Permanent deciduous teeth, also known as “shark teeth”.

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Seven percent of pet dogs—mostly small, “toy” breeds—have double teeth, reminiscent of a shark’s mouth. This condition, called permanent deciduous teeth, occurs when the puppy teeth are stuck in the jaw, near the adult teeth, instead of falling out, forming rows of teeth like those seen in sharks. .

To investigate these “shark teeth”, Corinne Wallace At the Waltham Pet Care Science Institute in Leicestershire, UK, and colleagues examined the records of 2.8 million purebred dogs.