Research suggests that humans suffer from toothache because teeth were sensory organs of ancient fish

Many people have experienced tooth pain due to cavities, hypersensitivity, etc. A study published in May 2025 by researchers at the University of Chicago suggested that teeth may be more susceptible to pain because they are organs derived from the sensory organs and therefore have a more sensitive sense.

The origin of vertebrate teeth and evolution of sensory exoskeleton | Nature
https://www.nature.com/articles/s41586-025-08944-w

Teeth hurt? It could be because of a 500-million-year-old fish
https://phys.org/news/2025-05-teeth-million-year-fish.html

Although teeth are not sensory organs like skin, they are one of the organs that can feel quite strong pain, unlike hair and nails. According to Julius Mantz, director of the dental hygiene program at San Juan College in the United States, teeth are made to feel pain as a defense mechanism when the ability to bite things is reduced. If there was no pain in the teeth, the worn teeth would bite things that they could not handle, causing serious damage.

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You may also feel a sharp pain in your teeth when you put something cold in your mouth. While the mechanism behind this was thought to be related to dentin, the main component of teeth, the exact principle was unknown. A study published in 2021 discovered that ion channels that respond sensitively to cold are present in the cells that form dentin, and concluded that strong sensory stimuli are sent from there to the brain.

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There are also approaches to determining why teeth are sensitive to pain and cold by elucidating the exact origin of teeth. Previous research has suggested that teeth originated from hard structures called 'denticles' found on the external armor of ancient fishes about 500 million years ago, but their exact origin and purpose remain unknown.

A paper published in the scientific journal Nature in May 2025 by Yara Halliday and colleagues from the Department of Biology and Anatomy at the University of Chicago supports the hypothesis that the dentary processes of ancient fish were not an exoskeleton for protection or to aid in movement, but were originally used as sensory organs to transmit sensations to the nerves.

Halliday and his team were not studying teeth, but were working on one of the big questions in paleontology: 'What is the oldest fossil of an animal with a backbone?' As part of their research, they were analyzing hundreds of vertebrate specimens with a CT scanner, and discovered that a fossil of the Plate Cambrian period called Anatrepis , which was previously thought to be the 'first fish in history,' may have contained dentin. As a result, they concluded that Anatrepis was not a vertebrate, but an arthropod similar to crustaceans and insects with an exoskeleton.

In arthropods such as crabs and spiders, sensory organs are used to detect temperature, vibration and smell. 'We found a striking similarity between the dentin-based exoskeleton of Anatolepis and the tooth-like scales of fish from about 465 million years ago, as well as modern fish such as catfish and rays, in that they both have highly sensitive sensory nerves,' the researchers report.

'The shared features of the dentin exoskeleton and denticles suggest that dental tissue may be a sensitive sensory tissue,' said Halliday. 'Over time, fish evolved jaws that formed denticles near the mouth, eventually extending directly into the mouth, which may be the origin of teeth. If this is the case, toothache is a remnant of an ancient sensory organ.'