In The Name of Allah, The Most Merciful, The Bestower of Mercy.

Abu Burda narrated, “My father [Abu Musa – may Allah be pleased with him] said: “I came to the Prophet [peace and blessings of Allah be upon him] and saw him carrying a Siwaak in his hand and cleaning his teeth, saying, ‘U’, ‘U’, as if he was retching while the Siwaak was in his mouth”.

It is legislated to use the Siwaak on the tongue for a longer time. As for the teeth, what is more desired is that the Siwaak is made to come into contact with them widthways – across the mouth. Siwaak is not specified for use on the teeth only. (1)

Listen here: The Virtues Of The Siwaak By Shaikh Abu Khadeejah [may Allaah preserve him]: https://www.salafisounds.com/the-virtues-of-the-siwaak-by-abu-khadeejah/

[1] Sahih Al-Bukhari. Number 244. Excerpt from ‘Faithful Bari 1/462-463. Publisher: Daarus Salaam 1st edition 1421AH (2000)]