The lips are composed of a muscular skeleton (the orbicularis oris muscle) and connective tissue, and are covered externally by skin and internally by mucous membrane.
What is the vermilion?
The red portion of the lip - Characteristic feature of humans.
What is the vermilion border?
The sharp junction between the vermilion and the skin is termed the vermilion border.
What is the tubercle?
In the upper lip, the vermillion protrudes in the midline to form the tubercle.
The lower lip shows a slight depression in the midline corresponding to the tubercle.
What are the nasolabial grooves?
Laterally, the upper lip is separated from the cheeks by nasolabial grooves.
What are the labiomarginal sulci?
The are grooves which appear with age at the corners of the mouth to delineate the lower lip from the cheeks
What is the labiomental groove?
The labiomental groove separates the lower lip from the chin.
What is the philtrum?
In the midline of the upper lip runs the philtrum.
What are the labial commissures?
They are the corners of the liips and they are usually located adjacent to the maxillary canine and mandibular first premolar teeth.
What sexual dimorphism to lips exhibit?
As a general rule, the skin of the male is thicker, firmer, less mobile, and hirsute.
What are competent lips?
Lips which are lightly closed at rest.
What are incompetent lips?
Incompetent lips describe a situation where, at rest and with the facial muscles relaxed, a lip seal is not produced.
It must be distinguished from conditions where the lips are merely held apart habitually ("mouth breathers")
What are potentially competent lips?
Lips which would be capable of producing a seal at rest if not prevented from doing so by something (such as protruding incisors)
What happens in swallowing for incompetent lips?
The pattern of swallowing is often modified to produce an anterior oral seal.
Accordingly an oral seal may be formed by contact between the lower lip (or tongue) and the palatal mucosa, and there may be a forcible tongue thrust.
What are the position and activity of lips important in controlling?
The position and degree of protrusion of the incisors.
With competent lips, the tips of the maxillary incisors lie below the upper border of the lower lip, this arrangement helping to maintain the 'normal' inclination of the incisors.
With incompetent lips, the maxillary incisors may not be so controlled and the lower lip may even lie behind them, thus producing an exaggerated proclination of these teeth. If there is tongue thrusting to provide an anterior oral seal, further forces that tend to protrude the incisors are generated.