Relationship Between Submental Superficial Layer Hardness and Tongue Pressure Determined Using a Tissue Durometer

Aging affects the tongue and suprahyoid muscles, causing dysphagia and undernutrition. We hypothesized that tongue function would affect submental superficial layer hardness. Tongue movements during water retention between the tongue and palate are the same as those required during bolus formation, involving internal and external tongue muscle movement. In 28 healthy adults (14 males, 14 females, average age 28.7 ± 2.9 years), we measured the submental superficial layer characteristics (frequency [tension], stiffness, decrement [inverse of resilience], relaxation, and creep [deformation over time]) using a simple tissue durometer (MyotonPRO^®), and examined their relationship with maximum voluntary tongue pressure. The tissue durometer sensor was placed in the submental region, where there is no intervening bone. Measurements were performed at rest and while retaining 5 mL water. Tongue pressure was measured using a tongue pressure-measuring device. The submental superficial layer hardness differed significantly between rest and during water retention. During water retention, frequency and stiffness were high, while decrement, relaxation, and creep were low. When pressure is applied to the palate, such as during water retention the inner tongue muscle, which changes the tongue's shape, and the outer tongue muscle, which moves the tongue laterally, are active. However, the change in the hardness of the submental superficial layer during water retention may be related to the suprahyoid muscles that are present in this layer. The results of this study suggested that the hardness of the submental superficial layer changed during water retention, and that tongue movement could be measured from outside the mouth.