35 Regional differences in perceived oral dryness Possible relationships among the RODI scores of the nine intra-oral regions, and the relation of the RODI scores with XI scores, UWS, CH-SWS, and A-SWS salivary flow rates were analyzed with a bootstrapped Spearman rank correlation test (1000 × bootstrapping). The Spearman’s rho coefficient and bias-corrected accelerated (Bca) 95% confidence interval were extracted. A significance level (α) of 0.01 was chosen for the correlation test. The Mann-Whitney U test (significance level of α = 0.05) was performed to explore a possible relation between a positive CODS score and the associated region in the RODI. RESULTS A total of 337 patients participated in this study with an average age of 54 ± 17 years. The majority of the patients were female (68.5%). The RODI scores, XI scores, CODS and UWS, CH-SWS, and A-SWS salivary flow rates were not normally distributed (Shapiro–Wilk test; p < 0.01). Table 1 presents the different salivary flow rates of the study sample. Based on the UWS, CH-SWS, and A-SWS flow rates, respectively, 26.9%, 48.6%, and 13.1% of the study sample respectively suffered from hyposalivation. Regional Oral Dryness Inventory In Table 2, the median and the corresponding IQR, and mean with standard deviation are shown for each of the nine intraoral regions of the RODI. There was a significant difference in perceived oral dryness between the nine intraoral regions (Friedman test p < 0.05, followed by Wilcoxon signed-rank tests p < 0.05). The highest scores were obtained for the posterior palate, while the lowest scores were obtained for the floor of the mouth (Table 2). The scores of all regions correlated significantly with each other (Table 3) indicating that patients who suffer from severe xerostomia at one location in general also have high levels of xerostomia at other intra-oral locations. The correlation coefficient varied between 0.51 (pharynx with lower lip) and 0.82 (lower lip and upper lip). Four different regions have a correlation coefficient ≥ 0.75: the lower lip and upper lip, the posterior palate and posterior tongue, the anterior tongue and posterior tongue, and the floor of the mouth and inside the cheeks. The correlations of the scores between these four regions can be considered strong, whereas the other regions have a moderate correlation according to the standards described by Mukaka and co-workers and Akoglu and co-workers [31, 32]. 2
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