The Tiny Dog Hiding a Double Row of Teeth — And Why Your Vet Wants to Know About It

There is something undeniably charming about small dogs. Their compact frames, outsized personalities, and tendency to act as though they own every room they enter have won them devoted followings around the world. What most owners do not immediately think about, however, is what is happening inside those little mouths — and the answer, for certain breeds, is considerably more dramatic than you might expect.

The phenomenon in question is known as retained deciduous teeth, a condition in which a dog’s baby teeth fail to shed as the adult teeth come through, leaving the animal with what can look remarkably like a double row of tiny, pointed teeth. Veterinarians have long been aware of the issue, but it is only in recent years that large-scale research has begun to reveal just how widespread it truly is.

A landmark study led by Dr. Corrin Wallis, Senior Research Scientist at Mars Petcare and the Waltham Petcare Science Institute in Leicestershire, examined the medical records of nearly three million dogs visiting veterinary hospitals across the United States over a five-year period, publishing its findings in the journal Research in Veterinary Science. The data, drawn from records representing 60 breeds, found an overall prevalence of seven percent for persistent deciduous teeth, or PDT, with extra-small breeds weighing under 6.5 kilograms showing a significantly higher rate of fifteen percent.

Topping the breed risk list was the Yorkshire Terrier, with a striking 25.1 percent likelihood of developing the condition, closely followed by the Toy Poodle and Maltese at 14.8 percent each, and the Chihuahua at 13.2 percent. Pomeranians, Shih Tzus, Dachshunds, and Miniature Schnauzers were also identified among the higher-risk breeds, while larger dogs such as Greyhounds, Great Danes, and English Bulldogs showed prevalence rates well below one percent.

The condition is more than an aesthetic quirk. According to Wallis and colleagues, persistent deciduous teeth are associated with a misaligned bite, soft tissue trauma, and an elevated risk of periodontal disease. Because there is so little space in a small dog’s mouth, the crowding created by two sets of teeth accelerates tartar buildup, which can become a precursor to serious gum disease if the retained teeth are not removed promptly. Aimee Warner, a resident veterinarian at Waggel, describes the result as a crowded mouth where the remaining teeth look more pointed and prominent, giving rise to the shark comparison that has caught so many owners off guard.

The study also found that dogs enrolled in regular wellness plans or receiving routine dental care had significantly reduced odds of PDT being detected, underlining that consistent veterinary checkups are among the most effective tools for catching the condition early. Researchers recommend that early identification and extraction of persistent deciduous teeth, ideally before six months of age, can significantly reduce the associated health risks.

A separate study focused specifically on Yorkshire Terriers found that persistent deciduous teeth affected 69 percent of puppies in the sample group, with smaller-bodied individuals more likely to require surgical extractions by a veterinarian, highlighting just how routine this issue can be within the breed. For owners of small dogs, the takeaway is clear: that sweet face deserves a close look inside the mouth now and then.

If your dog is one of the breeds named here, or if you have spotted something shark-worthy going on in their smile, share what your vet told you in the comments.