Pharyngeal Airway Changes with Twin Block Appliance in Skeletal Class II Patients: CBCT Study
Dr. BASWARAJ1*, Dr. JAYASUDHA. K2, Dr. MITHUN KASLEKAR3
*Correspondence to: Dr. BASWARAJ, Professor, Department of Dentistry, Dr. Chandramma Dayananda Sagar Institute of Medical Education and Research, Dayananda Sagar University, Kanakpura Road, Harohalli, Ramanagara Dt., Karnataka -562112
Copyright.
© 2026 Dr. BASWARAJ, This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received: 20 October 2026
Published: 09 November 2026
DOI: https://doi.org/10.5281/zenodo.24073453
Abstract
Background: The assessment of upper airway obstructions is an essential part of early orthodontic documentation. Traditional methods, such as lateral cephalograms, have limitations due to their two-dimensional representation of complex tridimensional structures. Cone-beam computed tomography (CBCT) has emerged as a more effective diagnostic tool for evaluating upper airways, providing three-dimensional (3D) images. However, despite the reliability of CBCT scans, there remains a diversity of methodologies for evaluating upper airways. Settings & design: 30 patients aged between 9 to 16 years, of Indian origin, were enrolled in the study.
Methods & materials: This study aimed to investigate the effects of orthopedic mandibular advancement using functional appliances on upper airway dimensions in patients with mandibular retrognathism and Class II malocclusion. CBCT scans were utilized to obtain accurate and reliable 3D data.
Statistical analysis: The significance of the data was assessed using Student’s t-test and Chi-square test, with a p-value < 0.05 considered statistically significant.
Results and conclusion: The results demonstrated significant enlargement in the hypopharynx and oropharynx after functional appliance treatment, supporting the use of early intervention to correct malocclusion and improve airway dimensions.
Keywords: Class II malocclusion, cone-beam computed tomography, functional appliances, pharyngeal airway passage.
Introduction
Class II malocclusions, caused by a deficient mandible and unfavorable maxilla-mandible relationship, are a persistent orthodontic concern. Removable appliances like Frankel Appliances, Bionators, and Twin Block Appliances have been used to address mandibular retrusion and improve dentofacial harmony [1, 2, 3]. It often leads to constricted upper airway, potentially causing sleep apnea [4, 5]. Various appliances, like the TB appliance and cervical headgear, have been found to improve airway dynamics post-treatment [6-9]. Researchers use Cone Beam Computed Tomography (CBCT) to assess upper airway changes in TB treatment, providing a detailed understanding of anatomy, breathing patterns, and nasal airflow resistance [10, 11].
Methodology
Study Design and Setting:
The study was conducted at the Department of Orthodontics & Dentofacial Orthopedics, India. Ethical clearance for the study was obtained from the recommendations of the ethical committee (Ref. No.PDCH/17/EC-60) before commencement.
Participants:
A total of 30 patients aged between 9 to 16 years, of Indian origin, were enrolled in the study. The inclusion criteria encompassed patients with Class II Division 1 or Division 2 malocclusion and mandibular retrusion. Exclusion criteria entailed a history of prior orthodontic treatment, anterior open-bite, severe proclination of anterior teeth, or any systemic condition affecting bone growth.
Treatment Protocol:
Patients in the treatment groups underwent specific appliance therapies. In the FFA group, patients were treated with fixed functional appliances, while the TB group received twin block appliances. The treatment involved a one-step mandibular advancement during wax bite registration. Throughout the study, patients maintained an edge-to-edge incisor relationship with a 2 to 3 mm opening between the maxillary and mandibular central incisors. The appliances were worn for 24 hours, especially during meals, and regular follow-up visits were scheduled approximately every four weeks.
Cone-Beam Computed Tomography (CBCT) Imaging and Analysis:
Pharyngeal airway passage (PAP) dimensions were evaluated using CBCT scans obtained by the CarestreamCS-9600 CBCT machine (Dental Volumetric Reconstruction, CMOS, India). The Dolphin 3D software (Dolphin Imaging & Management Solutions, Chatsworth, California, USA) was utilized for image reconstruction and dimension measurements. The software's airway analysis tool was employed to measure nasopharynx area, nasopharynx volume, oropharynx area, oropharynx volume, hypopharynx area, hypopharynx volume and minimal constricted area.
Data Analysis:
CBCT scans of pre-treatment and post-treatment were collected for the FFA and TB groups, while scans of the control group were obtained before therapy for baseline data (Figure 1,2 and 3). All scans were conducted by the same researcher with patients maintaining an upright sitting posture, natural head position, and tongue at rest position. The CBCT images were transformed into a 3-dimensional virtual model with a standardized threshold value of 73. Measurements were carried out using the Dolphin 3D software, and statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS) version 20.0 for Windows. The significance of the data was assessed using Student’s t-test and Chi-square test, with a p-value < 0.05 considered statistically significant.
Results
A total of 30 patients were included in the study. The age of clients ranged from 9-16 years. Table 1 presents the comparative analysis of pharyngeal airway passage variables (PAP) before treatment and after four months of treatment in fixed functional appliance (FFA) group. We observed significant differences in the hypopharynx Area between pre-treatment and post-treatment, while the other parameters (nasopharynx area, nasopharynx volume, oropharynx area, oropharynx volume, minimal constricted area) did not show significant differences between pre and post-treatment.
Table 2 presents the comparative analysis of PAP before and after treatment in twin block group. We observed a significant effect on the Nasopharynx Area and Nasopharynx Volume, while its impact on other parameters is less clear and not statistically significant.
Table 3 presents the results of statistical analyses comparing control and twin block group. The results suggested that the TB treatment might have a positive impact on increasing the nasopharynx area and nasopharynx Volume. Additionally, there were no significant differences in the other pharyngeal airway parameters between the TB treatment group and the untreated Control group.
Table 4 presents the results of statistical analyses of PAP between FFA and TB groups. Results indicated that there are significant differences between the TB and FFA groups in nasopharynx area and nasopharynx volume both before and after treatment. However, there are significant differences in oropharynx volume between the two groups only after treatment. The other parameters (oropharynx area, hypopharynx area, hypopharynx volume, and minimal constricted area) do not show significant differences between the TB and FFA groups, either before or after treatment. These results suggest that twin block may have a significant impact on the nasopharynx but does not show consistent effects on other anatomical features compared to the FFA group.
Discussion
The present study sought to delve into the effects of orthopedic mandibular advancement on upper airway dimensions in individuals grappling with mandibular retrognathism and Class II malocclusion. Employing the advanced technique of cone-beam computed tomography (CBCT), our investigation ventured beyond the limitations of traditional lateral cephalograms, which tend to encapsulate intricate tridimensional structures in a mere two-dimensional framework.
Our findings provide valuable insights into the effects of fixed functional appliances (FFA) and twin block appliances (TB) on various upper airway dimensions. Notably, the study illuminated a significant enhancement in the hypopharynx area post-treatment within the FFA group.
This aligns intriguingly with previous research, given by Koay WL [12], Bavbek et al. [13], Abdalla et al. [14], Oliviera et al. [15] and Rizk et al. [16] which have demonstrated favorable impacts on oropharyngeal and hypopharyngeal airway dimensions after FFA therapy. This convergence of outcomes underscores the potential of FFA in driving positive alterations in the upper airway landscape.
Similarly, our exploration into the TB group unveiled substantial effects on the nasopharynx area and volume. This congruence with findings by Alhammadi et al. [17] reaffirms the potential of twin block treatment to influence nasopharyngeal and oropharyngeal airway dimensions. Ghodke et al.'s [18] work further corroborates our observations, as their research evidenced augmented pharyngeal airway passage dimensions and posterior pharyngeal wall thickness in Class II malocclusion subjects after twin block appliance intervention.
Surprisingly, our investigation discovered significant differences in the nasopharynx area and volume between the TB and FFA groups both before and after therapy. This effect is similar to the findings of Li et al. [19], who discovered considerable expansion of the hypopharynx and oropharynx in patients following twin block treatment. The intriguing parallelism between our findings and those of Li et al. highlights the persistent ability of twin block treatment to shape upper airway dimensions.
These findings add weight to the growing body of evidence supporting the usefulness of functional appliances in correcting mandibular retrognathism and Class II malocclusion. Beyond malocclusion, our findings raise the intriguing potential that early therapies utilizing functional appliances could result in not only the harmonic alignment of dentition but also a fortuitous impact on airway dimensions. This, in turn, has the potential to reduce the risks of airway-related problems, particularly obstructive sleep apnea syndrome.
Conclusion
Orthopedic mandibular advancement using functional appliances can effectively improve upper airway dimensions in patients with mandibular retrognathism and Class II malocclusion. Early intervention with functional appliances offers potential benefits not only for correcting malocclusion but also for positively impacting airway dimensions, potentially reducing the risk of obstructive sleep apnea syndrome in the future. The adoption of CBCT as a diagnostic method in orthodontic practice can enhance the accuracy and reliability of upper airway evaluations, providing better insights for treatment planning and patient care.
Further research with larger sample sizes and standardized treatment protocols is warranted to validate and expand upon our findings, ultimately advancing the field of orthodontics and its contribution to overall patient health and well-being.
References