Introduction
Self-ligating brackets have been gaining popularity over the past several decades. Various advantages for these systems have been claimed. The purposes of this systematic review were to identify and review the orthodontic literature with regard to the efficiency, effectiveness, and stability of treatment with self-ligating brackets compared with conventional brackets.
Methods
An electronic search in 4 data bases was performed from 1966 to 2009, with supplemental hand searching of the references of retrieved articles. Quality assessment of the included articles was performed. Data were extracted by using custom forms, and weighted mean differences were calculated.
Results
Sixteen studies met the inclusion criteria, including 2 randomized controlled trials with low risk of bias, 10 cohort studies with moderate risk of bias, and 4 cross-sectional studies with moderate to high risk of bias. Self-ligation appears to have a significant advantage with regard to chair time, based on several cross-sectional studies. Analyses also showed a small, but statistically significant, difference in mandibular incisor proclination (1.5° less in self-ligating systems). No other differences in treatment time and occlusal characteristics after treatment were found between the 2 systems. No studies on long-term stability of treatment were identified.
Conclusions
Despite claims about the advantages of self-ligating brackets, evidence is generally lacking. Shortened chair time and slightly less incisor proclination appear to be the only significant advantages of self-ligating systems over conventional systems that are supported by the current evidence.
Editor’s comment
The evidence required to make an informed decision on the selection of self-ligating brackets has only recently been presented in the literature, despite the decades since their introduction. The accumulated information consists mostly of lower levels of evidence, such as case reports, cases series, opinion articles, and so on. Interest has been especially intense during the last 2 years, as reflected in the publication of several prospective trials and randomized clinical trials, on various clinical features of self-ligating brackets including treatment durations, force levels, periodontal and oral flora effects, root resorption, and dental arch changes. This systematic review is the first of its kind in the orthodontic literature. Of the 16 studies considered in the review, only 2 were randomized clinical trials.
The results of the meta-analysis support the advantages of self-ligating brackets in 2 areas. The first was a statistically significant reduction in chair time. The second was a statistically significant reduction in mandibular incisor proclination. However, this difference was only 1.5°.
Q&A
Eliades: Why do we need systematic reviews with or without a meta-analysis and what do they do? What would be the benefit for our specialty?
Huang: A systematic review is the most rigorous method to determine whether a treatment or therapy is truly effective. Specific guidelines are used to identify all pertinent literature, make decisions about a study’s inclusion or exclusion, and evaluate the quality of included studies. When the statistics from several studies are similar enough, a meta-analysis can be performed. This technique pools the data from several studies and can be considered a quantitative assessment, as opposed to a systematic review, which is a qualitative assessment. Systematic reviews and meta-analyses are important for our specialty, because they provide practitioners the best scientific information about a particular topic. Systematic reviews and meta-analyses are intended to be updated periodically, and, therefore, recommendations might change over time as new evidence is generated. Another benefit of systematic reviews and meta-analyses is that they show us gaps in our knowledge base; thus, they assist in directing topics and methods for future research.
Eliades: How does publication bias affect the validity of the results of a systematic review and consequently clinical practice?
Huang: Publication bias occurs when investigators submit positive results for publication, but not negative results. Obviously, publication bias can have a significant effect on the findings of a systematic review. Although it is impossible to eliminate publication bias, systematic reviews can assess this with funnel plots. Additionally, as study designs become increasingly rigorous, and as significant amounts of time and money are invested in conducting these trials, investigators are highly motivated to report results, whether positive or negative. In recent years, several international registries for prospective trials have been established (eg, ClinicalTrials.gov and Cochrane Controlled Clinical Trials Register). This also helps with publication bias, since one can search for registered trials on specific topics and the publications that should eventually arise from them.
Eliades: How is it possible to combine results from studies with different methodologies?
Huang: Different methodologies are a challenge for systematic reviews and meta-analyses. When the results are too different, combining results is not feasible. For example, it would be impossible to combine results in a systematic review assessing treatment success if 1 study measured occlusal outcomes, another measured periodontal health, and another measured treatment time. On the other hand, if all 3 studies measured occlusal outcomes with the peer assessment rating index, it would be relatively easy to combine the data and perform a meta-analysis. Usually, the outcomes from the included studies have some similarities. An example of this might be a systematic review in which various studies use the peer assessment index, the index of complexity, outcome and need (ICON), or the American Board of Orthodontics’ objective grading system to evaluate occlusal parameters. In this situation, it might be possible to adjust (ie, standardize) the values of the various indices to combine their results. Thus, a meta-analysis could be performed, and the results would be reported as standardized mean differences.
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