Saliva sample collection and salivary flow rate measurement

Saliva samples were collected between 9:00 a.m. and 12:00 p.m. to minimize circadian variability. Eating and drinking were prohibited for 2 hours prior to saliva sampling. After saliva collected for the first 2 min was discarded, unstimulated whole saliva was collected by drooling saliva passively into a tube at least for 15 min or until 10 ml was collected. Salivary flow rate was calculated based on the amount collected during the first 15 min. Salivary flow rate was recorded as mL/min. The unstimulated whole saliva samples were stored at −80°C until sent to the sequencing facility.