Oral mucosal wetness in hypo- and normosalivators

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After a person swallows, a film of residual saliva covers the oral hard- and soft-tissue surfaces. Here, the thickness of this film was measured at 11 selected mucosal surfaces on each side of the mouth (22 sites total) in two groups of dry-mouth and one group of normal individuals. Each group contained 25 individuals; one of the dry-mouth groups had resting flow rates ≤0.1 ml/min while the other and the normal had flow rates above that. Residual saliva thickness was determined by placing frying-pan-shaped filter-paper strips (Sialopaper™) against the mucosa at each site for 5 s and measuring the saliva volume collected with a modified Periotron 6000® micro-moisture meter; the thickness was then calculated by dividing the collected saliva volume by the strip area. The two groups with dry-mouth symptoms had mean resting (unstimulated) saliva flow rates of 0.04 and 0.19 ml/min and mean mucosal saliva thicknesses of 22.4 and 27.8 μm, respectively. The control group had a higher mean saliva flow rate of 0.39 ml/min and mucosal saliva thickness of 41.8 μm. As was observed in a previous study on normo salivators, the various sites had a characteristic pattern of wetness, with the hard palate and lips the least moist regions. In this study, these observations were also true in the two dry-mouth groups. Lower resting saliva flow rates were associated with lower mucosal thickness of saliva and with dryness symptoms becoming evident when hyposalivation was below about 0.1–0.2 ml/min. The characteristic pattern of mucosal wetness was not affected by saliva flow rate. As saliva readily collects in the floor of the mouth and is then spread over other mucosal surfaces upon swallowing, it was suggested that hyposalivation could also lead to the dryness symptoms because there was not enough saliva to cover the various oral surfaces, especially the palate and the lips. In this regard, a critical level of moisture was proposed as necessary to protect vulnerable mucosal surfaces from becoming dry. Lower resting saliva flow rates and correspondingly lower mucosal wetness were also associated with a more acidic salivary pH, which was shown earlier to be associated with lower dental plaque pH.