Tooth Nerves: Beyond Pain Detection, a Rapid Defense Mechanism
London. – Image by © Tim Sandle.
For years, it’s been understood that sensory neurons within teeth transmit pain signals to the brain. However, new research reveals these neurons have a crucial, additional function: triggering a rapid jaw-opening reflex designed to prevent tooth damage adn further injury.
While the existence of a craniofacial reflex causing the lower jaw to open suddenly was previously known, the specific cellular origins of this response remained a mystery until recently.
Researchers at the University of Michigan, spanning sensory neuroscience, dentistry, and mechanical engineering, utilized live imaging, behavioral tracking, and mouse molars to pinpoint the source of this reflex. Their work demonstrates that these neurons actively monitor both the inner tooth structure and the outer enamel.
This revelation underscores the vital role healthy, functioning nerves play in tooth preservation.
“We suspected tooth nerves had a more fundamental role than simply registering pain,” explains Joshua Emrick, senior author of the study and assistant professor at the U-M School of Dentistry. “Considering the potential for tooth pulp regeneration, restoring nerve function is paramount.”
The team observed nerve cell reactions to stimulation of mouse molars in real-time. These experiments identified a protective function for High-Threshold Mechanoreceptors (HTMRs) – specialized sensory neurons within the tooth that respond to damage. These HTMRs detect threats and quickly relay information to the brain, initiating an immediate response.
“Our study challenges the long-held belief that tooth nerves primarily exist to signal pain and prompt a dental visit,” Emrick states. “That jolt you feel when accidentally biting down on something hard, preventing a fracture? You can thank these intradental HTMRs for that.”
A Reflex Rooted in Self-Preservation
Emrick elaborates on the importance of the finding: “We believe this jaw-opening reflex, protecting teeth, is a conserved trait among mammals unable to replace teeth – like humans – and is also present in the molar teeth of mice. Furthermore, understanding these neurons’ ability to elicit pain opens avenues for developing improved toothache relief methods at the dentist’s office.”
The study details that damage to enamel or dentin triggers a response from these neurons.Subsequent experiments revealed that activating HTMRs not onyl causes acute pain, but also elicits a rapid jaw-opening reflex occurring within 5 to 15 milliseconds.
The protective capabilities of HTMRs may extend beyond teeth, perhaps safeguarding other oral and bodily structures, given the essential role sensory neurons play in tissue maintenance and protection throughout life.
The research findings are published in the journal Cell Reports under the title “Intradental mechano-nociceptors serve as sentinels that prevent tooth damage.”
