Evaluation of lower incisor changes in patients treated with a Herbst appliance: a retrospective study

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.