Nerves that act as pain detectors have another purpose: tooth protectors
Intradental sensory receptors act as sentinels to prevent tooth damage.
Sensory neurons inside teeth – primarily thought to send pain signals to the brain – are multitaskers that also trigger a jaw-opening reflex preventing damage to teeth, according to a new study.
The reflex that pops open the lower jaw is a widely-known craniofacial reflex, but until this study the cellular origins of this phenomenon were not known.
University of Michigan researchers in sensory neuroscience, dentistry and mechanical engineering found the origin using special live imaging, behaviour-tracking tools and mice molars to uncover the neurons’ additional role of monitoring the inner tooth and outer enamel.
The discovery and understanding of this additional role shows how important healthy, active nerves are for preserving teeth.
“We suspected there was a more fundamental role for tooth nerves,” said Joshua Emrick, senior author of the study and assistant professor at the U-M School of Dentistry. “When we consider regenerating a tooth pulp, we need to bring back the nerves.”
Emrick’s research team looked at how nerve cells reacted to stimulation of the molar teeth of mice in real time.
Their experiments revealed a newly defined, protective role for intradental high-threshhold mechanoreceptors (HTMR), highly specialised sensory neurons that respond to tooth damage. These HTMRs detect dangerous threats and send the message rapidly to the brain for instantaneous action.
“Our study challenges the prior assumption that nerves inside the tooth primarily function to elicit pain and force us straight to the dentist for help,” Emrick said. “If you’ve ever accidentally bitten down on your fork, you’ve probably experienced a startling jolt, but also stopped short of fracturing your teeth. You may thank these intradental HTMRs for that.
“We think protection of the teeth through this jaw-opening reflex is highly conserved among mammals that haven’t developed the ability to replace teeth—like humans or in the molar teeth of mice. Our work reports an ability to use these neurons to also elicit pain which will open up possibilities for developing new methods for relieving toothache at the dentist’s office.”
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