السواك
A twig from the arak (Salvadora persica) tree, chewed and brushed against the teeth and gums as a recommended daily — even pre-prayer — hygiene practice.
لَوْلَا أَنْ أَشُقَّ عَلَى أُمَّتِي لَأَمَرْتُهُمْ بِالسِّوَاكِ عِنْدَ كُلِّ صَلَاةٍ
“Were it not that it would be difficult for my community, I would have commanded them to use the tooth-stick before every prayer.” (meaning, not a literal translation)
'A'ishah reported he would begin with the miswak on entering his home, and would clean his mouth with it on waking at night (Sahih Muslim; Sunan an-Nasa'i).
Ibn al-Qayyim and later dental researchers alike note the arak twig's natural antibacterial compounds; the practice is now studied as an early precedent for regular mechanical tooth-cleaning.