Ann Arbor Times

Until recently, sensory neurons inside the tooth were primarily thought to send pain signals to the brain. However, a new study indicates these neurons have an additional role in triggering a jaw-opening reflex that prevents damage and further injury to teeth.

This reflex was previously recognized as a craniofacial reflex, but its cellular origins remained unknown until now. Researchers from the University of Michigan in sensory neuroscience, dentistry, and mechanical engineering used live imaging and behavior-tracking tools on mice molars to uncover this dual function of monitoring the inner tooth and outer enamel.

The study's findings highlight the significance of healthy nerves in preserving teeth. Joshua Emrick, senior author and assistant professor at U-M School of Dentistry, stated: “We suspected there was a more fundamental role for tooth nerves. When we consider regenerating a tooth pulp, we need to bring back the nerves.”

Experiments showed that nerve cells react instantly when stimulated by potential threats to teeth. This newly defined protective role is attributed to intradental High-Threshold Mechanoreceptors (HTMRs), specialized neurons that respond rapidly to potential damage.

“Our study challenges the prior assumption that nerves inside the tooth primarily function to elicit pain,” said Emrick. “If you’ve ever accidentally bitten down on your fork...you may thank these intradental HTMRs for that.”

Emrick emphasized that this self-preservation mechanism might be conserved among mammals unable to replace teeth naturally. The research also suggests new possibilities for relieving dental pain using these mechanisms.

Published in Cell Reports, the study demonstrated how damaged enamel or dentin activates HTMRs within milliseconds. Although initially focusing on their function within teeth, researchers believe these neurons could protect other oral structures too.

Elizabeth Ronan, lead author and postdoctoral fellow at U-M School of Dentistry noted: “While we typically think of sensation as giving rise to our perceived external experience...sensory neurons are equally essential in protecting and maintaining our tissues throughout life.” She added that much remains undiscovered about sensory neuron functions within internal tissues like teeth.

Other contributors included Akash Gandhi, Karin Uchima Koecklin,Yujia Hu among others from U-M; along with Maximilian Nagel from National Center for Complementary and Integrative Health.