Myrrh is widely considered to be one of the most effective substances for sore gums by herbalists and by practitioners of Chinese medicine. Even in the west it is renowned for its astringent and antiseptic properties as well as for promoting healing
It is so antiseptic that it was used for embalming and mummifying Egyptian Pharaohs; ancient Greek soldiers would carry it into battle to treat wounds and prevent gangrene. As an astringent and healing agent it was considered more valuable than gold during the storied time when the Magi brought it after the birth of Jesus.
Myrrh is the resin of a prickery bush (commiphora molmol) that grows up to nine feet tall in the arid Horn of Africa and southern Arabian Peninsula. A little bit goes a long way, so usable quantities could be carried by donkeys, camels and other pack animals along ancient trade routes that fanned out from the middle east. Its healing powers made it prized by royalty, nobles and wealthier people from Greece to India. Cultivation has extended its growth range, and it's estimated that current stocks of the plants are enough to fill the world's demand for myrrh.
In addition to its antiseptic, antimicrobial and astringent properties, it has used by people wishing to stimulate circulation in mucous membrane tissue (which includes the gums). It has historically been used by itself for swollen or spongy gums as well as for canker sores, sore throats and sinus infections.