced by age. As studies increase on 3D analysis, approaches to automatically determine the cross-sectional area at each level as well as the length and volume of the airway will increase.21

This present study evaluates the 3D analysis of the airway from a group of patients seeking orthodontic treatment and representing both genders over a rapid period of craniofacial development in patients between 8 and 18 years of age.

MATERIALS AND METHODS

Subjects

All patient records between March 2009 and December 2010 from a university-affiliated orthodontic clinic were screened for study inclusion in this retrospective study. Exclusion criteria were applied to patients greater than 18 years of age at the time of their record's appointment, CBCT scans that did not include the fourth cervical vertebra (C4), history of breathing problems, mouth breathing habit, complaint of airway restriction, presence of sinus inflammation, evidence of upper airway pathology, or history of any craniofacial surgery or anomaly. The mean ± one standard deviation (1SD) for age was 13.2 ± 2.5 years with a minimum of 7.7 years and a maximum of 18.0 years (Table 1). Patients were not evaluated by the type of malocclusion because the focus was on the type of airways that would be exhibited in a broad age range of children seeking orthodontic care in a university orthodontic setting. The retrospective study of the CBCT records of orthodontic clinic patients was submitted for and received ethical/institutional human research approval.

Table 1 Descriptive Statistics of the Airway of Entire Sample Population Stratified by Gender
Table 1

Data Analysis

Patients had a CBCT scan taken with a third generation i-CAT system (Imaging Sciences International, Hatfield, PA), as part of their orthodontic examination and diagnostic record. The scans were stored in a DICOM (Diagnostic Imaging and Communications in Medicine) format file and loaded into Dolphin Imaging (Chatsworth, CA) for viewing and screening. Each patient's DICOM file was loaded into the 3dMDvultus software (Atlanta, GA) for 3D airway analysis. The patient's head was initially oriented with the palatal plane parallel to the horizontal plane in the sagittal dimension and centered on the coronal and axial axes. This established a reference plane so that all scans could be standardized to this position prior to measuring the airway.

The upper airway extending from the palatal plane to the lowermost border of C4 was outlined by the measurement grid. The grid was constructed along the primary line that extended through the middle of the sagittal, axial, and frontal views of the airway over its whole length (Figure 1). The line was determined visually by a single investigator (Dr Chiang) attempting to maintain the orientation of the line with the orientation of the airway as it curved based on the midline sagittal view. Cross-sectional areas and two linear dimensions (anteroposterior and mediolateral) were calculated for each 2-mm distance over the entire length of the airway (Figure 2). The maximum and minimum cross-sectional areas, including their location along the airway length, were identified and displayed graphically for each subject. The lateral and anteroposterior lengths of the airway were also calculated at each level. This feature of the software provided a method to determine the site of maximum constriction in both the sagittal and frontal planes. Measurements of the total airway volume and length were calculated with the software.

Figure 1. Airway analysis with 3dMDvultus showing the airway in all three dimensions (left) with linear measurements and cross-sectional areas at 2-mm intervals for 20 successive sections.Figure 1. Airway analysis with 3dMDvultus showing the airway in all three dimensions (left) with linear measurements and cross-sectional areas at 2-mm intervals for 20 successive sections.Figure 1. Airway analysis with 3dMDvultus showing the airway in all three dimensions (left) with linear measurements and cross-sectional areas at 2-mm intervals for 20 successive sections.
Figure 1 Airway analysis with 3dMDvultus showing the airway in all three dimensions (left) with linear measurements and cross-sectional areas at 2-mm intervals for 20 successive sections.

Citation: The Angle Orthodontist 82, 6; 10.2319/122811-801.1

Figure 2. Airway analysis with 3dMDvultus showing a scatterplot of the dimensional changes in area (upper right) and linear lengths for the anteroposterior and mediolateral measurements along the airway from the palatal plane to C4.Figure 2. Airway analysis with 3dMDvultus showing a scatterplot of the dimensional changes in area (upper right) and linear lengths for the anteroposterior and mediolateral measurements along the airway from the palatal plane to C4.Figure 2. Airway analysis with 3dMDvultus showing a scatterplot of the dimensional changes in area (upper right) and linear lengths for the anteroposterior and mediolateral measurements along the airway from the palatal plane to C4.
Figure 2 Airway analysis with 3dMDvultus showing a scatterplot of the dimensional changes in area (upper right) and linear lengths for the anteroposterior and mediolateral measurements along the airway from the palatal plane to C4.

Citation: The Angle Orthodontist 82, 6; 10.2319/122811-801.1

Statistical Analysis

SPSS (SPSS Inc, Chicago, IL) version 19.0 was used for statistical analysis. Descriptive statistics were analyzed initially to establish sample mean values and 1SD. The mean airway length, volume, and cross-sectional area were also determined for gender and age stratification. To establish and quantify relationships between the calculated data, best-fit regression analyses were performed with Lowess smoothing for the measurement of all subjects, and then with a quadratic fit and 95% confidence limits for each gender.

RESULTS

Rostrocaudal Airway Length

The mean rostrocaudal length of the airway for the entire sample of patients was 63.7 ± 7.7 mm with a minimum of 44.0 mm and a maximum of 88.0 mm (Table 1). The mean airway length for male patients at 65.3 ± 8.2 mm was significantly longer than for the female population at 62.4 ± 7.1 mm (<.05). The length of the airway increased for female patients up to the age of 15 (Figure 3; Table 2). The length of the airway in male patients increased throughout the entire age range and did not plateau.

Figure 3. Scatterplot showing the distribution of airway length among all subjects with the line of best fit and for female (A) and male subjects (B).Figure 3. Scatterplot showing the distribution of airway length among all subjects with the line of best fit and for female (A) and male subjects (B).Figure 3. Scatterplot showing the distribution of airway length among all subjects with the line of best fit and for female (A) and male subjects (B).
Figure 3 Scatterplot showing the distribution of airway length among all subjects with the line of best fit and for female (A) and male subjects (B).

Citation: The Angle Orthodontist 82, 6; 10.2319/122811-801.1

Table 2 Overall Changes in Airway Dimensions From Ages 8 to 18 Years Among Male and Female Subjects
Table 2

Airway Volume

The mean airway volume for the entire sample of patients was 11,125.4 ± 4402.5 mm3 with a minimum of 1314.0 mm3 and a maximum of 26,530.0 mm3. Male patients had a significantly larger mean airway volume of 11,836.8 ± 4815.4 mm3 vs that for female patients of 10,550.0 ± 3956.9 mm3 (Table 1). The volume of the airway increased almost linearly from 8 to 18 years of age in the female patients (Figure 4; Table 2). In contrast, the airway volume increased from 8 to 10 years of age in the male patients, and then increased with an even greater rate of growth from 11 to 18 years of age.

Figure 4. Scatterplot showing the distribution of total airway volume among all subjects with the line of best fit and for female (A) and male subjects (B).Figure 4. Scatterplot showing the distribution of total airway volume among all subjects with the line of best fit and for female (A) and male subjects (B).Figure 4. Scatterplot showing the distribution of total airway volume among all subjects with the line of best fit and for female (A) and male subjects (B).
Figure 4 Scatterplot showing the distribution of total airway volume among all subjects with the line of best fit and for female (A) and male subjects (B).

Citation: The Angle Orthodontist 82, 6; 10.2319/122811-801.1

Smallest Cross-sectional Area of the Airway

The mean of the smallest cross-sectional area for the entire sample of patients was 101.9 ± 47.4 mm2 with the minimum of 9.7 mm2 and a maximum of 258.0 mm2. The cross-sectional area was significantly smaller in the female patients with 100.6 ± 44.7 mm2 than with the male patients with 103.5 ± 50.7 mm2 (Table 1). The smallest cross-sectional area of maximum constriction increased with age. Female patients demonstrated a linear relationship, while male patients showed little change from 8 to 11 years, and then a rapid increase from 11 to 18 years at a more rapid rate than seen in female patients (Figure 5; Table 2).

Figure 5. Scatterplot showing the distribution of smallest cross-sectional area among all subjects with the line of best fit and for female (A) and male subjects (B).Figure 5. Scatterplot showing the distribution of smallest cross-sectional area among all subjects with the line of best fit and for female (A) and male subjects (B).Figure 5. Scatterplot showing the distribution of smallest cross-sectional area among all subjects with the line of best fit and for female (A) and male subjects (B).
Figure 5 Scatterplot showing the distribution of smallest cross-sectional area among all subjects with the line of best fit and for female (A) and male subjects (B).

Citation: The Angle Orthodontist 82, 6; 10.2319/122811-801.1

Site of Maximum Cross-sectional Area Constriction

The area of maximum cross-sectional constriction was distributed along the entire rostrocaudal length of the airway, which began rostrally at the site of the hard palate and extended to the C4 vertebra (Figure 6). However, when the site for maximum constriction was evaluated across all the subjects, two particular sites showed a higher frequency of occurrence along the airway length. A distinct bimodal distribution was observed at the 40% and 80% area between the palatal plane and tangent to C4.

Figure 6. Distribution of the site of maximum constriction along the airway from the palatal plane to C4.Figure 6. Distribution of the site of maximum constriction along the airway from the palatal plane to C4.Figure 6. Distribution of the site of maximum constriction along the airway from the palatal plane to C4.
Figure 6 Distribution of the site of maximum constriction along the airway from the palatal plane to C4.

Citation: The Angle Orthodontist 82, 6; 10.2319/122811-801.1

Evaluation of the Airway Length and Total Volume

The total volume of the airway increased with an increase in rostrocaudal length of the airway from the hard palate to the epiglottis (Figure 7). The best fitting curve showed the airway volume increased at a greater rate when the length of the airway increased above 68 mm in length. Female patients demonstrated a slow increase in airway volume until the length of the airway exceeded 60 mm, and then a more rapid increase in volume to length occurred. Male patients showed a similar type of curve with a greater volume attained as the length increased compared with female patients.

Figure 7. Scatterplot showing the distribution of total airway volume to the length of the airway among all subjects with the line of best fit and for female (A) and male subjects (B).Figure 7. Scatterplot showing the distribution of total airway volume to the length of the airway among all subjects with the line of best fit and for female (A) and male subjects (B).Figure 7. Scatterplot showing the distribution of total airway volume to the length of the airway among all subjects with the line of best fit and for female (A) and male subjects (B).
Figure 7 Scatterplot showing the distribution of total airway volume to the length of the airway among all subjects with the line of best fit and for female (A) and male subjects (B).

Citation: The Angle Orthodontist 82, 6; 10.2319/122811-801.1

DISCUSSION

Overall Changes With Age

This study, using an automated evaluation of the airway in subjects seeking orthodontic treatment at a university clinic, indicates the length of the airway increases in subjects but with distinct gender differences in which female patients do not demonstrate further lengthening of the airway after 15 years of age, while male patients continue to increase the length of the airway. In contrast, the 3D volume of the entire airway continues to increase through the entire 11-year period from 7 to 18 years but at a faster rate in male patients compared with female patients. The smallest cross-sectional area also slowly increases in size with increase in age but demonstrates a faster rate of increase about 12 years of age for male patients. When evaluating the rostrocaudal site of the airway where the smallest cross-sectional area is located, it can occur at almost any level of the airway but particularly at two regions, which are the oropharynx and hypopharynx. As the rostrocaudal length of the airway increases, the airway volume increases and changes to even higher rate of increase when the airway begins to exceed the length of 60 mm.

Gender Changes

Male patients had longer and larger airways than female patients with a greater increase in dimensions with age. The pattern of increase in airway length, when analyzed by gender, may relate to the pubertal growth spurt of the individual. Female patients showed a significant increase in length from ages 7 to 15 years of age as opposed to male patients who showed significant increase in dimensions among all age groups from 7 to 18 years. This is consistent with the general growth of the skeletal and soft tissue growth curves. The airway volumes increased in both female and male patients with each age group from 7 to 18 years, with the male patients just indicating a faster rate. The smallest cross-sectional area increases with age in both female and male patients but at a faster rate in male patients after 12 years of age.

Comparison Among Studies

Fagala et al.22 demonstrated findings similar to our study that the airway volume increased in children between 5 and 20 years of age but with a faster growth in boys of about 1200 mm3/year vs 900 cm3/year in girls. Our study indicated a much greater rate of growth of the airway volume in boys after the age of 11, while girls demonstrated a more consistent and steady rate of increase in airway volume. The study by Alves et al.19 of 50 children with a mean age of 9.2 years found no difference in airway volume or smallest cross-sectional area between the two genders, but the volume and area were different between those defined clinically as nasal breathers and mouth breathers. Our study found the same results demonstrating that the children from 7 to 11 years of age of both genders have similar airway volumes and smallest cross-sectional areas at this young age. The Alves study showed that the normal subjects as nasal breathers had an average airway volume of 8171.3 mm3 ± 1710.3 mm3, while mouth breathers had a significantly smaller volume of 5594.7 ± 1878.8 mm3. Our study attempted to exclude mouth breathers using minimal clinical test standards but showed similar findings that children from 7 to 11 years of age had an average airway volume of 8029.1 ± 2594.1 mm3. The study by Valiathan et al.23 examined 40 patients between the age of 12 and 15 years and showed that the control subjects seeking orthodontic treatment without extraction had a smaller oropharyngeal airway volume (10,301.5 ± 3060.8 mm3) than those subjects who were designated for orthodontic treatment by extraction (11,593.0 ± 4513.0 mm3). Our study of 11- to 15-year-old children indicated that the average airway volume was similar (10,758.8 ± 3669.0 mm3) to the orthodontic patients seeking treatment through nonextraction.

Limitations of the Study

Limitations of this study include potential inaccuracies in history and clinical exam of the patients as they were dependent upon residents collecting and entering the information into the patient database. The reliance on a number of operators working in conjunction and using the exclusion criteria in the same way was a factor. The airway is a dynamic and complex structure, and current 3D analysis has limited measuring capability for a structure that is in constant motion. Future studies with 4D measurement techniques need to address changes in airway with time, and then need to define the physiological parameters of airway resistance and pressure.24 The airway may also change with the type of malocclusion as well as with treatment, which will require further study.

CONCLUSIONS

  • An automated analysis of the human airway in 387 subjects between the ages of 7 and 18 years indicated that the rostrocaudal length of the airway increased up to the age of 15 years and then showed a plateau without further changes in female subjects but continued to increase in male subjects.

  • The 3D total volume of the airway increased through the entire 11-year period, from 7 to 18 years of age. The total volume of the airway increased at a faster rate in male than in female patients with the rate of growth in the volume increasing after the age of 11 years.

  • The smallest cross-sectional area of the airway occurred in the youngest subjects and then increased with age, with male patients showing a higher rate of increase after 11 to 12 years of age. The airway volume increased with an increase in length of the airway and increased that rate after the airway exceeded 60 mm in length.

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Copyright: The EH Angle Education and Research Foundation, Inc.
Figure 1
Figure 1

Airway analysis with 3dMDvultus showing the airway in all three dimensions (left) with linear measurements and cross-sectional areas at 2-mm intervals for 20 successive sections.

Figure 2
Figure 2

Airway analysis with 3dMDvultus showing a scatterplot of the dimensional changes in area (upper right) and linear lengths for the anteroposterior and mediolateral measurements along the airway from the palatal plane to C4.

Figure 3
Figure 3

Scatterplot showing the distribution of airway length among all subjects with the line of best fit and for female (A) and male subjects (B).

Figure 4
Figure 4

Scatterplot showing the distribution of total airway volume among all subjects with the line of best fit and for female (A) and male subjects (B).

Figure 5
Figure 5

Scatterplot showing the distribution of smallest cross-sectional area among all subjects with the line of best fit and for female (A) and male subjects (B).

Figure 6
Figure 6

Distribution of the site of maximum constriction along the airway from the palatal plane to C4.

Figure 7
Figure 7

Scatterplot showing the distribution of total airway volume to the length of the airway among all subjects with the line of best fit and for female (A) and male subjects (B).

Contributor Notes

Corresponding author: Chuen Chie Chiang, DMD, Roseman University of Health Sciences College of Dental Medicine Advanced Education in Orthodontics and Dentofacial Orthopedics, Henderson, NV (e-mail: drchiangc@gmail.com)
Received: 01 Dec 2011
Accepted: 01 Mar 2012
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