A Mechanical Simulator of Tongue–Palate Compression to Investigate the Oral Flow of Non-Newtonian Fluids

Understanding oral processing is of great interest for the food and drink industry, and for many groups of people who have difficulties in eating and drinking it is of critical importance for their health and quality of life. This paper describes a simulator which bridges a gap in experimental capability between idealized laboratory-based materials-characterization studies and human investigations, which lack detailed objective measurement. This novel in-vitro mechanical oral simulator was constructed to simulate the in-mouth compression of a bolus of food or thick drink between the tongue and hard palate. Tongue compliance was matched to physiological values. A stepper motor-controlled platform reproduces motion of the tongue to compress a fluid bolus against a palate, propelling it posteriorly. The palate surface contains five pressure transducers. Internal bolus flow is imaged using a laser-lit particle image velocimetry system at 1000 frames per second. Each component of the simulator was calibrated. Example results are included from a case study demonstrating differences in pressure-flow characteristics between two model food materials created with starch and gum. Consistent with the invivo studies, pressure was higher anteriorly (bolus tail) than posteriorly near ejection into the oropharyngeal space. Bolus transport, with intrabolus shear rates 0-40 s
^-1
, required relatively low tongue pressure: 0.5-1.4 kPa for both the boluses. However, clearing the bolus (<;0.5 mm residual coating) required much higher pressure (5.4 versus 1.7 kPa), for example, starch-based material versus the gum-based sample despite both having equal apparent viscosity of 0.47 Pa.s at 50 s
^-1
. The simulator has, thus, demonstrated the ability to quantify how rheologically different materials may behave differently within the mouth.