A study of basal movement with rapid maxillary expansion.

This investigation was undertaken to examine the effect of rapid maxillary expansion horizontally and posterior to the dental arch, there being some doubt that the expansion would be carried in this dimension and whether dilation of the non-tooth-bearing bones (palatines and sphenoidal pterygoid processes) was possible. The increases in the intermolar arch widths and the interpterygoid hamular widths were recorded in a group of thirty-two orthodontic patients. (twelve male and twenty female, aged 8 to 24 years), before and after rapid maxillary expansion. The mean percentage increase in interhamular widths to intermolar widths was 58 percent (range, 35 percent to 89 percent). The correlation between the relative increases was weak (r = +0.55). A slight reduction in the percentage increases in interhamular widths to intermolar widths as age advanced suggested an age factor, but the correlation was very weak (r = -0.33). From this evidence, it would seem that rapid maxillary expansion will separate the palatine bones and splay outward the pterygoid processes of the sphenoid bone.