INTRODUCTION

Class II division 1 malocclusions with a mandibular deficiency have been treated for more than a century with different types of functional appliances. Esthetics is one of the main reasons for seeking orthodontic treatment.1 It has been suggested that maxillary, mandibular, and dental morphologies have an indirect effect on the perception of facial beauty.2 It seems clear that at least Caucasians prefer a straight profile.3 Therefore, one of the goals of functional treatment is to attain a straighter profile from a starting retrognathic profile, characteristic of Class II division 1 patients.4 From the hundreds of reports emphasizing changes produced by functional appliance use, only a relatively small proportion reported soft tissue changes.

For Class II corrections, several removable functional appliances are available, but only a few fixed functional appliances exist (ie, Crossbow, Forsus, Herbst, Jasper Jumper, MARA). Fixed functional appliances have the advantage of not requiring patient compliance. They can also be used concurrently with brackets. Their disadvantages are that they are prone to breakage and difficult to clean or remove.5

Although literature reviews about skeletal and dental changes with the use of fixed functional appliances have been made, no such review has been made for the soft tissue changes. It has been shown that fixed functional appliances enhance mandibular growth and that they tend to produce a more horizontal condylar growth compared with removable functional appliances.6 A comparison of dentoalveolar and skeletal effects between Herbst and Twin Block7 showed that most of the changes were dental in nature, with proclination of mandibular incisors and retroclination of maxillary incisors, which can potentially alter the lip-profile relationship.

Because of the volume of new publications produced every year, the development of a systematic approach to search, identify, and summarize available evidence has become increasingly necessary. In the past, conventional literature reviews were written by people deemed experts on a particular topic. However, such reviews were based on the authority of the most popular lecturers and researchers rather than relying on the best available evidence and, therefore, prone to bias. Conversely, a systematic review can be defined as “a review that has been prepared using a systematic approach to minimize biases and random errors which is documented in a materials and methods section.”8 The distinct advantage of the systematic review compared with the conventional literature review is the transparency and reproducibility of its literature search.9 In this manner, systematic reviews can both deduce consensus among previous research with minimized bias and identify topics requiring further research.

Although a significant improvement of the facial profile after fixed functional appliance use has been reported previously, no study has yet systematically reviewed these claims. The objective of this systematic review is to evaluate facial soft tissue changes after the use of fixed functional appliances in Class II division 1 malocclusion cases using lateral cephalograms. This will permit a distinctive differentiation between the changes reported on the basis of sound methodological study designs and the anecdotal reported information.

MATERIALS AND METHODS

A computerized search was conducted using Medline (from 1966 to week 1 of August 2005), Medline In-Process & Other Non-Indexed Citations (up to August 12, 2005), Lilacs (from 1982 to July 2005), Pubmed (1966 to week 1 of August 2005), Embase (from 1988 to week 32 of 2005), Web of Science (1945 to week 32 of 2005), and all EBM reviews (Cochrane Database of Systematic Reviews [CCTR], ASP Journal Club, Database of Abstracts of Reviews of Effects, and CCTR) (to the second quarter of 2005) databases. Terms used in this literature search were “functional appliances,” “soft tissue,” “profile” or “facial changes,” and “human studies.” The selection and specific use of each term inside every database search were made with the help of a senior librarian who specialized in Health Sciences database searches (Table 1).

TABLE 1.  Abstract Search Results from Different Electronic Databases^a,b

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The following inclusion criteria were chosen to initially select potential articles from the published abstract results: human clinical trials; facial soft tissue changes; fixed functional appliances to correct Class II division 1 malocclusions; nonsyndromic or medically compromised patients; no individual case reports or series of cases; and no surgical intervention.

No attempts were made at this stage to identify which studies did not use adequate control groups to factor out growth changes. It was considered improbable that the abstracts would report enough information regarding control groups. This would potentially exclude some articles.

All the article abstracts that appeared to meet the initial inclusion criteria were selected, and the actual articles were collected irrespective of the language in which they were published. The selection process was independently conducted by two researchers, their results compared and any discrepancies settled through discussion. The Lilacs database articles were evaluated only by one of the researchers because of language limitations. If an article abstract did not provide enough information to make a decision, the actual article was obtained.

The articles ultimately selected were chosen with the following additional inclusion criteria: evaluation of soft tissue changes through lateral cephalograms; a comparable control group to factor growth changes if required; and only fixed functional appliances used.

The actual articles from the selected article abstracts were independently evaluated by two researchers. A consensus was reached regarding which articles fulfilled the final selection criteria and were to be included in the systematic review. Articles that did not factor out growth when required (growing samples) were rejected at this stage. Factoring out craniofacial growth in the analysis was considered important to make an accurate assessment of the amount of treatment produced soft tissue change. Failure to consider craniofacial growth changes would result in a potential overestimation of the amount of change produced by the treatment. Simultaneous use of fixed banded appliances was considered a confounder and a reason for exclusion. Although measurement error is needed for a correct interpretation of the clinical significance of the findings, it was not considered a reason to reject an article but was considered in the interpretation of the data.

Knowing that more methodologically sound studies may provide more reliable conclusions, a methodological scoring process was developed to identify which selected studies would be most valuable (Table 2). No attempt was made to imply that this evaluation tool has been properly validated. Previous reports10–12 have shown that there is no sound evidence about the validity of the use of quality assessments of clinical trials, and they recommend researchers examine individually the influence of key components of methodological quality.

TABLE 2.  Studies that Fulfilled Initial Selection Criteria But Were Later Rejected

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The reference lists of the retrieved articles were also hand-searched for additional relevant publications that may have been missed in the database searches. In cases where extra information was required for discussion or statistical analysis, and was not specifically stated in the article, contact with the authors was sought to obtain the required information.

RESULTS

The search results and the final number of abstracts selected according to the initial selection criteria from the various databases are provided in Table 1.

From the nine studies which based on the abstracts seemed to be potentially useful, only five413–16 (56%) actually fulfilled the final selection criteria after reading the complete article. Of these five studies, three41516 were done with adolescents and two1314 with adults. From the remaining four articles, three17–19 were rejected because of the lack of an adequate control group to factor out expected normal growth changes and one20 because it only used lateral extraoral photos (Table 2). A flow diagram of the literature search is shown in Table 3.

TABLE 3.  Flow Diagram of the Literature Search

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A methodological quality checklist (Table 4) was developed to evaluate the methodological soundness of the selected articles and the application of the same is provided in Table 5. Further details about the methodology of the selected studies can be found in Table 6.

TABLE 4.  Methodological Score for the Clinical Trials

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TABLE 5.  Methodological Score of Selected Articles^a

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TABLE 6.  Key Details About the Selected Articles^a

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The following data represent a summary of the soft tissue changes stated in each individual study. Please refer to Table 7 for specific information about the measurements used and the magnitude of the changes.

TABLE 7.  Reported Soft Tissue Measurements from the Finally Selected Studies^a,b

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DISCUSSION

The present systematic review was performed to systematically analyze the soft tissue changes that were produced by fixed functional appliances in Class II division 1 malocclusions. Despite the extensive amount of published studies regarding therapeutic effects produced by fixed functional appliances, almost exclusively with the use of the Herbst appliance, only a few clinical trials fulfilled the selection criteria. Furthermore, the level of evidence found in them was low. The use of properly designed clinical trials with an adequate nontreated control group, if growth is expected, is the only scientific approach to quantify changes produced by therapeutic appliances. Consideration of retrospective clinical trials, series of cases, or case reports is prone to bias and exaggeration of changes attained.9 This has been shown in a randomized clinical trial about the Herbst compared with retrospective studies.7

CONCLUSIONS

The following systematic review conclusions should be considered with caution because only a secondary level of evidence was found. Long-term prospective double-blinded randomized clinical trials are needed to support these conclusions.

• An improvement of the facial convexity was found.

• Changes produced by fixed functional appliances seem to restrict the forward movement of the upper lip.

• No change in the anteroposterior position of the lower lip and soft tissue menton was found.

• Soft tissue changes are similar between nongrowing young adult and growing adolescent samples.