Using the Mann–Whitney U test, a comparison was made of the mean mucositis grade of both case and control groups at similar weeks. Mann–Whitney’s analysis showed that the mean mucositis grade has a signifcant statistical diference between the two groups from the 7th session of OE onwards. The present study results showed that the mucositis grade in the frst and second sessions of OE in both case and control groups was similar. The mucositis grade difered between the two groups from 3 to 7th session of the OE, but this diference was not statistically signifcant (p > 0.05). The mucositis grade of both groups after the 7th OE session was statistically signifcant (p < 0.05). Mucositis grading was signifcantly diferent in the case and control groups from the seventh OE session to the 30th session of OE (Table 2). Mucositis grade in the synbiotic group was signifcantly lower than in the normal saline group (p < 0.05). These results show that mouthwash containing synbiotic strains signifcantly reduces the incidence of grade 3 OM.