Profile changes following lower incisor repositioning: a comparison between patients with different growth pattern

Individual growth changes might play a large role in the variability of treatment results for the soft-tissue profile. The aim of this study is to evaluate the real existence of the relationship between the repositioning of lower incisors, evaluated by Frankfort Mandibular Incisor Angle (FMIA), and the enhancement of profile, evaluated by the angle formed by its intersection with Frankfort plane (Z-angle). We finally compared this relationship in patients with different growth pattern.

A sample of 81 subjects all treated with Merrifield Directional Force System was divided in two group on the basis of INDEX value (ratio between posterior and anterior facial height): Group 1 (INDEX value ≤0.65, non-favorable growth pattern) and Group 2 (INDEX value >0.65, favorable growth pattern). Differences between post-treatment and pre-treatment values of FMIA and Z-angle were calculated for each group and was named respectively ∆ FMIA and ∆ Z-angle. A ratio between ∆ Z-angle and ∆ FMIA was also calculated.

The results of this study show a statistically significant correlation between lower incisors uprighting and profile outcome. A statistically significant difference between Group 1 and Group 2 was not found.

These results underline the difficulty to quantify and separate the effects of growth and orthodontic treatment of growing patients in determining the final facial configuration.