Transverse dentoalveolar changes after slow maxillary expansion

Introduction: In this study, we evaluated the transverse dentoalveolar changes in the maxillary first molar region after early treatment with the quad-helix appliance. Methods: Seventy-three consecutive patients (39 boys, 34 girls) who had phase 1 quad-helix treatment were evaluated with cone-beam computed tomography scans taken before phase 1 (mean age, 9.2 years) and phase 2 (mean age, 11.9 years) treatments. Buccal bone thickness, buccal cortical plate thickness, lingual bone thickness, alveolar width, palatal width, and intermolar width were measured by using standardized orientations. Results: Slow palatal expansion with the quad-helix decreased buccal bone thickness (1.6 mm +/- 0.8), and increased lingual bone thickness (1.6 mm +/- 1.3) and alveolar width (0.5 mm +/- 1.0). Intermolar widths and palatal widths increased 6.5 mm +/- 2.9 and 3.9 mm +/- 1.8, respectively. At the beginning of phase 2, approximately one third of the patients showed little or no buccal cortical plate on at least 1 side. Patients retained with the Hawley demonstrated some relapse tendencies; patients without retention had the greatest relapse tendencies. Conclusions: Early treatment with the quad-helix appliance proved to be highly effective in increasing intermolar, palatal, and alveolar widths. The teeth moved through the alveolus, leading to substantial decreases in buccal bone thickness and increases in lingual bone thickness. (Am J Orthod Dentofacial Orthop 2011;140:317-25)