Effect of muscle exercise with an oral screen on lip function.

The study aimed at evaluating how training of the lips with an oral screen affects the strength of the lips and the pressure of the lips on the teeth. In addition, the effect of the treatment with an oral screen on the dentition was studied. The treatment and lip training programme was instituted for 9 months in 16 children, 7-11 years old, with protruding maxillary incisors. The effect on the dentition was studied on dental casts made before and at the end of the treatment, and 5 months thereafter, as well as on lateral cephalograms. The lip strength was recorded with a dynamometer. The pressure from the lips on the upper and lower central incisors at rest, and during chewing and swallowing was measured with an extra-oral pressure transducer incorporated in a water-filled system with an intra-oral measuring point. Measurements of lip strength and pressure were made regularly before and during the treatment, and continued for up to 10 months thereafter. The treatment resulted in a decrease of the overjet and upper dental arch length, but with some relapse after the treatment. The strength of the lips increased during the treatment, but decreased afterwards. The pressure from the lips on the teeth at rest and during swallowing was unaffected by the lip training. The pressure from the lower lip during chewing increased temporarily during the treatment period.