RESUMEN
The effects of lip bumper treatment on the mandibular arch were observed in 32 patients with late transitional and early permanent dentitions. Dental cast measurements were made for arch perimeter, arch length, and arch width. Cephalometric radiographs were used to determine labial tipping of the incisors and distal movement of the molars. Arch circumference increased in all patients, ranging from 0.7 mm to 8.8 mm, with an average of 4.1 mm. The mean increase in arch length was 1.2 mm and was largely attributed to anterior tipping of the mandibular incisors. Change in arch length was the most predictive variable for the increase in arch circumference. Passive changes in arch width were recorded, with a mean increase of 2.0 mm in the intercanine distance and 2.5 mm in the first premolar distance. Arch width increments contributed to the increase in arch circumference, but the increases in arch width were not found to be predictive of the change in arch circumference. Changes in either arch circumference or arch length were not related to the duration of treatment, age and sex of the patient, or the eruption status of the permanent second molars.