Perioral forces and dental changes resulting from mandibular lip bumper treatment.

This prospective study compares pretreatment and posttreatment forces produced by a lip bumper on the mandibular first molars and determines the dental effects of this appliance after 1 year of treatment. Twenty-five patients, ages 10 to 17 years, received fixed 0.045-inch passive stainless steel lip bumpers positioned at the level of the gingival margin, 2 mm from the labial surface of the teeth as the only form of treatment in the mandibular arch. At the end of 1 year, cephalometric radiographs and dental casts were taken, and lower lip forces remeasured during rest, speech, and swallowing. Lip force measurements were performed using specially designed strain gauges mounted bilaterally in the lip bumper tubes. Measurements of lip forces made before and after treatment were compared to explore the changes, if any, due to muscle adaptation to the appliance. Dental changes were measured from casts and cephalometric radiographs. Correlation analyses were performed to determine whether a relationship existed between initial force levels and resulting tooth movement. Pretreatment and posttreatment forces did not demonstrate a statistically significant difference. On the other hand, measurement of the dental casts revealed a significant increase in arch length caused by incisor proclination and protrusion, combined with molar distalization. The arch width significantly increased at the canines, first and second premolars, and first molars. The amount of force exerted by the lower lip on the molars was not correlated to the degree of tooth movement recorded in this sample.