Small dogs have worse teeth than larger breeds primarily because they have the same number of teeth (42) packed into much smaller jaws. This crowding, combined with shallow bone support, a higher rate of retained baby teeth, and bite misalignments from selective breeding, creates a perfect storm for dental disease. Small breeds are two to three times more likely to be diagnosed with periodontal disease than larger dogs.
Too Many Teeth, Not Enough Jaw
A Chihuahua and a Labrador both have 42 adult teeth. The difference is that the Chihuahua has to fit all of them into a jaw that may be a fraction of the size. This means teeth end up packed tightly together, sometimes rotated or overlapping, with almost no natural spacing between them. In brachycephalic (short-nosed) small breeds like Pugs, Shih Tzus, and French Bulldogs, the problem is even more pronounced. The altered facial skeleton forces a normal number of teeth into a dramatically compressed space, causing premolars to rotate and crowd severely.
That crowding matters because the tight gaps between teeth trap food particles and bacteria that would otherwise be cleared by saliva or chewing. Plaque builds up faster in those narrow crevices, hardens into tartar, and begins irritating the gum line. In a larger dog with well-spaced teeth, the same plaque accumulation happens more slowly and is easier to manage with chewing alone.
Shallow Bone and Vulnerable Roots
The bone that holds a dog’s teeth in place doesn’t scale down proportionally with jaw size. A study using CT imaging of 101 dogs found that mandibular bone height ranged from about 10 mm in the smallest dogs to over 33 mm in larger ones. The critical measurement is the ratio of bone height to root length. On average, that ratio was 1.70, but in dogs with mandibular bone height of 15 mm or less (typical of small breeds), tooth roots frequently extended deep enough to overlap with the mandibular canal, the channel carrying nerves and blood vessels through the lower jaw.
In practical terms, this means small dogs have proportionally less bone cushioning around each tooth root. When periodontal disease erodes even a small amount of that bone, there’s less margin before the tooth loosens or the infection reaches sensitive structures. A large dog can lose some bone support and still have a firmly anchored tooth. A toy breed losing the same percentage of bone may end up with a wobbly tooth or a jaw fracture, which is a recognized complication in very small dogs with advanced dental disease.
Retained Baby Teeth
Small dogs are significantly more likely to hold onto their baby teeth past the point when adult teeth have already erupted. A study of nearly 3 million veterinary records across the United States found that persistent deciduous teeth occurred in about 7% of dogs overall, but in extra-small breeds (under about 14 pounds), that rate jumped to 15%.
When a baby tooth doesn’t fall out on its own, the adult tooth erupts alongside it. Two teeth now occupy a space meant for one, creating an immediate crowding problem on top of the crowding that already exists in a small jaw. The narrow gap between the retained baby tooth and the permanent tooth becomes a trap for bacteria and debris, accelerating plaque buildup and gum inflammation. This is why veterinarians typically recommend extracting retained baby teeth early, before they set up the conditions for periodontal disease and bite misalignment.
Bite Misalignment From Breeding
Selective breeding has reshaped small dog skulls in ways that create dental problems as a side effect. The upper jaw (maxilla) is easier to change through breeding than the lower jaw (mandible). When breeders select for shorter noses or blockier heads, the upper and lower jaws often end up mismatched. Short-nosed breeds tend to develop underbites, where the lower jaw protrudes past the upper. Breeds selected for longer, narrower faces tend toward overbites.
Either type of misalignment means the upper and lower teeth don’t meet correctly. Teeth that don’t contact their opposing tooth properly miss out on the natural cleaning effect of chewing. Misaligned teeth can also cause soft tissue trauma, where a tooth repeatedly pokes into the gum or palate, creating wounds that invite infection. These malocclusions are far more common in toy and miniature breeds than in medium or large dogs whose skull proportions have been less dramatically altered.
Why It Gets Worse With Age
Periodontal disease in small dogs tends to progress faster and hit harder than in larger breeds. The combination of crowding, shallow bone, and retained teeth means that by the time gum inflammation becomes visible, the underlying bone loss may already be significant. Studies consistently show that both the incidence and severity of periodontal disease increase with age in all dogs, but small breeds start from a worse baseline and have less structural reserve to absorb the damage.
The consequences go beyond the mouth. A retrospective study of 136 dogs found a statistically significant link between periodontal disease and cardiac disease, with small breeds under 10 kg making up the majority of the periodontal disease group. The mechanism is bacterial: chronic gum infection allows bacteria to enter the bloodstream, where they can seed inflammation in the heart valves, kidneys, and liver over time.
What You Can Do About It
Daily tooth brushing is the single most effective thing you can do for a small dog’s teeth. Even a few seconds of brushing with a dog-safe toothpaste disrupts the plaque film before it mineralizes into tartar. For dogs that won’t tolerate a brush, dental wipes or water additives with enzymatic action offer a partial alternative, though they’re less effective.
Regular veterinary dental cleanings under anesthesia allow a thorough exam below the gum line, where the real damage happens in small breeds. X-rays taken during these cleanings often reveal bone loss and root problems that aren’t visible just by looking at the teeth. Many veterinarians recommend starting dental cleanings earlier and scheduling them more frequently for toy and small breeds compared to larger dogs, precisely because the disease progresses faster in smaller mouths. Dental chews sized appropriately for small dogs can also help mechanically scrape plaque, though they’re a supplement to brushing rather than a replacement.