Purpose: There is little information available regarding swallowing tongue dynamics in cases that show remarkable discordance in the relationship between the upper and lower jaws. In this study, we measured the tongue motion during swallowing by ultrasonography in patients with mandibular prognathism and compared them with volunteers with normal occlusion.
Methods: The subject group comprised 10 patients with mandibular prognathism （6 males, 4 females）. Ten volunteers with normal occlusion （2 males, 8 females） served as controls. The subjects were instructed to swallow about 4ml of tasteless jelly, and the tongue movement during swallowing was measured by ultrasonography. We measured the following times on the M-mode waveform in the center of the tongue, “Duration of grooving formation （T1）”, “Duration of grooving disappearance （T2）”, “Duration from grooving disappearance until tongue-palate contact （T3）”, “Duration of tongue-palate contact （T4）”, “Duration of return to rest （T5）” and “Total swallowing duration （T6）”. In the periphery of the tongue, we measured “Total swallowing duration （T7）” and qualitatively assessed the tongue waveform as well.
Results: In the center of the tongue, T3, T5 and T6 were significantly longer in the subject group than in the control group. In the periphery of the tongue, T7 was also significantly longer in the subject group than in the control group. The tongue position of patients with mandibular prognathism tends to be low, so a longer time was necessary to lift the tongue to the palate and the anchoring effect of the contact between the tip of the tongue and the anterior palate became weak. Due to this, a longer swallowing time at the periphery of the tongue was possibly needed in the subject group. Further, the type of tongue movement seems to have been specialized because of frequent up-and-down movement of the tongue during swallowing.
Conclusions: The present findings suggest that patients with mandibular prognathism, due to their morphological disharmony, need excessive time to lift the tongue surface to the palate, resulting in a longer swallowing time at the periphery of the tongue as well as a specialized tongue movement.
