Why Do Toothaches Hurt So Much?

Have you ever had a toothache that caused blinding pain? If so, you’re not alone. According to researchers at Duke University, people consistently rate pain in the head, face, eyeballs, ears and teeth as more disruptive and emotionally draining than pain located in other parts of the body. Further study has apparently found why this may be, as reported in a recent Dental Tribune article.

The research team has found that the sensory neurons in the head and face are wired directly to one of the brain’s primary emotional signaling “hubs.” The sensory neurons from other parts of the body are only connected indirectly, making them less sensitive than those that are wired directly. While this discovery is very interesting, however, it does not explain the greater fear and emotional suffering often experienced by patients when suffering from pain in the head and face.

“Usually doctors focus on treating the sensation of pain, but this shows that we really need to treat the emotional aspects of pain as well,” said Professor Fan Wang, senior author of the study, from the university’s Department of Neurobiology.

Supported by functional magnetic resonance imaging, greater fear and suffering in response to head pain vs. body pain has been shown by with greater activity in the amygdala, a region of the brain involved in emotional experiences.

“There has been this observation in human studies that pain in the head and face seems to activate the emotional system more extensively,” Wang added, “but the underlying mechanisms remained unclear.”

In order to examine the brain activity during the two types of pain, Wang and the team tracked the brain activity of mice after irritating either a paw or the face. They found that after facial irritation, higher activity in the brain’s parabrachial nucleus (PBL), a region that is directly wired to the brain’s instinctive and emotional centers, was observed.

“It was a eureka moment because the body neurons only have this indirect pathway to the PBL, whereas the head and face neurons, in addition to this indirect pathway, also have a direct input,” Wang said. “This could explain why you have stronger activation in the amygdala and the brain’s emotional centers from head and face pain.”

The team furthered showed that activating this pathway prompted facial pain, while silencing the pathway reduced it.

“We have the first biological explanation for why this type of pain can be so much more emotionally taxing than others,” said co-author Prof. Wolfgang Liedtke, who operates at the Duke University Medical Center and treats patients with head and facial pain. “This will open the door toward not only a more profound understanding of chronic head and face pain, but also toward translating this insight into treatments that will benefit people.”

The study, “A craniofacial-specific monosynaptic circuit enables heightened affective pain,” was published on November 13 in the Nature Neuroscience Journal. Researchers are hopeful that the results may help create more effective treatments for craniofacial pain, such as chronic headaches, neuropathic facial pain and discomfort after dental surgery.