Summary
Objective:
To systematically investigate review in literature the effects of the Herbst appliance for patients with Class II malocclusion patients.
Method:
We performed a comprehensive literature survey on PubMed, Web of Science, Embase, CENTRAL, SIGLE, and ClinicalTrial.gov up to December 2014. The selection criteria: randomized controlled trials or clinical controlled trials; using any kind of Herbst appliances to correct Class II division 1 malocclusions; skeletal and/or dental changes evaluated through lateral cephalograms. And the exclusion criteria: syndromic patients; individual case reports and series of cases; surgical interventions. Article screening, data extraction, assessment of risk of bias, and evaluation of evidence quality through GRADE were conducted independently by two well-trained orthodontic doctors. Consensus was made via group discussion of all authors when there is inconsistent information from the two. After that, sensitivity analysis and subgroup analysis were performed to evaluate the robustness of the meta-analysis.
Results:
Twelve clinical controlled trials meet the above-mentioned criteria, and were included in this analysis. All included studies have eleven measures taken during both active treatment effect and long term effect periods, including four angular ones (i.e., SNA, SNB, ANB, mandibular plane angle) and seven linear ones (i.e. Co-Go, Co-Gn, overjet, overbite, molar relationship, A point-OLp, Pg-OLp) during active treatment effect period were statistically pooled. Meta-analysis and sensitivity analysis demonstrated that all these measures showed consistent results except for SNA, ANB, and overbite. Subgroup analysis showed significant changes in SNA, overbite, and Pg-OLp. Publication bias was detected in SNB, mandibular plane angle, and A point-OLp.
Conclusion:
The Herbst appliance is effective for patients with Class II malocclusion in active treatment period. Especially, there are obvious changes on dental discrepancy and skeletal changes on Co-Gn. As to its long-term effects, more evidence is needed to draw conclusions.
Introduction
In patients with Class II malocclusion, large overjet and unfavorable profile may lead to negative feelings of self-image and self-esteem (1). Therefore, aesthetic improvement is a main treatment objective (2). Among all functional appliances for Class II malocclusion, the Herbst appliance is one of the most commonly used one. It was developed by Emil Herbst in the early 1900s and reintroduced by Pancherz in the late 1970 (3). As a bilateral telescope anchored to the upper and lower arches, it keeps the mandible in a continuous anteriorly postured position during all the mandibular functional movements (3), thereby resulting in sagittal and vertical dentoskeletal changes. In clinical settings, there are several variants of the Herbst appliance, including cast Herbst appliance and acrylic splint Herbst appliance (4–6). Herbst appliance does not require patients’ cooperation due to its fixation on dental arches (7).
Although pertinent systematic reviews have been published previously (8,9), definitive conclusions are not drawn due to limited number of included studies. With new evidences in the past several years, we revisit this topic and present here an up-to-date systematic review and meta-analysis to investigate the effectiveness of Herbst appliance for patients with Class II malocclusion.
Materials and methods
Data acquisition
Literature query
Literature search was conducted online on several major medical databases, including PubMed, Web of Science, Embase, CENTRAL, SIGLE, and ClinicalTrial.gov up to December 2014. In particular, we included grey literature on SIGLE and ongoing studies for ClinicalTrial.gov. The specific search strategies are detailed in Table 1.
Table 1.
Database search and results.
| Database | Search terms | Results | Included |
|---|---|---|---|
| Pubmed | #1:Malocclusion, Angle Class II OR Angle Class II OR Class II, Angle OR Class II OR Distocclusion* OR Distal occlusion* #2: Herbst appliance* OR Herbst #3: randomized controlled trial [pt] OR controlled clinical trial [pt] OR randomized [tiab] OR placebo [tiab] OR clinical trials as topic [mesh: noexp] OR randomly [tiab] OR trial [ti] #4: #1 AND #2 AND #3 |
29 | 2 |
| Web of science | #1: Angle Class II OR Class II, Angle OR Class II OR Distocclusion*OR Distal occlusion* #2: Herbst appliance* OR Herbst #3: #1 AND #2 |
375 | 2 |
| Embase | #1:Angle Class II OR Class II, Angle OR Class II OR Distocclusion* OR Distal occlusion* #2: Herbst appliance* OR Herbst #3: #1 AND #2 |
211 | 11 |
| Central | #1: Angle Class II OR Class II, Angle OR Class II OR Distocclusion* OR Distal occlusion* #2: Herbst appliance* OR Herbst #3: #1 AND #2 |
39 | 0 |
| SIGLE | (Angle Class II or distocclusion) and (Herbst or Herbst appliance) | 0 | 0 |
| ClinicalTrial.gov | (Angle Class II or distocclusion) and (Herbst or Herbst appliance) | 0 | 0 |
Article inclusion and exclusion criteria
The following inclusion criteria were adopted to select abstracts from potential articles retrieved from the databased: randomized controlled trials or clinical controlled trials; using any kind of Herbst appliances to correct Class II division 1 malocclusions; skeletal and/or dental changes evaluated through lateral cephalograms. The exclusion criteria included syndromic patients, individual case reports and series of cases and surgical interventions.
Data extraction
The following data were extracted: study design, participant information, the skeletal maturation of subjects, appliance types and active treatment durations. The skeletal maturity indicators were HWM (hand wrist maturation) and CVM (cervical vertebrae maturation). The stage of CVM 2 (HWM 3–4) and CVM 3 (HWM 5–6) are around the peak growth period (10).
Quality assurance
To avoid subjectiveness during data acquisition, two orthodontic doctors independently conducted the acquisition following the above-mentioned strategies. Risk of bias was assessed according to Downs and Black quality assessment tool. Any disagreement was solved by discussion or judged by a third reviewer.
Meta-analysis
The present study adopted Pancherz cephalometric analysis or PCA, which is considered as the standard method, to evaluate effects of the Herbst appliance. Besides the common items covered in PCA, other important clinical indices were also included for the evaluation. In specific, proposed outcomes included angular measurements (SNA, SNB, ANB, mandibular plane angle) and linear measurements [mandibular ramus height (Co-Go), total mandibular length (Co-Gn), overjet, overbite, molar relationship, sagittal position of the maxillary base (A point-OLp), sagittal position of the mandibular base (Pg-OLp)].
Egger’s test (11) and Begg’s test (12) were used to assess the publication bias through Stata 12.1. Furthermore, sensitivity analysis and subgroup analysis were performed to evaluate the robustness of the pooled results from the meta-analysis.
Moreover, the quality of evidence was assessed by using GRADE system of rating quality of evidence (13–18).
Results
The procedures of the electronic searching and selection are presented in Figure 1. Moreover, the details of the search strategy, as well as the number of abstracts selected from each database, are displayed in Table 1. According to the procedure in Figure 1 and strategy in Table 1, we retrieved 654 articles from those databases and 597 of them were identified as irrelevant initially. The remaining 57 articles were further assessed for eligibility resulting 12 final controlled clinical trial studies (CCTs). All inclusions were prospective studies and recruited only adolescents. The sample size ranges from 8 to 55; the active Herbst treatment duration ranges from 5 months to 30 months. The general information of each study is summarized in Table 2. The study quality scores using Downs and Black scale (19) were shown in Table 3. Because of the differences between studies and the high heterogeneity, we used the random model in all the outcomes’ analysis.
Figure 1.
PRISMA flow diagram for studies retrieved through the searching and selection processes.
Table 2.
General information provided in the included studies.
| Study | Design | Participates | Criteria | Skeletal maturation | Active treatment duration (m) | Appliance |
|---|---|---|---|---|---|---|
| Baysal and Uysal (20) | CCT (prospective) | T: n = 20, M/F = 9/11, age = 12.74±1.43 y C: n = 20, M/F = 11/9, age = 12.17±1.47 y |
Skeletal class II | Stage 4 – Stage 5 (HWM) | T: 15.81±5.96 C: 15.53±3.13 |
Cast splint Herbst appliance |
| Baysal and Uysal (21) | CCT (prospective) | T: n = 20, M/F = 9/11, age = 12.74±1.43 y C: n = 20, M/F = 11/9, age = 12.17±1.47 y |
Skeletal class II | Stage 4–Stage 5 (HWM) | T: 15.81±5.96 C: 15.53±3.13 |
Cast splint Herbst appliance |
| de Almeida et al. (22) | CCT (prospective) | T: n = 30, M/F = 15/15, age = 8.2 y–11 y C: n = 30, M/F = 15/15, age = 8.0 y–10.9 y |
Skeletal class II | Stage 1–Stage 3 (CVM) | T: 12 C: 12 |
Banded type Herbst appliance |
| Franchi et al. (5) | CCT (prospective) | T: n = 55, M/F = 28/27, age = 12 y 10 m ± 1 y 2 m C: n = 30, M/F = 15/15, age = 14 y 2 m ± 1 y 2 m |
Skeletal class II | Stage 3–Stage 4 (CVM) | T: 1 y (±6 m) C: 1 y (±2 m) |
Acrylic splint Herbst appliance |
| Küçükkeleş and Sandalli (23) | CCT (prospective) | T: n = 10, C: n = 10 8 F (10.2 y), 12M (10.6 y) |
Skeletal class II | Peak growth period (HWM) | T: 12 C: 12 |
Banded type Herbst appliance |
| LaHaye et al. (24) | CCT (prospective) | T: n = 19, M/F = 9/10, age = 11.7±3 y C: n = 29, M/F = 14/15, age = 12.4±1.5 y |
Skeletal class II | N/A | T: 12.7±7 C: 2.2±0.6 y |
Edgewise crowned Herbst appliances |
| McNamara et al. (25) | CCT (prospective) | T: n = 45, M/F = 27/18, age = 12 y C: n = 21, M/F = 8/13, age = 11 y 1 m |
Skeletal class II | N/A | T: 12 C: 22 |
Acrylic splint Herbst appliance |
| Pancherz et al. (26) | CCT (prospective) | T: n = 22, M/F = 19/3, age = 12 y C: n = 20, M/F = 17/3, age = 12 y |
Skeletal class II | Peak growth period (HWM) | T: 6 m 7d ± 14 d C: 6 m 6 d ± 11 d |
Banded type Herbst appliance |
| Pancherz et al. (27) | CCT (prospective) | T: n = 22, M/F = 19/3, age = 12 y 1 m ± 11 m C: n = 20, M/F = 17/3, age = 11 y 2 m ± 9 m |
Skeletal class II | Peak growth period (HWM) | T:6 m 7 d ± 14 d C:6 m 6 d ± 11 d |
Banded type Herbst appliance |
| Sidhu et al. (28) | CCT (prospective) | T: n = 8, M/F = 0/8, age = 11 y 9 m C: n = 8, M/F = 0/8, age = 11 y |
Skeletal class II | N/A | T: 8 C: 8 |
Acrylic splint Herbst appliance |
| Wigal et al. (29) | CCT (prospective) | T: n = 22, M/F = 7/15, age = 8.4±1.0 y C: n = 22, age = 8.4±1.1, M/F(N/A) |
Skeletal class II | NA | NA | Edgewise crowned Herbst appliance |
| Jakobsone et al. (30) | CCT (prospective) | T: n = 40, M/F = 20/20, age = 13.6±1.3 y C: n = 18, M/F = 11/7, age = 13.9±1.6 |
Skeletal class II | Stage 3–Stage 5 (CVM) | T: 12 m C: 12 m |
Stainless steel crown Herbst appliance |
M, male; F, female; N/A, not available; T, Herbst appliance treatment; C, control group; HWM, hand wrist maturation; CVM, cervical vertebrae maturation.
Table 3.
Study quality scores using Downs and Black scale: checklist for measuring study quality (n = 12).
| Study | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | Quality score |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Baysal and Uysal (20) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 0 | 2 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 17 |
| Baysal and Uysal (21) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 0 | 2 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 17 |
| de Almeida et al. (22) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 2 | 2 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 19 |
| Franchi et al. (5) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 13 |
| Küçükkeleş and Sandalli (23) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 0 | 2 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 19 |
| LaHaye et al. (24) | 1 | 1 | 1 | 1 | 0 | 2 | 1 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 13 |
| McNamara et al. (25) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 1 | 2 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 16 |
| Pancherz (26) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 0 | 2 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 15 |
| Pancherz (27) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 0 | 2 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 15 |
| Sidhu et al. (28) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 0 | 2 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 18 |
| Wigal et al. (29) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 0 | 2 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 16 |
| Jakobsone et al. (30) | 1 | 1 | 1 | 1 | 0 | 2 | 2 | 0 | 2 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 18 |
Key:
Reporting: ‘Yes = 1,’ ‘No = 0’
1. Is the hypothesis /aim /objective of the study clearly described?
2. Are the main outcomes to be measured clearly described in the Introduction or Methods section?
3. Are the characteristics of the patients / samples included in the study clearly described?
4. Are the interventions of interest clearly described?
5. Are the distributions of principal confounders in each group of subjects to be compared clearly described
‘Yes = 2,’ ‘Partially = 1,’ ‘No = 0’
6. Are the main findings of the study clearly described?
7. Does the study provide estimates of the random variability in the data for the main outcomes?
8. Have all important adverse events that may be a consequence of the intervention been reported?
9. Have the characteristics of patients lost to follow-up been described?
10. Have actual probability values been reported (e.g., 0.035 rather than <0.05) for the main outcomes except where the probability value is less than 0.001?
External validity: ‘Yes = 1,’ ‘No = 0,’ ‘Unable to determine = 0’
11. Were the subjects asked to participate in the study representative of the entire population from which they were recruited?
12. Were those subjects who were prepared to participate representative of the entire population from which they were recruited?
13. Were the staff, places, and facilities where the patients were treated, representative of the treatment the majority of patients receive?
Internal validity—bias: ‘Yes = 1,’ ‘No = 0,’ ‘Unable to determine = 0’
14. Was an attempt made to blind study subjects to the intervention they have received?
15. Was an attempt made to blind those measuring the main outcomes of the intervention?
16. If any of the results of the study were based on ‘data dredging’ was this made clear?
17. In trials and cohort studies, do the analyses adjust for different lengths of follow-up of patients, or in case-control studies, is the time period between the intervention and outcome the same for cases and controls?
18. Were the statistical tests used to assess the main outcomes appropriate?
19. Was compliance with the intervention/s reliable?
20. Were the main outcome measures used accurate (valid and reliable)?
Internal validity—confounding (selection bias): ‘Yes = 1,’ ‘No = 0,’ ‘Unable to determine = 0’
21. Were the patients in different intervention groups (trials and cohort studies) or were the cases and controls (case-control studies) recruited from the same population?
22. Were study subjects in different intervention groups (trials and cohort studies) or were the cases and controls (case-control studies) recruited over the same period of time?
23. Were study subjects randomized to intervention groups?
24. Was the randomized intervention assignment concealed from both patients and health care staff until recruitment was complete and irrevocable?
25. Was there adequate adjustment for confounding in the analyses from which the main findings were drawn?
26. Were losses of patients to follow-up taken into account?
Power
27. Did the study have sufficient power to detect a clinically important effect where the probability value for a difference being due to chance is less than 5%? Sample sizes have been calculated to detect a difference of x% and y%.
Size of smallest intervention group
1. A 1<n1 0
2. B n1-n2 1
3. C n3-n4 2
4. D n5-n6 3
5. E n7-n8 4
6. F n8+5
Description of outcomes
For each outcome examined in this meta-analysis, measurements at active treatment effect period (the changes between before-Herbst treatment and immediately-after-Herbst treatment) were conducted. All included studies investigated the net changes before and after Herbst treatment except that the study reported annualized outcome changes instead.
The GRADE assessments for quality of evidence for each outcome were shown in Table 4.
Table 4.
GRADE assessment for quality of evidence.
| Outcome | Downgrade | Upgrade | Overall quality | ||||
|---|---|---|---|---|---|---|---|
| Study limitations | Imprecision | Inconsistency | Indirectness | Publication bias | |||
| SNA | Serious | None | Serious | None | None | None | 3 (Low) |
| SNB | Serious | None | Very serious | None | Serious | None | 1 (Very low) |
| ANB | Serious | Serious | Very serious | None | None | None | 1 (Very low) |
| Mandibular plane angle | Serious | None | None | None | Serious | None | 3 (Low) |
| A-OLp | Serious | None | None | None | Serious | None | 3 (Low) |
| Pg-OLp | Serious | Serious | Very serious | None | None | None | 1 (Very low) |
| Co-Go | Serious | None | None | None | None | None | 4 (Low) |
| Co-Gn | Serious | None | Serious | None | None | None | 3 (Low) |
| Overjet | Serious | None | Very serious | None | None | None | 2 (Low) |
| Overbite | Serious | None | Very serious | None | None | None | 2 (Low) |
| Molar relationship | Serious | None | Very serious | None | None | None | 2 (Low) |
Description of interventions
The intervention in this meta-analysis was Herbst appliance—one of the most commonly used treatment modality for Class II patients.
Effects of interventions
In this section, we reports the meta-analysis results for each examined measure as follows.
Skeletal angular measurements
SNA and SNB
Eight studies (20,22–25,28–30) investigated SNA and SNB. However, all of them examined the active treatment effects only. As depicted in Figure 2, our meta-analysis revealed that the pooled differences in mean or MDs of SNA and SNB for active treatment effect were −0.56 degrees [95% CI: −0.99, −0.14] and 1.06 degrees [95% CI: 0.53, 1.60], respectively.
Figure 2.
Forest plot of pooled MD regarding SNA, SNB, ANB, and mandibular plane angle for Herbst appliance versus control group.
ANB
Eight studies (20,22–25,28–30) investigated this outcome. The meta-analysis revealed that the pooled MD of ANB for active treatment effect was −1.08 degrees [95% CI: −2.16, −0.00] (Figure 2).
Mandibular plane angle
Eight studies (5,20,22–26,30) investigated this outcome. The meta-analysis revealed that the pooled MD for active treatment effect was 0.17 degrees [95% CI: −0.09, 0.42] (Figure 2).
Linear measurements
Overjet
Seven studies (5,21,23,27–30) investigated overjet. The meta-analysis revealed that the pooled MD of overjet for active treatment effect was −4.82mm [95% CI: −5.83, −3.80] (Figure 3).
Figure 3.
Forest plot of pooled MD regarding A point-OLp, Pg-OLp, Co-Go, Co-Gn overjet, overbite, and molar relationship for Herbst appliance versus control group.
Overbite
Six studies (21,23,26,28–30) investigated overbite. The active treatment effect outcome was a significant decrease in overbite and the meta-analysis revealed that the pooled MD of overbite was −1.69mm [95% CI: −3.18, −0.21] (Figure 3).
Co-Go
Four studies (5,21,25,30) investigated the outcome of Co-Go. The active treatment effect was a significant increase in Co-Go with the pooled MD being 1.76mm [95% CI: 1.27, 2.26] (Figure 3).
Co-Gn
Five studies (21,22,25,29,30) investigated the outcome of Co-Gn. The meta-analysis revealed that the pooled MD for active treatment effect was 1.74mm [95% CI: 0.95, 2.53] (Figure 3).
Molar relationship.
Four studies (5,21,27,29) showed a significant decrease in molar relationship in active treatment period with the pooled MD being −5.70mm [95% CI: −6.71, −4.69] (Figure 3).
A point-OLp
Six studies (5,21,22,24,27,29) showed a significant decrease in A point-OLp with the pooled MD being −0.52mm [95% CI: −0.73, −0.30] (Figure 3).
Pg-OLp
Seven studies (5,21,22,24,27–29) showed a significant increase in Pg-OLp with the pooled MD being 1.45mm [95% CI: 0.43, 2.47] (Figure 3).
Sensitivity analysis and subgroup analysis
The results of sensitivity analysis and subgroup analysis are summarized in Table 5 and Table 6, respectively.
Table 5.
Sensitivity analysis for Herbst appliance versus control.
| Outcome | Original estimates | Exclusion of studies* | Effect model | |
|---|---|---|---|---|
| Fixed | Random | |||
| SNA | −0.56 (−0.99, −0.14) | −0.52 (−0.99, −0.06) | −0.62 (−0.88, −0.37) | −0.56 (−0.99, −0.14) |
| SNB | 1.06 (0.53, 1.60) | 1.08 (0.49, 1.66) | 0.89 (0.66, 1.13) | 1.06 (0.53, 1.60) |
| ANB | −1.08 (−2.16, −0.00) | −0.96 (−2.12, 0.20) | −0.60 (−0.81, −0.38) | −1.08 (−2.16, −0.00) |
| Mandibular plane angle | 0.17 (−0.09, 0.42) | — | 0.17 (−0.09, 0.42) | 0.17 (−0.09, 0.42) |
| Overjet | −4.82 (−5.83, −3.80) | −4.51 (-5.51, -3.51) | −4.40 (-4.75, -4.05) | -4.82 (-5.83, -3.80) |
| Overbite | −1.69 (−3.18, −0.21) | −1.57 (−3.23, 0.08) | −2.40 (−2.69, −2.11) | −1.69 (−3.18, −0.21) |
| Co-Go | 1.76 (1.27, 2.26) | — | 1.76 (1.27, 2.26) | 1.76 (1.27, 2.26) |
| Co-Gn | 1.74 (0.95, 2.53) | 2.03 (1.30, 2.76) | 1.94 (1.41, 2.48) | 1.74 (0.95, 2.53) |
| Molar relationship | −5.70 (−6.71, −4.69) | −5.50 (−6.74, −4.26) | −5.75 (−6.15, −5.34) | −5.70 (−6.71, −4.69) |
| A point-OLp | −0.52 (−0.73, −0.30) | −0.53 (−0.75, −0.30) | −0.52 (−0.73, −0.30) | −0.52 (−0.73, −0.30) |
| Pg-OLp | 1.45 (0.43, 2.47) | 2.00 (0.27, 2.50) | 1.23 (0.89, 1.56) | 1.45 (0.43, 2.47) |
The numbers in bold means different from original estimates.
*Exclusion of study bonded brackets on the upper anterior teeth Wigal et al. (29).
Table 6.
Subgroup analysis for Herbst appliance versus control.
| outcome | Original estimates | Banded type Herbst appliance* | Splint Herbst appliance** | Edgewise crowned Herbst appliance*** |
|---|---|---|---|---|
| SNA | −0.56 (−0.99, −0.14) | −0.37 (−1.12, 0.38) | −0.53 (−1.63, 0.57) | −0.50 (−0.90, −0.11) |
| SNB | 1.06 (0.53, 1.60) | 1.01 (−0.30, 2.32) | 1.60 (0.42, 2.78) | 0.56 (0.22, 0.89) |
| ANB | −1.08 (−2.16, −0.00) | −1.47 (−2.62, −0.32) | −1.65 (−3.88, 2.57) | −1.08 (−1.62, −0.55) |
| Mandibular plane angle | 0.17 (−0.09, 0.42) | 0.23 (−0.13, 0.59) | 0.05 (−0.51, 0.60) | 0.20 (−0.32, 0.72) |
| Overjet | −4.82 (−5.83, −3.80) | −4.90 (−5.80, −4.00) | −4.80 (−5.36, −4.24) | −4.77 (−8.98, −0.56) |
| Overbite | −1.69 (−3.18, −0.21) | −2.80 (−4.04, −1.56) | −0.23 (−4.59, 4.13) | −2.31 (−2.81, −1.81) |
| Co-Go | 1.76 (1.27, 2.26) | — | 1.78 (1.24, 2.33) | — |
| Co-Gn | 1.74 (0.95, 2.53) | — | 2.50 (1.79, 3.22) | 1.04 (0.11, 1.97) |
| Molar relationship | −5.70 (−6.71, −4.69) | — | −4.92 (−5.97, −3.88) | — |
| Apoint-OLp | −0.52 (−0.73, −0.30) | −0.46 (−0.84, −0.08） | −0.45 (−0.98, 0.07) | −0.57 (−0.88, −0.27) |
| Pg-OLp | 1.45 (0.43, 2.47) | 1.40 (−0.85, 3.66) | 1.91 (0.81, 3.01) | 0.87 (−0.84, 2.57) |
‘a’ group: the heterogeneity : SNA (I 2 = 0), SNB (I 2 = 44%), Pg-OLp (I 2 = 91%). ‘b’ group: the heterogeneity: SNA (I 2 = 86%), ANB (I 2 = 99%), Apoint-OLp (I 2 = 0). ‘c’ group: Pg-OLp(I 2 = 70%). The data in bold means different from original estimates.
*Banded type Herbst appliance: de Almeida et al. (22), Küçükkeleş and Sandalli (23), Pancherz (26), Pancherz (27).
**Splint Herbst appliance: Baysal and Uysal (20), Baysal and Uysal (21), Sidhu et al. (28), McNamara et al. (25), Franchi et al. (5).
***Edgewise crowned Herbst appliance: LaHaye et al. (24), Wigal et al. (29), Jakobsone et al. (30).
We conducted sensitivity analysis to examine the stability of present meta-analysis. In Wigal et al. (29), the brackets were bonded on upper anterior teeth. When this article was excluded in the sensitivity analysis, results regarding to ANB and overbite are unstable.
We also performed a subgroup analysis since different types of Herbst appliances in the included studies may influence the results of present meta-analysis. These studies were divided into three subgroups, that is banded type (22,23,26,27), splint type (5,20,21,25,28) and edgewise crowned type (24,29,30), as shown in Table 6. Our results demonstrated that different types of Herbst appliances have significant effect toward some examined measures. In specific, the subgroup analysis for the banded Herbst appliance resulted in a significant change in SNA, SNB, and Pg-OLp; the subgroup analysis for splint Herbst appliance revealed a significant change in SNA, ANB, overbite, and A point-OLp; and, Pg-OLp was detected to change significantly for the subgroup analysis of edgewise crowned Herbst appliance. Moreover, we divided the splint type into cast and acrylic splint types for a further subgroup analysis. The results showed significant differences exist in SNA (pooled MD = 0.02, 95% CI: −1.10, 1.15) and ANB (pooled MD = 0.10, 95% CI: −4.08, 4.27).
Furthermore, changes in effect models (fixed-effect or random-effect model) failed to reveal any significant change.
Meta-regression
Taking into account of the main factors of the Herbst treatment, the meta-regression was performed for this analysis. We extracted the age of the subjects and the treatment duration for the main factors. The results showed that age has no effect on the meta-analysis, and the treatment duration has effect on the results of Pg-OLp (P = 0.007) and molar relationship (P = 0.001).
Assessment of publication bias
Neither Egger’s test nor Begg’s test revealed any evidence of publication bias except for SNB, mandibular plane angle, and A point-OLp (Table 7).
Table 7.
Publication bias (Egger’s test and Begg’s test).
| Outcome | Egger’s test | Begg’s test |
|---|---|---|
| Angular measurements | ||
| SNA | 0.751 | 0.902 |
| SNB | 0.053 | 0.386 |
| ANB | 0.347 | 0.108 |
| Mandibular plane angle | 0.075 | 0.118 |
| Linear measurements | ||
| A point-Olp | 0.154 | 0.086 |
| Pg-Olp | 0.337 | 0.452 |
| Overjet | 0.371 | 1.000 |
| Overbite | 0.269 | 0.260 |
| Co-Go | 0.342 | 0.308 |
| Co-Gn | 0.905 | 1.000 |
| Molar relationship | 0.234 | 0.308 |
Those highlighted in bold indicates P < 0.1.
Discussion
In the present study, we examined eleven outcomes (SNA, SNB, ANB, mandibular plane angle, Co-Go, Co-Gn, overjet, overbite, molar relationship, A point-OLp, and Pg-OLp) from 12 studies. Although some outcomes are sensitive to the included studies and types of Herbst appliances, most outcomes describing direct dental and skeletal effects of Herbst appliance are robust.
As shown in Figure 2, the present study was indicative of a significant increase in SNB (pooled MD = 1.06, 95% CI: 0.53, 1.60), a significant decrease in SNA (pooled MD = −0.56, 95% CI: −0.99, −0.14), and ANB (pooled MD = −1.08, 95% CI: −2.16, −0.00). SNA is an indicator of the anterio-posterior relation of the maxilla to the cranial base (31), and ANB is used to determine the relationship between maxillae and mandibles (32). The increase in SNB and decrease in SNA and ANB revealed that Herbst appliance could forward mandibles while restricting the maxillary position and growth. These findings agree with previous observations by Pancherz (33), so are the linear results, that is the decrease in A point-OLp and increase in Pg-OLp.
Moreover, our results showed that Pg-OLp and Co-Gn were increased following Herbst treatments, indicative of anteriorly positioned mandibular base and increased mandibular length (Figure 3). This may suggest that the sagittal changes of mandibular are brought about by changes in both condylar positions and mandibular lengths. Since Herbst appliances could restrict anterior movement of maxillae, we suggest that Herbst appliance is most suitable to be indicated in the patients with mandibular retrognathism and that it may also be effective for maxillary prognathism. However, it needs note that even through the skeletal changes (Pg-OLp, Co-Gn) were statistically significant, it may still not be clinically significant (1.45 and 1.74mm). Besides, most of the subjects included in the meta-analysis were treated during the pubertal growth spurt, and we suggest that the effect of growth contributed to the changes should not be ignored. We need further analysis for that.
In addition, our results on linear measurements showed that Herbst appliance could reduce dental overjet, dental overbite and molar discrepancies (Figure 3). As mentioned above, Herbst appliance could forward mandibles, which may partially contribute to the improvement of dental discrepancies. However, since the skeletal change (Co-Gn = 1.74) was smaller than the total improvement in dental discrepancy (molar relationship = 5.70), we suggest that skeletal changes and true dental changes both contributed to the dental discrepancy which was also reported by previous study (34), and the present meta-analysis cannot quantify their relative contribution. Therefore, the Herbst appliance can correct the sagittal relationship of upper and lower teeth through both skeletal and dental changes. Meanwhile, it is worth noting that there are substantial heterogeneity for SNA (I 2 = 57%), SNB (I 2 = 77%), ANB (I 2 = 96%), and molar relationship (I 2 = 82%) (Figures 2 and 3). Thus, these results should be interpreted with caution.
In this study, we found that Herbst appliances have no effect on the mandibular plane angle. This measure is indicative of the vertical jaw base relationship (35). It has been suggested that with the initial construction bite in an incisor edge-to-edge relationship, the increase in the distance between pogonion and condyle primarily results from a positional change of pogonion inferiorly, which is accompanied by a significant increase of the mandibular plane angle (36). In our meta-analysis, our results indicate an increase in the length of Co-Go (Figure 3), which can offset the increase in mandibular angle. This result may suggest that the Herbst appliance have little effect for the mandibular plane angle in clinical settings, yet we should use Herbst appliance carefully for high angle cases.
Besides, the including studies showed many types of Herbst appliance that induced differences of the items changes. The biomechanics of these different designs of appliance can result in different reconstruction. However, because of the limited including studies and the high heterogeneity between studies, we also cannot suggest that the differences exist in clinical treatment. We need more including studies to explore the mechanism.
In clinics, a variety of removable appliances for Class II malocclusion have demonstrated to be effective, such as the Twin-Block appliance which can induce more sagittal skeletal changes (21) and the Forsus device which exhibits a significant improvement of the sagittal dentoalveolar changes (37). Therefore, the Herbst appliance may be recommended as an optimal choice for dental discrepancy of Class II malocclusion due to its obvious effect on changes of dental discrepancy. Beside, some of the included studies used CVM methods to detect the skeletal maturation that is a classical standard used in clinical diagnosis. However, some studies suggest that many other growth indicators should be taken into consideration in evaluating adolescent skeletal maturation (38).
The limitations of this analysis include limited number of high-quality studies, preferably RCTs, lack of long-term treatment results and uncontrolled of cephalometric magnifications. Due to low quality of evidence and publication bias, the results should be interpreted with caution.
Conclusion
Herbst appliance can improve sagittal intermaxillary positions, probably by restricting maxillae and forwarding mandibles. However, it may have no effects on mandibular angle. Moreover, Herbst appliance is able to improve the sagittal dental discrepancy. Our results indicate Herbst appliance is effective for patients with Class II malocclusion.
Funding
The National Natural Science Foundation of China (81100778 and 81400549).
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