It was narrated from Abu Umamah that:
The Messenger of Allah said: "Use the tooth stick, for the tooth stick purifies the mouth and is pleasing to the Lord. Jibril never came to me but he advised me to use the tooth stick, until I feared that it would be made obligatory for me and my Ummah. Were it not that I fear that it would be too difficult for my Ummah, I would have enjoined it upon them. And I use the tooth stick until I fear that I may make the front of my mouth sore.' (i.e. my gums) (or cause my teeth to fall out due to brushing them so often)."
English reference: Vol. 1, Book 1, Hadith 289
Arabic reference: Book 1, Hadith 304