INTRODUCTION

Class II malocclusion is one of the most common orthodontic discrepancies,^1–3 and it is likely to produce significant negative esthetic⁴ and social⁵ effects on children's lives, affect their dental health,⁶ or predispose them to dental trauma.⁷

Plenty of evidence is available to support that Class II, division 1 individuals have smaller transverse maxillary dental or skeletal dimensions.^8–11 For this reason, it has been proposed that the treatment of this malocclusion should comprise previous maxillary expansion.^12–15 It has been reported that after expansion, a “spontaneous” correction of the Class II malocclusion takes place as a result of a forward posturing of the mandible.^13–15 However, such observations have mostly relied upon clinical experience, and the research intended to analyze that question is controversial and presents diverse study methods.^16–22

Therefore, the objective of this investigation was to evaluate the effectiveness of rapid maxillary expansion (RME) on the sagittal dental or skeletal parameters of growing children with Class II malocclusion through a systematic review of available clinical trials.

MATERIALS AND METHODS

The Preferred Reporting Item for Systematic Review and Meta-Analysis (PRISMA) checklist²³ was used as a guideline for conducting and reporting this review.

Articles were selected if growing individuals who underwent orthodontic treatment with RME for Class II malocclusion were investigated. Studies including adults or growing patients treated with any orthodontic Class II treatment method other than RME were excluded.

In order to be included, the study outcomes should have referred to either dental (molar relationship) or skeletal (cephalometric mandibular parameters) status of Class II malocclusion, and evaluations should have been performed both before and after RME treatment. In addition, included articles should have necessarily presented results derived from inferential statistics.

No language or time restrictions were applied to the searches. Case reports, literature reviews, editorials, interviews, and letters were not considered. Interventional clinical trials, including randomized and nonrandomized controlled studies, as well as case series were accepted.

The following databases were searched: Medline, Embase, Cochrane Library and Scopus. The key words used for this literature search were “maxillary expansion,” “palatal expansion,” and “Class II,” A search strategy was designed first for Medline (Appendix 1) and was applied accordingly to all other databases. The electronic database searching was conducted between September 10 and 15, 2014. A hand search of the reference lists of selected articles was conducted to identify any additional relevant publications that might have been missed by the database search.

Once the search was completed, duplicate results were removed. In the first phase of the selection, two reviewers independently evaluated titles and abstracts, when available. Clinical studies that reported the use of RME for the correction of Class II malocclusion in growing individuals were considered as preselected after phase I screening. Full articles were then retrieved for those preselected publications, as well as for those with inadequate or unavailable abstracts. In the final phase of the study selection, the same reviewers independently evaluated the full-text articles according to critical application of the remaining eligibility criteria. Disagreements between reviewers in any selection phase were resolved through consensus.

The following variables were extracted from the final selected studies: sample and treatment characteristics; examination methods and parameters used to evaluate treatment effects, as well as main results, including baseline status; treatment effect (Δ) observed in the experimental group; net difference (Net Δ) between values observed in the treatment and control groups after observation period; and inferential statistics, which referred to either treatment vs control analysis if a control group was present, or initial vs final analysis in the case of noncontrolled studies. Two reviewers extracted the data independently, and all of the authors reviewed them afterwards. The extracted data were then combined and compared for accuracy, and discrepancies were resolved by reexamination of the literature. Authors were eventually contacted if any information appeared to be unclear.

Two reviewers appraised the selected studies according to the Methodological Index for Non-Randomized Studies (MINORS) (Appendix 2).²⁴ This tool was conceived and validated to assess methodological quality for nonrandomized studies, whether comparative or noncomparative.

RESULTS

A flowchart illustrating the selection of studies for this systematic review is presented in Figure 1. After the first phase selection, 25 full texts were obtained for the second phase evaluation, of which 18 articles^{13–15,25–39} were excluded. The reasons for exclusion are listed in Table 1. Finally, seven clinical trials met the eligibility criteria and were considered for this systematic review.^16–22

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Table 1.  Articles Excluded After Full Text Evaluation Based on Eligibility Criteria

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A summary of the key methodological data and study characteristics can be found in Table 2. Study samples were observed during the mixed dentition phase and presented a wide spectrum of Class II malocclusions. Samples were characterized as having either dental^18–20 or skeletal discrepancies.^16,17,21,22 Transverse maxillary deficiency was reportedly present in the sample of part of the studies.^16,19,21,22

Table 2.  Summary of Study Characteristics and Results of the Included Studies^a

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Table 2.  Continued

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Table 2.  Continued

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All subjects in the included studies were treated with RME, either as a sole treatment approach,^16,21,22 or associated with other appliances, such as passive transpalatal arches.^17–19 The subjects were observed for varying periods of time, according to different outcomes, which related to either skeletal^{16–19,21,22} or dental characteristics.^18–20

Methodological appraisal of the selected studies is presented in Table 3. None of the included studies was a randomized clinical trial. All of the researches^16–22 clearly stated the aim of the investigation, presented an appropriate period of observation, and reported no sample loss during follow-up. However, limitations were identified for most of the studies, such as the retrospective enrollment of the sample and collection of the data^20,22 or unclear report of these features.^16,17 None of the studies^16–22 reported if the outcome examiners were blinded during the end-point evaluation, and two trials^18,19 utilized a critical examination method (cephalometry) to assess the molar relationship outcome. These two studies,^18,19 however, were the only ones that demonstrated that their samples were appropriate in size.

Table 3.  Methodological Appraisal of the Selected Studies, According to MINORS Assessment Tool

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Three^20–22 of the seven included articles were noncontrolled studies. The other controlled studies^16–19 presented adequate paired control groups, although none of them reported if control and experimental groups were contemporary. Among the controlled studies,^16–19 two^16,17 lacked statistical analysis for comparison between the experimental and control groups changes. Of the remaining two controlled studies,^18,19 one of them¹⁹ had a baseline difference between the experimental and control groups.

Due to the large variability among the included studies, this systematic review was not designed in a meta-analysis format. Nonetheless, a comprehensive extraction of the study data can be found in Table 2.

DISCUSSION

The results observed during this systematic review are not only contradictory, but also frequently based on deficient methodology, or lack clinical relevance. Even though important studies have been published,^16–22 more solid scientific evidence based on reliable methods of assessment and proper study designs is still lacking in order to thoroughly test whether dental correction or mandibular anterior shift and/or supplementary growth take place after RME in Class II individuals.

According to Volk et al.,²⁰ maxillary expansion did not predictably improve Class II molar relationships. And even though the best evidence available^18,19 reported statistically significant occlusal improvements, these changes could be attributed to other reasons, eg, the use of passive transpalatal arches during transition from mixed to permanent dentition. As previously documented,^9,41,42 most of the flush terminal planes are naturally converted to solid first molar Class I during transition. This fact had been wisely mentioned before,⁴³ and it indicates that most of the end-to-end Class II cases in mixed dentition are self-corrected, and demand neither RME nor transpalatal arches to assure first molar adjustment.

The transformation into a Class I molar relationship, during transition to permanent dentition, depends on a number of dental and facial skeletal changes.⁴⁴ However, if one assumes that it is possible to preserve additional space by preventing upper molars mesial drift with transpalatal arches, as suggested,⁴⁵ even more severe than end-to-end Class II occlusions might be supposedly exempt from RME to attenuate their sagittal occlusal imbalances. Unless space management is critical, or transversal discrepancies are proved to be present, RME for sole attenuation of Class II malocclusion thus seems unnecessary.

As for the mandibular skeletal changes, most of the selected studies^16–18,20 indicated no mandibular shift, nor supplementary growth after RME. One may claim that the mandibular changes demonstrated by Guest et al.¹⁹ might have been a result of the mandibular shift or growth, but differences still seem clinically irrelevant. Moreover, other Class II standard therapies, such as functional removable appliances,⁴⁶ headgears,⁴³ or bite-jumping appliances,⁴⁷ have already proved to be effective for the Class II correction; in addition, these therapies promote maxillary expansion, that reduces the usefulness of RME in skeletal Class II cases with no transverse deficiency.

Even though Baratieri et al.²¹ and Farronato et al.²² have presented data indicating significant mandibular anterior displacement, these changes were not compared to a control group, which considerably decreases the scientific relevance of these evidences.

In order to have a better predictability of the effectiveness of any therapy, it is advisable to consider not only controlled groups, but also randomization.⁴⁸ Unfortunately, no randomized controlled trial has been performed on that matter so far, and those that were carried out with paired control groups still lack methodological accuracy. Because of the absence of randomized trials, the investigators had to choose to include nonrandomized controlled trials and case series in this systematic review. Unfortunately, no meta-analysis could be executed because of the many methodological differences among the selected studies and the excessively large variability observed in relation to the sample characteristics, treatment features, follow-up period, and outcome measurements.

RME is considered to be one of the safest and most predictable therapies in orthodontic practice.⁴⁹ However, the effect of maxillary expansion on the sagittal dimension of Class II is still controversial and has not been substantially proved yet. The demonstration of the induced change theory¹² still requires methodological concerns, principally in relation to clinical trials design, which should ideally enroll adequate control subjects, randomization, and blindness during outcome assessment.

During performance of future studies, special emphasis must be directed to objectively identify those Class II patients more likely to present favorable sagittal responses to RME therapy. Moreover, long-term studies would be advisable in order to investigate the stability of effects, if present, as well as to verify if RME therapy is likely to avoid Class II specific therapy in late mixed dentition or diminish comprehensive orthodontic treatment time.