Objectives: To demonstrate that patients without posterior crossbite (PCB) but with maxillary transverse deficiency, not previously observed due to an increased curve of Wilson, can benefit from the same palatal expansion as patients with PCB, after correction of the buccal inclination.
Materials and methods: A total of 41 patients presenting a maxillary skeletal transverse deficiency were treated: 26 without PCB and 15 with PCB. In the non-PCB group, quad-helix compression was followed by a Hyrax expander (QH+HY), whereas the PCB group only underwent Hyrax expander treatment (HY). The maxillary intercanine, interpremolar, intermolar widths (cusp tips and gingival level) and molar inclination were measured at baseline and at the end of treatment in both groups.
Results: No significant differences were found between groups at the end of treatment, and no PCBs remained. The same maxillary expansion was achieved in the QH+HY and HY groups in the region of the canines, at both the gingival (3.4 ± 2.0 vs. 3.4 ± 2.7 mm; P = 0.999) and cusp tip levels (4.5 ± 3.1 vs. 3.8 ± 2.2 mm; P = 0.981). The molar inclination in the QH+HY group decreased, while there was a slight increase in the HY group (-6.50° ± 5.34° vs. 2.3° ± 4.1°; P < 0.001).
Conclusions: Some patients with maxillary transverse deficiency do not present with PCB, due to an increased curve of Wilson. However, these patients require skeletal expansion similar to that of patients with a bilateral PCB. The curve of Wilson should be flattened prior to expansion in order to increase the amount of maxillary skeletal expansion.
Keywords: Dentoalveolar compensation; Hyrax; Maxillary expansion; Posterior crossbite; Rapid maxillary expansion.