Three-dimensional assessment of morphological variations in oropharyngeal airway of skeletal class III malocclusions among different age groups in adolescent patients: A retrospective study

INTRODUCTION

The soft palate, tongue, pharyngeal fat pads, mandible, and maxilla have been found in literature to influence airway volume through their positions.^[1] Many previous studies have assessed the relationship between the morphology of the craniofacial region and pharyngeal airway using cephalometric radiographs.^[2-4] From a two-dimensional to a three-dimensional (3D) study with the introduction of cone beam computed tomography in the maxillofacial region has brought a true paradigm shift.^[5] It has been reported in previous research that the radiation exposure for one cone beam computed tomographic scan is about 0.25 mSv. The International Radiation Protection Association stated that the radiation exposure received by each person every year is about 2.5 mSv.^[6] Hence, the cone beam computed tomographic scans for the patients in this study were safe.

A study on airway volume for different dentofacial skeletal patterns concluded that oropharyngeal airway volumes of class III and class I patients were larger when compared with class II patients.^[7] Some authors have studied the association between the surgical outcomes and the morphology of the airway among patients having sleep apnea.^[8,9] Therefore, it seems very important to provide adequate and scientific information regarding airway development in children and airway changes in adults for different treatment methods.

It has been reported by authors that the airway size increases until the age of 20 years and then gradually decreases by the age of 40 years; also, it has been reported that there is an increase in the reduction rate after the age of 40 years.^[10] While another research reported that the various measurement values of the upper airway and anteroposterior dimensions of the pharynx were significantly higher in the 21–40-year-old age group compared to the 6–20-year age group.^[11]

Although a variety of different studies have been conducted regarding pharyngeal airway measurements, there is very little research on oropharyngeal airway considering different age groups in adolescent skeletal class III patients; hence, this study was done.

MATERIAL AND METHODS

The protocol used in this research study was approved by the institutional ethical committee at Government Dental College and Hospital, Chhatrapati Sambhajinagar, approval number: SR NO/ Prostho/GDCH/274/2024, dated 28th March 2024. A retrospective study was performed on pre-treatment cone beam computed tomographic images obtained from the oral radiology department and department of orthodontics of the dental college and hospital.

All the essential pretreatment cone beam computed tomography (CBCT) images were taken as pretreatment supplementary diagnostic records for orthodontic patients. CBCT scans were done for the patients having impacted teeth or other orofacial abnormalities. The consent forms with a statement allowing the use of their CBCT scans and orthodontic records without individual identification were signed by all patients and parents of minor age (age below 15 years). All the CBCT scans were done by a trained and experienced technician. Hence, the data collected was consistent and reliable.

A sample size for this study was determined using the estimates of mean and standard deviation values from a previous study.^[7] A sample size of at least 53 patients with a test power of 0.80 (α = 0.05) would be necessary in this study in each group. The formula used was described by Chow et al.^[12]

A total of 318 CBCT scans/patients having the skeletal class I control group and skeletal class III group were observed and analyzed. These were divided equally into three adolescent age groups – 10–13 years (early adolescence), 14–16 years (middle adolescence), and 17–19 years (late adolescence) – for both skeletal Class I (ANB 1°–3°, non-skeletal dental malalignment and/or impacted teeth) and skeletal Class III (ANB <1°) patients. Thus, each age group comprised approximately 53 subjects (27 girls and 26 boys) as per the sample size calculation.

Lateral cephalograms were obtained from cone beam computed tomographic data that were opened with the Carestream CS9300S CBCT model. Cephalometric linear and angular measurements were made using Carestream CS 9300S 3D Imaging Software to rule out the skeletal class III and skeletal class I malocclusions, which are shown in [Figure 1].

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Figure 1:

Linear and angular measurements used in this study: (1) ANB, angle between the maxilla and the mandible; (2) SNA, angle between the base of the cranium and maxilla; (3) SNB, angle between the base of the cranium and mandible; (4) FMA, mandibular plane angle.

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To rule out the morphological variations of the oropharyngeal airway among different adolescent age groups in the skeletal class III and skeletal class I malocclusion patients, different oropharyngeal variables were measured and compared among themselves. Further, the comparison was done between skeletal class III and skeletal class I control group patients having different adolescent age groups to rule out the variations in the oropharyngeal airway. All oropharyngeal variable measurements and landmark identifications, except for oropharyngeal (OP) volume, were made using Carestream CS 9300S 3D Imaging Software, which is shown in [Figure 2].

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Figure 2:

(a) Oro-pharyngeal vertical length is the vertical length between the upper and lower borders of the oropharynx airway. (b) PAS (posterior airway space in sagittal slice). (c) minAx transverse (posterior airway space in axial slice).

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OP volume in all sample sizes was measured with the ITK-SNAP 4.0 software. Further, ITK-SNAP 4.0 software has significantly improved efficiency and reliability.^[13] The superior and inferior limits of the OP airway volume are shown in Figure 3 and 3D rendering of the OP volume is shown in Figure 4.

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Figure 3:

The inferior and superior limits of the OP airway volume: pp: Palatal plane (the line passing and extending to the posterior wall of the pharynx from ANS and PNS); 2cv: the line passing from the most anteroinferior point on the second cervical vertebrae and that is parallel to the palatal plane.

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Figure 4:

Three-dimensional rendering of the oropharynx volume: (a) Axial view; (b) Sagittal view; and (c) Coronal view.

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RESULTS

Descriptive demographics of our study sample are shown in [Tables 1 and 2]. The groups consisted of skeletal Class III patients and skeletal Class I patients with a total sample size of 318. Each group was further divided into three different age groups: 10–13 years (early adolescence), 14–16 years (middle adolescence), and 17–19 years (late adolescence). Each age group consisted of 53 subjects (27 girls and 26 boys).

In subjects with skeletal class I in the age group 14 to 16 years, the mean value of PAS measurements for oropharyngeal airway variables was higher by 12.21 ± 2.80 mm compared to other age groups [Table 1]. In the age group 14–16 years, we found a higher mean value of OP volume, with a difference of 1646.33 mm³ around the mean value of 10073.32 mm³.

[Table 3] shows the results for intergroup pairwise comparisons with Tukey Honestly Significant Difference (HSD) post hoc tests among skeletal class I subjects. Comparison between age group 14–16 and age group 17–19 showed a highly significant mean difference of 4.36 mm. While comparing age groups 10–13 and 17–19, the highly significant mean difference was 4.19 mm. Comparison of OP volume between age groups 10–13 and age group 14–16, the highly significant mean difference found was −2521.84 mm³. While comparing age groups 10–13 and 17–19, the highly significant mean difference was −2413.30 mm³.

Intergroup comparison of oropharyngeal airway variables for skeletal class III subjects showed [Table 2] that PAS showed a higher mean value of 14.53 ± 2.42 mm in the age group of 17–19. OP volume showed a higher mean value of 11477.28 ± 2299.38 mm³ in the age group of 17–19. There was a statistically nonsignificant difference seen for the values between the groups for all other variables.

Intergroup pairwise comparison using Tukey HSD post hoc tests for skeletal class III subjects showed [Table 4] that the comparison for PAS between age groups 10–13 and age group 17–19 had a highly significant mean difference of −2.01 mm. While comparing age groups 14–16 and 17–19, the significant mean difference was −1.33 mm. Comparison of OP volume between age groups 10–13 and age groups 17–19, the highly significant mean difference was −3282.50 mm³. While comparing age groups 10–13 and 14–16, the highly significant mean difference was −2568.60 mm³.

Intergroup comparison of oropharyngeal airway variables between skeletal class I and skeletal class III subjects showed [Table 5] that comparison for PAS in age group 17–19 showed a higher mean value of 14.53 ± 2.42 mm in subjects with skeletal class III. OP volume showed that there was a higher mean value of 11477.28 ± 2299.38 mm³ in skeletal class III in the age group 17–19.

Detailed statistics about intergroup comparison of males versus females for oropharyngeal airway variables of skeletal class I subjects in adolescent age groups are shown in [Tables 6-8].

Detailed statistics about intergroup comparison of males versus females for oropharyngeal airway variables of skeletal class III subjects in adolescent age groups are shown in [Tables 9-11].

DISCUSSION

A number of previous studies^[7,14,15] evaluated airway volumes and measurements of the pharyngeal airway in adolescents using CBCT. In all these previous studies, adolescents included were between the ages of 12 and 20, according to chronological age. In the present study, oropharyngeal airway variations were evaluated and compared among early adolescents (10–13 years), middle adolescents (14–16 years), and late adolescents (17–19 years).

It has been reported that in the previous studies, pharyngeal structures continue to grow rapidly until 13 years of age;^[16] between the ages of 14 and 18 years, a quiescent period has been reported for the pharyngeal structures,^[17-19] and it has been established in the long-term follow-up studies that, between the ages of 20 and 50 years, the soft palate of the oral cavity becomes thicker and longer, and the pharyngeal region gets narrower.^[20,21]

In this present study, the PAS was also smaller in the skeletal class I control group subjects in late adolescents as compared to early adolescents and middle adolescents. However, while comparing in skeletal class III, it was vice versa. The reason for the results obtained in skeletal class III could be due to the anterior position of the tongue, which increases the PAS in skeletal class III subjects.

OP volume in late adolescents and middle adolescents was higher than in early adolescents among both skeletal class III and skeletal class I groups. The reason for the results obtained in skeletal class III could be due to the anterior position of the tongue increasing the PAS in skeletal class III subjects, but the results obtained in subjects having skeletal class I malocclusion here are controversial compared to some of the previous studies’ results that are stated above.

To describe anteroposterior dentofacial discrepancies for the selection of skeletal class III and skeletal class I patients in this study, the cephalometric ANB angle was the measurement of choice because it is a widely used method. ^[22,23]

It has been mentioned in previous studies that there is no influence of growth pattern and malocclusion type on lower pharyngeal airway width.^[24] It was observed that skeletal Class III and skeletal Class I subjects had significantly larger airway volumes when compared with skeletal Class II subjects.^[7] Furthermore, it has been reported that the skeletal Class III malocclusion group had the widest airway width when compared with the skeletal Class I malocclusion group.^[25] In this present study, it was found that while comparing skeletal class III and skeletal class I subjects, PAS and OP volumes in late adolescents were significantly lower in skeletal class I subjects than in skeletal class III subjects.

In one study, results showed that the pharyngeal dimensions were not affected by sex in any of the studied groups.^[7] Another study reported that the width of the lower pharyngeal airway was wider in males than in females in the skeletal class III malocclusion group. ^[25]

In this study, while comparing different age groups for skeletal class I subjects, OP volume was found to be higher in early adolescent females and in late adolescent males. minAx transverse was higher in middle and late adolescent males. OP VERT. was higher in late adolescent females.

While comparing different age groups for skeletal class III subjects, PAS was higher in early adolescent males. minAx transverse was higher in middle adolescent females, and OP VERT. was higher in late adolescent females.

CONCLUSION

Among skeletal Class III subjects, PAS was significantly greater in late adolescents compared to early and middle adolescents, whereas the opposite trend was observed in skeletal Class I subjects.

OP airway volume in both skeletal Class I and Class III groups was significantly higher in middle and late adolescents compared to early adolescents. In addition, late adolescents with skeletal Class III patterns demonstrated significantly greater PAS and OP volumes than their Class I counterparts.

Males and females differed significantly in oropharyngeal variables among different adolescent age groups.