The soft tissues comprise the lips, cheeks and tongue and these guide the crowns of the teeth into position as they erupt. Ultimately, the teeth will lie in a position of soft tissue balance between the tongue on one side and the lips and cheeks on the other (Fig. 9).
In patients with a Class I incisor relationship the soft tissues rarely play an important part unless there is an anterior open-bite. The anterior open-bite may be caused by a digit sucking habit, a large lower anterior facial height, localised failure of eruption of the teeth, proclination of the incisors or to an endogenous tongue thrust. The latter cause is very rare and is usually identified by a large thrusting tongue that seems to permanently sit between the upper and lower incisors. This type of anterior open-bite is extremely difficult to correct. It is usually possible to reduce it, but on completion of treatment the tongue invariably pushes between the teeth and they move apart once again.
An important aspect of lip position is seen in patients with an increased overjet. If the upper incisor prominence is reduced, stability usually depends on the lower lip covering the upper incisors in order to prevent the overjet increasing post-treatment. Therefore, careful examination of the position of the lower lip in relation to the upper incisors is important. If the lower lip does not cover the upper incisors sufficiently after treatment, relapse of the overjet may occur. Similarly, if the overjet is to be reduced, full reduction is very important in order to give the lip the best possible chance of stabilising the incisors. Figure 10 illustrates the point; partial reduction of the overjet does not allow the lip to cover the upper incisors and they are likely to return to their pre-treatment position.
Whilst many young children have incompetent lips, this is often just a normal stage of development. As they pass through puberty, the lip length increases relative to the size of the face and the degree of lip competence gradually improves (Fig. 11).1
Fig. 11 Lip length is thought to increase as children pass through the pubertal growth spurt. This will aid retention of overjet reduction
Fig. 11 Lip length is thought to increase as children pass through the pubertal growth spurt. This will aid retention of overjet reduction the skeletal pattern is unfavourable in either the vertical or anterior-posterior position then even with normal lip length the soft tissues are still widely separated.
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