FAMILY MEDICINE® COLUMN
By John C. Wolf, D.O.
Associate Professor of Family Medicine®
Ohio University College of Osteopathic Medicine

[POTASSIUM NITRATE IN TOOTHPASTE NOT CAUSE OF READER'S LEG PAIN]

Question: I used Sensodyne toothpaste for about one and one-half years for my sensitive teeth and gums. I read on the box of a new tube the other day that the manufacturer suggests this product should not be used for more than four weeks, so I stopped using it. I had been having vague calf pains for several months, and now a few days after switching to a "regular" toothpaste, the pain seems to have gone away. Could my leg pain be due to the toothpaste? The major ingredients are potassium nitrate and sodium monofluorophosphate. Perhaps the nitrate works like nitroglycerin.

Answer: Sensodyne contains 5 percent potassium nitrate. This chemical is responsible for the relief of tooth and gum pain. It is not clear exactly how potassium nitrate provides relief, but it probably works by interfering with the activity of pain nerves in the gums and teeth. The sodium monofluorophosphate is present to reduce the risk of cavities.

I don't think that your toothpaste has been responsible for your leg pain, and this is why. First, while the drug reduces tooth pain by being absorbed through the gums, the relative concentration within the blood in that area is substantially less than in the tissue in that area. This blood is then mixed with blood from the rest of the body before it is pumped by the heart to the legs. This dilution makes it unlikely that the potassium nitrate would be of sufficient strength to have any impact on the nerves or muscles of the legs. In addition, if it relieves pain in the teeth, why would it cause discomfort in the legs?

The nitroglycerin you mentioned is used to cause dilation of arteries, particularly the coronary arteries. (These are the arteries that supply the heart muscle.) The drug is used to treat those with angina pectoris and other heart conditions. Nitroglycerin is different in chemical structure from potassium nitrate and also in the way the body uses it. Further, I would not expect that dilation of the leg arteries would cause discomfort.

Assuming that there is always a cause-and-effect link between two events that occur in proximity to one another is a very common error. This type of assumption leads to many incorrect beliefs and even to superstitions. As an example, do you know someone with a ėlucky hatî or similar object? Usually the person hit a home run, had a great golf game or some similar positive experience that they link to the wearing the ėlucky hat.î The hat did not cause the ėgreat game,î but the person now feels wearing it is necessary to have another ėgreat game.î Your leg discomfort disappeared because of something other than changing toothpaste or wearing your ėlucky hat.î

Family Medicine® is a weekly column. To submit questions, write to John C. Wolf, D.O., Ohio University College of Osteopathic Medicine, Grosvenor Hall, Athens, Ohio 45701.