The relation between normodivergent and hyperdivergent skeletal patterns and the outcome of activator treatment

This study evaluated the effect of pretreatment skeletal pattern and the type of appliance on the development of the mandible in a sagittal forward position during activator treatment.

A retrospective cohort study compared cephalograms of 188 patients before and after treatment with a Ton Kooiman appliance (T-appliance) and a headgear activator (HAC). All patients were stratified according to divergence. The cephalograms were calibrated, and 5 sets of measurements were performed. The primary outcome was the development of the mandible in the sagittal forward direction, which was evaluated with the sagittal development of the landmarks Infradentale, B-point, and Pogonion. Secondary landmarks were used to evaluate vertical and sagittal development.

The sagittal development of the Pogonion was found to be statistically significant in all groups. In the hyperdivergent group, the T-appliance demonstrated a statistically significant increase in mean forward development of 1.3 mm compared with the HAC. In the normodivergent group, no statistically significant differences in the sagittal development of primary landmarks were found between the HAC and the T-appliance. However, in this group, Gonion-Gnathion distance and Lower Facial Height showed statistically greater increase during treatment with a HAC compared with the T-appliance.

When myofunctional therapy is indicated for a normodivergent patient, both the T-appliance and HAC can be applied. For a hyperdivergent patient, the T-appliance should be preferred. Nevertheless, the development of a guideline to assist in the choice among different myofunctional appliances for a specific patient would need a comparison of more types of activators and should also include hypodivergent groups.