A Miswaq toothbrush is an organic toothbrush which was used by the prophet and salaf.
Siwak is a method of cleaning the mouth which also earns the pleasure of Allah, as is proven in the hadith of ‘Aishah (may Allah be pleased with her) who said: The Messenger of Allah (peace and blessings of Allah be upon him) said, Siwak cleanses the mouth and pleases the Lord. (Reported by al-Bukhari in his Sahih, 2/274, and by Ahmad, 6/47, and al-Nasai, 1/50. Its isnad is sahih, see al-Irwa 1/105)