Facial Soft tissue considerations in diagnosis

Facial Soft tissue considerations in diagnosis

Form and behaviour of facial soft tissue  

The lips: The lip contour is examined in profile, when the patient is sitting upright and relaxed. When the underlying teeth are proclined, the lips may appear everted rather than vertical. Lip incompetence is when the lips do not form a seal at rest as they may be too short to do this, when the mandible is also in its resting position. The flattening out of the submental fold of the lower lip and a slight dimpling over the anterior surface of the chin may be seen in such case.  The relationship of the crest of the lower lip with respect to upper central incisors tips is called the lip line. Normally, the lower lip covers between a third and a half of the labial surface of the upper central incisors. In class II division 1 malocclusion the lip line will be lower and often fail to control the upper incisors, contrarily, in Class II division 2 incisor relationship it will be much higher, sometimes covering the entire labial surface of the crown.

Upper lip thickness is measured from the greatest curvature of the labial surface of the maxillary central incisor to the vermilion border of the upper lip. The total chin thickness is measured horizontally from the NB line (a line drawn from soft tissue nasion to point B on lateral head film tracing) extended to soft tissue pogonion. Total chin thickness should equal upper lip thickness. When facial balance is present, the ideal relationship of profile line is to be tangent to the chin & the vermilion border of both lips & should lie in the anterior one third of the nose. This profile line makes an angle with the extented Frankfort Horizontal line, called the Z angle which is ideally 75 degrees to 78 degrees depending on age and gender. Z angle gives immediate guidance relative to anterior tooth repositioning.  

The vermilion border of the upper lip should bisect the distance from the vermilion border of the lower lip to the ala of the nose. The vermilion border of the lower lip should bisect the distance between the bottom of the chin & the ala of the nose, for facial balance & harmony. 

The Tongue: When the lips are incompetent the tongue will be used to produce a seal at the front of the mouth during swallowing, resulting in a tongue thrust. Sometimes the tongue may lie resting on the lower incisors, where it may prevent the full vertical development of the anterior dentoalveolar processes, leading to an openbite. Signs of tongue thrust -  proclination of both upper & lower incisors, an absence of lip incompetence associated with the thrust, presence of a large part of the tongue between the anterior teeth at all times, a reversed curve of spee in both arches, a marked lisp.