Evaluation of changes in the upper airway after Twin Block treatment in patients with Class II malocclusion

Abstract The purpose of this prospective case control study is to describe in growing patients with mandibular hypoplasia, treatment outcomes following functional therapy in terms of volumetric changes in nasopharynx and oropharynx, that is, upper and lower pharynx. We recruited 60 study participants aged between 8 and 12 years having mandibular Class II malocclusion and a reduced upper airway (UA) size, as determined by McNamara cephalometric analyses. Forty patients received Twin Block treatment, whereas the remaining 20 patients did not receive treatment, thus constituting the control group. The control group included patients who did not start treatment after their first visit but returned for a consultation one or 2 years later. All patients underwent an initial teleradiography examination of the skull and a final teleradiography examination to measure changes using McNamara cephalometric analysis of the UA. Pretreatment and posttreatment changes were assessed using Student's t test for independent samples with a significance level of 0.05. Both anatomical structures analyzed—the upper pharynx (nasopharynx) and lower pharynx (oropharynx)—showed significant increases after treatment regardless of whether the patients were boys or girls. The controls showed a decrease in UA size on average after approximately 2 years of growth. A clear relationship exists between the mandibular advancement achieved with TB treatment and an increased UA size. Therefore, the appliance is considered suitable for improving the respiratory quality of growing patients with a decreased UA size.

From a dental perspective, the upper airway (UA) has received increasing attention in orthodontics (Elfeky & Fayed, 2015;Li et al., 2014). The anatomy and function of the nasopharyngeal airways are directly associated with craniofacial development (Ali, Shaikh, & Fida, 2015a;Pavoni, Lombardo, Franchi, Lione, & Cozza, 2017). Due to this close relationship, mutual interaction is expected to occur between pharyngeal structures and the dentofacial pattern, validating the increasing interest among the orthodontic community (Pavoni et al., 2017). The indication to treat the cause of obstruction should be established by a pediatrician, otolaryngologist, or allergist, although orthodontics and dentofacial orthopedics can also improve such obstructions; therefore, interdisciplinary coordination is essential (Morales & Varela, 2017).
This study evaluates the changes produced in the UA after TB treatment in growing patients with mandibular hypoplasia and examines respiratory improvement in patients with clinical manifestations that may predict SAHS. This prospective case-control study was conducted with 60 patients   from the Asturian Institute of Dentistry (IAO for its acronym in   Spanish), including 30 children and 30 girls aged between 8 and   12 years with a decreased UA size and mandibular Class II malocclusion.

| MATERIALS AND METHODS
The treatment group consisted of 40 patients with mesofacial and brachyfacial growth patterns treated with functional TB appliances, including 20 children and 20 girls. Patients with a very vertical pattern and a tendency towards an open anterior bite were excluded because although one benefit of TB appliances is control of the vertical dimension (without trimming bite blocks to avoid favoring posterior tooth extrusion; Quintero & Mariaca, 2013), another type of functional appliance is better suited for these patients. With TB treatment, vertical development is achieved by gradually trimming the bite blocks, favoring posterior tooth extrusion, and leveling the occlusal plane (Ysla, Manso, Laffite, López, & Carrera, 2005).
The remaining 20 patients formed the control group, which included patients who did not start treatment after their first visit but returned for a consultation one or 2 years later.
However, treatment should be ideally initiated before or during peak growth to produce more favorable results (Quintero & Mariaca, 2013;Saldarriaga-Valencia, Alvarez-Varela, & Botero-Mariaca, 2013). The appliance should be retained-either the TB itself or a Hawley plate with an advancement splint-until the end of growth to ensure long-term stability.
Lateral teleradiography of the skull has been the main method to assess the effectiveness of the TB device and evaluate the changes produced in the UA after treatment. They were asked not to swallow and not to move their heads or tongues.
To measure the UA and assess its patency, McNamara analysis has been used ( Figure 3). Two anatomical structures are measured to identify alterations in the respiratory airways:   (Table 1).

| Control group
The control group consisted of 10 boys and 10 girls who did not start treatment after their first visit (T1) because the parents of these patients did not aesthetically appreciate Class II malocclusion. They returned for a consultation one or 2 years later (T2) because it became evident after this time the worsening of the malocclusion. Note that the initial data of the oropharynx differ from the experimental group because in these patients was not as reduced as in patients treated with Twin Block (Table 2).

| Final lower pharynx (oropharynx) measurements (control group)
Twenty valid cases were available for final lower pharynx measurements. The average value was 9.39 units with a standard deviation of 2.43, and the median value was 9.25 units.

| Experimental group
The experimental group consisted of 20 boys and 20 girls. These patients were evaluated at the start of treatment, T1, and after 12-18 months of TB treatment, T2 (Figures 4 and 5; Table 3).

| Initial upper pharynx (nasopharynx)
Forty valid cases were available for baseline upper pharynx measurements. The average value was 7.88 units with a standard deviation of 1.94, and the median value was 7.55 units.

| Initial lower pharynx (oropharynx)
Forty valid cases were available for baseline lower pharynx measurements. The average value was 8.93 units with a standard deviation of 1.82, and the median value was 9.35 units.

| Final lower pharynx (oropharynx)
Forty valid cases were available for final lower pharynx measurements.
The average value was 11.04 units with a standard deviation of 2.27, and the median value was 10.55 units.

| Behavior of the upper pharynx (nasopharynx [mm]) in the different groups (control and experimental groups)
To determine whether the behavior of the upper pharynx differed between the two groups, several comparisons were performed, which are detailed below.
Because the hypothesis of normality was not rejected for all modalities (Shapiro-Wilk test, control group, p value = 0.21; experimental group, p value = 0.05) and the hypothesis of equality of the two population variances was not rejected (variance test F, p value = 0.37), the hypothesis of equality of the population means was rejected (Student's t test, p value < 0.001).
Assessment: The groups showed different behaviors. The control group showed a tendency for a decreased nasopharynx, whereas the experimental group exhibited a tendency for an increased nasopharynx ( Figure 6; Table 4).

| Behavior of the lower pharynx (oropharynx [mm]) in the different groups (control and experimental groups)
To determine whether the behavior of the lower pharynx differed between the two groups, several comparisons were performed, which are detailed below.   experimental group exhibited a tendency for an increased nasopharynx ( Figure 8).

| Behavior of the lower pharynx (oropharynx [mm]) in the different groups (control and experimental)
To determine whether the behavior of the lower pharynx differed between the two groups, several comparisons were performed, which are detailed below.
Because the hypothesis of normality was not rejected for all modalities (Shapiro-Wilk test, control group, p value = 0.296; experimental group, p value = 0.079) and the hypothesis of equality of the two population variances was not rejected (variance test F , p value = 0.486), the hypothesis of equality of the population means was rejected (Student's t test, p value < 0.001).
Assessment: The groups showed different behaviors. The control group showed a tendency for a decreased oropharynx, whereas the experimental group exhibited a tendency for an increased oropharynx ( Figure 9).

| DISCUSSION
This study shows that correction of mandibular retrognathism with a TB appliance in growing patients not only improves the facial profile and intermaxillary relationship but also increases UA dimensions (Ali et al., 2015b;Roque-Torres, Meneses-López, Bóscolo, de Almeida, & Neto, 2015), thus reducing the risk of future respiratory problems (Verma et al., 2012) and representing a suitable oral appliance to treat children with SAHS (Caridi & Galluccio, 2013;Zhang et al., 2013).
However, few studies have shown the long-term effectiveness of TB appliances; therefore, their permanency remains to be determined.
Similarly, the most important limitation of this study is that the main diagnostic method was lateral teleradiography of the skull, which provides a two-dimensional (2D) representation, but the UA is a 3D space, limiting the accuracy of the technique because 2D images only show the anteroposterior dimension in the sagittal plane rather than a complete view (Abdelkarim, 2012;Elfeky & Fayed, 2015;Li et al., 2014). However, lateral teleradiography of the skull is commonly used in routine clinical practice due to its relative simplicity, accessibility, low cost, and low radiation exposure (Feng et al., 2015;Rojas, Corvalán, Messen, & Sandoval, 2017;Santamaria-Villegas, Manrique-Hernandez, Alvarez-Varela, & Restrepo-Serna, 2017).
Teleradiography remains a valuable diagnostic tool for evaluating the airways (Ali et al., 2015b;Elfeky & Fayed, 2015;Ghodke et al., 2014;Jena et al., 2013;Pavoni et al., 2017) and can be used to predict OSA (Armalaite & Lopatiene, 2016). Furthermore, this method has been shown to provide reliable linear measurements and is a valid tool for measuring the dimensions of the nasopharyngeal and retropalatal regions. Teleradiography is a highly reproducible examination using the natural head position of the patient when performed properly (Rojas et al., 2017).
Radiographic computer tomography (CT) provides a more accurate estimate of the UA volume and more detail compared with teleradiography (Abdelkarim, 2012;Iwasaki et al., 2014;Li et al., 2016;Maspero et al., 2015). However, the patient, and in this case the growing child, becomes exposed to higher radiation contrary to the ALARA principle and is difficult to justify from a research ethics perspective (Ali et al., 2015b;Ghodke et al., 2014).
Evidence-based data on the radiation dose to acquire CBCT images are severely lacking, with some authors reporting lower radiation compared with conventional CT (Elfeky & Fayed, 2015). The   TB devices are some of the most common and popular functional appliances due to their effectiveness in skeletal Class II correction, thus improving the facial profile. In addition, these devices may be effective for treating children with RSDs and mandibular retrognathia, thus decreasing the risk of SAHS development in adulthood.
Whenever CBCT is performed in orthodontic practice, the clinical benefits to the patient must be weighed against the potential risk of radiation.
Currently, more research is being conducted on the benefits of intraoral orthopedic appliances for the treatment of SAHS and other RSDs; however, few studies have demonstrated the long-term stability of such devices.