66 Chapter 3 concentrations of sodium, chloride, and phosphate [20]; a higher protein concentration on the palate [37]; a significantly reduced saliva film on the hard palate; a reduced spinnbarkeit of UWS; and an altered glycosylation of salivary mucins [38]. In conclusion, a drier mouth could be induced in SS patients when altered rheological properties of saliva, reduced mucosal hydration (due to a reduced saliva film), and altered glycosylation combine to cause functional loss of the salivary coating and the lubricating properties of saliva [38]. Low Med and High Med patients experienced the anterior tongue as the most dry. Other studies reported that the thickness of saliva film on the anterior tongue was significantly less in dry-mouth patients—including those with medication-induced hypofunction—than in healthy controls [28, 31, 37, 39]. The saliva-film thickness on the anterior tongue was approximately half of that in controls. In some dry-mouth patients who could not secrete unstimulated saliva, it was even less than that [28]. This finding was confirmed by another study that indicated that oral mucosal wetness varied with the resting salivary flow rate; the lower the flow rate, the thinner the salivary film [27]. Thus, xerostomia was apparent when the salivary flow rate was half of its normal value [9, 40, 41]. Reduction of the salivary flow rate and thereby a reduced salivary film thickness on the anterior tongue might therefore explain why Low Med and High Med patients experienced the anterior tongue as the most dry. Besides, the threshold for perceiving dryness is about ≤ 10 μm—the same as that seen in the study of Lee and co-workers [28]. The significantly lower salivary flow rates in High Med patients than in controls (Table 4) may have induced a very low saliva-film thickness on the anterior tongue below this threshold, thereby causing dryness of the tongue. Some of the controls in our study had a low salivary flow rate and at times even had hyposalivation of UWS and CHSWS (Table 4). Explanations for this may lie in these participants’ age and the possibility that participants had systemic disorders other than Sjögren’s syndrome that were associated with salivary dysfunction. The salivary flow rate in older people, even those not using systemic drugs, was significantly lower, especially in non-medicated women in the 45–54 age groups [42]. This finding corresponds with the mean age in our control group (50.6 ± 17.7 years), in which most participants were female (64.2%). Other systemic conditions such as endocrine disorders (diabetes mellitus), neurological disorders (Parkinson’s disease), and metabolic disorders (dehydration) have also been associated with a lower salivary flow rate [1]. Within our study sample, the SS and SS + High Med patients had the lowest salivary flow rates and a reduced pH of A-SWS: proof of hypofunction of the
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