Table of Contents  
Year : 2020  |  Volume : 12  |  Issue : 2  |  Page : 131-138

Assessment of Airway Dimensions and Hyoid Bone Position in Class II Patients Treated with Fixed Twin Block and Forsus Fatigue Resistant Device − A Retrospective Cephalometric Study

1 Private Practioner at The Dentist, Mumbai, Maharashtra, India
2 Department of Orthodontics, KLE VKIDS, KAHER, Belagavi, Karnataka, India

Date of Submission11-Mar-2020
Date of Decision31-Aug-2020
Date of Acceptance09-Jan-2021
Date of Web Publication16-Feb-2021

Correspondence Address:
Dr. Tejashri Pradhan
Professor and Head, Department of orthodontics, KLE VKIDS, KAHER, Belagavi 590010, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jofs.jofs_36_20

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Introduction: Obstructive Sleep Apnea Syndrome (OSAS) regulate pharyngeal airway volume. Forward displacement of mandibular repositioning appliances has advantage over an improvement of pharyngeal airway space and a change in the hyoid bone position. This study aims to assess the changes in the pharyngeal airway dimensions and hyoid bone position in growing individuals with retrognathic mandible treated with Fixed Twin Block (FTB) and Forsus Fatigue Resistant Device (FRD) to correct the skeletal Class II pattern. Materials and Methods: 40 skeletal Class II pattern patients were included in the study, to assess the pharyngeal airway space at three levels, upper pharyngeal width (UPW), middle pharyngeal width (MPW), and lower pharyngeal width (LPW). Hyoid bone measurements were Vertical dimension H-HOR and Horizontal dimension was H- VER. The study patients were divided into three groups and in each group 20 patients. Group-A treated with FTB appliance and Group-B treated with Forsus FRD appliance and Group C served as control group. At pre and post functional treatment condition, lateral cephalograms were evaluated. Results: Cephalometric analysis revealed a significant increase in the mean change of MPW (P = 0.005) between the FTB and the control group. There was significant, mean change seen of pre, post UPW, mean change of MPW over groups (P<0.01). Statistical significant difference was noted in the mean change of mandibular corpus length over groups and also when compared with FTB-Control (P<0.01). A significant difference in the mean change of the mandibular unit length, premandibular corpus length over the groups was noted. Conclusion: The FTB appliance was more effective in correcting the skeletal class II malocclusion as compared to the Forsus FRD appliance and therefore, there was marked improvement in the oropharyngeal airway dimensions (UPW, MPW) and hyoid bone displacement (anterior and superior).

Keywords: Forsus FRD, Hyoid bone, Pharyngeal airway, Twin block

How to cite this article:
Dedhiya N, Pradhan T, Sethia A. Assessment of Airway Dimensions and Hyoid Bone Position in Class II Patients Treated with Fixed Twin Block and Forsus Fatigue Resistant Device − A Retrospective Cephalometric Study. J Orofac Sci 2020;12:131-8

How to cite this URL:
Dedhiya N, Pradhan T, Sethia A. Assessment of Airway Dimensions and Hyoid Bone Position in Class II Patients Treated with Fixed Twin Block and Forsus Fatigue Resistant Device − A Retrospective Cephalometric Study. J Orofac Sci [serial online] 2020 [cited 2021 Jun 13];12:131-8. Available from:

  Introduction Top

The pharyngeal airway volume is of concern to the orthodontist due to the prevalence of Obstructive Sleep Apnea Syndrome (OSAS); a disorder caused by obstruction of the upper airway. Even a small diameter change can result in a substantial volumetric change and can have a great effect on airflow because the resistance decreases to the fourth power as the radius increases.[1] Severe mandibular deficiency, has been linked to reduced oropharyngeal airway dimensions.[2] As a result, the space between cervical column and the mandibular corpus decreases and leads to a posteriorly postured tongue and soft palate, increasing the chances of impaired respiratory function during the day and possibly causing nocturnal problems such as snoring, upper airway resistance syndrome (UARS) and OSAS.[3] Robin et al.[4] used an intraoral appliance to bring the lower jaw forward in newborns with mandibular deficiency, thereby preventing posterior relocation of the tongue during sleep and the occurrence of oropharyngeal collapse. Reportedly night time use of a mandibular repositioning device for 2 years by obstructive sleep apnea (OSA) patients and snorers was found to increase their airway passages because of an increase in pharyngeal area. [5] The hyoid bone is attached to the mandible by geniohyoid, mylohyoid, and the anterior belly of digastric muscles, which are responsible for downward movement of the mandible, treatment with functional appliance results in hyperactivity of these muscles. Therefore, the balance between the suprahyoid and infrahyoid muscles is disturbed.

The fixed Twin Block (FTB) has become a popular appliance in the recent times. Also, Forsus being a hybrid appliance is preferred as it has less breakage and is rigid enough to bring about favorable dentoskeletal changes. However, to our knowledge there are no studies in the literature which evaluate and compare the effects of a FTB functional appliance with a Forsus Fatigue Resistant Device (FRD) on the oropharyngeal airway dimensions and hyoid bone position in growing patients who have skeletal Class II patterns with retrognathic mandibles. Therefore, the objectives of this study were to evaluate and compare the effect of Fixed Twin block and Forsus FRD on oropharyngeal airway dimensions using cephalometric analysis and to evaluate and compare the effect of Fixed Twin block and Forsus FRD on hyoid bone position using cephalometric analysis.

  Materials and Methods Top

Study design

This retrospective cephalometric study was designed to evaluate and compare the effect of two different treatment modalities for correcting class II malocclusion on oropharyngeal airway and on hyoid bone position with respect to the control group of subjects having untreated class II malocclusion. Ethical approval for this retrospective cephalometric study (No: KAHER’S/VKIDS/779) was obtained from the ethics and research committee of KLE VK Institute of Dental Sciences, Belagavi, Karnataka, India on 31st October, 2013. 40 pretreatment and postfunctional treatment cephalometric patient data were taken from the record database of the Department of Orthodontics and Dentofacial Orthopedics, KLE’s V.K. Institute of Dental Sciences, Belagavi, Karnataka, India. The samples were matched for the growth status using CVMI stages through lateral cephalogram. The study period was from 2013 to 2019. Study subjects were equally divided into three groups, Group A was subjected to Fixed block group, Group B was subjected Forsus FRD and Group C as control group. Inclusion criteria for study was class II skeletal base and mandibular retrognathism, ANB ≥ 4°, Overjet more than 5 mm, no missing teeth in both the arches were included in the study. Exclusion criteria of study was, patients with respiratory disorders, naso-oropharyngeal obstruction, history of orthodontic treatment, history of surgical intervention, history of any systemic disease affecting bone & general growth were excluded from the study.

Data collection

In group I subjects, lateral cephalograms recorded before the start of treatment and at the end of active twin-block therapy were considered for analysis. In group II subjects, lateral cephalograms recorded before ligation of Forsus FRD and immediately after removal of Forsus FRD were considered for analysis. All lateral cephalograms were traced manually, and various landmarks were identified. The following are the measurements: Skeletal measurements for Angular: Sagittal maxillary position (SNA), Sagittal mandibular position (SNB), Sagittal intermaxillary relation (ANB) [Figure 1]a. Skeletal measurements for Linear: Effective mandibular length (Co-Gn), Ramal length (Co-Go) and Mandibular body length (Go-Gn). [Figure 1]b Pharyngeal airway space: linear measurements; [6] Upper pharyngeal width: Smallest distance between the posterior border of the soft palate to the closest point on the posterior pharyngeal wall. Middle pharyngeal width: Smallest distance between the posterior borders of the tongue to the closest point on the posterior pharyngeal wall, through the tip of the soft palate. Lower pharyngeal width: Smallest distance from the intersection of posterior border of tongue and inferior border of the mandible to the closest point on the posterior pharyngeal wall [Figure 1]c. Hyoid bone measurements were Vertical dimension H-HOR- linear distance from point H to Hor and Horizontal dimensions were H- VER- linear distance from point H to Ver. [Figure 1]b and [Figure 2].
Figure 1 (a) Skeletal Angular measurements. (b) Skeletal Linear measurements. (c) 1=UPW, 2=MPW, 3=LPW

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Figure 2 (a) Pre and Post Treatment tracings of patients treated with Forsus FRD. (b) Pre and Post Treatment tracings of patients treated with Fixed Twin Block

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All the cephalograms were traced initially by the same operator and were checked by the second operator to verify the anatomical outlines, landmark placement, and superimposition. Twenty randomly selected radiographs were retraced and remeasured by the same operator to determine the method error.

Statistical analysis

The data was analyzed using statistical software R (University of Auckland, NewZealand, 1995) version 4.0.2 and MS Excel. Continuous variables are represented in the form of mean± standard deviation. Categorical variables were represented by frequency. To compare the mean between pre-post time points paired t test was used. To compare mean over groups t test/ANOVA was used. To check the normality of variables Quantile-Quantileplot (Q plot)/Shapiro-Wilk’s test was used. P value less than or equal to 0.05 shows statistical significance.

  Results Top

The study had total 33 females and 27 males. The mean age of study subjects in years and gender distribution was described in [Table 1]. It was found that there is no significant difference found in the distribution of gender over groups [Table 1].
Table 1 Distribution of gender over groups.

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There was no statistical difference found in the pre, post SNA and mean change of SNA over the groups however the mean of Pre-SNA was significantly higher than the Post SNA in the Forsus group. There was difference in the mean of SNB over groups. There was also significant difference between the FTB-control (P = 0.0005905) and FTB-Forsus (P = 0.03530) [Graph 1].

The mean of pre-ANB between the forsus-control (P<0.01) and FTB control (P =0.02) was significantly different. Also, the mean change of ANB was significantly different between FTB- Control (P value: 0.0001994), FTB- Forsus (P value: 0.0200). It was also found that a statistical significant difference was noted in the mean change of Co-Gn over groups and also when compared with FTB-Control (P<0.01).

There was significant difference in the mean change of Co-Go, pre-Go-Gn over groups, mean of pre, post UPW, mean change of MPW, H-Hor over the groups (P<0.01) [Graph 2].

When pre-UPW was compared to post-UPW within FTB group, it was found non-significant. There was a significant difference in the mean change of MPW with FTB- control group (P value: 0.01). The mean of LPW was not significant in preLPW when compared to postLPW within the control group [Figure 3]. When the mean of H-VER was compared, it was found that the pre-test was significantly more compared to post-test within the FTB group. There was a statistical significance in the mean change of H-Hor in contrast to FTB- Control (P value: 0.04) [Table 2] [Graph 3].
Figure 3 Superimposition of the airway dimensions

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Table 2 Comparison of pre and post treatment scores of different measurements over and within the groups

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  Discussion Top

Today the concept of dentofacial orthopedics to stimulate the mandibular growth in skeletal Class II cases with mandibular deficiency is widely used due to the fact that the functional orthopedic treatment in such patients leads to increase in oral airway dimensions, thereby reducing the risk of respiratory problems in future.[7] Small pharyngeal dimensions established early in life may predispose one to sleep-disordered breathing later when subsequent soft tissue[8] changes caused by age, obesity, or genetic background further reduce the available oral airway dimensions.

In this study, we took measurements in patients who were at their advanced stage of puberty (mean age of group-A was 13.82 years and group-B was 14.2years) with little growth capacity remaining. All our results must therefore be regarded as the summation of natural growth processes and therapeutically induced effects, thus the changes in distances and angles are combined effects. And control group with untreated class II malocclusion was considered in the study.

Limitations of lateral cephalometry in airway studies have been discussed[9],[10],[11]particularly the inadequate representation of upper airway structures in a two-dimensional (2D) radiograph. A systematic review by Major et al[12] concluded that lateral cephalometrics can be considered a reliable initial screening tool of upper airway obstruction. Conventional lateral cephalogram remains not only a solid and routine diagnostic tool for orthodontics but also a legitimate instrument for airway measurements.[13] Airway dimension and tongue and hyoid-position measurements are highly reproducible.

The study showed a significant difference between pre and post treatment was significant in the groups for SNB0, and only significant in the forsus group for SNA0. According to a study by Goymen M et al.[14] who evaluated the effect of fixed and removable functional treatment on pharyngeal airway measurements the difference between the pre-post treatment values were not significant for SNB and significant in the twin block group (TWB) for SNA. Our study showed positive results for ANB0 in all the three groups. This can be compared to a study where the ANB0values within the groups such as the TWB and forsus was statistically significant but didn’t change in the control group.[14] The study witnessed a significant increase in the mandibular length (Co-gn) in the FTB group partially comparable to the results of the study by Franchi et al.

There was increase in the mean observed for UPW and MPW in the FTB group whereas in the LPW there was a significant change seen in the control group.[15] In a study by Godt et al.[16] investigated the upper airways for various class II treatments. In this study there were not much changes seen with the different treatment modalities. While another study by Akcam et al.[17] where the pharyngeal airway dimensions in the upper part showed a consistent growth and a positive change in the pre-peak, peak and post peak group. In the same study the lower oropharyngeal airway space measurement showed a statistically significant difference among the groups.

In the present study, a statistically significant forward movement of horizontal and vertical plane was seen in the FTB group. The vertical plane decreased at post treatment condition. Similar results were reported by Verma et al,[7] Yassaei et al.[18] Battagel et al.[19] and Ulusoy et al.[20] in their studies. This positional change in their study was anterior and downward movement of the hyoid bone.

A study has shown that the skeletal contribution in Class II therapy decreases gradually as the patient ages, and that dental effects become dominant—in other words, the upper dentition is destabilized, and the lower dentition is mesialized.[21] The hyoid bone showed a statistically significant forward movement in the present study.

Limitation of study is all the linear measurements for the oropharyngeal airway space were carried out on a lateral cephalogram. Oropharyngeal airway is a 3D space and the lateral cephalogram gives a 2D representation of a 3D space. A 3-dimensional analysis can be carried out to evaluate variables in all three planes using cone beam computed tomography (CBCT) or magenetic resonance imaging (MRI). A more comprehensive study involving both the cephalometric and clinical data (general obesity, neck circumference, breathing efficiency/severity of OSA).

  Conclusion Top

Cephalometric analysis revealed a significant increase in the UPW, MPW after fixed twin-block appliance treatment in Class II subjects with retrognathic mandible. This was associated with an anterior and superior movement of the hyoid bone. In contrast, in the Forsus FRD group there was no significant increase in the pharyngeal width dimensions but, the hyoid bone moved anteriorly. The FTB appliance was more effective in correcting the skeletal class II malocclusion as compared to the Forsus FRD appliance and therefore, marked improvement in the oropharyngeal airway dimensions (UPW, MPW) and hyoid bone displacement (anterior and superior) was seen with FTB as compared to Forsus FRD.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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Murat Özbek M, Miyamoto Keisuke, Lowe Alan A, Fleetham John A. Natural head posture, upper airway morphology and obstructive sleep apnoea severity in adults. Eur J Orthod 1998;20:133-43.  Back to cited text no. 3
Robin P. Glossoptosis due to atresia and hypotrophy of the mandible. Am J Dis Child. 1934;48:541-47.  Back to cited text no. 4
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Verma G, Tandon P, Nagar A, Singh GP, Singh A. Cephalometric evaluation of hyoid bone position and pharyngeal spaces following treatment with Twin block appliance. J Orthod Sci 2012;1:77–82.  Back to cited text no. 7
Martin SE, Mathur R, Marshall I, Douglas NJ. The effect of age, sex, obesity and posture on upper airway size. Eur. Resp J 1997;10:2087–2090.  Back to cited text no. 8
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Battagel JM, L’Estrange PR. The cephalometric morphology of patients with obstructive sleep apnoea (OSA). Eur J Orthod 1996;18:557-69.  Back to cited text no. 10
Finkelstein Y, Wexler D, Horowitz E et al. Frontal and lateral cephalometry in patients with sleep-disordered breathing. Laryngoscope. 2001;111:634-41.  Back to cited text no. 11
Major MP, Flores-Mir C, Major PW. Assessment of lateral cephalometric diagnosis of adenoid hypertrophy and posterior upper airway obstruction: a systematic review. Am J OrthodDentofacial Orthop 2006;130:700–8.  Back to cited text no. 12
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Franchi L, Alvetro L, Giuntini V, Masucci C, Defraia E, Baccetti T. Effectiveness of comprehensive fixed appliance treatment used with the Forsus Fatigue Resistant Device in Class II patients. Angle Orthod 2011;81:67883.  Back to cited text no. 15
Godt A, Koos B, Hagen H, Göz G. Changes in upper airway width associated with Class II treatments (headgear vsactivator) and different growth patterns. Angle Orthod. 2011;81:440-46. doi:10.2319/ 090710-525. 1  Back to cited text no. 16
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Yassaei S, Bahrololoomi Z, Sorush M. Changes of Tongue Position and Oropharynx following treatment with functional appliance. JClinPediatr Dent 2007;31:287–90.  Back to cited text no. 18
Battagel JM, Johal A, L’Estrange PR, Croft CB, Kotecha B. Changes in airway and hyoid position in response to mandibular protrusion in subjects with (OSA). Eur J Orthod 1999;21:363-76.  Back to cited text no. 19
Ulusoy C, Bavbek NC, Tuncer BB, Tuncer C, Turkoz C, Gencturk Z. Evaluation of airway dimensions and changes in hyoid bone position following class II functional therapy with activator. Acta Odontol Scand 2014;72:917-25.  Back to cited text no. 20
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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]


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