Pressure from the lips on the teeth and malocclusion.

The relationship between lip strength and lip pressure (pressure from the lips on the teeth) was studied in 84 children (aged 7 to 16 years) with varying types of malocclusion. The lip strength was recorded with a dynamometer. The lip pressure was measured on the upper and lower central incisors in the rest position, and during chewing and swallowing of crispbread. The lip pressure measurements were made with an extraoral pressure transducer incorporated in a water-filled system with an intraoral mouthpiece. The muscle activity of the lips was recorded electromyographically. Bite and facial morphologies were studied on dental casts and profile cephalograms. There was no correlation between lip strength and lip pressure. Lip strength was lower in children with Angle Class II, Division 1 malocclusion than in children with Class I malocclusion. The lip pressure on the upper incisors, on the other hand, was higher in Class II, Division 1 than in Class I malocclusion, and was lowest in children with Class II, Division 2 malocclusion. The findings suggest that the pressure from the lips on the teeth is a result of the incisor position.