Changes in hyoid bone position following rapid maxillary expansion in adolescents

Objective: To examine changes in hyoid to mandibular plane distance (H-MP) and tongue length (TL) between children who had orthodontic treatment with and without rapid maxillary expansion (RME). Materials and Methods: Lateral and frontal cephalograms of 138 patients treated with RME and 148 controls treated without RME were used to measure pretreatment (T(1)) and posttreatment (T(2)) intermolar (IM) distance, lateronasal width (LNW), H-MP, and TL. Medical histories were used to collect demographic information, history of mouth breathing, difficulty breathing through the nose, and previous adenotonsillectomy. Groups were group-matched for age and gender. Descriptive statistics were calculated. Group means were compared using t-tests and chi-square statistics. Reliability was estimated using intraclass correlations and kappa statistics. Statistical significance was set at P < .05. Results: At T(1), the RME group showed smaller LNW (24.83 +/- 1.99 vs 26.18 +/- 2.05) and IM (50.17 +/- 2.3 vs 51.58 +/- 2.83). The distance from H-MP was longer in the RME group (15.69 +/- 3.95 vs 13.86 +/- 3.4). Mean changes (T(2) - T(1)) in the RME group were increased LNW (+2.48 +/- 1.38 vs +0.94 +/- 1.11 for the non-RME group) and IM (+3.21 +/- 1.72 vs +0.98 +/- 1.67). The mean change (T(2) - T(1)) in H-MP for the RME group was -0.68 +/- 3.67 compared with +1.1 +/- 2.96 for the non-RME group. Mean changes for TL were not statistically significant. No significant differences were noted at T(2) between groups for LNW, H-MP, or TL. Conclusions: In this sample, RME produced significant changes in H-MP, and TL was unaffected. (Angle Orthod. 2011;81:632-638.)