Evaluation of the change in the tongue posture and in the hyoid bone position after Twin Block appliance therapy in skeletal class II subjects.

Abstract

The tongue is posteriorly postured in a retrognathic mandible, and Twin Block appliance (TBA) therapy places the tongue and the hyoid bone in a favorable position to eliminate the risk of causing respiratory obstruction. The aim of this study was to evaluate the change in the tongue posture and in the hyoid bone position after TBA therapy. This cross-sectional study was conducted using the pre-functional (PF1), postfunctional (PF2) and post-treatment (PT) cephalograms of 30 growing subjects. The tongue posture at 6 distances and the hyoid bone position with 4 parameters were digitally measured using the Rogan-Delft View Pro-X® software. A digital vernier caliper was used to determine the inter-canine and inter-molar widths on the dental casts. The Wilcoxon signed-rank test was used to compare the PF1 and PF2 values, and the PF1 and PT values. The comparison of the PF1 and PF2 values showed significant differences in the tongue posture at distances 1-5. In the case of the hyoid bone, only the linear distance from the sella (S) to the most anterior point on the hyoid bone (H) - the SH distance - revealed a significant difference (p < 0.01). The change in the tongue posture and in the hyoid bone position achieved at the PF2 stage remained stable at the PT stage. Significant differences occurred in the PF1 and PF2 maxillary and mandibular inter-canine and inter-molar widths (p = 0.01 and p = 0.04, and p < 0.01 and p = 0.02), respectively. Twin Block appliance therapy resulted in the advancement of the mandible with a lowered posturing of the tongue. The hyoid bone was displaced inferiorly after TBA therapy, whereas the angular position of the hyoid bone remained unchanged.