The addition of a starch or gum-based thickener to patient fluids with dysphagia is commonly carried out, but the mechanism behind the efficacy of this treatment is not fully understood. This paper describes the rheological behavior of two commercially available thickening powders and an additional xanthan gum solution with a view to explaining the efficacy of thickened fluids in terms of their rheology. Both linear viscoelastic and steady shear data were obtained for the fluids together with filament extensional stretch, decay, and breakup data. In order to follow the behavior of the fluids in a processing situation, a mechanical "Cambridge Throat" was designed and tested. The action of the tongue was modeled using a constant torque cam that forced fluid contained within a flexible membrane through a model throat. Movie photography captured images of the fluid behavior and showed that for a constant tongue torque, the transit time within the model throat increased with increasing fluid viscosity, with implications for the time available for the successful function of the larynx, throat muscles, and epiglottis. V

Background: Clear aligner therapy (CAT) is a prominent orthodontic treatment option. CAT was formerly only used to treat mild malocclusions, but with developments in technology, it can now treat much more complex malocclusions. With the increasing popularity of CAT and technological improvements, led to the development of Invisalign's SmartTrack technology, the first commercially available aligner material that used multi-layer plastic to facilitate tooth movement. Multiple layers provide superior mechanical properties that eluded previous single layer plastics. Aim: To study the cytotoxicity properties of different thermoplastic multilayer clear aligner materials on human primary gingival fibroblasts (HGFs). Materials and methods: Three multilayered clear aligner materials were considered in this study: SmartTrack (Align Technology, San Jose, CA, USA), Zendura FLX (Bay Materials, Fremont, CA, USA), and ComfortTrack (Great Lakes Dental Technologies, Tonawanda, NY, USA). The samples were incubated at 37 o C in DMEM (0.1 mg/mL) for 21 days. The cell viability of HGFs cultured with each sample medium was then compared to a negative control assessed by MTT assay. Results: The results showed slight toxicity for each one of the samples tested. The highest cytotoxicity level seen in the HGFs was SmartTrack (65.5% ± 2.5 of cell viability), followed by Zendura FLX (72.3% ± 8.6), and the least was observed by ComfortTrack (80.8% ± 2.1). Conclusion:The Under the experimental conditions of the study, all of the materials tested displayed slight levels of cytotoxicity. SmartTrack was measured as the most cytotoxic. There were no statistical differences found between the three aligner materials (P< 0.05).