Brain unable to localise tooth pain
ERLANGEN/LEIPZIG, Germany: The brain is not able to discriminate between a painful upper tooth and a painful lower tooth, researchers found. The results of a new imaging study, which will be published in the journal Pain, may help devise better treatments for acute tooth pain, such as cavities or infections, and more chronic conditions like phantom pain of a tooth after it has been removed.
The researchers led by Prof Clemens Forster of the University of Erlangen-Nuremberg in Germany analysed the brain activity in healthy volunteers as they experienced tooth pain. By delivering short electrical pulses to either the upper left or the lower left canine tooth, a painful sensation similar to that felt when biting into an ice cube was triggered. To see how the brain responds to pain emanating from different teeth, the researchers used functional magnetic resonance imaging (fMRI) to monitor changes in activity when the upper or the lower tooth was stimulated.
“At the beginning, we expected a good difference, but that was not the case,” Forster stated. Many brain regions responded to top and bottom tooth pain—carried by signals from two distinct branches of a fibre called the trigeminal nerve—in the same way. The maxillary branch (V2) carries pain signals from the upper jaw, and the mandibular branch (V3) carries pain signals from the lower jaw.
The researchers found that regions in the cerebral cortex, including the somatosensory cortex, the insular cortex and the cingulate cortex, all behaved similarly for both toothaches. These brain regions are known to play important roles in the pain projection system, yet none showed major differences between the two toothaches. “The activation was more or less the same,” Forster said, although, he added, their experiments might have missed subtle differences that could account for why some tooth pain can be localised.
Because the same regions were active in both toothaches, the brain—and the person—couldn’t tell where the pain was coming from. “Dentists should be aware that patients aren’t always able to locate the pain,” Forster says. “There are physiological and anatomical reasons for that.”