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

Abu Burda narrated, “My father (Abu Musa) said, ‘I came to the Prophet [sallal laahu alayhi wasallam] 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'”.

Benefits From This Hadeeth:

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. [Ref 1]

More about benefits of Siwaak, listen here:

The Virtues Of The Siwaak By Shaikh Abdul Waahid [Abu Khadeejah]

https://www.salafisounds.com/the-virtues-of-the-siwaak-by-abu-khadeejah/

The Siwaak – [Ustaadh Abu Humayd- Saalim]

https://learnaboutislam.co.uk/2017/08/08-explanation-fiqh-abu-humayd-saalim-manchester/

[Ref 1: Saheeh Al-Bukhaari. Hadeeth Number 244. Excerpt from ‘Faithful Baari 1/462-463. Publisher: Daarus Salaam 1st edition 1421AH (2000)]