Shiva Purana
अग्रेण तस्य मृदुना प्राङ्मुखो वाप्युदङ्मुखः ॥ वाचं नियम्य चासीनश्शिष्यो दंतान्विशोधयेत् ॥ ३७ ॥
The disciple shall sit silently facing the east or the north and clean his teeth with its soft tip.
english translation
agreNa tasya mRdunA prAGmukho vApyudaGmukhaH ॥ vAcaM niyamya cAsInazziSyo daMtAnvizodhayet ॥ 37 ॥
hk transliteration by Sanscript