This one's an old at-home remedy, and it's completely false -- you should never put aspirin directly on or near an aching tooth. After all, you wouldn't put aspirin on your forehead if you had a headache, would you?
The only safe and effective way to take an aspirin tablet is to swallow it. When you swallow aspirin, it gets absorbed into your body through your digestive tract. It then enters your bloodstream and travels throughout your body. Aspirin works by stopping the production of prostaglandins, molecules that send pain messages from the injured part of your body to your brain. When the aspirin reaches your aching tooth, it inhibits prostaglandin production there, reducing the pain you feel [source: National Institutes of Health]. So even though it may be tempting to bypass the digestive process by putting the aspirin directly on your tooth, it just doesn't work that way.
Need another reason to put this ineffective rumor to rest? Placing aspirin directly on the aching tooth or your gums can cause an acidic chemical burn to your gums and lips. So if the pain of a toothache isn't bad enough, you'll have to deal with more pain when the aspirin leaves a sore in your mouth [source: Fries].