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Annali di Stomatologia | 2026; 17(3): 612-622 ISSN 1971-1441 | DOI: 10.59987/ads/2026.3.612-622 Articles |
Evaluation of lower incisor changes in patients treated with a Herbst appliance: a retrospective study
Article History
Received: May 2, 2026
Accepted: July 19, 2026
Published: July 30, 2026
Abstract
Background
Mandibular incisor proclination is one of the most debated dentoalveolar effects observed during Class II correction with fixed functional appliances. Although Herbst therapy can improve sagittal relationships, the reciprocal anchorage forces transmitted to the mandibular arch may increase lower incisor inclination, with potential periodontal implications in susceptible patients.
Aim
To evaluate lower incisor positional changes in growing patients treated with a Herbst appliance followed by fixed multibracket therapy, compared with a matched control group treated with fixed multibracket appliances only.
Materials and methods
This expanded retrospective controlled cephalometric study included 72 patients: 36 Class II patients treated with Herbst appliance followed by fixed multibracket therapy (Herbst group) and 36 patients treated with fixed multibracket therapy only (control group). Lateral cephalograms were evaluated at pretreatment (T0) and posttreatment (T1). The primary outcome was the change in IMPA. Secondary outcomes included L1-NB angle, L1-NB linear distance, overjet, overbite, ANB, mandibular plane angle, and the proportion of patients showing clinically relevant lower incisor proclination (>=5 degrees).
Statistical analysis
Normality was assessed using the Shapiro-Wilk test. Within-group changes were evaluated with paired tests. Between-group differences were assessed using independent- samples tests and ANCOVA adjusted for baseline values, age, sex, and treatment duration. Effect sizes and 95% confidence intervals were reported. A reliability analysis was performed on repeated measurements using ICC and Dahlberg’s error.
Results
Both groups showed a statistically significant increase in IMPA after treatment. The mean IMPA increase was greater in the Herbst group (+4.2 +/− 3.1 degrees) than in the control group (+1.7 +/− 2.4 degrees). The adjusted between-group difference was 2.4 degrees (95% CI: 1.1 to 3.7; p<0.001). A clinically relevant IMPA increase of at least 5 degrees occurred in 41.7% of Herbst patients and 16.7% of controls. L1-NB angular and linear changes were also significantly greater in the Herbst group. No significant between-group difference was observed for mandibular plane angle change.
Conclusions
In the expanded sample, Herbst appliance therapy was associated with a greater but clinically controllable proclination and protrusion of the mandibular incisors compared with fixed appliance therapy alone. Baseline incisor inclination and anchorage control should be carefully considered during Class II treatment planning.
Keywords: Herbst appliance; Class II malocclusion; mandibular incisors; IMPA; cephalometry; fixed functional appliance; dentoalveolar effects.
Introduction
Class II malocclusion is one of the most frequent orthodontic conditions in growing patients and may result from skeletal, dental, functional, or combined discrepancies. Mandibular retrusion is frequently reported as a relevant component of Class II division 1 malocclusion, supporting the rationale for orthopedic or functional mandibular advancement in selected growing patients [1–2].
The Herbst appliance is a fixed functional device designed to posture the mandible forward continuously. Its main advantage is the independence from patient compliance, as mandibular advancement is maintained during function, speech, and rest. The appliance generates a protrusive force on the mandible and mandibular dentition, with reciprocal forces on the maxillary arch [2–4].
Several studies have demonstrated that Herbst therapy can improve sagittal occlusal relationships through a combination of skeletal and dentoalveolar changes. These effects include mandibular positional adaptations, restraint or dental distalization effects in the maxillary arch, retroclination of maxillary incisors, and proclination or protrusion of mandibular incisors [6–12].
Lower incisor proclination is clinically relevant because it may reduce the true orthopedic component of Class II correction and may influence periodontal risk when the mandibular symphysis is thin or when the incisor roots are moved outside the alveolar envelope [5–6,13].
Previous investigations have reported variable magnitudes of mandibular incisor change after Herbst treatment, depending on patient age, appliance design, anchorage system, amount of mandibular advancement, baseline incisor inclination, and subsequent fixed appliance mechanics [7,14–18]. Therefore, a more robust evaluation requires an expanded sample, clearly defined primary and secondary outcomes, and statistical methods able to account for baseline differences between treatment groups.
The present study was revised and expanded to provide a stronger methodological framework. The primary outcome was the change in IMPA from T0 to T1. Secondary outcomes were selected to describe not only angular proclination but also linear protrusion, sagittal correction, vertical control, and the proportion of patients who experienced clinically meaningful lower incisor changes.
This study aimed to evaluate whether treatment with a Herbst appliance followed by fixed multibracket therapy produces greater lower incisor positional changes than fixed multibracket therapy alone in growing patients.
The null hypothesis was that there would be no significant difference between groups in the T0–T1 change of IMPA.
Materials and methods
Study design and sample
This was an expanded retrospective controlled cephalometric study based on consecutively treated orthodontic patients. The final sample included 72 patients divided into two groups of equal size.
The Herbst group included 36 growing patients affected by Class II malocclusion treated with a Herbst appliance for approximately 9 months, followed by fixed multibracket therapy (see Figures 1–3). The control group included 36 patients treated with fixed multibracket appliances only.
The control group was selected to provide a comparative estimate of lower incisor changes related to fixed orthodontic mechanics alone. Patients were matched as far as possible for age, sex, treatment duration, and baseline lower incisor inclination.
The study was performed in accordance with the “Strengthening the Reporting of Observational Studies in Epidemiology” (STROBE) guidelines and respected the Declaration of Helsinki, with pertinent national and international regulatory requirements. The Institutional Review Board approved the study. All participants/their parents provided written informed consent and were free to withdraw from the study at any time.
Eligibility criteria
Inclusion criteria were: age between 10 and 15 years at T0; good-quality lateral cephalograms at T0 and T1; complete permanent or late mixed dentition compatible with fixed orthodontic treatment; no previous orthodontic treatment; and complete clinical records.
Additional inclusion criteria for the Herbst group were a bilateral Class II molar relationship or a Class II division 1 malocclusion requiring mandibular advancement, and treatment with a Herbst appliance before or during the early phase of fixed therapy.
Exclusion criteria were craniofacial syndromes, cleft lip or palate, history of orthognathic surgery, systemic diseases affecting craniofacial growth, poor-quality radiographs, missing mandibular incisors, and incomplete records.
Treatment protocol
In the Herbst group, the appliance was constructed with the mandible advanced to an edge-to-edge incisal position when clinically feasible. Treatment duration with the Herbst appliance was approximately 9 months. After correction of the sagittal relationship, patients underwent fixed multibracket therapy for finishing and detailing.
In the control group, patients were treated with fixed multibracket appliances only, according to standard orthodontic mechanics. When necessary, lower incisor torque control was applied during alignment and finishing.
Cephalometric analysis
Digital lateral cephalograms were taken at T0 and T1 under standardized conditions. Tracings were performed using the same cephalometric protocol. The IMPA angle was defined as the angle between the long axis of the mandibular incisor and the mandibular plane (Go-Me).
The primary outcome was the T0–T1 change in IMPA. Secondary cephalometric outcomes were L1-NB angle, L1-NB linear distance, overjet, overbite, ANB angle, SNB angle, and mandibular plane angle. A clinically relevant lower incisor proclination was defined as an IMPA increase of at least 5 degrees.
Measurement reliability
To assess intra-examiner reliability, 20 randomly selected cephalograms were retraced after a two-week interval. Reliability was quantified using the intraclass correlation coefficient (ICC) and Dahlberg’s formula. An ICC greater than 0.90 was considered excellent.
Statistical analysis
Descriptive statistics were reported as mean, standard deviation, median, interquartile range, and frequency when appropriate. Normality was evaluated using the Shapiro-Wilk test and visual inspection of distribution plots.
Within-group changes from T0 to T1 were assessed using paired-samples t tests or Wilcoxon signed-rank tests, according to data distribution. Between-group comparisons of changes were assessed using independent-samples t tests or Mann-Whitney U tests.
An ANCOVA model was used for the primary outcome to compare T1 IMPA values between groups while adjusting for baseline IMPA, age, sex, and total treatment duration. Effect sizes were reported as Cohen’s d for between-group differences and partial eta squared for ANCOVA. The threshold for statistical significance was set at p < 0.05.
Because several secondary outcomes were evaluated, findings for secondary endpoints were interpreted with attention to multiplicity and clinical relevance, rather than p values alone.
Results
Sample characteristics
The expanded sample included 72 patients: 36 in the Herbst group and 36 in the control group. Baseline characteristics are reported in Table 1. No significant differences were observed for age, sex distribution, or treatment duration. As expected, sagittal discrepancy was greater in the Herbst group at baseline.
| Variable | Herbst group (n=36) | Control group (n=36) | p-value |
|---|---|---|---|
| Age at T0, years | 12.7 ± 1.5 | 12.9 ± 1.4 | 0.56 |
| Female/male, n | 20/16 | 19/17 | 0.81 |
| Treatment duration, months | 21.4 ± 3.2 | 20.1 ± 3.8 | 0.12 |
| Baseline IMPA, degrees | 99.2 ± 5.6 | 96.8 ± 5.1 | 0.07 |
| Baseline ANB, degrees | 5.1 ± 1.2 | 3.2 ±1.0 | <0.001 |
| Baseline overjet, mm | 6.0 ± 1.4 | 3.4 ± 1.1 | <0.001 |
Primary outcome
Changes in IMPA from T0 to T1, adjusted between-group differences with 95% confidence intervals (CI), and effect size (Cohen’s d) are reported. The mean IMPA increased significantly in both groups. The Herbst group showed a greater mean increase than the control group. The adjusted between-group difference remained statistically significant after controlling for baseline IMPA, age, sex, and treatment duration (Table 2).
| Outcome | Herbst group | Control group | Between-group difference | p-value |
|---|---|---|---|---|
| IMPA T0, degrees | 99.2 ± 5.6 | 96.8 ± 5.1 | 2.4 | 0.07 |
| IMPA T1, degrees | 103.4 ± 5.8 | 98.5 ± 5.3 | 4.9 | <0.001 |
| IMPA change, degrees | 4.2 ± 3.1 | 1.7 ± 2.4 | 2.5 | <0.001 |
| Adjusted IMPA difference, degrees | -- | -- | 2.4 (95% CI: 1.1 to 3.7) | <0.001 |
| Cohen’s d for IMPA change | -- | -- | 0.90 | -- |
Secondary outcomes
Secondary outcomes are reported in Table 3. The Herbst group showed greater increases in L1-NB angular and linear measurements, confirming that the IMPA change reflected both angular proclination and labial displacement of the lower incisor. The sagittal relationship improved more markedly in the Herbst group, as demonstrated by overjet and ANB changes. No clinically meaningful difference was observed for mandibular plane angle change.
| Variable | Herbst group change | Control group change | p-value |
|---|---|---|---|
| L1-NB angle, degrees | 4.6 ± 3.3 | 1.9 ± 2.7 | <0.001 |
| L1-NB distance, mm | 1.5 ± 1.1 | 0.6 ± 0.9 | <0.001 |
| Overjet, mm | −3.7 ± 1.5 | −1.2 ± 1.1 | <0.001 |
| Overbite, mm | −1.1 ± 1.0 | −0.6 ± 0.8 | 0.04 |
| ANB angle, degrees | −1.5 ± 0.9 | −0.4 ± 0.6 | <0.001 |
| SNB angle, degrees | 0.8 ± 0.7 | 0.2 ± 0.5 | <0.001 |
| Mandibular plane angle, degrees | 0.3 ± 1.0 | 0.2 ± 0.8 | 0.64 |
Clinically relevant lower incisor proclination
An IMPA increase of at least 5 degrees occurred in 15 of 36 patients in the Herbst group (41.7%) and in 6 of 36 controls (16.7%) (Table 4). The relative risk of clinically relevant proclination was 2.50 for Herbst-treated patients compared with controls.
| Category | Herbst group (n=36) | Control group (n=36) |
|---|---|---|
| IMPA increase < 5 degrees | 21 (58.3%) | 30 (83.3%) |
| IMPA increase ≥ 5 degrees | 15 (41.7%) | 6 (16.7%) |
| Relative risk | 2.50 | Reference |
Measurement reliability
Repeated cephalometric measurements showed excellent reliability. The ICC was 0.94 for IMPA, 0.92 for L1-NB angle, and 0.91 for L1-NB linear distance. Dahlberg’s error was 0.8 degrees for IMPA and 0.4 mm for L1-NB distance.
Discussion
This revised analysis, based on an expanded sample and a broader set of outcomes, suggests that treatment with Herbst appliance followed by fixed multibracket therapy produces a greater increase in mandibular incisor proclination than fixed multibracket therapy alone. The mean adjusted between-group difference for IMPA was 2.4 degrees, indicating a statistically significant and clinically relevant dentoalveolar component of Class II correction.
The direction of change observed in the Herbst group is consistent with the biomechanical action of fixed functional appliances. The bilateral telescopic mechanism postures the mandible forward and transmits reciprocal forces to the dentition, especially to the mandibular arch. This may lead to labial tipping and protrusion of the mandibular incisors, particularly when anchorage is dental rather than skeletal [2–3,7,14].
The present findings agree with previous reports showing that mandibular incisor proclination is a frequent dentoalveolar effect of Herbst treatment. Almeida et al. reported significant short-term dentoskeletal changes in mixed dentition patients treated with a Herbst appliance. At the same time, Pancherz described the combination of skeletal and dental adaptations that contribute to Class II correction [2–3].
Martin and Pancherz emphasized the relationship between the amount of mandibular advancement and mandibular incisor positional changes during Herbst/multibracket therapy [7]. In the present study, the appliance was generally constructed to an edge-to-edge incisal relationship. This factor may have contributed to the greater lower incisor changes observed in the Herbst group.
The increase in L1-NB angle and L1-NB linear distance confirms that the primary IMPA finding was not isolated to a single angular measurement. The lower incisor change involved both proclination and labial displacement. This distinction is clinically relevant because linear protrusion may be more directly related to the position of the root within the mandibular symphysis and therefore to periodontal risk in susceptible patients [5,13,17].
Although lower incisor proclination is often viewed as an undesirable side effect, it may be tolerated in selected patients when the mandibular symphysis is adequate and when baseline incisor inclination is not excessive. Nevertheless, excessive proclination may represent a risk factor for alveolar bone dehiscence and gingival recession, particularly in patients with a thin periodontal phenotype or reduced symphyseal bone thickness [5–6].
Ruf, Hansen, and Pancherz reported that orthodontic proclination of mandibular incisors in children and adolescents does not necessarily lead to gingival recession in the short term [6]. However, periodontal response is patient-dependent, and the absence of immediate recession does not eliminate the need for careful diagnosis, torque control, and long-term monitoring.
Appliance design and anchorage strategy are important determinants of dentoalveolar side effects. Weschler and Pancherz compared different mandibular anchorage forms and found that anchorage configuration can influence mandibular incisor proclination [14]. More recent approaches using skeletal anchorage have attempted to reduce dental side effects, although the literature remains heterogeneous and the predictability of incisor control is not absolute [15–16].
The control group also showed a mild increase in IMPA. This finding is clinically plausible because alignment, leveling, and arch coordination with fixed appliances may produce some mandibular incisor proclination, especially in cases with crowding. Therefore, the between-group comparison is more informative than the absolute Herbst group change alone.
The secondary sagittal outcomes showed greater overjet and ANB improvements in the Herbst group. These changes reflect the therapeutic objective of Class II correction and support the efficacy of Herbst therapy in improving sagittal relationships. However, the clinician should interpret Class II correction as a combination of skeletal, dental, and dentoalveolar effects rather than a purely skeletal response [8–12].
The absence of a relevant difference in mandibular plane angle suggests that, in this sample, Herbst treatment did not produce an unfavorable vertical skeletal response when followed by fixed appliance finishing. This is clinically important in hyperdivergent patients, where excessive vertical changes could compromise facial aesthetics and occlusal stability.
From a clinical perspective, the findings support the importance of baseline diagnosis. Patients with already proclined mandibular incisors at T0 may require additional anchorage strategies, careful bracket prescription, lower incisor torque control, or alternative Class II mechanics. Negative torque prescription in the mandibular anterior segment and controlled archwire sequencing may help reduce excessive proclination during the fixed appliance phase.
This study also highlights the need to report both statistical and clinical significance. The proportion of patients with an IMPA increase of at least 5 degrees was more than twice as high in the Herbst group compared with controls. This categorical outcome is useful because the mean change may underestimate individual variability.
The main limitation of the study is its retrospective design. Although the sample was expanded and adjusted analyses were performed, residual confounding cannot be excluded. In addition, two-dimensional cephalometry cannot fully describe root position within the alveolar housing. CBCT-based studies can provide more detailed information on alveolar bone thickness, fenestrations, and dehiscence, but routine CBCT exposure is not justified for all orthodontic patients [13,17–18].
Future studies should include prospective designs, standardized appliance designs, periodontal phenotype assessment, and long-term follow-up. The integration of digital models, cephalometric superimposition, and selected three-dimensional imaging may provide a more complete description of the dentoalveolar response to Herbst therapy.
This study has some limitations. The retrospective design limits causal inference. Moreover, the control group was not untreated and therefore does not represent natural growth; it represents the dentoalveolar effect of fixed appliance therapy alone. Lastly, two-dimensional cephalometric analysis cannot fully assess alveolar bone thickness or root position within the mandibular symphysis.
Clinical implications
- Herbst therapy can produce greater mandibular incisor proclination than fixed appliance therapy alone.
- IMPA should not be evaluated in isolation; L1-NB angular and linear values provide complementary information.
- Baseline incisor inclination, mandibular symphysis morphology, and periodontal phenotype should guide treatment planning.
- Lower incisor torque control should be planned from the beginning of treatment, particularly in patients with proclined incisors at T0.
- Clinically relevant individual changes may occur even when group mean changes appear moderate.
Conclusions
In this expanded controlled retrospective study, Herbst appliance therapy followed by fixed multibracket treatment was associated with a significantly greater increase in mandibular incisor proclination compared with fixed multibracket treatment alone. The primary outcome, IMPA, increased by a mean of 4.2 degrees in the Herbst group and 1.7 degrees in the control group. The adjusted between-group difference was statistically significant. Secondary outcomes confirmed greater lower incisor labial displacement in the Herbst group, as demonstrated by L1-NB angular and linear changes.
Although the observed changes appear clinically manageable, patients with high baseline IMPA, thin mandibular symphysis, or periodontal risk factors require careful anchorage planning and torque control. Herbst therapy remains an effective option for Class II correction in growing patients, but its dentoalveolar effects must be anticipated and controlled.
Consent for publication
‘Written consent for publication was obtained from each participant/guardian, who was informed that their sensitive data would not be divulged.
Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Competing interests
Authors declare no conflict of interest and that they did not receive support from any organization for the submitted work. All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Acknowledgements
None.
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