Evaluation and quantification of airway changes in Class II division 1 patients undergoing myofunctional therapy using twin block appliance

Abstract

Background

The purpose of the present study was to determine the airway changes in skeletal class II division 1 malocclusion patients with mandibular retrognathism, treated with Twin-Block (TB) appliance.

Methods

Airway assessment was carried for twelve patients (mean age 11.7 ± 1.1 years) who underwent myofunctional therapy using TB appliance for correction of skeletal class II division 1 malocclusion with mandibular retrognathism. Acoustic pharyngometry (AP) was used to assess and quantify the comparative changes in the upper airway, pretreatment and posttreatment.

Results

Data acquired was subjected to appropriate statistical analysis. The paired ‘t’ test was used to compare pre-treatment (T0) and after the positive pterygoid response (T1). TB appliance increased mean minimum airway area by 0.28 ± 0.25 cm² and mean airway by 0.47 ± 0.44 cm² with 95% CI. Posttreatment minimum airway and mean area changes were found to be statistically significant (P-value<0.01).

Conclusion

TB appliance therapy has a positive effect on upper airway and is beneficial for the treatment of sleep-related disorders associated with Class II division 1 malocclusion for achieving positive functional changes, esthetics, and healthier quality of life.

Introduction

Skeletal Class II division 1 is a prevalent condition affecting around 30 percent of the population in the world. Literature has shown the incidence of this skeletal malocclusion to be as high as 15 percent in the Indian population.¹ The malocclusion can be attributed either to maxillary prognathism, mandibular retrognathism, or a combination of both. This skeletal malocclusion not only affects the esthetics and function of the patients but can also lead to compromised airway due to retro positioning of the jaws and tongue, leading to poor quality of life of an individual.

As airway problems have a profound negative impact on craniofacial growth and development, it is imperative that the airway examination be an integral part of the diagnosis and treatment of cases of skeletal Class II malocclusion with a retrognathic mandible. These cases are also predisposed to the development of future systemic and respiratory complaints, such as Sleep Disordered Breathing (SDB) because of compromised airway dimensions.2, 3, 4

Various designs of myofunctional appliances have been used to advance the mandible and correct such skeletal class II division 1 malocclusion starting from Monobloc, Activator, Bionator, Frankel to one of the most commonly used appliance i.e., Twin-Block (TB) appliance. Monoblock appliance developed by Dr. Robin is considered to be the pioneer of all Functional appliances.⁵ The origin of TB follows way back in history with the introduction of the Monoblock appliance used in a new-born by Dr. Robin to maintain the airway and prevent the tongue from falling back during sleep. The same concept is being used in present-day Functional appliances.⁶ William Clark in 1977 developed TB appliance, which is a versatile and popular functional appliance as it is comfortable and aesthetically accepted by majority of patients.⁷ TB provides a favorable environment for correction of underlying skeletal bases along with positive changes in functional and soft tissue environment associated with the mandible, including the upper airway.

Assessment of the airway has been done using 2D cephalometric radiograph, 3D Cone-beam CT, Magnetic Resonance Imaging (MRI), and Acoustic Pharyngometry (AP). Acoustic pharyngometry has an advantage of recording the 3D dynamic airway without any radiation effect in comparison to other previously mentioned methods, which are mostly static in nature.⁸

The functional respiratory requirement of an individual must be fulfilled with an adequate airway, which directly corresponds to the dimensions of the upper airway. There is a definite correlation amongst respiratory function, airway and mandibular posture.⁹ Since limited data is available in literature in terms of quantification of upper airway changes after Twin-block therapy, a study was formulated to assess the dynamic changes in airway among skeletal class II division 1 malocclusion due to mandibular retrognathism patients treated with twin block (TB) appliance.

Materials and methods

The present pilot study was carried out in a tertiary care Government hospital providing free comprehensive dental care to all patients after institutional ethical committee clearance. The study was planned as a prospective interventional study with a controlled sampling procedure. A total of twelve patients fulfilling inclusion and exclusion criteria (5 male, 7 female) with a mean age of 11.7 ± 1.1 years were selected for the study. Written consent was taken from the parents prior to initiation of treatment, and only those parents consenting for being part of the study were included.

Inclusion criteria

• •Cases of skeletal Class II division 1 with a retrognathic mandible
• •CVMI stage 3 and 4
• •Positive Visual Treatment Objective (VTO)
• •Compliant patients

Exclusion criteria

• •Syndromic cases
• •Cases with cleft lip and palate
• •Any other systemic, respiratory disease, or condition.

All patients were provided treatment with standard TB appliance and recommended protocol. Upper Airway evaluation using Eccovision® Acoustic pharyngometry (AP), was carried out, pretreatment (T0) and after the achievement of positive pterygoid response (T1) in all sample cases. The AP records and dynamically evaluates the upper airway dimensions. It works on the principle of sound waves that are produced from wave tubes and reflected back to the sensor, which, in turn, generates a graph known as pharyngogram [Fig. 1]. All patients were advised to sit upright and look at a distant point on the opposite wall to bring them into a relaxed, natural head position before recording. Four subsequent trials were recorded to generate a reproducible graph. The four curves obtained from each patient were averaged.¹⁰ [Fig. 2].

Fig. 1.

Pharyngogram.

Fig. 2.

Acoustic Pharyngometry Recording.

Results

Statistical analysis was carried out using Statistical Package for Social Sciences (SPSS ver 21.0, IBM Corporation, USA). The paired t-test was used to compare T0 and T1 values [Table 1].

Table 1.

Comparison of Pre-Treatment (T0) and, at Positive pterygoid response (T1) mean area and minimum area.

	Pretreatment (T0) (n = 12)		At positive pterygoid response(T1) (n = 12)		Difference (n = 12)		P-value
Parameters	Mean ± SD	95% CI Mean	Mean ± SD	95% CI Mean	Mean ± SD	95% CI Mean
Minimum area (cm2)	1.98 ± 0.50	1.66–2.30	2.26 ± 0.51	1.94–2.58	0.28 ± 0.25	0.13–0.44	0.002∗∗
Mean area (cm2)	3.06 ± 0.89	2.49–3.63	3.54 ± 1.02	2.88–4.19	0.47 ± 0.44	0.19–0.76	0.003∗∗

Values are Mean and Standard deviation (SD) along with 95% CI of means. P-value by paired t test, P-value<0.05 is considered to be statistically significant. ∗∗P-value<001.

The Mean ± SD pre-treatment (T0) and after positive pterygoid response (T1) minimum area was found to be 1.98 ± 0.50 cm² and 2.26 ± 0.51 cm², respectively. The mean ± SD along with 95% CI of T0 and T1 was 0.28 ± 0.25 cm² [95%CI: 0.13–0.44] The distribution of T1 average minimum area was significantly higher compared to the pre-treatment average mean area (P-value<0.01).

The Mean ± SD pre-treatment (T0) and after positive pterygoid response (T1) Mean area was 3.06 ± 0.89 cm² and 3.54 ± 1.02 cm² respectively. The mean ± SD along with 95% CI of T0 and T1 difference was 0.47 ± 0.44 cm² [95%CI: 0.19–0.76]. The distribution of T1 average Mean area was significantly higher compared to the pre-treatment average minimum area (P-value<0.01).

Discussion

The present study was conducted as a prospective pilot study to evaluate and quantify the changes in upper airway following TB appliance therapy in patients with skeletal class II div 1 patients with mandibular retrognathism.

TB appliance is commonly used treatment modality for correction of skeletal class II div 1 patients with mandibular retrognathism in growing individuals. Correction achieved by TB appliance therapy is due to an improved functional environment provided by the appliance, leading to muscular adaptation and favorable dental and skeletal changes.

Many studies have shown that TB therapy may be one of the most efficient treatment modalities available for improvement in the upper airway for growing patients with skeletal Class II malocclusion.^11,12 However, the controversy still remains in terms of quantifiable change in upper airway dimensions. Recent research and study by Khalil et al supports that Twin Blocks has a positive effect on airway and hyoid bone position.¹³ The results of the present study also validate the significant positive effect of TB appliance on airway dimensions as increase in minimum area of upper airway by 0.28 ± 0.25 cm² [95%CI: 0.13–0.44] and mean increase of mean area of airway by 0.47 ± 0.44 cm² [95%CI: 0.19–0.76]. Area of maximum constriction i.e., the minimum area is probably more clinically significant, in terms of improvements in the airway, which is directly correlated with improvement in quality of life in a patient with skeletal Class II malocclusion; changes are clearly visible in the individual appearing alert with marked clinical improvement facial features and bright eyes. The dull, lackadaisical attitude disappears possibly due to the achievement of good sleep due to improved oxygenation and improved upper airway dimensions.

In the era of airway centric orthodontics, the effect of any orthodontic appliance, especially myofunctional appliance therapy on the airway, should be evaluated. It is important to determine and evaluate the minimum area that is an area of maximum constriction. Li et al. reported that changes in the upper airway were significant after TB therapy using 3D CBCT.¹⁴ Their findings were concurred by Elfeky and coworkers, showing the positive three-dimensional changes in the upper airway.¹⁵ However, most of the previous studies been conducted either on 2D lateral cephalogramor on 3D CBCT, both of which fail to assess the upper airway in a dynamic state. The present study utilized AP to assess the dynamic change in the upper airway. AP also had an added advantage of utilizing a noninvasive approach in comparison to CBCT or conventional radiograph, which utilize radiation for assessment. It works on the principles of reflection of sound waves, which are projected down the subject's airway through the mouth and reflected back and assessed by the processing unit. The validity of this technique in measuring the airway has been established by Fredberg et al. compared with chest radiographs.¹⁶ D'Urzo et al. also concluded in their CT-based study that acoustic pharyngometry evaluation of upper airway was comparable and reliable for physiological or clinical studies.¹⁷ Marshall et al. also concluded that pharyngeal airway measurements have been found to be comparable to those obtained by MRI.¹⁸

The present study had the limitation of a small sample size being a pilot study; however, further larger prospective randomized controlled trials can be performed in a large Indian population to validate the results of the pilot study. It is also recommended that long-term follow up should be considered before extrapolating the results of the present study.

Conclusion

The study showed a definitive upper airway improvement in skeletal Class II division 1 subjects with TB myofunctional therapy with the achievement of positive functional changes, esthetics, and a healthier quality of life.

Conflicts of interest

The authors have none to declare.