Data collection
STERILE
Before saliva collection, participants rinsed with 5 mL of water. Before and after the intervention, participants were asked to expectorate for a maximum of 3 min into a 50-mL sterile centrifugation tube (Creative Biotechnology, Taipei, Taiwan). The collected specimens were immediately placed in a portable ice box for storage and sent to a laboratory for same-day bacterial DNA extraction. The volume and weight of each saliva sample were recorded.