Data analysis
As for the RCT, all statistical analyses were performed using SPSS software v25.0 (SPSS Inc. New York, NY, USA). Description of the subjects was carried out by descriptive statistics. Shapiro-Wilk test was used as a normality test. Wilcoxon Signed Ranks was used to compare the quality-of-life scores between before and after intervention in CMC and trehalose group. Mann-Whitney U test was used to compare the quality-of-life before-after difference scores between both treatment group. Chi-square test was used to compare the percentage of cases with concomitant chemotherapy between both treatment group. Independent T-test was used to compare the means of duration (month) post treatment and the means of parotid gland mean doses between ipsilateral and contralateral sides in each intervention group and between trehalose and CMC solution spray groups, unstimulated salivary flow rate and salivary pH between trehalose and CMC solution spray groups. Paired T-test was used to compare unstimulated salivary flow rate and salivary pH pre- and post-intervention in each treatment group. The significance level was set at 5%.