Methods: Cephalograms of eighty-four subjects (22 males and 62 females, aged 20.18 + 3.65 years) diagnosed as having incompetent lips were collected (Incompetent Group: IG) and compared to a control group (CG), matching in age and sex distribution. Thirty-five linear and angular measurements were evaluated and compared between the two groups using independent t-test. Stepwise discriminant analysis of lip incompetence was performed.
Results: Compared to the CG, subjects in the IG had significantly different skeletal, dental and lip features, which included: thinner upper lips, shorter upper and lower lips, more retrognathic facial types, greater ANB angle, shorter anterior and posterior cranial bases, shorter palatal length, shorter mandibular body length, shorter ramal length, steeper mandibular plane, less prominent chin, bimaxillary dental protrusion, and smaller inter-incisal angle. Among these variables, the significant discriminant ones were: inter-incisor angle, inclination of upper incisors, ramal height, anterior cranial base, PP to FH angle, lower and then upper anterior dental height, upper lip thickness, and length.
Conclusion: Patients with incompetent lips are characterized by different cephalometric skeletal, dental and lip features. The presence of incompetent lips can be attributed to more than one factor and not only bimaxillary protrusion.