Three-dimensional lip morphology in skeletal Class I malocclusion with labial inclination of the upper central incisors

Purpose

The purpose of the present study was to examine the three-dimensional (3D) lip morphology in cases of skeletal Class I malocclusion with labial inclination of the upper central incisors.

Materials and methods

Thirty-five Japanese patients with malocclusion were divided into 2 groups: 20 patients (Test group; 9 males and 11 females; 7 years 5 months–14 years 2 months) who exhibited Class I malocclusion with labial inclination of the upper central incisors and 15 patients (Control group; 7 males and 8 females; 8 years 0 month–14 years 4 months) who exhibited skeletal Class I malocclusion with standard inclination of the upper central incisors. The 3D morphology of the facial soft tissue was recorded using a 3D surface-imaging device for both groups. The differences in the lip morphology variables between the Test and Control groups were then analyzed statistically.

Results

The central, right and left upper lip inclination angle in the lateral and three-quarter views in the Test group were significantly larger than those in the Control group. The upper lip base area, protrusion surface area, protrusion volume, and protrusion depth were significantly increased compared with the Control group, as were also the lower lip protrusion volume and depth. However, no significant differences in the lower lip base area and surface area were determined between the Test and Control groups.

Conclusions

The upper lip wholly showed labial inclination and forward protrusion in Class I malocclusion with labial inclination of the upper central incisors.