Hyoid Bone Position Changes Following Rapid Palatal Expansion in Adolescents

Objectives: The purpose of this study was to examine changes in hyoid to mandibular plane distance (HMP) and tongue length (TL) between children who had orthodontic treatment with RPE and children who had orthodontic treatment without RPE.

Methods: Lateral and frontal cephalograms of 138 orthodontic patients treated with RPE and 148 control patients treated without RPE were used to measure pre-treatment (T1) and post-treatment (T2) intermolar distance (IM), lateronasal width (LNW), HMP and TL. Demographic information,history of mouth breathing, difficulty breathing through nose, and previous adeno-tonsillectomy were also collected. Samples were group matched by age and gender. Data were collected at T1 and T2 for all measures. Groups were compared using t-tests, and Chi-square. A level of p≤0.01 was used to assign statistical significance. Reliability was estimated using intraclass correlation or Kappa statistics.

Results: At T1, the RPE group showed smaller LNW (24.83 ± 1.99 vs. 26.18 ± 2.05) and IM was (50.17 ± 2.3 vs. 51.58 ± 2.83). The distance from HMP was also longer in the RPE group (15.69 ± 3.95 vs. 13.86 ± 3.4). There were no differences at T1 for the categorical variables (tonsils and adenoids removed, mouth breathing and difficulty breathing through nose) or tongue length. Mean changes (T2-T1) in the RPE group were increased lateronasal width +2.48±1.38 vs. +0.94 ± 1.11 for the non-RPE group and increased IM (+3.21 ± 1.72 vs. +0.98 ± 1.67). Mean change (T2-T1) in HMP for the RPE group was -0.68 ± 3.67 mm compared to a +1.1 ± 2.96 mm change for the non-RPE group. All mean changes were statistically significant except TL. At T2, there were no significant between group differences for LNW, HMP or TL.

Conclusions: In this sample, RPE produced statistically significant changes in HMP distance and did not affect TL.