Expansion of the lower arch concurrent with rapid maxillary expansion.

The effect of rapid maxillary expansion on the mandibular intercanine and intermolar widths during treatment and its stability after retention was studied. In addition, the relationships between the interarch change and the facial types and ages of the subjects of the sample were evaluated. The sample consisted of 17 cases for the study of intercanine width, and 22 nonextraction cases for the study of the intermolar width. Initial, final, at least 2-years postretention models, and initial lateral cephalograms were analyzed. Treatment and postretention changes for the intercanine width and the mesial and distal intermolar widths were calculated and tested for significance. Mean expansions of the intercanine width of 1.1 mm and of the intermolar width of 2.8 mm postretention were found to be statistically significant. There were no correlations found between the amount of increase in arch width and the facial types and ages of the subjects.