Long-term effects of the Herbst appliance on the dental arches and arch relationships: a biometric study

The purpose of this study was to evaluate biometrically the treatment and post-treatment effects of the Herbst appliance on the dental arches and arch relationships. The sample consisted of 53 Class II, division 1 malocclusion patients (33 boys and 20 girls) treated with the Herbst appliance. The mean age of the patients before treatment was 12.5 years (SD = 1.2 years). Dental casts were analysed before treatment, after treatment, 6 months post-treatment and at the end of the growth period (5-10 years post-treatment). The following variables were assessed: sagittal molar and canine relationships, overjet, overbite, maxillary and mandibular arch perimeters, and inter-molar and inter-canine dental arch widths. During treatment, the overjet, overbite, and sagittal molar relationship were overcorrected in most of the cases, while the sagittal canine relationship was normalized. The maxillary and mandibular arch perimeters increased during treatment, as did dental arch widths (molar and canine). In the long-term (mean = 6.7 years after treatment), Herbst appliance treatment resulted in a normal or over-corrected sagittal molar relationship in 79 per cent and a normal canine relationship in 68 per cent of the cases. Eighty-three per cent of the subjects had an overjet of 4.5 mm or less. In the long-term, the arch perimeters seemed to follow a normal dental development pattern. The increase of the upper molar and canine dental arch widths during treatment remained virtually stable whilst the lower intermolar arch widths seemed unaffected by treatment.