Incompetent lips refer to:
The term 'incompetent lips' implies that the lips are unable to form an adequate seal under similar unstrained conditions, i.e. excessive separation of the lips at rest. As a general guideline, which holds for all ethnic groups, lip separation at rest should be no more than 3-4 mm; above this, the lips are termed incompetent.
Inability of the lips to cover the incisors in the mandibular relaxed position
Inability of the lips to cover the incisors in occlusion
The lips come in between the upper and lower incisors
Tongue thrusts against the lips during swallowing