Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah (PBUH) said, "Had I not thought it difficult for my Ummah, I would have commanded them to use the Miswak (tooth-stick) before every Salat."[Al-Bukhari and Muslim].
We learn from this Hadith that the Prophet (PBUH) liked to clean his teeth with Miswak (a softened stick used as tooth brush for cleaning the teeth) with every Salat, but he did not made it obligatory for the reason that it would be inconvenient for his followers. It shows that he was extremely affectionate and kind to his Ummah.
This Hadith also shows that using Miswak is an admirable act. Every Muslim should make it a routine to use it as frequently as possible especially before performing prayers.