Effect of the position of the hyoid bone relative to the oral cavity on occlusion and skeletal patterns

Abstract

Persistent problems involving the tongue, especially the root of the tongue, are often encountered in clinical orthodontics. We devised a method of measurement referred to as the perpendicular line passing upward from the hyoid bone to the palatal plane (PHP), which locates the root of the tongue in the oral cavity. We investigated the influence of the location of the tongue root in the oral cavity on denture and skeletal patterns in 51 adult Japanese females. Our results revealed that the greater the PHP value, the greater was the incidence of open bite with accompanying tongue thrust, and the greater was the probability that the person would be classified as having Angle Class Ⅰ bimaxillary protrusion. Conversely, the more negative the PHP value, the greater was the incidence of deep bite. These results indicate that location of the tongue root is closely related to the status of the maxillary and mandbular anterior teeth, and has a strong correlation with overbite. We therefore think that evaluation of the location of the tongue root using PHP values can contribute to determination of the appropriate orthodontic treatment of problems that are related to the tongue.