The objective of this study was to perform a systematic review and meta-analysis to test the null hypothesis that there is no difference in postoperative skeletal stability between bicortical screw and monocortical plate fixation after mandibular advancement surgery with bilateral sagittal split ramus osteotomy (BSSO). A comprehensive search of major databases (PubMed, EMBASE, and Cochrane CENTRAL) was conducted to locate all relevant articles published from inception to October 2015. Studies were selected based on inclusion criteria; randomized controlled trials, controlled clinical trials, and retrospective studies comparing bicortical screw vs. monocortical plate fixation after BSSO, reported in peer-reviewed publications in the English language, were considered eligible. Changes in linear measurements (horizontal and vertical) were analyzed. Five relevant studies were identified, involving 203 patients (bicortical screw n = 98, monocortical plate n = 105). No significant difference was found between monocortical plate and bicortical screw fixation in horizontal ( P = 0.099) or vertical measurement ( P = 0.882). Based on this review, there is overall agreement in the literature that the amount of advancement has a direct relationship with postoperative changes. The results of this meta-analysis support the hypothesis that there is no statistically significant difference in skeletal stability between bicortical screw and monocortical plate fixation of the BSSO following mandibular advancement surgery.
The bilateral sagittal split ramus osteotomy (BSSO) is one of the most useful mandibular orthognathic surgeries. Among the many fixation methods commonly used to stabilize the BSSO, bicortical titanium screws and monocortical miniplate/screw fixation are the most common.
In spite of the extensive use of the BSSO, there is still controversy regarding the best method of fixation. Several clinical studies have found the two methods of fixation (bicortical screws and monocortical miniplates) not to differ significantly from each other when comparing the amount of advancement with the amount of postsurgical instability, so their use is a matter of surgical choice. However, in vitro studies have demonstrated that bicortical screw fixation tends to be more rigid and less susceptible to deformation than a monocortical plate.
As no evidence-based report has addressed this controversial issue, the present study was performed to test the null hypothesis that there is no difference in postoperative skeletal stability between bicortical screw and monocortical plate fixation after mandibular advancement surgery with BSSO.
Materials and methods
Literature search strategy
In order to ensure a systematic approach and more reliable findings, this systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement for reporting systematic reviews. Studies aimed at assessing the stability of bicortical screw fixation vs. plate fixation with BSSO, published from inception to October 2015, were sought using three electronic databases: PubMed, Cochrane CENTRAL, and EMBASE. Other sources were searched manually, including the reference lists of the studies included and five journals highly likely to contain studies relevant to the review topic: Journal of Oral and Maxillofacial Surgery , International Journal of Oral and Maxillofacial Surgery , British Journal of Oral and Maxillofacial Surgery , Oral Surgery , Oral Medicine , Oral Pathology , Oral Radiology , and Journal of Cranio-Maxillo-Facial Surgery . The searches were limited to articles published in the English language. An attempt was made to identify unpublished material and to contact authors of published studies for further information. To complete the search, the references of each selected publication that compared skeletal stability after BSSO using either bicortical screws or monocortical plates were searched by hand. The electronic search strategy is shown in Table 1 .
|Population||(1) MeSH term: Angle class II OR short face deformity OR retrognathic mandible
(2) Text word: Angle class II OR short face deformity retrognathic
|Intervention||(3) MeSH term: bicortical osteosynthesis OR positioning screws OR lag screws OR rigid fixation
(4) Text word: bicortical osteosynthesis OR positioning screws OR lag screws OR rigid fixation
|Comparison||(5) MeSH term: monocortical osteosynthesis OR miniplate fixation OR miniplate with monocortical screws at superior-lateral surface OR semi-rigid fixation
(5) Text word: monocortical osteosynthesis OR miniplate fixation OR miniplate with monocortical screws at superior-lateral surface OR semi-rigid fixation
|Outcomes||(7) MeSH term: skeletal stability OR relapse OR vertical postsurgical changes OR horizontal postsurgical changes|
|Study design||(8) MeSH term: randomized controlled trials AND controlled clinical trials AND retrospective studies AND case series|
|Search combination||1 AND 2 AND 3 AND 4 AND 5 AND 6 AND 7 AND 8|
|Electronic database||MEDLINE/PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), EMBASE|
|Focused question||Are bicortical screw and plate osteosynthesis techniques equal in providing skeletal stability after mandibular advancement with the BSSO?|
Study eligibility and focused question
The inclusion criteria were adapted using the PICOS criteria ( Table 2 ). The focused question was ‘Are bicortical screw and plate osteosynthesis techniques equal in providing skeletal stability after mandibular advancement with the bilateral sagittal split osteotomy?’
|Patients or population (P)||All patients had a jaw deformity diagnosed as mandibular retrognathism or small mandible, with or without bimaxillary asymmetry and maxillary hypo/hyperplasia, and required a BSSO to perform mandibular advancement; age was 15–50 years|
|Intervention (I)||Bicortical osteosynthesis|
|Comparator or control group (C)||Monocortical osteosynthesis (miniplate with monocortical screws at the superior-lateral surface)|
|Outcomes (O)||Postoperative skeletal relapse (linear and angular measurements)|
|Study design (S)||Clinical human studies including randomized controlled trials, controlled clinical trials, and retrospective studies whose aim was to compare skeletal stability and post/intraoperative complications between bicortical and monocortical fixation after BSSO|
|Focused question||Are bicortical screw and plate osteosynthesis techniques equal in providing skeletal stability after mandibular advancement surgery with the BSSO?|
The exclusion criteria encompassed case reports, technical reports, animal and in vitro studies, review papers, uncontrolled clinical studies, studies that did not report the data required to perform a meta-analysis (mean and standard deviation), publications in which the same data were published by the same group of authors, and studies that used BSSO for mandibular setback, because the relapse pattern is different (opposite direction).
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, sex distribution (male, female), mean age in years, number of patients in the groups, fixation methods, follow-up period, outcomes assessed, use of intermaxillary fixation, magnitude of the advancement (in millimetres), and amount of relapse at B point (in millimetres).
Critical appraisal of individual studies
The critical appraisal of each included study was performed independently by the two authors according to the domain-based evaluation described in the Cochrane Handbook for Systematic Reviews of Interventions. The following specific domains were used: sequence generation, allocation concealment, blinding, and incomplete outcome data. The domains were recorded as ‘Yes’ (low risk of bias), ‘Unclear’ (uncertain risk of bias), or ‘No’ (high risk of bias).
Synthesis of results
Meta-analyses were to be conducted only if there were studies of similar comparisons, reporting the same outcome measures. For binary outcomes, it was planned to calculate a standard estimation of risk reduction (RR) by random-effects model if heterogeneity was detected. Otherwise a fixed-effects model with 95% confidence intervals (CI) was to be used. The weighted mean difference (WMD) or standard mean difference (SMD) (if the studies used different instruments to measure the outcome) was used to construct forest plots of continuous data. The data were analyzed using Comprehensive Meta-Analysis statistical software, version 2.0 (Biostat, Englewood, NJ, USA).
Assessment of heterogeneity
The significance of any discrepancies in the estimates of the treatment effects from the different trials was assessed by means of Cochran’s test for heterogeneity and the I 2 statistic. Any identified heterogeneity was investigated. Heterogeneity was considered statistically significant if P < 0.1. I 2 was interpreted according to the Cochrane handbook, 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 high heterogeneity.
The article selection process is presented in Fig. 1 . The search strategy resulted in 247 articles on bicortical vs. monocortical fixation after BSSO with mandibular advancement surgery. After selection according to the inclusion/exclusion criteria, five articles qualified for the final review. These five studies assessed skeletal stability for bicortical vs. monocortical fixation in BSSO following mandibular advancement surgery, with follow-up ranging from 1.2 weeks to 1.5 years. The studies involved a total of 203 patients, 98 in the bicortical screw fixation groups and 105 in the monocortical plate groups.
Characteristics of studies included
Detailed characteristics of the studies included are shown in Table 3 . Two studies were controlled clinical trials, one was a randomized controlled trial (RCT), and two were retrospective studies. Concerning the fixation method, four-hole titanium miniplates with four 2.0-mm screws were placed monocortically along the superior-lateral surface in the plate fixation group. In the bicortical screw fixation group, three bicortical position screws were placed above the mandibular canal. All of these studies used cephalograms to assess the postoperative skeletal changes.
|Author||Year||Study design||Age, years (mean)||Male to female ratio||No. of patients||Fixation methods||Outcomes and how measured||Follow-up||Use of IMF||Magnitude of advancement (mm)||Amount of relapse at B point (mm)|
|Blomqvist et al.||1997||CCT||Plate: 33
|Plate, Bico: 24:36||30||30||Plate: one plate was applied on each side using 2.0-mm screws||Skeletal changes, cephalometric analysis||6 months||Plate, Bico: 7–10 days||5.6||6.05||−0.8||−0.6|
|Kahnberg et al.||2007||CCT||Plate: 28
|15||17||Plate: two plates, one 6-hole plate (2 mm) at marginal part and one 3- or 4-hole plate placed inferior to the first||Skeletal changes, cephalometric analysis||1.5 years||Splint for 6 weeks||6.4||7.8||−0.1||−0.7|
|Becktor et al.||2008||RS||Plate: 31
|45||37||Plate: two 2.0-mm screws + miniplate
Bico: three bicortical screws at superior border
|Skeletal changes, cephalometric analysis||Plate: 3.5 weeks
Bico: 1.2 weeks
|Plate, Bico: IMF with splint for 1 to 2 weeks||5.4||4.9||5||2.4|
|Nooh 13||2009||RCT||Plate, Bico: 23||NM||8||8||Plate: 2-mm plating system with four screws, two anterior of 5 mm length and two posterior of 7 mm length
Bico: 2-mm wide and 12 mm in length
|Skeletal changes, cephalometric analysis||Up to 1 year||Plate: 4 weeks
Bico: 1 week
|Sato et al.||2014||RS||Plate: 23.67
|7||6||Plate: miniplate with four monocortical screws at external oblique ridge
Bico: three bicortical screws at superior border
|Skeletal stability, cephalometric analysis||After 6 months||Plate, Bico: 7 days||NM||NM||0.71||0.17|