Effects of open mouth and rubber dam on upper airway patency and breathing.

OBJECTIVES: Rubber dams increase the quality and safety of dental treatment. However, the condition of a rubber dam over an open mouth may also obstruct the route for respiration. We tested whether an open mouth with or without a rubber dam would affect upper airway patency and breathing pattern. MATERIALS AND METHODS: Twenty young healthy volunteers were imaged with a magnetic resonance (MR) system under three conditions: mouth closed, mouth open, and rubber dam with mouth open. Respiration was concurrently monitored with plethysmography. MRI slices of the upper airway were obtained at 5-mm thicknesses, and the size of the cross-sectional area of the upper airway was measured by image analysis software. Respiratory cycle duration and tidal volume were also measured with digital signal analysis software. RESULTS: The volume of the upper airway became significantly decreased with the mouth open. Analysis of each cross-sectional area of the upper airway revealed that while the oropharyngeal area was significantly narrower with an open mouth, the retropalatal and hypopharyngeal areas were not affected. Placing a rubber dam had no additional influence on upper airway patency but was seen to significantly shorten mean respiratory duration and decrease tidal volume. CONCLUSIONS: Open mouth position plays the largest role in decreased upper airway patency, and open mouth position with a rubber dam may further disrupt breathing pattern. CLINICAL RELEVANCE: Breathing pattern may become deteriorated by airway obstruction during dental treatments requiring a rubber dam.

Effect of viscosity on food transport and swallow initiation during eating of two-phase food in normal young adults: a pilot study.

When eating food containing both liquid and solid phases (two-phase food), the liquid component frequently enters the hypopharynx before swallowing, which may increase the risk of aspiration. We therefore tested whether preswallow bolus transport and swallow initiation would change as the viscosity of two-phase food was increased. Fiberoptic endoscopy was recorded while 18 adult subjects ate 5 g of steamed rice with 3 ml of blue-dye water. Liquid viscosity was set at four levels by adding a thickening agent (0, 1, 2, and 4 wt%, respectively). We measured the timing of the leading edge of the food reaching the base of the epiglottis, as well as the location of the leading edge at swallow initiation. As viscosity increased, the leading edge of the food reached the epiglottis significantly later during chewing and was higher in the pharynx at swallow onset. The time after the leading edge reached the epiglottis did not vary among the viscosities of the two-phase food. This study found that the initial viscosity of two-phase food significantly altered oropharyngeal bolus flow and the timing of swallow initiation. Accordingly, increased two-phase food viscosity may delay food entry into the pharynx and be of use in dysphagic diets.