Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:There is a significant increase in the levels of cariogenic bacteria in the saliva and plaque of patients undergoing fixed appliance treatment.(21,22) However, during the initial phase of caries growth, S mutans is the most frequently associated microorganism.
Category: