LAUSR

Abstract Background The number of persons with difficulty in mastication and swallowing is increasing and causes a social problem. Commercially available soft gels for disadvantaged persons are known to be crushed between the tongue and the hard palate, but the detailed mechanism is not well understood. Scope and approach After reviewing the safety and difficulty in eating, the significance of the tongue pressure is discussed. To avoid the complexity of the simultaneous action of the teeth and the tongue, squeezing with the tongue without teeth is studied. Squeezing of gels with different deformabilities between the tongue and palate is analyzed using an ultrathin sensor, and compared with the in vitro test using an artificial tongue and panellists’ judgements of the strategy change from tongue-palate compression to chewing. Key findings and conclusions It was clarified that the work of the tongue just before swallowing depends not only on the initial mechanical properties of foods but also on the oral processing before the swallowing. This poses a question on the prevailing view that the final mechanical properties just before swallow does not depend on the initial mechanical properties of ingested foods. The transition of the strategy from the tongue-palate squeezing to the teeth chewing was shown to be determined using an artificial tongue compression approach in combination with sensory evaluation to select the strategy. These findings can be a basis for understanding better the conditions necessary for designing food gels. The tangential force during squeezing should be analyzed in the future.