The Prophet (SAWA) said in his advice to Imam Ali (AS), 'One must brush his teeth at every ablution. O Ali, one must brush his teeth as frequently as possible, for verily a single prayer that one performs after having brushed his teeth is better than forty days worth of prayers performed without doing so. (Bihar al-Anwar, v.76, p.137, no.48)
He also said: "Jibra'il continuously advises me about brushing teeth, that I really thought he would lay it down as an obligation (WAJIB)."
Imam al-Sadiq (AS) said, 'You must brush your teeth for it removes whisperings of the heart.(Bihar al-Anwar, .76, p.139, no.52)
Imam al-Sadiq (AS) said,
'There are twelve distinctive features to brushing one's teeth: it is a recommended prophetic practice, it purifies one's mouth, brightens...