Messenger of Allah ﷺ said, "Were I not afraid that it would be hard on my followers, I would order them to use the siwak (as obligatory, for cleaning the teeth).
أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لَوْلاَ أَنْ أَشُقَّ عَلَى أُمَّتِي لأَمَرْتُهُمْ بِالسِّوَاكِ