Māṇḍūkī Śikṣā 39

39

vāgyataḥ prātaruttthāya bhakṣayeddantadhāvanam
tenāsyakaraṇaṃ sūkṣmaṃ mādhuryaṃ copajāyate

having risen in the morning and restraining his speech, he should chew a tooth-stick; / through that, the articulatory organ of the mouth becomes refined, and sweetness arises.