Effect of functional appliances on the airway dimensions in patients with skeletal class II malocclusion: A systematic review.

OBJECTIVES: The aim of the present systematic review was to assess the effect of functional appliances on the airway dimensions in patients with skeletal Class II malocclusion.
MATERIALS AND METHODS: Articles were identified through a literature survey carried out through the following databases: (1) PUBMED, (2) Google Scholar, (3) The Cochrane Library, (4) Embase, (5) Lilac, and (6) Web of Scholars. The systematic review analyzed 12 articles comprising removable functional appliances, 3 articles with fixed functional appliances, and 2 articles having both fixed and removable functional appliances.
RESULTS: Qualitative assessment was done for all the 17 studies. The effect of functional appliances in the dimensions of three airway spaces - nasopharynx, oropharynx, and hypopharynx were analyzed.
CONCLUSIONS: Significant increase in the dimensions of nasopharynx and oropharynx was observed with Activator. Significant increase in the nasopharynx and hypopharynx (male patients) was observed with Bionator. Insignificant increase in the oropharynx was observed with the same. Significant increase in the oropharynx and hypopharynx was observed with Twin Block. Insignificant increase in the nasopharynx was observed with the same. Significant increase was observed only in the hypopharynx for Frankel II. Decreased or insignificant change was observed with FMA, MPA IV, and Herbst appliances.

Introduction

Facial esthetics plays a pivotal role in the perception of beauty and is also the key reason for patients with skeletal Class II malocclusion to seek orthodontic treatment. This malocclusion is frequently caused by a mandibular deficiency. Mandibular deficiency can be attributed to a small or retruded mandible relative to the maxilla. From the days of Edward Angle, a frequently debated area in orthodontics has been the efficacy of various modalities in treating patients with Class II malocclusion with a retruded mandible. According to him, when a normal function is established, the adaptation of the craniofacial morphology subsequently follows it.[1] Growth modifications are attempted to alter a developing skeletal Class II relationship in young children, predominantly during the growth phase by modifying the patients’ remaining facial growth to a favorable size or position of the jaws using functional appliances. Functional appliances enhance the proprioceptive sensory feedback mechanisms of various perioral musculatures that control the function and position of the mandible and transmit the generated forces to the dentition and basal bone.[2345] This modifies the growth of the mandible and maxilla, guiding them into a favorable relationship.[4]

Severe mandibular deficiency has been linked to reduced oropharyngeal airway dimension increasing the chances of impaired respiratory function and possibly causing problems such as snoring, upper airway resistance syndrome, and obstructive sleep apnea-hypoapnea syndrome.

Harvold et al. suggested that in patients with skeletal Class II malocclusion caused by a retrognathic mandible, the reduced space present between the cervical column, and the mandibular body may lead to posterior positioning of the tongue and soft palate causing impairment in the airway.[6] This obstruction in the nasal airway can also lead to changes in the physiological rest position of the mandible.[7] Similarly, Linder-Aronson et al. and Quinn et al. have shown that, in children with decreased anterior facial height, retrognathism of mandible, and steeper mandibular planes, constriction is present in the nasopharyngeal region.[89] Further, airway disturbances can lead to a myriad of developmental deformities such as “long face syndrome,” anterior and posterior open bites, and temporomandibular joint problems.[9]

Thus, it has been hypothesized that, as the mandible is repositioned forwards with the help of functional appliances, an increase in the airway space occurs indirectly. Graber et al. further added that, as the size and shape of the nasopharyngeal space enlarges, due to the usage of functional appliances, the effectiveness of these appliances also tends to improve simultaneously, which automatically results in improved respiration.[10]

However, contrary to these studies, Vig et al. and Horowitz et al. concluded that the mentioned interrelationship between the mandibular position and airway dimension is unproven.[1112]

Zymperdikas et al. and Kevin O’Brien et al. have concluded that functional appliances do not have clinically significant skeletal effect on the mandible,[1314] though other clinical studies proved functional appliances to be effective.[1516171819202122232425262728293031323334] Hence, it can be inferred from their study that, through functional appliance therapy, no significant change occurs in the airway dimensions.

Lateral cephalograms and cone beam computer tomography (CBCT) have been used often in evaluating the airway dimensions in several airway spaces. Whether the three-dimensional measurements obtained using a CBCT will be able to make a significant difference to the assessment of the airway over the linear measurements acquired with lateral cephalograms is debatable with no consensus.

Research question

With the current controversy in the literature regarding the relationship between the airway dimension and functional appliances, a systematic review is needed to assess the changes seen in different airway spaces using functional appliances; no systematic review exists that provides this information.

Objectives

The aim of the present systematic review was to assess the effect of functional appliances on the airway dimension in patients with skeletal Class II malocclusion.

Materials and Methods

Search method

Articles were identified through a literature survey carried out through the following databases: (1) PUBMED, (2) Google Scholar, (3) The Cochrane Library, (4) Embase, (5) Lilac, and (6) Web of Scholars. The search algorithms used in each database are given in Table 1. A manual search was also performed by reviewing the references within the studies examined and the titles of the papers published over the last twenty years in various journals.

Table 1

Summary of the search database

As this research was a systematic review, the institutional ethics committee was not required to approve the data abstraction.

Data abstraction

The selection process was done by two authors. The data extracted from each article was compared and discussed to resolve any discrepancies to reach a unanimous consensus.

Inclusion criteria

Randomized controlled trials (RCTs), prospective, or retrospective case control studies

Healthy growing patients with skeletal Class II malocclusion without any systemic diseases treated with functional appliances

Studies with a comparable control group.

Exclusion criteria

Case reports, case series with no statistical analysis, comments, letters to the editor, and reviews

Studies using functional appliances for the treatment of obstructive sleep apnea

Studies using headgear as treatment modality in Class II patients and other functional appliances in treating patients’ with Class III malocclusion

Class I control groups.

The selected and rejected articles, after assessment of the full text articles, are listed in Tables 2 and 3, respectively; Figure 1 describes the search strategy. A summary of the articles included in this systematic review is presented in Table 4.

Table 2

Selected articles based on title and abstract

Table 3

Rejected articles after full text assessment

Figure 1

Flow chart describing the search strategy

Table 4

Summary of full text articles included in qualitative synthesis

Quality assessment

The selected articles were graded based on the criteria proposed by the Cochrane Collaboration for Prospective Case- Control studies [Table 5] and the National Institutes of Health, Department of Health and Human Services, U.S.A for Retrospective Case-Control studies [Table 6].[3536] The risk of bias within studies was assessed independently by the two authors and across studies by an independent reviewer. Any disagreement was resolved by discussion with the reviewer.

Table 5

Summary of the quality assessment of prospective case control studies

Table 6

Summary of the quality assessment of retrospective case control studies

Results

The results were analyzed based upon the effect of functional appliances in the dimensions of three airway spaces – the nasopharynx, oropharynx, and hypopharynx.

Nasopharynx

Significant increase in the dimension was observed with Activator, Bionator, Bite jumping appliance, and Farmand appliance

Significant increase was observed with Twin Block in two studies, whereas three studies did not show any significant change

Insignificant increase was observed with Frankel II and Herbst appliance

A decrease was observed with MPA IV and FMA appliances [Table 7].

Table 7

Summary of the influence of the appliance on the airway spaces

Oropharynx

Significant increase was measured with Twin block, Bite jumping appliance, MPA IV, and X bow

Significant increase was measured with Activator in four studies and insignificant increase in one study

Insignificant increase was measured with Bionator, Forsus, and Herbst appliance

Significant increase was measured with Farmand appliance, although 2 years after treatment, a decrease in the airway, when compared to the posttreatment values, were measured with this appliance

A decrease was measured with FMA appliance [Table 7].

Hypopharynx

Significant increase was observed with Twin block and Frankel II

Significant increase was observed in male patients with Bionator, and an insignificant increase was observed in female patients

Significant increase was observed with Farmand appliance, although 2 years after treatment, a decrease in the airway, when compared to the posttreatment values, were seen with the same

Insignificant increase was observed with Herbst appliance, FMA, and MPA IV [Table 7].

Discussion

Functional appliances are primarily used in growing children to bring about a change in the position of the mandible.[12] As the mandible moves forward, it is said to cause an indirect increase in the airway size. Although the restricting effect on the airway caused by the retrognathic mandible is no longer present, variable results are seen with the airway space dimensions.

Though the articles studied in this systematic review support the view of functional appliances bringing about a clinically significant skeletal change to the mandible,[1516171819202122232425262728293031323334] Zymperdikas et al. and Kevin O’Brien et al. concluded that functional appliances do not provide a clinically significant skeletal effect. Kevin O’Brien et al.'s study found that the Twin Block does not appreciably modify mandibular growth and that it is simply a tooth modifying appliance. Thus, it can be inferred from their results that no pharyngeal size modification occurs with functional treatments as the advancement of mandibular position is not significant enough to cause the change.[1314]

The need for clarity regarding the effect of functional appliances on airway space sizes led to this systematic review.

The literature search revealed absence of RCTs in this area of research. RCTs are considered the gold standard among all research designs in the evidence pyramid. In orthodontics, a lacuna is present in this topic probably due to the ethical considerations in denying treatment to a patient with malocclusion. Absence of historic growth studies with untreated Class II subjects where airway was assessed was taken into account while contemplating the inclusion criteria. This led to the inclusion of both retrospective and prospective studies in this systematic review. Studies which had a comparable Class II control group, or those in which Class II patients were assessed pre and posttreatment, were included. Class I control groups were not taken into consideration due to difference in growth pattern between them and Class II patients.[373839404142]

Case reports and case series were not taken into consideration due to the inadequacies in their study designs to address the objective of this systematic review. Studies involving functional appliances to treat obstructive sleep apnoea patients were not used as the patients have a pathological reason for decreased airway space.

The literature is divided about the accuracy in measuring airway spaces dimensions using lateral cephalograms, with the main concern being inadequacy to give a three-dimensional perspective.[43444546] Pirila-Parkkinen et al. and Vizzotto et al. concluded in their studies that lateral cephalograms can be used as a reliable method in assessing the airway.[4344] Studies having both lateral cephalogram and CBCT imaging techniques have been included in this systematic review, although volumetric quantification is possible with CBCT. Linear measurements were taken in studies involving lateral cephalograms.

The literature search showed that Yassaei et al. had the same content published in two different journals. Their study dealt with the effect of the Farmund appliance on 28 Class II patients, namely in Arabic, in the Shiraz University Dental Journal, 2007, and in English, in the Journal of Clinical Paediatric Dentistry; the article, published in the English language, was taken into consideration.[33]

The present systematic review analyzed 12 articles comprising removable functional appliances, 3 articles with fixed functional appliances, and 2 articles having both fixed and removable functional appliances [Tables 8 and 9].

Table 8

Removable functional appliance

Table 9

Fixed functional appliance

A significant number of selected studies appeared in the PUBMED database. A few of the studies did not specify the precise regions where the airway spaces were measured. Correlating with the anatomical structures, measurements of the airway dimensions were taken into consideration.

An insignificant increase in the region of the nasopharynx with Twin Block was seen with three studies that have a higher rating in the quality of assessment scale than the two studies which show a significant increase.[2425262728]

Lin et al. in 2011 reported an insignificant increase in the oropharyngeal region while using Bionator due to the connection of the lateral wall of the soft palate to the base of the tongue through the palatoglossus arch. In relation to the hypopharyngeal area, an insignificant increase was reported in the same study only in female patients.

Though Herbst and FMA appliances are known to have better patient compliance, Kinzinger et al. have shown them to have an insignificant or adverse effect, respectively, in the airway dimensions. Further, they have questioned the reliability of the assessment of posterior airway space with lateral cephalograms due to its limitations in studying three-dimensional structures.[29] Yassaei et al. in 2012 also found a decrease in the airway space in the long term with the usage of the Farmund appliance.[34]

The interrelationship present between the craniofacial form and the function of the airway gets established during the growth and development stage, making it vital to establish a good harmony between them as early as possible.[47] Future research is required to unearth the reasons behind the insignificant increase or decrease in a specific airway space with some appliances, though an increase is seen in other airway spaces.

Limitations of the study

Many studies did not have a Class 2 untreated control group. Thus, quantification of the changes due to functional appliances alone, without the effect of growth changes, could not be assessed. Absence of blinding while analyzing cephalometric or CBCT values could have eliminated reviewer bias. All these point out the need for additional RCTs in this area

Absence of a standard rating scale for quality assessment of retrospective studies.

Potential studies should consider analyzing the most proficient functional appliance using dynamic contrast magnetic resonance imaging as it provides stereoimaging of the airway region. Although a volumetric quantification is possible with CBCT imaging, a potential underestimation of the same is present when compared to that of MRI.[48]

Conclusions

Cephalometric and CBCT imaging provide sufficient data to analyze the airway dimension changes in the nasopharynx, oropharynx, and hypopharyngeal areas. A significant change was seen in the airway due to the repositioning of the mandible, especially with removable functional appliances.

Significant increase in the nasopharynx and oropharynx was observed with Activator

Significant increase in the nasopharynx and hypopharynx (male patients) was observed with Bionator. Insignificant increase in the oropharynx was observed with the same

Significant increase in the oropharynx and hypopharynx was observed with Twin Block. Insignificant increase in the nasopharynx was observed with the same

Significant increase was observed only in the hypopharynx with Frankel II

Decrease or insignificant change was observed with FMA, MPA IV, and Herbst appliances.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.