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16 February 2023

Researchers discover unique way snakes replace their teeth

Method to detect signs of tooth replacement can also aid in identification of snake fossils in the future, even from isolated jaws.

A skeleton of a Gaboon viper
A skeleton of a Gaboon viper (Bitis gabonica). Attribution: Stefan3345, CC BY-SA 4.0, via Wikimedia Commons

A new study, led by a researcher from the Centre for Oral, Clinical & Translational Sciences at King’s College London, has identified key differences in tooth replacement between snakes and other reptiles, and identified the mechanism that allows snakes to shed their old teeth.

Most reptiles replace their teeth with new ones constantly. However, snake teeth show no signs of how old teeth are removed from the jaw. In contrast, other reptiles have a ‘replacement pit’ that forms when a new tooth begins to grow. This replacement pit eats away at the base of the older tooth helping it to be shed in a process known as external tooth resorption. The study’s findings revealed that snakes lack these pits and instead are able to shed old teeth through the unusual action of odonoclasts (cells that remove tooth tissues), which break down dentine from within the tooth.

A lizard jaw, left, showing a replacement pit forming along the base of a tooth (arrow). Snake jaws, like the one on the right, never show resorption pits.
A lizard jaw, left, showing a replacement pit forming along the base of a tooth (arrow). Snake jaws, like the one on the right, never show resorption pits.

The study’s findings demonstrated the evidence of this internal tooth resorption can even be detected non-invasively, using computerized tomography scanning to look inside a tooth. By combining these approaches, the researchers revealed that this unique form of tooth replacement is found all across the snake evolutionary tree.

As new discoveries of more ancient fossil snakes push their origins into the age of the dinosaurs, there may come a time where the lines between “lizard” and “snake” seem blurred. We need anatomical markers that are unique to snakes, conserved across living and extinct species, and that can be identified in fossils. From this tooth shedding mechanism in extant snakes, we may be able to provide a new line of evidence, independent of the anatomy of the skull and body, to support the identification of fossil jaws as belonging to early snakes.

Dr Aaron LeBlanc, lead author on the study and lecturer in Dental Biosciences at the Faculty of Dentistry, Oral & Craniofacial Sciences
Snake diagram
Model of the snake tooth replacement cycle from (1) attachment, (2) ankylosis, (3) pre -resorption, (4) early resorption, (5) late resorption, and (6) shedding stages.

Snake-type tooth replacement has no equivalent in other lizards, or any other reptile. At some point in the life of each snake tooth, it undergoes a dramatic transformation: the inner pulp of each tooth becomes filled with large cells that begin to eat away at it from the inside. This process eventually weakens the tooth base enough to break it away from the jaw, allowing the new tooth to jostle into position and replace its predecessor.

Using computerized tomography, the researchers looked inside skeletons of extant species, and identified the ‘bite marks’ in the tooth tissues left behind by the odontoclasts that would have been resorbing the inside of the tooth.

Researchers then used this method to detect these ‘bite marks’ inside the teeth of the fossil snake Yurlunggur and one of the oldest snake fossils, a 150 million-year-old jaw fragment of Portugalophis, suggesting that it is one of the earliest innovations in the snake lineage, even preceding the loss of limbs.

LeBlanc, A.R.H., Palci, A., Anthwal, N. et al. A conserved tooth resorption mechanism in modern and fossil snakesNat Commun 14, 742 (2023).

In this story

Aaron LeBlanc

Lecturer in Dental Biosciences

Abigail  Tucker

Dean for Research

Neal  Anthwal

Research Associate