Editorial Type:
Article Category: Research Article
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Online Publication Date: 06 Sept 2016

Changes in apical base sagittal relationship in Class II malocclusion treatment with and without premolar extractions: A systematic review and meta-analysis

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Page Range: 338 – 355
DOI: 10.2319/030716-198.1
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ABSTRACT

Objective: To evaluate the changes in apical base sagittal relationship in Class II treatment with and without premolar extractions.

Materials and Methods: Controlled studies evaluating ANB angle changes after Class II Division 1 malocclusion treatment with or without premolar extractions were considered. Electronic databases (PubMed, Embase, Web of Science, Scopus, The Cochrane Library, Lilacs, and Google Scholar) without limitations regarding publication year or language were searched. Risk of bias was assessed with Risk Of Bias in Non-randomized Studies—of Interventions tool of the Cochrane Collaboration. Mean difference (MD) and 95% confidence interval (CI) were calculated from the random-effects meta-analysis. Subgroup and sensitivity analyses were also performed.

Results: Twenty-five studies satisfied the inclusion criteria and were included in the qualitative synthesis. Eleven nonextraction and only one extraction Class II treatment studies presented untreated Class II control group. Therefore, meta-analysis was performed only for the nonextraction protocol. In treated Class II nonextraction patients, the average of the various effects was a reduction in the ANB angle of 1.56° (95% CI: 1.03, 2.09, P < .001) compared with untreated Class II subjects. Class II malocclusions treated with two maxillary-premolar extractions and four-premolar extractions produced estimated mean reductions in ANB of −1.88° and −2.55°, respectively. However, there is a lack of low-risk-of-bias studies.

Conclusions: According to the existing low quality evidence, the apical base sagittal relationship in nonextraction, two-maxillary and four-premolar extractions Class II treatments decreases −1.56°, 1.88° and 2.55°, respectively. Further studies are necessary to obtain more robust information.

Keywords: Orthodontics; Malocclusion, Angle Class II; Systematic review

INTRODUCTION

The ANB angle has frequently been used to evaluate the skeletal sagittal severity of Class II malocclusions.1–6 However, it seems that there has been excessive importance given to the anteroposterior discrepancy depicted by a cephalometric variable to evaluate the actual treatment difficulty in correcting the Class II occlusal anteroposterior discrepancy.7,8

To correct a complete Class II malocclusion without premolar extractions (XP0) or with four-premolar extractions (XP4), Class I molar and canine relationships must be obtained.2,5 If the correction is performed with 2 maxillary premolar extractions (XP2), the molars will finish in a complete Class II and the canines in Class I relationships.9,10 A Class I canine relationship will allow correction of the severe pretreatment overjet to a normal overjet.9 Therefore, the occlusal Class II anteroposterior discrepancy is more informative regarding treatment difficulty than a cephalometric variable.11,12

Additionally, in cases wherein the cephalometric anteroposterior discrepancy is accentuated, as evaluated by the ANB, even if the severe occlusal Class II anteroposterior discrepancy has been completely corrected, the ANB may not be significantly reduced to its standard value.13–19 That is, reduction of the apical base anteroposterior discrepancy only by orthodontic means is very limited, as has been demonstrated by some studies.2,4,10,13–20 However, to provide stronger scientific evidence to this fact, a systematic review including controlled clinical trials assessing the change in ANB angle in Class II malocclusion patients treated with or without premolar extractions was conducted.

MATERIALS AND METHODS

This systematic review is reported according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement.21 The systematic review protocol was registered at PROSPERO database (http://www.crd.york.ac.uk/PROSPERO, CRD42015026677).

Eligibility Criteria

  • Participants: Growing patients with Class II Division 1 malocclusion.

  • Intervention: Class II treatment with or without premolar extractions, all using multibracket appliance (MBA) treatment.

  • Comparison: Class II subjects with or without orthodontic treatment, all after MBA treatment.

  • Outcome: ANB angle treatment changes.

  • Study design: Controlled clinical trials (randomized, prospective, or retrospective).

Exclusion Criteria

Studies of patients having craniofacial anomalies, adults, surgical-orthodontic treatment, or absence of a control group; and systematic reviews and meta-analyses.

Electronic databases (Pubmed, Embase, Web of Science, Scopus, The Cochrane Library, Lilacs) and a partial grey literature (academic literature that is not formally published) through Google Scholar without limitations regarding publication year or language were searched until June 20, 2016 (Appendix 1). In addition, the evaluators went through the reference lists of the selected articles to ensure that no potential articles were missed.

Two evaluators independently screened the titles and abstracts identified from the electronic database results after elimination of duplicates. Next, full articles were retrieved to confirm their eligibility. The same evaluators selected the articles for inclusion in the qualitative synthesis independently. Disagreements were resolved by verbal discussion between them and by consultation with another evaluator when necessary.

The following data were extracted independently by the two reviewers: study design, participants, interventions, initial and final ANB angle or ANB angle mean change, treatment duration, Class II diagnosis, and treatment timing. Factors for subgroup analyses were selected a priori to evaluate any influence of them on the ANB change after treatment. These factors included (1) patient's sex, (2) skeletal growth stage based on the cervical vertebral maturation method or on hand-wrist radiographs, (3) patient's growth pattern, (4) type of appliance used (functional appliances [FA] + MBA or headgear [HG] + MBA, (5) treatment time (up to or greater than 24 months).

The risk of bias (RoB) in individual studies was assessed using Cochrane Collaboration's ROBINS-I tool (Risk Of Bias in Non-randomized Studies—of Interventions).22 For all included studies, the RoB for each domain and the overall RoB for each study were judged as Low, Moderate, Serious, Critical, or No information (Appendix 2).22 When more than 10 studies were identified, standard funnel plots and Egger's test were planned to identify publication bias.23

The quality of evidence for the main outcome was rated by using the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) approach.24 Evaluation of RoB in individual studies and across studies were independently performed by two evaluators. Any disagreement was resolved through verbal discussion between the evaluators and with another third evaluator.

Data were summarized in three groups according to the protocol used: XP0, XP4, and XP2, to independently evaluate the ANB change in each group. Performance of a meta-analysis was possible only in the XP0 comparison. When data were summarized from the premolar extraction studies, only one5 had an untreated Class II control group (UCIICG). Nonetheless, the evaluators considered it important to show the data (without performing a meta-analysis) from the extraction protocols, as well.

For the XP0 group, mean difference and its 95% confidence interval (CI) were obtained. The random-effects model was chosen, supported by both clinical and statistical reasoning.25,26 The between-study heterogeneity/inconsistency was assessed by inspecting the forest plot and calculating Tau2, Chi2, and I2 statistics, respectively (the interpretation of I2 was made together with the P value for the Chi2 and the 95% CI for I2).23 The 95% prediction interval was also calculated.

For the XP4 and XP2 groups, an estimated ANB angle mean change and standard deviation were obtained by combining studies data of each group.23 Sources of heterogeneity in meta-analysis were evaluated with subgroup analyses. Differences between subgroups was assessed by considering the P value of the standard test for heterogeneity across subgroup results.23 Sensitivity analyses based on study design and precision were performed to check the robustness of the results.23

The statistical analyses were performed using RevMan statistical software (version 5.3 for Windows; Nordic Cochrane Centre, Rigshospitalet, Denmark). Comprehensive meta-analysis statistical software (version 3.0; Biostat Inc, Englewood, NJ) was used only to identify publication bias (funnel plots and Egger's regression test).23 All P values were two sided with α = 5%, except for the tests of between-studies or between-subgroups heterogeneity (α = 10%).23

RESULTS

Initially, 1147 records were identified, and 15 hand-searched articles were added. After exclusion of duplicates, 662 studies remained. The full texts of 57 articles were obtained and assessed for eligibility, and 32 articles were excluded with reasons, leaving 25 articles for qualitative analysis (Figure 1, Table 1). Of the 25 articles, only 1 was a prospective, controlled clinical trial18 and 24 were retrospective, controlled clinical trials. No randomized, controlled clinical trials satisfying the inclusion criteria were found.

Figure 1. PRISMA flow diagram.Figure 1. PRISMA flow diagram.Figure 1. PRISMA flow diagram.
Figure 1. PRISMA flow diagram.

Citation: The Angle Orthodontist 87, 2; 10.2319/030716-198.1

Table 1. Characteristics of the 25 Articles Included in the Quality Assessment
Table 1.
Table 1. Extended
Table 1.

XP0

Twenty-three articles2–6,10,14–19,27–37 were characterized by reporting samples with nonextraction treatment. Thirteen articles3,5,14,17–19,27–29,31,33,35,36 reported a UCIICG. Three3,17,19 did not report the ANB change standard deviation. Standard deviation could be estimated for only one study.17 Therefore, 11 articles were included in the meta-analysis (nonextraction Class II vs UCIICG). All 11 studies reported one-phase treatment either with an FA or HG followed by MBA. The FA reported in seven studies were: Forsus fatigue resistant device,27,28 Twin-block,28 MARA,17,29 AdvanSync,29 Sydney Magnoglide,18 Jasper Jumper,33 and Herbst.5 HG use was reported in five studies,5,14,31,33,36 and one study reported the use of HG-activator combination.35 Treatment timing was reported in five studies.14,17,18,28,29 Two studies18,28 reported combined data of various pubertal stages. Two other studies17,29 reported data of pubertal subjects only and another14 presented separate data of subjects in different pubertal stages. Only 2 studies18,33 of the 11 had a treatment duration of 24 months or less. The mean treatment duration of the XP0 protocol was 30.39 months.

XP4

Nine2,4,5,13,16,20,30,32,37 of the 25 articles included samples with XP4. Three articles2,13,20 did not present standard deviations of the ANB change so they could not be estimated. The remaining six articles were included for analysis. Treatment timing was reported in three articles, two articles30,32 presented data of pubertal patients, and one article16 showed combined data of prepubertal and pubertal patients. They had a mean treatment duration of 34.9 months. Only one article5 had an UCIICG; the other five did not. Although a meta-analysis should not be performed in this situation, the evaluators calculated the mean change of the six articles with the intention of evaluating the ANB angle behavior with this treatment protocol.

XP2

Three articles10,15,20 of the 25 included samples with XP2. One article20 was excluded because it did not present the standard deviation of ANB mean change and it could not be estimated. They did not report treatment timing information and they had a mean treatment duration of 27.96 months. They did not have an UCIICG, preventing a meta-analysis. Nevertheless, the mean change of the two articles was calculated.

After the assessment of RoB, an overall RoB for each study was assigned (Table 2). No study showed an overall Low RoB, so none could not be comparable to a well-performed randomized trial. Eighteen studies* showed overall Moderate RoB. Although these 18 studies presented Moderate RoB, a meta-analysis was performed with only 11 studies that reported data from UCIICG. Therefore, only a comparative analysis of nonextraction vs. UCIICG was performed. Seven studies2,3,6,13,19,20,34 presented Serious RoB.

Table 2. Risk of Bias (RoB) of Studies Included in the Qualitative Synthesis Based on ROBINS-I Tool
Table 2.

ANB angle mean changes and standard deviations of the studies included for quantitative analyses are summarized in Table 3. A meta-analysis was performed only regarding the XP0 protocol because of the absence of UCIICG in the studies involving premolar extractions.

Table 3. Studies Included in the Quantitative Analyses
Table 3.

XP0

In nonextraction Class II patients, the average of the various effects was a reduction in the ANB angle of 1.56° compared with UCIICG (Figure 2, Table 4). Multi-arm studies5,28,29,33 were pooled prior to meta-analysis, except for one study,14 which reported three different groups with specific control groups for each one, so 13 groups of nonextraction treatment present in the 11 studies were used.

Figure 2. Forest plot (mean difference [MD] and 95% confidence interval [CI]) for the ANB angle mean changes between Class II nonextraction treatment and UCIICGs. *Multi-arm studies pooled before meta-analysis.Figure 2. Forest plot (mean difference [MD] and 95% confidence interval [CI]) for the ANB angle mean changes between Class II nonextraction treatment and UCIICGs. *Multi-arm studies pooled before meta-analysis.Figure 2. Forest plot (mean difference [MD] and 95% confidence interval [CI]) for the ANB angle mean changes between Class II nonextraction treatment and UCIICGs. *Multi-arm studies pooled before meta-analysis.
Figure 2. Forest plot (mean difference [MD] and 95% confidence interval [CI]) for the ANB angle mean changes between Class II nonextraction treatment and UCIICGs. *Multi-arm studies pooled before meta-analysis.

Citation: The Angle Orthodontist 87, 2; 10.2319/030716-198.1

Table 4. Meta-analysis, Subgroup Analyses, and Sensitivity Analyses: Nonextraction vs Untreated Cl II
Table 4.

Regarding the risk of publication bias, the funnel plots as Egger's regression test (P = .16) did not show asymmetry (Figure 3). The evidence rated by the GRADE approach was considered as Low quality (Table 5).

Figure 3. Funnel plots of ANB changes for the studies (11 studies, 13 groups) included in the meta-analysis.Figure 3. Funnel plots of ANB changes for the studies (11 studies, 13 groups) included in the meta-analysis.Figure 3. Funnel plots of ANB changes for the studies (11 studies, 13 groups) included in the meta-analysis.
Figure 3. Funnel plots of ANB changes for the studies (11 studies, 13 groups) included in the meta-analysis.

Citation: The Angle Orthodontist 87, 2; 10.2319/030716-198.1

Table 5. GRADE Summary of Findings Table for the ANB Mean Change Outcome of the Systematic Review and Meta-analysis Directly After Treatment Completion Without Premolar Extractionsa
Table 5.

Subgroup analyses including patients' sex and growth pattern were not feasible due to lack of reporting data in the studies. The ANB change varied according to the skeletal growth spurt and type of appliance used. Treatment in prepeak and peak patients and the HG-activator combination + MBA induced greater decreases on ANB. (Table 4, Appendixes 3 and 4) Treatment duration did not produce significant differences between subgroups (Table 4, Appendix 5). Sensitivity analysis based on the study design did not find significance difference between the prospective and retrospective studies. Sensitivity analysis by precision, selecting studies14,17,18,28,36 with narrower confidence intervals, showed a smaller decrease in ANB angle compared with the original one; however, it was statistically significant when compared with the UCIICG (Table 4).

XP4 and XP2

The estimated ANB reductions obtained without using data from UCIICG were 2.55° and 1.88° for the XP4 and for the XP2 treatment, respectively.

DISCUSSION

This systematic review is one of the few reviews38,39 that include studies with completed Class II malocclusion treatment with MBA in growing patients using protocols with or without premolar extractions. The purpose was to obtain an estimate of anteroposterior apical base relationship changes during Class II malocclusion treatment with the different protocols.

The systematic review showed a lack of Low RoB studies. However, a meta-analysis was performed only in the nonextraction group including nonrandomized studies with Moderate RoB with matched UCIICGs (Figure 2, Table 4). This usually implies the use of historical Class II controls due to ethical issues. Therefore, we have included retrospective controlled trials, as performed in other systematic reviews.38 Regarding the extraction protocols, the systematic review showed a lack of studies with UCIICGs data reporting and Low RoB. Only one extraction study5 reported data of UCIICG (Tables 1 and 2). Nevertheless, in the absence of stronger evidence, they can provide information to orient clinicians (Table 3).

The meta-analysis results showed statistically significant improvement of the apical base sagittal relationship (ANB angle) in the XP0 protocol (Figure 2, Table 4). Treatment performed before or at the peak of growth showed greater ANB changes when compared with postpeak patients, as reported previously.26,38 Differences in ANB changes between the use of FA + MBA or HG + MBA were minimal (Table 4), as expected.39 However, a greater ANB change with the HG-activator combination, used in only one study, was reported.35 Nevertheless, it is necessary to have more studies to support these findings.

Some reviews used annualized data to account for the different follow-up periods of the studies,40 or because most of their samples reported annualized data.38,39 In this systematic review, data were not annualized because the objective was to evaluate ANB changes in the complete period of treatment.

ANB reduction was greater in the XP4 protocol (2.55°) compared with the XP2 (1.88°) and with XP0 protocol (1.56°). Evidently, the results of the XP0 protocols have a greater reliability because they consisted of results of a meta-analysis, but they represent Low quality of evidence (GRADE), based on the nature of the included studies and must be regarded with caution. Although the results of the XP4 and XP2 protocols may provide some guidance to the clinician, they lack some consistency because they were derived from estimates.

Clinical Implications

The current results confirm previous speculations that Class II malocclusion anteroposterior apical base skeletal changes are small, especially regarding ANB.2,4,10,15,16,20 Therefore, Class II malocclusion severity should be expressed primarily as the occlusal anteroposterior discrepancy and not as the skeletal discrepancy.8,11,12 This would provide treatment strategies with more predictable results. A complete Class II anteroposterior discrepancy is likely to be corrected to a normal occlusion in most cases.5,10,14 However, a severe cephalometric skeletal discrepancy, such as an ANB of 10° will on average be reduced only by about 2°,,resulting in an ANB of 8°, which is far from the ideal. This does not mean that the skeletal apical base discrepancy is not important in orthodontic diagnosis. It is, but its purpose is to provide additional information for diagnosis and not to define treatment planning.

Limitations

The great limitation found was the lack of Low RoB studies. No randomized, controlled clinical trial that satisfied our inclusion criteria was found. Meta-analysis was performed only with Moderate RoB studies for the XP0 protocol because of the lack of UCIICG data reporting in the extraction studies.

The use of nonannualized data for ANB changes was important to describe the ANB changes in the total treatment period. It may have provided greater ANB values in treatments with longer duration. However, the subgroup analysis showed no significant difference in ANB change considering this factor.

CONCLUSIONS

Overall, based on the low-quality evidence found:

  • Class II malocclusion XP0 treatment produces an average reduction of 1.56° in ANB compared with untreated Class II subjects.

  • Class II malocclusion treated with XP2 produces an estimated mean reduction of 1.88° in ANB.

  • Class II malocclusion treated with XP4 produces an estimated mean reduction of 2.55° in ANB.

  • However, further research is necessary to obtain the most robust results.

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APPENDIX 1. Database and Search Strategy
APPENDIX 1.
APPENDIX 2. Criteria for Assessing Risk of Bias (Rob) With the Risk of Bias in Nonrandomized Studies of Interventions (ROBINS-I) Tool
APPENDIX 2.
APPENDIX 3. APPENDIX 3. APPENDIX 3.
APPENDIX 3.

Citation: The Angle Orthodontist 87, 2; 10.2319/030716-198.1

APPENDIX 4. APPENDIX 4. APPENDIX 4.
APPENDIX 4.

Citation: The Angle Orthodontist 87, 2; 10.2319/030716-198.1

APPENDIX 5. APPENDIX 5. APPENDIX 5.
APPENDIX 5.

Citation: The Angle Orthodontist 87, 2; 10.2319/030716-198.1

Copyright: © 2017 by The EH Angle Education and Research Foundation, Inc.
Figure 1.
Figure 1.

PRISMA flow diagram.

Figure 2.
Figure 2.

Forest plot (mean difference [MD] and 95% confidence interval [CI]) for the ANB angle mean changes between Class II nonextraction treatment and UCIICGs. *Multi-arm studies pooled before meta-analysis.

Figure 3.
Figure 3.

Funnel plots of ANB changes for the studies (11 studies, 13 groups) included in the meta-analysis.

APPENDIX 3.
APPENDIX 3.

APPENDIX 4.
APPENDIX 4.

APPENDIX 5.
APPENDIX 5.

Contributor Notes

Corresponding author: Dr Guilherme Janson, Department of Orthodontics, Bauru Dental School, University of São Paulo, Alameda Octávio Pinheiro Brisolla 9-75, Bauru, São Paulo 17012-901, Brazil (e-mail: jansong@travelnet.com.br)
Received: 01 Mar 2016
Accepted: 01 Jul 2016
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