Mandibular basal structure response to lip bumper treatment in the transverse dimension.

The effect of orthopedic or orthodontic treatment on the transverse dimension has been the subject of endless debate among orthodontists. The purpose of this investigation was to examine the response on the transverse dimension of the basal structure of the mandible and maxilla following two different modalities of treatment: group A-standard edgewise orthodontic treatment and group B-maxillary orthopedics with a bonded (tissue borne) rapid palatal expander (RPE) combined with a mandibular lip bumper. Each group had a matched paired untreated control according to age, sex, race, and treatment duration. For all subjects the width of the maxilla (Mx-Mx) and mandible (Ag-Ag) were measured on pre- and posttreatment posteroanterior cephalograms. The rate of width change in the maxilla and mandible was calculated (in mm/y). Results showed that group A had no treatment effect on the transverse dimension of the maxilla and mandible when compared with controls. However, group B had a significant increase in the transverse dimension of Mx-Mx (P < .001) and Ag-Ag (P < .001) when compared with controls. It was concluded that the RPE treatment increased the maxillary skeletal width, and the lip bumper increased the transverse dimension of the basal structure of the mandible.