Skeletal and dental characteristics of subjects with incompetent lips

To evaluate the cephalometric features of subjects with incompetent lips, and to find the most discriminant variables for lip incompetence among the following: dental protrusion and proclination, antero-posterior and vertical skeletal relationships, and lip dimensions.

This retrospective study was conducted at King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia, between 2011 and 2012. Cephalograms of 84 subjects (22 males and 62 females, aged 20.18+/-3.65 years) diagnosed as having incompetent lips were collected (incompetent group [IG]) and compared with the control group (CG), matching in age and gender distribution. Thirty-five measurements were compared between the 2 groups using independent t-test. Stepwise discriminant analysis of lip incompetence was performed.

Compared to the CG, subjects in the IG had thinner upper lips, shorter upper and lower lips, more retrognathic facial types, greater angle between nasion-point A and nasion-point B, 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. The significant discriminant variables, in order, were inter-incisor angle, inclination of upper incisors, ramal height, anterior cranial base,  palatal plane to Frankfort horizontal plane angle, lower and then upper anterior dental height, upper lip thickness, and length.

The presence of incompetent lips can be attributed to more than one factor and not only bimaxillary protrusion. This should be considered during the treatment planning of such problem.