Abstract
Objective
This systematic review intends to evaluate the dimensional changes in upper airway dimensions (UAD) of the respiratory tract subsequent to orthodontic treatment of skeletal Class II malocclusion with Twin Block Appliance (TBA).
Methods
The quality of reporting systematic reviews and meta-analyses was decided by the PRISMA standards with PROSPERO registration number CRD42017060317. The systematic search included EMBASE, MEDLINE, Psych INFO, Scopus, CINAHL, and other reference journals and review articles. The article search was performed from March 2017 until November 2017. Cochrane’s risk of bias in non-randomized studies – of interventions (ROBINS-I) was used to grade the methodological quality of the included studies.
Results
The screening procedure identified 302 studies, among which seven studies satisfied the inclusion criteria for eligibility. The UAD at the pretreatment time varied from 7.2 mm to 41.9 mm with a mean of 14.16 mm. The post-treatment change in UAD ranged from 8.2 mm to 43.7 mm with a mean of 15.6 mm.
Conclusion
There was a significant increase in UAD following the TBA treatment in the patient group as compared to the control group.
Keywords: Systematic review, twin block appliance, upper airway, Class II malocclusion
INTRODUCTION
Class II malocclusion is one of the most commonly encountered problems in orthodontic practice and is associated with functional, esthetic, and psychological problems of varying intensities. A change in the upper airway volume due to narrowing of the airway dimensions is a commonly encountered problem in developing Class II malocclusion with a retrognathic mandible (1). The retarded mandible causes the backward displacement of the tongue and hyoid bone, which in turn leads to a reduction in the upper airway volume. Constriction of the upper airway is one of the causative factors for the development of obstructive sleep apnea (OSA) syndrome (2). A majority of patients with OSA present with skeletal Class II malocclusion with a deficient mandible. Studies have shown that the nasopharyngeal area and depth were significantly higher among individuals with normal occlusion as compared to subjects with Class II malocclusion and the oropharyngeal airway volume was directly correlated with the length of the mandible (1, 2).
Many treatment modalities have been developed to treat Class II malocclusion with a retrognathic mandible. Functional appliances like mandibular advancement devices, activator headgear treatment, Twin block appliances, and fixed appliances like Forsus-fixed functional appliance and fixed appliance with activator headgear were used with or without surgical correction (3–7). Studies have shown that if the skeletal Class II malocclusion is diagnosed at an early age, the best treatment option is the use of functional appliances, which allows the forward growth of the mandible and prevents upper airway collapse during sleep (7, 8). However, the functional appliance treatment requires patient cooperation in order to be effective, which is often a major problem. The Twin Block appliance (TBA) is one of the preferred removable functional appliances used in correcting retrognathic mandible in Class II malocclusion (7, 9–16). A majority of the studies showed the use of TBA increases pharyngeal airway dimensions through the forward movement of the mandible and hyoid bone (7, 9–14); few studies showed negative results (15, 17). Thus, the effect of TBA on upper airway dimensions (UAD) remains uncertain. Previously, two systematic reviews have been conducted to assess the changes in airway dimensions following functional appliance treatment of Class II malocclusion (18, 19). The evaluation of the dimensional changes in upper airway subsequent to orthodontic treatment of skeletal Class II malocclusion with TBA was the principal objective of this systematic review.
METHODS
The systematic review is constructed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards of quality for the planning, conducting, and reporting of systematic reviews and meta-analyses (20). The review did not necessitate the approval from the Institutional Review Board and is registered under PROSPERO (CRD42017060317).
Questions
The study focused on the quantitative effects of the TBA on UAD changes in Class II malocclusion. The PICO format was used to define the research questions of the present systematic review, which is as follows:
P (Population/Patients): The human subjects with skeletal Class II malocclusion treated with TBA.
I (Intervention): TBA in skeletal Class II malocclusion.
C (comparison): Subjects not received or receiving any treatment with another appliance.
O (Outcome): Changes in UADs (in mm).
Study Eligibility
Only previously published studies in the English language that investigated the changes in UAD following TBA treatment of Class II malocclusion were included in the study. The editorial letter, case report, in vitro studies, not investigating the changes in UAD subsequent to Class II malocclusion treatment with TBA, studies with syndromes, and cleft lip or palate studies were excluded from the research
Study Identification
The database search performed included Medline (PubMed, OVID Medline, and Ebsco), Cochrane library (Cochrane review, Trails), Web of Knowledge (Social science, conference abstract), Embase (European studies, pharmacological literature, conference abstract), CINAHL (Nursing and allied health), PsycInfo (Psychology and psychiatry), SCOPUS (Conference abstracts, scientific web pages), and ERIC (Education) for specific search strategy with focused key terms (Class II malocclusion, skeletal, occlusion, upper airway, pharyngeal airway, nasopharyngeal airway, oropharyngeal airway, volume, dimensions, changes, evaluation, Twin block appliance, Clarks twin block, TB).
The gray literature search was performed using the following databases: Google Scholar, National Library of Medicine, Social science research for thesis (EthOS, DART-Europe), Open Grey, Institutional repositories (OpenDOAR, Bielefeld Base, Lenus, RIAN, e-publications@RCSI). In addition, four key orthodontic journals (Angle Orthodontics, American Journal of Orthodontics and Dentofacial Orthopedics, Journal of Clinical Orthodontics, and European Journal of Orthodontics) were searched from their table of contents for relevant articles. The article search was performed from March 2017 until November 2017.
Study Selection
All the titles and abstracts were screened independently and duplicated to be included in the study. An intra-class correlation coefficient of 0.86 was achieved in inter-rater agreement for study inclusion. Any conflicts among the reviewers were addressed by discussion to arrive at a consensus.
Risk of Bias Assessment
Cochrane’s tool of the risk of bias in ROBINS-I was used to assess the risk of bias (21). The domains used to assess the risk of bias are summarized in Table 2. The included studies were further graded for each domain as low risk, moderate risk, serious risk, and critical risk of bias using standardized criteria. The studies were comparable to a well-performed clinical randomized trial and the domain in question was considered as having a low risk of bias. The studies which could not be compared to well-performed randomized trials but were sound for a non-randomized trial within the domain were considered as having a moderate risk of bias. The studies containing some important problems were categorized under serious risk of bias. The studies which were too problematic to provide any useful evidence on the effect of the intervention or which give no information on the basis of the judgment were categorized under critical risk of bias.
Table 2.
Risk of bias assessment of included studies using Cochrane’s risk of bias in non-randomized studies of interventions (ROBINS-I)
| ROBINS –I criteria | Author | ||||||
|---|---|---|---|---|---|---|---|
|
| |||||||
| Verma | Vinoth | Jena | Zhang | Ghodke | Ali | Chand | |
| BC | L | L | L | L | L | L | L |
| BSP | L | L | L | L | M | L | M |
| BCI | S | L | L | L | L | M | L |
| BDI | M | M | L | M | M | M | M |
| BMD | M | M | L | L | L | L | L |
| BMO | L | L | L | L | M | M | L |
| BSR | L | L | L | L | L | L | L |
| Overall bias | M | M | L | L | M | M | M |
BC: bias due to confounding; BSP: bias in selection of participants into the study; BCI: bias in classification of interventions; BDI: bias due to deviations from intended interventions; BMD: bias due to missing data; BMO: bias in measurement of the outcomes; BSR: bias in selection of the reported result; L: low risk of bias; M: moderate risk of bias; S: serious risk of bias; C: critical risk of bias; NI: no information
Data Extraction and Data Synthesis
The data was extracted independently by two reviewers for the included studies using a data extraction sheet and any discrepancies were resolved by arriving at a consensus through discussion. The data extracted from each included study was: first author, publication year, study type, study quality, sample size, inclusion criteria, treatment type, UAD changes (before, after, and long-term treatment), statistical analysis used, and the authors’ conclusion.
RESULTS
Trail Flow
Our search strategy yielded 293 articles and an additional 9 articles were identified from the review of references and journal indices. Among these, 7 articles were identified as suitable for inclusion in the present systematic review (Figure 1).
Figure 1.
Flow diagram showing the subject selection of the systematic review
Study Characteristics and Study Quality
The data were available from the year 2012 to 2017. Out of the 7 studies included in the review, 4 were prospective studies (2 without controls and 2 without control). Three studies were retrospective studies (2 without controls and 1 with control) (Table 1). Five studies were graded as a moderate risk of bias and 2 studies were graded as low risk of bias (Table 2). The number of study participants ranged from 14 to 74 (total n=274), with a mean of 39.14. In all of the included studies, lateral cephalogram was used to analyze the upper airway changes. Mean active treatment duration ranged from 4 months to 14.5 months (Table 3).
Table 1.
Descriptive data of included studies
| Author/year | Study design | Malocclusion criteria | Intervention type | Statistical analysis | Study conclusion |
|---|---|---|---|---|---|
| Verma /2012 | R | Class II division 1 G1, G2, G3, ANB >4o (SN +3 mm) | TBA | Paired t-test and One-way ANOVA | Significant increase in PAD |
| Vinoth /2013 | R | Skeletal Class II with RM (SNB < 80), ANB > 4o, CVM- stage 2 or 3 | S - TBA | Paired t-test | Significant increase in PAD |
| Jena /2013 | P | Class II, division 1 malocclusion with RM, FMA −20o to 25o | S – TBA C –MPA |
Paired t-test and One way ANOVA | TBA more effective in increasing PAD compared to MPA |
| Zhang / 2013 | P | Skeletal Class II with RM, ANB > 3o, SNB < 80o, incisor over jet > 3mm | TBA | Paired t-test | Significant increase in PAD |
| Ghodke/2014 | P | Skeletal Class II with RM, SNB ≤ 76o, FMA −20o to 28o | S – TBA C – Minor ortho treatment |
Paired t-test | Significant increase in PAD following TBA |
| Ali /2015 | R | Skeletal Class II malocclusion with RM, SNB < 78o, ANB > 4o | S – TBA followed by fixed mechanotherapy C – no treatment |
Mann-Whitney U test | Significant increase in PAD following TBA, remained stable for 2.5 years |
| Chand / 2017 | P | Skeletal Class II with RM | TBA | Paired t-test | Significant increase in PAD |
P: prospective study; R: retrospective study; S: study group; C: control group, G: growing subjects; RM: retrognathic mandible; CVM: cervical vertebral maturity; FMA: frankfort mandibular plane angle; TBA: twin block appliance; MPA: mandibular protraction appliance; PAD: pharyngeal airway dimensions; PAV: pharyngeal airway volume; ANOVA: analysis of variance; S: strong; M: moderate; W: weak; G1: group 1; hypo-divergent (SN-MP: <31°); G2: group 2, normodivergent (SN-MP: 31°–34°); G3: group 3, hyper-divergent (SN-MP: >34°)
Table 3.
Summary of sample size, malocclusion type, extraction, retainers used, and treatment duration
| Author | Sample size (male, female)/ mean age in years | Reliability measurement | Measurement technique | Upper Airway measurement | Mean active treatment duration |
|---|---|---|---|---|---|
| Verma | 40 (18, 22)/11.4 | 12 radiographs at 15 day interval | Cephalometric | Posterior outline of soft palate to PPW | NA |
| Vinoth | 25 (12, 13)/11–13 y | NA | Cephalometric | AA to PNS | 14.5 m |
| Jena | S – 21 (11, 10)/11.3 C – 16 (9, 7)/12.8 |
NA | Cephalometric | NA | S – 9.3 m, C −6.1 m |
| Zhang | 46 (31, 15)/9.7 | 10 randomly selected radiographs | Cephalometric | PNS to Gonion plane | 10.8 m |
| Ghodke | S – 20 (11, 9)/ 10.9 C – 18 (9, 9)/ 10.9 |
10% randomly selected radiographs at 15 day interval | Cephalometric | NA | S – 8.2 m C – 7.3 m |
| Ali | S – 42 (21, 21)/10.4 C – 32 (16, 16)/10.1 |
30 radiographs at 1 month interval, ANB > 4mm | Cephalometric | Perpendicular line dropped on S-Ba from PNS. | S - 8.1 m followed-fixed therapy, 28.3 m C – 3 m |
| Chand | 14/12–14 y | 14 radiographs at 15 days interval | Cephalometric | PNS to the posterior wall of the pharynx | 4–5 m |
S: study group; C: control group; m: months; y: years, CBCT: cone-beam computed tomography scans; AB: anterior boundary; PB: posterior boundary; SB: superior boundary; IB: inferior boundary; S: sella; PNS: posterior nasal spine; SPW: superior pharyngeal wall; SP: soft palate plane; EB: epiglottis plane; PNS: posterior nasal spine; AA: anterior arch of atlas; PPW: posterior pharyngeal wall; PTM: pterygomaxillary points; NA: not available
Changes in Upper Airway Dimension (UAD)
The UAD at the pretreatment time varied from 7.2 mm to 41.9 mm with a mean of 14.16 mm. The post-treatment change in UAD ranged from 8.2 mm to 43.7 mm with a mean of 15.6 mm. All of the included studies showed a significant increase in UAD following the TBA treatment as compared to the control group (Table 4).
Table 4.
Summary of results of included studies (Upper airway dimensions (UAD): before, after, and long-term follow-up)
| Author | T1 UAD mm mean (SD) | T2 UAD mm mean (SD) | T3 UAD mm mean (SD) | T2-T1 mm (SD) | T3-T1 mm (SD) | |
|---|---|---|---|---|---|---|
| Verma | G1 | 12.4 (2.4) | 13.6 (2.3) | NA | 1.3 (2.3)* | NA |
| G2 | 12.1 (3.5) | 13.2 (3.0) | NA | 1.3 (1.3)* | NA | |
| G3 | 10.5 (1.4) | 12.0 (1.8) | NA | 1.4 (0.9)* | NA | |
| Jena | S | 7.2 (2.04) | 9.4 (2.7)* | NA | NA | NA |
| C | 7.7 (3.6) | 8.6 (3.7) | NA | NA | NA | |
| Zhang | 8.7 (1.8) | 12.4 (2.3)** | NA | NA | NA | |
| Ghodke | S | 9.1 (2.03) | 10.7 (2.4)** | NA | NA | NA |
| C | 7.8 (2.1) | 8.7 (1.8) | NA | NA | NA | |
| Ali | S | 32.9 (4.5) | 33.8 (4.2)* | 35.5 (4.6) | 0.69 | 2.6 (1.5) * |
| C | 41.9 (4.5) | 43.7 (4.4) | NA | NA | 1.8 (1.9) | |
| Chand | 7.6 (0.7) | 8.2 (0.8)* | NA | 0.6 (0.5) | NA | |
| Vinoth | 12.02 | 13.1* | NA | 1.08 | NA |
- P <0.05,
P <0.001,
G1: Group 1, hypo-divergent (SN-MP: <31°), G2: Group 2, normodivergent (SN-MP: 31°–34°), G3: group 3, hyper-divergent (SN-MP: >34°), S: study group, C: control group
DISCUSSION
The use of functional appliances in the treatment of developing Class II malocclusion with retrognathic mandible can bring the mandible forward, prevent the posterior relocation of the tongue, and improve pharyngeal airway passage (8). The present systematic review was conducted to evaluate the dimensional changes in upper airway following orthodontic treatment of skeletal Class II malocclusion with TBA.
Inclusion Criteria
In the present study, individuals with Class II skeletal malocclusion were included because the degree of displacement of hyoid bone (superiorly and posteriorly) was greater in Class II malocclusion as compared to Class I. TBA is most commonly used in these malocclusions to increase the UAD by causing functional mandibular displacement (10–13). The present systematic review is done in accordance with PRISMA standards (20) because they are associated with better reporting of included study quality with a better assessment of bias within and across the studies included in the present review.
Changes in Upper Airway Dimension
All the included studies showed a significant increase in UAD following the TBA treatment as compared to the controls. The expansion of the maxillary arch, along with the forward growth of mandible leads to forward relocation of the tongue, thereby increasing the posterior tongue space (7, 10–13, 15, 16). The study by Verma et al. (13) showed a significant increase in UAD among individuals with skeletal Class II malocclusion following treatment with TBA. However, there were no significant changes in the lower pharynx. This may be attributed to the fact that TBA causes mandibular advancement and forward positioning of the tongue, which in turn relieves the pressure on the soft palate, thus leading to an increase in upper oropharyngeal dimension and improved airway permeability. The growth of oropharyngeal muscles caused by forward movement of the mandible increases UAD. Studies (1–4) have shown a positive correlation between upper airway space and the length of the mandible. Retrognathic mandible results in the reduction in UAD by causing the tongue to be positioned posteriorly. TBAs are constructed in a protrusive bite that effectively modifies the occlusal inclined plane, which causes forward growth of the mandible and in turn increases UAD (9, 14).
Method of measurement of airway dimensions
All the studies which measured the UAD used the two-dimensional lateral cephalograms (7, 10–13, 15, 16). The main limitation with lateral cephalogram is that it cannot reveal changes in the transverse dimension but the alternative of CBCT imaging is associated with high radiation dose (9, 14, 22, 23). As the area measurements of the pharyngeal airway correlate more closely with linear measurements than that of the three-dimensional measurements, the conventional lateral cephalogram still remains a reliable diagnostic tool for monitoring the pharyngeal dimensions when utilizing area measurements.
This systematic review presented with a limitation; a meta-analysis could not be performed because there was heterogeneity across the studies. Heterogeneity results from differences in race and variations in growth patterns, which act as confounders and controls in case of ethical limitations. The construction of forest plots or funnel plots was not appropriate for the included studies. A simple descriptive and stratified comparison was able to be reported due to the disparate nature of the studies.
CONCLUSION
From the results of the explicitly selected studies included in this systematic review, it can be concluded that the use of Twin Block appliance for the correction of Class II skeletal malocclusion resulted in significantly greater improvement in increasing the UAD from 7.2 mm to 41.9 mm with a mean of 14.16 mm at pretreatment time to 8.2 mm to 43.7 mm with a mean of 15.6 mm at post-treatment time as compared to the controls.
Footnotes
Peer-review: Externally peer-reviewed.
Author Contributions: Supervision - R.N.M, S.B, Y.A.T.; Design - R.N.M, S.B, Y.A.T.; Supervision - R.N.M, S.B.; Resources - R.N.M, S.B, Y.A.T.; Materials - R.N.M, S.B, Y.A.T.; Data Collection and/or Processing - R.N.M, S.B, Y.A.T.; Analysis and/or Interpretation - R.N.M, S.B.; Literature Search - R.N.M, S.B.; Writing Manuscript - R.N.M, S.B, Y.A.T.; Critical Review - R.N.M, S.B, Y.A.T.
Conflict of Interest: The authors have no conflict of interest to declare.
Financial Disclosure: The authors declared that this study has received no financial support.
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