54 Chapter 3 Sialometry and salivary pH The patients were instructed not to eat, drink, chew gum, brush teeth, use mouthwash, or smoke at least 1 h before their visit to the saliva clinic. The salivary flow rate was determined as described in the following references [18, 19]. At the time of saliva collection, patients were placed in a quiet room and asked to sit in an upright position. The UWS was collected by the draining method in a pre-weighed plastic container [19]. Patients were asked to collect unstimulated saliva immediately after an initial swallow, by expectorating into the container as soon as they had collected the saliva in their mouth. During saliva collection, patients were not allowed to swallow. To collect CH-SWS, they were asked to chew a 5 × 5-cm sheet of parafilm (Parafilm M, Pechiney, Chicago, IL, USA) at a frequency of approximately 60 chews per minute and to expectorate into a pre-weighed plastic container every 30 s. To stimulate A-SWS secretion, a citric acid solution (2% w/v) was applied with cotton buds to the lateral borders of the tongue at 30 s intervals [20]. When the collection period had finished, the plastic containers were reweighted, and the collected volume was determined by subtracting the weight of the container before collection. Salivary flow was calculated by dividing the volume collected (assuming 1 g of saliva equals 1 mL) by the collection time (min). Salivary flow rates were expressed in mL/min [19]. To limit circadian variations, all patients were randomly assigned a time slot between 8:00 and 12:00 A.M. [21]. To determine whether patients suffered from hyposalivation, the following cut-off values were used: UWS < 0.10 mL/min, CH-SWS < 0.70 mL/min, and ASWS < 0.70 mL/min [1]. The pH of saliva was measured immediately after saliva collection, within 5 min to minimize loss of CO2 to the atmosphere. The saliva pH was measured with pH paper (Merck KGaA, Darmstadt, Germany). Data analysis The data were processed in Microsoft Excel and then converted into SPSS, version 25.0 (IBM Corp SPSS statistics, Armonk, NY, USA) for the statistical analysis. The Shapiro– Wilk test was used to assess the normality of the data. As not all variables were normally distributed, the data were presented as medians with their interquartile range (IQR). To clarify relatively small differences, the mean and standard deviation (SD) were also reported. A Friedman test was conducted for the RODI scores of the total study sample, followed by a Wilcoxon signed-rank test as a post hoc procedure.
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