Elusive Source of Tooth Pain

People may be notoriously bad at pinpointing which tooth is aching because, to the brain, a painful upper tooth feels a lot like a painful lower tooth, according to a new study.

It's more difficult for the brain to distinguish between different areas of pain in the mouth than in any other part of the body, according to a study set to be published in the journal "Pain." Researchers led by Clemens Foster, Ph.D., of the University of Erlangen-Nuremberg in Germany analyzed brain activity in healthy volunteers as they experienced tooth pain.

The researchers delivered short electrical pulses to either the upper left canine tooth (the pointy one) or the lower left canine tooth. The bursts produced a painful sensation similar to if the subjects bit into an ice cube.

The level of the bursts were tuned so that the subject always rated the pain to be about 60 percent, with 100 percent being the worst pain imaginable. To see how the brain responded to pain emanating from different teeth, the researches used fMRI to monitor the changes in activity when the upper or lower tooth was zapped.

"At the beginning, we expected a good difference, but that was not the case," Dr. Forster said.

Many brain regions responded to top and bottom tooth pain — carried by signals from two distinct branches of a fiber called the trigeminal nerve — in the same way. Separate regions in the brain's cerebral cortex, known to play an important role in the pain projection system, behaved similarly for both toothaches.

"Dentists should be aware that patients aren't always to locate the pain," Forster said. "There are physiological and anatomical reasons for that."

Forster did state that the experiments might have missed subtle differences that could account for why some tooth pain can be localized.

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