INTRODUCTION

When a skeletal constricted maxillary arch is diagnosed, orthopedic skeletal expansion involving separation of the midpalatal suture is the treatment of choice. Three treatment alternatives are available for this purpose: rapid maxillary expansion (RME), slow maxillary expansion (SME), and surgical-assisted RME (SARME). Both SME and RME are indicated for growing patients, whereas SARME is the alternative selected for nongrowing adolescent and young adult patients.

Even though RME treatments were reported to bring clinically stable results,1 others reported relapse after expansion was attained.2 Years later, other studies demonstrated that the attained changes were produced primarily in the underlying structures and, therefore, stable results were expected.34

Although, SME and RME were reported to bring similar results,5 theoretically RME delivers forces ranging from 15 to 50 N whereas the SME incorporates forces that only reach 10 N of magnitude. Because RME treatments exert a greater force on paramaxillary structures, changes in skeletal structures other than in the maxilla are more feasible. Some disadvantages have been reported in RME including: bite opening,6 relapse,78 microtrauma of the TMJ and the midpalatal suture,78 and root resorption.78

Because a direct relationship has been reported between increased resistance to skeletal expansion and increased patient age, the use of SME in adolescents may be questioned because it may not offer enough expansion force to separate the midpalatal suture in young adults.9 Even in young children, no scientific evidence in favor or against is available.10 Several disadvantages for SME are minor maxillary and mandibular plane changes,11 poor fit, fracture or loss of the appliance,12 and palatal irritation.12

SARME treatment has been successful in splitting the palatine suture and thus widening the maxilla in young adults.13 However, this surgical procedure is costly and requires outpatient surgery or hospitalization with attendant morbidity and loss of work time. Other complications reported with the SARME are tissue irritation, hemorrhage, infection, pain, unilateral or asymmetric expansion, periodontal problems, and relapse.14 For these reasons, a careful cost-effectiveness analysis should be made by patients and orthodontists before undergoing the procedure.13

From this literature review, RME appears as the treatment of choice in growing adolescents. Previous reports on RME skeletal and dental effects are contradictory because of variable study designs, sample sizes, and research approaches.1516 Two meta-analyses regarding the transverse dental effects of RME have been published.1517 One systematic review18 about the long-term dental effects of RME has been published, but to date there are no systematic reviews regarding long-term skeletal effects.

The purpose of this systematic review is to evaluate long-term (minimum of one-year postactive treatment) transverse, anteroposterior, and vertical skeletal changes obtained after RME.

MATERIALS AND METHODS

The following inclusion criteria were chosen to initially select the appropriate articles from the published abstracts: human clinical trials; measurements made from facial radiographs (anteroposterior and lateral cephalograms); no surgical or other simultaneous treatment that could affect RME effect during the evaluation period.

A computerized search was then conducted using Medline (from 1966 to week 1 of September 2004), Medline In-Process & Other Non-Indexed Citations (from week 1 of September 2004 to week 2 of September 2004), Lilacs (from 1982 to September 2004), PubMed (1966 to week 2 of September 2004), Embase (from 1988 to week 37 of 2004), web of science (1945 to week 2 of September 2004) and all EBM reviews (Cochrane Database of Systematic Reviews, ASP Journal Club, DARE and CCTR) (to the third quarter of 2004) databases for skeletal changes in RME. Terms used in this literature search were rapid palatal expansion or RME, bone and bones or skeletal changes. The selection of these terms were made with the help of a senior librarian specialized in Health Sciences databases.

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

Eligibility of potential studies was determined by reading the title and abstracts of each article identified by each search engine. Two researchers selected the articles to be collected on the basis of the abstract information. An interexaminer agreement of 0.900 (interexaminer Kappa) was obtained. Any discrepancies were settled through discussion. All the articles that appeared to meet the inclusion criteria on the basis of their abstracts were selected and collected. In addition, the actual articles were also obtained from abstracts in which not enough relevant information was stated.

The final selection was independently completed by three researchers reading the complete articles and their results were compared. An interexaminer agreement of 0.885 (interexaminer Kappa) was obtained. Use of an adequate control group to factor out growth changes was considered necessary at this stage. Any discrepancies were settled through discussion. Reference lists of the selected articles were hand-searched for additional relevant publications that may have been missed in the database searches. In cases where specific data was necessary for the discussion, and was not specified in the article, efforts were made to contact the authors to obtain the required extra 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. Comparing the database results, Medline obtained the greatest diversity of finally selected abstracts (78.6%), whereas the other databases obtained significantly fewer finally selected abstracts (<33.3%). The different databases repeated most of the abstracts, except Lilacs, which included only Latin-American publications and accounted for a significant percentage (21.4%) of the finally selected abstracts. From the 42 studies that on the basis of the abstracts seemed to be potentially useful, only 17 studies actually fulfilled the initial selection criteria after reading the complete article. Manual searching of the references from these 42 studies did not reveal any study that had not appeared in the electronic search.

TABLE 1.  Search Results from Different Databases

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At the final stage of article selection, eleven51219–27 of the 17 articles were rejected because of the lack of an adequate control group, one28 because it used the same database as another selected study and two2930 because they only evaluated short-term (six and three months after insertion of appliance, respectively) skeletal changes. Lack of reported measurement error19–22242627 or use of unconventional cephalometric analysis28 were also found in some studies (Table 2).

TABLE 2.  Studies that Fulfilled Initial Selection Criteria but Were Later Rejected^a

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Finally, only three articles that met all the inclusion criteria remained. A summary of the sample size, retention period, radiographs, and appliance used is given in Table 3. A methodological quality checklist was developed to evaluate the selected articles (Table 4), and the application of the methodological quality checklist is provided in Table 5. A flow diagram of the literature search appears in Table 6. From the three final articles, one measured transverse changes, two anteroposterior changes, and two vertical changes. All the three articles measured long-term RME stability (more than five years after finishing full active treatment).

TABLE 3.  Studies Finally Included

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TABLE 4.  Methodological Score for the Clinical Trials^a

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TABLE 5.  Methodological Score of Selected Articles^a

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TABLE 6.  Flow Diagram of the Literature Search

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DISCUSSION

Much information about RME has been published, but the conclusions have been contradictory. Two meta-analyses1517 and one systematic review16 analyzed only RME dental changes. These meta-analyses and systematic review concluded that trial results for dental changes were inconclusive and recommendations for clinical practice could not be supported. However, one previous systematic review18 found that long-term transversal changes were clinically significant. No previous systematic review or meta-analysis has been published regarding the long-term skeletal effects of RME.

Even though there are a considerable number of studies dealing with skeletal changes with RME procedures, the majority of reports about RME skeletal changes were excluded because of the absence of a control group to factor out the normal growth changes that could have happened during the expansion and retention periods. Also, some of them did not provide the error of methods. Knowledge of the measurement error is essential in judging the clinical significance of any reported statistically significant findings.

Finally, methodological factors such as different postactive treatment evaluation periods and differences in the landmarks evaluated between the two studies that met the inclusion criteria and evaluated skeletal anteroposterior and vertical changes prevented use of a meta-analysis. The individual significant differences found were statistically significant not clinically significant, and therefore, a meta-analysis would not have added significantly to our knowledge about long-term skeletal changes after RME.

Although three studies satisfied the final inclusion criteria for this systematic review, conclusions should be made and evaluated with caution. The finally selected studies presented methodological issues such as a lack of description of a statistical estimation process for the sample size, dropouts, and intra- and interexaminer reliability. Although assessing study quality is subjective and dependent on adequate reporting in the journal articles,33 it gives a comparative idea of the methodological quality of the studies. Within the limitations of the quality score list used, scores for the finally selected studies were limited. Long-term randomized clinical trials are required to obtain sound clinical conclusions about the effectiveness of RME at the skeletal level.

Also, these studies failed to give the higher level of scientific evidence, which is only attainable through the use of randomized clinical trials.34 In the absence of the highest level of evidence, clinicians have to make decisions based on lower levels of evidence. Nonrandomized controlled trials, such as the ones found, represent only the second level of evidence and are prone to confounding and selection bias.35 Therefore, a careful analysis of their results that considers their limitations is required.

Differences were found for the transverse maxillary skeletal changes according to the maturation stage of the subjects. For the lateronasal width (+1.5 mm), the expansion effects were significant for both groups. On the other hand, the maxillary width increase was only significant (three mm) for the early-treated group but not for the late-treated group. The authors concluded that patients treated before pubertal peak growth exhibit clinically significant and more effective long-term changes at the skeletal level in both maxillary and circummaxillary structures.31 Therefore, maxillary skeletal width increase appears to be approximately 20% of the total appliance activation in prepubertal adolescents but not significant for postpubertal adolescents.

Concerning anteroposterior changes in the maxilla and mandible, no significant alterations were found in any of the studies reviewed.632 After the posttreatment and postretention, the maxilla and mandible of the treated groups presented similar behavior to the ones of the control group, ie, the differences presented no statistical or clinical significance.

Short-term and long-term vertical skeletal changes associated with RME appear to be restricted to the maxilla. The magnitude of change reported by Garib et al32 was small and, in view of the range of measurement error, has little, if any, clinical significance. The long-term changes in mandibular plane angle reported by Chang et al6 are also of little, if any, clinical significance.

Scientific evidence alone does not automatically dictate the selection of the treatment. A combination of values from the patient and professional (clinical, personal, and social) should determine whether the intervention benefits are worth the costs.36 Therefore, the application of evidence into clinical practice has to be related to professional expertise and patient value needs. As in any usual clinical environment, clinicians will need to rely on their clinical experience, the opinion of experts, and the presented limited evidence concerning RME skeletal short- and long-term results.

CONCLUSIONS

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

• Long-term stability of transverse skeletal maxillary increase is better in skeletally less mature individuals (prepubertal growth peak) than skeletally more mature (pubertal and postpubertal growth peak) individuals. The clinical significance of long-term maxillary expansion in skeletally more mature groups is questionable.

• Long-term transverse skeletal maxillary increase is approximately 25% of the total appliance adjustment (dental expansion) in prepubertal adolescents but not significant for postpubertal adolescents.

• RME did not produce significant anteroposterior or vertical changes in the position of the maxilla and mandible.