Traditionally people use clove oil (2-4 drops) to do the mouthwash in 1/4 glass of water will work better as clove has a numbing effect and kill the bacteria also. Dentists also use the clove oil applied directly using appropriate devices, to the area of cavities. Often 1% hydrogen peroxide with baking soda, for me works the best in preventing cavities from getting any larger. However, if the mouth has high number of bacterium, using them a couple of times is helpful. I do it say 2-3 times. The cavities tooth pain goes away quite quickly. The key is to make sure there is no food residue after eating, which means a peroxide mouthwash is to be done after eating of every meal.
The use of either black tea bag, or a green tea (no sugar, no fructose, no milk) is a broad spectrum antibiotics.
Sometimes, if my budget is limited, I mixed a 1/8 teaspoon of tannic acid in 1/2 glass of water to do the mouthwash, with frequent swishing of course! They work too, of course, whenever I don't have green tea or 1% hydrogen peroxide at my home.
In the long run, the key is to make sure the saliva pH exceeds 7 or at least 7. Cavities don't form if the saliva are at this level. It seems drinking green tea occasionally caused the saliva gland to worked better and raising the pH can be done with baking soda 1/4 teaspoon taken twice a day helps a lot in prevention. It must be noted that peroxide reduce the bacteria, but baking soda prevents the bacteria in the mouth from growing (that and no food particles and sugary food).
In other times I can do 2-4 drops of iodine in 1/2 glass of water as a good mouthwash also. It prevents iodine deficiency when this is done occasionally, such as once a week, for example."
04/22/2006: Ted from Bangkok, Thailand writes: "The best cure I can think of for a tooth abscess that helped me is when I mixed a 1/4 teaspoon of potassium carbonate into 1/2 glass of water and use this as a mouthwash. Do it three for four times should reduce the pain in a couple of hours. Basically a relatively strong alkaline solution will usually destroy the bacteria. At least it really helped with my cavities pains.
Also I sometimes mixed sodium perborate also (after dissolving it which takes an hour in water!) keeps my teeth free from the abscess also. If you can't find potassium carbonate, a good alternative might be sodium carbonate, however, I think you might need a little less. Ideally a sodium perborate and potassium carbonate should do the trick. I have also resorted to using H2O2 1.5% as a mouthwash now and then just to be sure also.
However, a longer term solution of taking some vitamin B3 in particular plus a B complex vitamins will help reduce it too. If everything works out as expected, some improvement should be noticed within the next day. The theory is basically simple, the bacteria in your mouth has a weakness against alkaline, for the very same reason why they cause cavities by creating acid to dissolve your tooth enamel which causes tooth abscesses whenever they too get into your gums. Flossing also helps in later stages also. However, if the condition still persist it is best to see your dentist. Oh yes, by the way, take a fairly large daily dose of vitamin C also as it is also helps with tooth abscess, such as 1-2 grams (1000-2000 mg) per day. This will also really help relieve the conditions of fibromyalgia if taken together with magnesium and malic acid (apple cider vinegar is high on malic acid).