Search Strategy

The strategy for performing this systematic review was mainly influenced by the National Health Service (NHS) Centre for Reviews and Disseminations.17 To identify all the studies that examined the stability of bimaxillary surgical correction of permanent dentition and adult patients with skeletal Class III malocclusion, a literature survey was done by applying the Medline database (Entrez PubMed, www.ncbi.nlm.nih.gov) followed by a manual search. The survey covered the period from September 1959 to October 2007, and using the Medical Subject Headings (MeSH) terms: “malocclusion, Angle Class III” and “prognathism” which were crossed with combinations of the following MeSH terms: “surgery,” “surgical procedures, operative,” and “long-term stability.” In addition, a search in the Cochrane Controlled Clinical Trials Register was performed (www.cochrane.org/reviews). The inclusion and exclusion criteria are given in detail in Table 1.

Table 1.  Inclusion and Exclusion Criteria

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Data Collection

To perform an analysis of the available scientific studies, according to the recommendations by Petrén et al,18 data were collected for each selected article on the following items: year of publication, study design, sample size, treatment strategy, age, methods/measurements, surgical stabilization and/or surgical-orthodontic treatment time, follow-up, success rate, presurgical dentoskeletal features, correction of dentoskeletal features, relapse, and authors' conclusions. In addition, to document the methodological soundness of each article, a quality evaluation modified by the methods described by Antczak et al19 and Jadad et al20 was performed. The following characteristics were used: study design, previous estimate of sample size, selection description, withdrawals (dropouts), method error analysis, blinding in measurements, statistical analysis, and its adequacy. The quality was categorized as low, medium, and high. Two independent reviewers assessed the articles separately. The data were extracted from each article with blinding to the authors, and interexaminer conflicts were resolved by discussion on each article to reach a consensus. One author performed the quality evaluation of the statistical methods used in the articles.

Results of Quality Analysis

The results of the quality analysis are given in detail in Table 4. The analysis revealed that the research quality or methodological soundness was low in two studies,2531 medium in twelve studies,21–2426–283032–35 and medium/high in one article.29 This article was represented by a RCT, and it specified the probabilities of type-1 (α) and type-2 (β) errors. The lack of blinding in measurement (a common feature of all retrieved studies) provides explanation for a medium/high score instead of a high score for this study.29

Table 4.  Quality Analysis of the Selected Studies

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Effectiveness of Bimaxillary Surgery

In this systematic review, the literature search was aimed to select all randomized and nonrandomized controlled clinical trials (RCCTs; CCTs) that examined the stability of bimaxillary surgical correction of skeletal Class III malocclusion. Bimaxillary surgery is the major surgical technique for Class III patients, even if some patients may require modifications or more limited surgical approaches. Fifteen studies were retrieved, and several of them showed consistent results.

Seven articles232527–293235 showed correction of the sagittal intermaxillary relationships after surgery and follow-up. Only two studies2327 considered skeletal Class III patients with a long face, increased intermaxillary angle, and anterior open bite; after the longest follow-up period these articles showed an improvement in the values for facial divergence, a reduced lower anterior facial height, and an increased lower posterior facial height. In seven papers222527–293235 presurgical OVJ value was negative and it appeared positive after the longest follow-up period; in one article23 OVJ value increased after 12 months of follow-up, but it resulted still negative. OVB value was corrected in the four studies22232527 in which it was negative before surgery, while it was improved in the other four articles28293235 where it had a small but positive value before surgery. Only two studies2430 declared the success rate of bimaxillary surgery in Class III malocclusion; a >90% success rate was reported in one article,24 and an 80% rate in the second article.30

Despite of the not negligible percentages of patients reported in several studies with relapse changes large enough to be outside the range of method error, and thus clinically significant, bimaxillary surgical therapy could be considered an effective procedure in skeletal Class III malocclusion correction.

Factors of Stability After Bimaxillary Surgery

The analysis of the 15 retrieved studies suggested that horizontal stability of surgical outcomes in the maxilla might be negatively influenced by its surgical advancement greater than 6 mm28 and by the use of semirigid fixation29 or resorbable plates and screws35 to stabilize its advancement when this was greater than 5 mm.33 The data indicated also that double-jaw surgery improved vertical stability of the maxilla, when it was to be moved down at surgery.222430

Factors accounting for mandibular relapse were several: the degree of intraoperative clockwise rotation of the mandibular proximal segment,2132 the amount of mandibular setback (measured at Pg,2832 Go,2232 B-point, and Ar-B length33) and the excessive posterior condylar displacement in the glenoid cavity.2631 One of the common factors was the altered orientation and stretching of the pterygomasseteric sling that exerted an upward and forward force at the gonial angle accounting for mandibular relapse.2126 The one study with the greatest methodological soundness29 indicated that a larger amount of relapse has to be expected in patients presented with presurgical sagittal intermaxillary discrepancies greater than 7 mm, thus requiring a large amount of mandibular setback.

From a speculative point of view, the analysis of the results of this systematic review suggests that one of the objectives of early orthopedic intervention in Class III patients can be seen as the reduction of the sagittal intermaxillary discrepancy in order to enhance the stability of the outcomes of orthognathic surgery, when needed at the completion of growth. Even in those Class III patients who do not show a complete resolution of the discrepancy after orthopedic therapy, early intervention may entail the favorable effect of creating more suitable candidates for a stable surgical correction.

Quality of the Studies

As proposed in a previous article38 the quality of the articles was judged as low, medium, or high according to the characteristics in Table 4. In some studies, there were shortcomings such as small sample size,222430 thus implying low power with high risk to achieve insignificant outcomes as declared by the authors themselves. Other frequent limitations were the absence of previous estimate of sample size (present only in two studies2430) or of discussion on the possibility of type II (β) error occurring (calculated in one article29). Problems of lack of method error analysis2134 and systematic error analysis (present only in four studies26283235) blinding in measurements, and lack of statistical methods24253031 were other examples of drawbacks in some of the analyzed articles.

However, comprehensive analysis of retrieved articles revealed that the research quality was low only in two studies,2531 medium in twelve studies,21–2426–283032– 35 and medium/high in one article,29 which was represented by a RCT. Therefore, the quality of the retrieved articles allows for some conclusions on the factors affecting the outcomes of surgery in Class III malocclusion.