It has long been widely believed that sensory neurons within teeth primarily transmit pain signals to the brain.
However, new research from the University of Michigan has overturned this understanding, demonstrating that these neurons actually have multiple functions, triggering a rapid mouth-opening reflex that protects the teeth before potential damage occurs.
This reflex, which rapidly snaps the jaw open, is a well-known craniofacial reflex, but its cellular basis has only recently been revealed.
The study, conducted by University of Michigan experts in sensory neuroscience, dentistry, and mechanical engineering, combined real-time imaging, behavioral tracking tools, and experiments with mouse teeth to reveal that dental neurons can monitor the internal structure of the tooth and the state of its enamel. This new discovery further underscores the crucial role of the nervous system in tooth protection.
“We suspect that dental nerves do more than just transmit pain,” said Joshua Emrick, senior author of the study and an assistant professor at the University of Michigan School of Dentistry. “This has significant implications for regenerative dental pulp research, as we need to not only rebuild structure but also restore neural function.”
By stimulating mouse molars and recording the neural responses in real time, the research team revealed that a type of sensory neuron called a high-threshold mechanoreceptor (HTMR) has a unique protective role.
HTMRs not only detect danger signals but also rapidly transmit information to the brain, triggering defensive responses, such as rapid jaw opening, to prevent further damage to the tooth.
“Our study challenges the long-held belief that nerves in teeth are simply there to cause us pain so we can see the dentist,” Emrick explained. “If you’ve ever bit down on a piece of metal and experienced severe pain but didn’t break your tooth, you can thank these HTMRs.”
The study suggests that this jaw-opening reflex is a self-defense mechanism, particularly important in mammals like humans and mice that don’t have the ability to replace their teeth. Thanks to the presence of these neurons, our teeth are able to quickly protect themselves from sudden external forces.
In addition, the study, published in Cell Reports, also found that when enamel or dentin is damaged, HTMR neurons trigger a mouth-opening reflex within 5 to 15 milliseconds.
Although HTMRs were previously known to trigger acute pain responses, this is the first time such rapid motor reflexes have been demonstrated.
Elizabeth Ronan, a postdoctoral researcher at the School of Dentistry and the study’s lead author, noted that this study reveals that sensory neurons are far more versatile than previously appreciated.
“We often think of sensory neurons as solely responsible for sensing external stimuli, but they actually play a crucial role in protecting and maintaining the health of tissues within the body.”
She emphasized that the specific function of sensory neurons, especially in internal organs like teeth, remains an unresolved scientific area, and much research remains worthy of further exploration.
This groundbreaking research not only provides new insights into the nature of toothache but also may offer new approaches to pain intervention in dental practice, promoting the development of dental pulp regeneration and nerve repair therapies.