Comparisons of facial soft tissue characteristics in adult patients with various mandibular divergence patterns

The alignment of craniofacial structures in three dimensions-transverse, vertical, and sagittal-determines facial esthetics. While skeletal and dental factors influence these outcomes, soft tissue characteristics, especially facial soft tissue (FST) thickness, are increasingly recognized as important. However, few studies have examined the impact of vertical facial divergence on soft tissue variation, particularly in the middle and lower thirds of the face.

This study aimed to evaluate the association between vertical facial divergence and facial soft tissue characteristics of lower and upper thirds in adult patients.

A total of 120 non-growing individuals (60 men, 60 women) with an average age of 27.87 years (range: 18-56) seeking orthodontic treatment were included. Participants were stratified into four groups based on mandibular plane inclination to anterior cranial base (MP/SN): Group 1: MP-SN ≤ 27°, group 2: 27°< MP-SN ≤ 32º, group 3: 32°< MP-SN < 37°, and group 4: MP-SN ≥ 37°. Lateral cephalometric radiographs were used to measure FST thickness in the horizontal plane at specific anatomical landmarks, including the base of the forehead, nose, lips, and chin. Additionally, lip length, chin projection, and angular inclinations were assessed. Group comparisons were performed using one-way ANOVA followed by the post-hoc Benferroni test. The strength of the linear relationship between variables was investigated using the Pearson correlation test. Statistical significance was set at p = 0.05.

Significant differences in facial soft tissue characteristics were observed across groups. Hyperdivergent individuals (Group 4) exhibited significantly (p < 0.001) increased total facial height (TFH), lower facial height (LFH), and longer upper and lower lips compared to hypodivergent individuals (Group 1). Group 4 also had thinner soft tissue (p < 0.001) at the chin (Gn-Gn' and Me-Me'). Shallower mental sulcus and more obtuse chin angle existed in Group 4. Gender differences were noted in chin extension and throat angle. Positive correlations were found between MP/SN and various soft tissue measurements, including lip length and chin projection. No statistically significant differences were observed among the four groups in the upper face neither in linear nor in angular measurements.

Vertical facial divergence significantly influences soft tissue characteristics, particularly in the lower third of the face. Hyperdivergent individuals exhibit increased lip length and reduced chin thickness. Nose length and projection did not differ between the different divergent groups. These findings have clinical implications for orthodontic treatment planning, highlighting the need for individualized approaches based on vertical facial patterns.