The pressures from the lower lip on the lower incisors were measured at the midline between the central incisors and between the left lateral incisor and canine. The measurements were made with the lip at rest and during swallowing of water in 24 boys and 40 girls aged 9-15 years. The children were divided into four groups, two treated with a lip bumper with and without an oral shield, and two with a lingual arch with and without springs for proclination of the lower incisors. Recordings of the pressures were made before the start of the treatment, and 3 and 8 months after the use of the appliance, as well as 4 months after the removal of the lip bumper or lingual arch. The treatment with a lip bumper did not change the pressure from the lip on the lower incisors at rest. The pressure at the midline during swallowing was also unaffected by the lip bumper therapy, but the pressure between the lateral incisor and canine increased. Thus, lip bumper therapy did not lead to decreased pressure from the lip on the incisors. Proclination of the lower incisors with a lingual arch resulted in an increase of the pressure from the lip at rest. Thus, no adaptation of the lower lip to the proclination occurred. After relapse of the proclination the pressure from the lip decreased to a value no different from that before the start of the treatment.