Skeletal, Dental, and Soft Tissue Features With Increased Interlabial Gap

Objectives: The aim of this study was to investigate skeletal, dental, and soft tissue features in patients with increased interlabial gap (IG) using cone-beam computed tomography (CBCT) data.
Methods: CBCT scans for 74 patients (21 males and 53 females) taken prior to undergoing orthognathic surgery were reviewed. All scans were obtained in Natural Head Position with the lips at rest. Mimics Innovation Suite™ Research Edition software (version 24) (Leuven, Belgium) was used for analysis. Sixty-eight landmarks were chosen representing cranial, maxillary, mandibular, and soft tissue segments. Forty-three measurements between points and/or planes were selected to evaluate relationships between skeletal, dental, and facial features and varying IG. Descriptive statistics included the mean, range, and standard deviation for each measurement. Pearson correlation was used to test the relationship between IG and the other variables. Multiple linear regression models evaluated how the IG changed per unit change of a significantly correlated variable. SAS 9.4 was used for the statistical analysis.
Results: Twenty-three measurements showed significant correlations with IG (P value<0.05). Subjects with increased IG had many signs of increased vertical dimension clockwise mandibular rotation, including increased mandibular plane angle and lower facial height, decreased chin prominence, mandibular retrognathia, bimaxillary dental protrusion, and shorter lips. Multiple linear regression models revealed significant relationships between IG and ANB, mandibular plane angle, lower facial height, incisor inclination, maxillary incisor display, SNB, mandibular body length, thickness of the buccal cortex over the incisors, soft tissue chin prominence, lower lip length, and nasal tip projection.
Conclusions: An increased IG is associated with increased anterior vertical dimension which is manifested skeletally, dentally, and in the soft tissue. Planning treatment for a patient with existing increased IG will need to address all these facial components.