124 Chapter 6 p > 0.05). Besides, the two palatal dimensions (small vs. large surface area) did not have any significant correlation with the salivary film thickness and/or MUC5B levels of the palate as well (Pearson correlation p > 0.05). A multivariate regression analysis was performed, taking the palatal surface area, sex, the UWS and CH-SWS flow rate into consideration. For both the anterior and posterior salivary film thickness, no association was found with any of the independent variables (regression p > 0.05). The R squared for the anterior palate was 0.19 and for the posterior palate 0.09. So, the palatal surface area did not affect the salivary film thickness on either the anterior or posterior palate. The same applied to all other independent variables. DISCUSSION The results of this study, in which we explored the salivary film thickness and MUC5B levels at various locations in the oral cavity in healthy volunteers, demonstrated that both are unequally distributed over the various intra-oral surfaces. The anterior tongue had the thickest salivary film and contained the highest levels of MUC5B, while the anterior palate had the thinnest salivary film and lowest MUC5B levels. Furthermore, the palatal surface area did not correlate with the palatal salivary film thickness or the palatal MUC5B levels, indicating that in healthy individuals, a larger surface area was not associated with a relatively thinner salivary film and/or lower MUC5B levels. Therefore, our hypothesis should be rejected. The mean UWS flow rate of the included participants was 0.28 mL/min, which was comparable with the average values of 0.3–0.4 mL/min previously reported [42]. The median XI score was 19.5, indicating that included participants on average did not experience serious dry-mouth complaints. The current XI scores were comparable with the XI scores found in other studies with healthy volunteers (age from 18 to 92 years), ranging between 16.0 and 20.82 [43–49]. Also, the RODI scores for all intra-oral locations were < 2, indicating they did not experience any intra-oral dryness. Dry-mouth patients in previous studies showed RODI scores ≥ 3 for most intra-oral locations [9, 10]. So, although the salivary flow rate seems to deviate slightly from earlier reports, it can be stated the included volunteers had healthy salivary flow rates and experienced no dry-mouth complaints. The average palatal surface area found was 2123.8 mm2, which was comparable with other studies, who included adults with an average of 1990–
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