Abstract
The study objective was to evaluate, through a meta-analysis, the impact on the pharyngeal airway space (PAS) of different orthognathic surgeries for the treatment of the prognathic mandible. An electronic search of three databases and hand searches were carried out up to December 2014. The inclusion criteria were clinical human studies, including randomized controlled trials (RCTs), controlled clinical trials (CCTs), and retrospective studies, with the aim of comparing bilateral sagittal split osteotomy (BSSO) to intraoral vertical ramus osteotomy (IVRO), or one-jaw to two-jaw surgery for the treatment of the prognathic mandible. The PAS changes (anterior–posterior dimensions and cross-sectional area) at the level of the nasopharynx, oropharynx, and hypopharynx were analyzed. A statistically significant difference was found between BSSO and IVRO groups and one-jaw surgery and two-jaw surgery with regard to PAS changes after the treatment of mandibular prognathism. The results of this meta-analysis indicate that BSSO presents less change in the PAS after mandibular setback surgery compared to IVRO. Furthermore, the results of this study suggest that bimaxillary surgery is superior to mandibular setback surgery alone for the correction of the prognathic mandible, particularly in patients with factors predisposing them to the development of breathing problems.
The surgical correction of mandibular prognathism was initially achieved by mandibular setback surgery alone. With advances in knowledge and techniques, corrective surgery has progressed to include bimaxillary procedures. In the last decade, mandibular setback surgery has declined in frequency to fewer than 10% of mandibular prognathism patients; bimaxillary surgery is used in approximately 40% of patients and maxillary advancement alone is performed in the remaining patients. Both mandibular setback surgery and bimaxillary surgery can improve occlusion, masticatory function, and aesthetics by markedly changing the position of the mandible. Changes in the positions of the hyoid bone and tongue also occur, resulting in narrowing of the pharyngeal airway space (PAS). PAS narrowing has been associated with the development of obstructive sleep apnoea (OSA). OSA is considered a risk factor for systemic and pulmonary hypertension and cardiac arrhythmias, and might increase morbidity and mortality.
After mandibular setback operations, head posture can also change to sustain normal breathing. However, maxillary advancement operations, mainly together with mandibular advancement operations, can be used for the treatment of OSA syndrome because of the positive effect on breathing.
Most previous studies have investigated only the effect on PAS of mandibular setback surgery using the sagittal split ramus osteotomy (SSRO) to correct prognathism. The effect of the intraoral vertical ramus osteotomy (IVRO) or bimaxillary surgery to correct mandibular prognathism has not been sufficiently explored; thus a study on the effect of other modalities of orthognathic surgery on PAS is needed. The purpose of the present study was to test the hypothesis that there is no difference between the different orthognathic surgeries for the treatment of mandibular prognathism (bilateral sagittal split osteotomy (BSSO), IVRO, or bimaxillary) in relation to changes in PAS.
Materials and methods
Literature search strategy
This systematic review and meta-analysis was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-Equity 2012 checklist. An electronic search of PubMed, Ovid MEDLINE, and Cochrane CENTRAL online databases was conducted from their respective dates of inception to December 2014. Free text words and medical subject heading (MeSH) terms were used. The headings ‘pharyngeal airway space’, ‘orthognathic surgery’, ‘bimaxillary surgery’, ‘mandibular setback’, and ‘maxillary advancement’ were used in combination with ‘nasopharynx’ or ‘oropharynx’ or ‘hypopharynx’.
A low yield led to the use of another search term, omitting the reference to AND (skeletal class III OR mandibular hyperplasia OR mandibular prognathism OR long face OR maxillary anterior–posterior deficiency) AND (mandibular setback OR bimaxillary surgery) OR (one jaw surgery) OR (two jaws surgery) OR (BSSO versus IVRO) OR (LeFort 1 osteotomy) AND (pharyngeal airway space) OR (nasopharynx) OR (oropharynx) OR (hypopharynx volume) OR (obstructive sleep apnoea) AND [limit to OR clinical trial OR randomized controlled trial OR controlled clinical trial OR retrospective study]. The abstracts of the articles identified were reviewed and the full texts of those with apparent relevance obtained. The references of these papers were cross-checked for unidentified articles, and the individual databases of key subject journals were searched using the same terms as above. These journals were the Journal of Oral and Maxillofacial Surgery , International Journal of Oral and Maxillofacial Surgery , Journal of Oral Surgery , and British Journal of Oral and Maxillofacial Surgery . The searches were limited to articles published in English. An attempt was made to identify unpublished material or to contact authors of published studies for further information. To complete the search, the references of each selected publication on the effect of different orthognathic surgery procedures on the PAS were hand-searched.
Study eligibility and focused question
The inclusion criteria were formulated using the PICOS criteria ( Table 1 ).
| Patients or population (P) | Patients with a hyperplastic mandible (prognathic mandible) and Angle class III malocclusion who had undergone setback of the mandible alone or in combination with a Le Fort I to obtain a class I relationship; age 13–50 years |
| Intervention (I) | Mandibular setback surgery using either IVRO for the IVRO versus BSSO group comparison, or bimaxillary surgery for the one-jaw versus two-jaw surgery group comparison |
| Comparator or control group (C) | Mandibular setback surgery using standardized BSSO in both groups (IVRO versus BSSO group and bimaxillary surgery in one-jaw versus two-jaw group) |
| Outcomes (O) | Pharyngeal airway space changes for hypopharynx, nasopharynx, and oropharynx (anterior–posterior dimension and cross-sectional area) |
| Study design (S) | Clinical human studies including randomized controlled trials, controlled clinical trials, and retrospective studies with the aim of comparing pharyngeal airway space changes between one-jaw and two-jaw surgery for the prognathic mandible |
| Focused question | Do patients treated with two-jaw surgery have a lesser amount of pharyngeal airway space change than those who have undergone one-jaw surgery for the prognathic mandible? |
Exclusion criteria
The following were excluded: (1) case reports, (2) technical reports, (3) animal or in vitro studies, (4) review papers, (5) uncontrolled clinical studies, (6) studies that did not report the data required to perform a meta-analysis (mean and standard deviation), (7) publications in which the same data were published by the same groups of authors, and (8) publications for which the full text could not be obtained.
Data collection process
The eligibility of all studies retrieved from the databases was assessed carefully. The following data were extracted from the studies included in the final analysis: authors, year of publication, study design, gender (male, female), mean age in years, number of patients in the groups, follow-up period, how the outcomes were measured, and fixation methods.
Risk of bias in individual studies
A methodological quality rating was performed by combining the proposed criteria of the Meta-Analysis of Observational Studies in Epidemiology statement (MOOSE), the Strengthening the Reporting of Observational Studies in Epidemiology statement (STROBE), and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) to verify the strength of scientific evidence in clinical decision-making. The classification of the risk of potential bias for each study was based on the following five criteria: random selection in the population, definition of inclusion and exclusion criteria, report of losses to follow-up, validated measurements, and statistical analysis. A study that included all of these criteria was classified as having a low risk of bias and a study that did not include one of these criteria was classified as having a moderate risk of bias. When two or more criteria were missing, the study was considered to have a high risk of bias.
Synthesis of results
Meta-analyses were conducted only if there were studies of similar comparisons, reporting the same outcome measures. The weighted mean difference (WMD) or standard mean difference (SMD) (if the study used a different instrument to measure outcomes) was used to construct forest plots of continuous data. The random-effects model was performed if heterogeneity was detected; otherwise a fixed-effects model with a 95% confidence interval (CI) was performed. The data were analyzed using the statistical software Review Manager (version 5.2.6; The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark, 2012).
Assessment of heterogeneity
The significance of any discrepancies in the estimates of the treatment effects of the different trials was assessed by means of Cochran’s test for heterogeneity and the I 2 statistic, which describes the percentage total variation across studies that is due to heterogeneity rather than chance. Heterogeneity was considered statistically significant if P < 0.1. A rough guide to the interpretation of I 2 given in the Cochrane handbook is as follows: (1) from 0% to 40% the heterogeneity might not be important, (2) 30–60% may represent moderate heterogeneity, (3) 50–90% may represent substantial heterogeneity, and (4) 75–100% may represent considerable heterogeneity.
Results
The article selection process and the final number of articles selected according to the initial and final selection criteria are presented in Fig. 1 . The search strategy resulted in 263 articles on the effect of different orthognathic surgical procedures for the treatment of mandibular prognathism (namely BSSO, IVRO, Le Fort I, and bimaxillary surgery) on PAS changes. After selection according to the inclusion/exclusion criteria, eight articles qualified for the final review. Two studies compared BSSO and IVRO for the retrognathic mandible, and six studies compared two-jaw and one-jaw surgery with regard to PAS changes.
Characteristics of studies included
Details of the studies included are shown in Tables 2 and 3 . One study was an RCT, five were CCTs, and two were retrospective studies.
| Author | Year | Study design | Male to female ratio | Mean patient age, years | No. of patients | Follow-up period | How was the outcome measured | Fixation methods | |
|---|---|---|---|---|---|---|---|---|---|
| BSSRO | IVRO | ||||||||
| Kitahara et al. | 2010 | RCT | BSSRO, 0:25 IVRO, 0:21 |
BSSRO, 25.1 IVRO, 24.2 |
25 | 21 | 1 year after surgery | Cephalometric analysis | BSSRO: miniplate + 2 MCO + IMF for 13.6 days IVRO: IMF for 21.5 days |
| Abdelrahman et al. | 2011 | RS | BSSRO, 9:8 IVRO, 1:5 |
BSSRO, 28.2 IVRO, 24.8 |
17 | 6 | 1 year after surgery | Cephalometric analysis | NM |
| Author | Year | Study design | Male to female ratio | Mean patient age, years | No. of patients | Follow-up period | How was the outcome measured | Fixation methods | |
|---|---|---|---|---|---|---|---|---|---|
| Two-jaw | One-jaw | ||||||||
| Chen et al. | 2007 | CCT | 0:66 | NM | 31 | 35 | 2 years after surgery | Cephalometric analysis | Rigid fixation |
| Degerliyurt et al. | 2008 | RS | 13:34 | 1-jaw, 2-jaw: 23.3 |
23 | 24 | NM | CT | Rigid fixation + MMF for 1 week |
| Hwang et al. | 2010 | CCT | 30:30 | 1-jaw, 2-jaw: 23.3 |
45 | 15 | 16.62 months | Cephalometric analysis, lateral | Stainless steel wire for the first 2 weeks |
| Aydemir et al. * | 2012 | CCT | 2-jaw, 15:17 1-jaw, 3:4 |
NM | 32 | 7 | NM | Cephalometric analysis | Rigid fixation |
| Hong et al. | 2011 | CCT | 14:7 | 26.60 | 9 | 12 | NM | CBCT | Rigid fixation + IMF for 1 week |
| Kobayashi et al. | 2013 | CCT | 29:49 | 24 | 57 | 21 | 6 months later | Cephalometric analysis | Titanium miniplates and poly- l -lactic acid |
* This study included 48 patients divided into three groups: bimaxillary ( n = 32), maxillary advancement ( n = 9), and mandibular setback ( n = 7).
Concerning the quality assessment of the studies included, one study showed a low risk of bias, and seven studies showed a moderate risk of bias. The scores are summarized in Table 4 .
| Authors | Published | Random selection in population | Defined inclusion/exclusion criteria | Loss to follow-up reported | Validated measurement | Statistical analysis | Estimated potential risk of bias |
|---|---|---|---|---|---|---|---|
| Kitahara et al. | 2010 | Yes | Yes | Yes | Yes | Yes | Low |
| Abdelrahman et al. | 2011 | No | Yes | Yes | Yes | Yes | Moderate |
| Chen et al. | 2007 | No | Yes | Yes | Yes | Yes | Moderate |
| Degerliyurt et al. | 2008 | No | Yes | Yes | Yes | Yes | Moderate |
| Hwang et al. | 2010 | No | Yes | Yes | Yes | Yes | Moderate |
| Aydemir et al. | 2012 | No | Yes | Yes | Yes | Yes | Moderate |
| Hong et al. | 2011 | No | Yes | Yes | Yes | Yes | Moderate |
| Kobayashi et al. | 2013 | No | Yes | Yes | Yes | Yes | Moderate |
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