Oral behavior from food intake until terminal swallow.

We analyzed oral behavior from food intake until terminal swallow for mastication and swallowing under a freely eating condition with a natural food. Measurements, including movement of the mandible and tongue, the size of the gape, different sequences involved in the oral aspect of the swallowing action, and bolus size and movement were carried out in five "freely eating subjects" using videofluorography. During food intake, the tongue moved forwards and backwards to introduce food into the mouth, to compress the food against the hard palate, and to transport food to the occlusal surface of the molar teeth. Most of the food was swallowed in the first swallow, and any residual food was aggregated by the tongue into a bolus and then swallowed in the last swallow. These findings suggest that 1) tongue manipulation plays an important role in recognizing and evaluating the volume of bite taken, 2) the intra-oral compression of food has a role in the recognition of food texture, 3) stage I transport is closely bound to the texture recognition process, 4) humans need at least two swallows, even with one bite of food, when ingesting food freely, and 5) the duration time of the oral stage of swallowing may depend on the bolus volume and be longer for smaller volumes unlike those measured under the command swallow.