The bacteria that proliferates in your mouth, or any other place of your digestive track, is unexpectedly associated with many diseases, from heart valve damage, arthritis, to death. That applies to the "good" bacteria too - it's good only while it stays in your digestive track, where the immune system keeps it in check. One can even die if the bacteria from a tooth cavity gets in your blood stream, although that is rare. Bacteria species common to your digestive tract or skin can be deadly if they get access to the blood stream. This is shocking and the public is oblivious about it.
I recently looked into probiotics designed to populate the mouth to displace the "bad" bacteria, but was put off by Amazon reviews claiming that they got sore throats from the probiotics, which is a red flag for immunocompromised people.
The studies on those probiotics weren't very convincing against gum disease either - they always combine them with dental cleaning and a lot of the studies show unadvertedly a larger effect from dental cleaning followed by chlorhexidine antibiotic treatment of the gums.
There were chlorhexidine mouthwashes in the past, but they were discontinued, due to concerns about the bacteria developing resistance and also chlorhexidine tints the tongue and teeth brown.
The current alternative are mouthwashes with 1.5% Hydrogen Peroxide, which you can easily do yourself by diluting cheap 3% Hydrogen Peroxide.
A "natural" antibiotic for the mouth is Propolis - the resin that bees gather from trees and buds to protect the hive from pathogens. It is shown in studies to kill some bad bacteria and fungi in the mouth. Just add 5 drops of Propolis to your toothpaste every time you brush your teeth.
