Ask Dr. Jenn: Can My Pet's Teeth Tell Me Their Age?

Veterinarians use teeth as one of many ways to determine a pet’s age. But this technique has its limitations, and the ages are often estimates. In addition to teeth, veterinarians rely on other physical factors such as changes in the eyes, hair coat, gait, and overall health. 

How to Estimate Dogs’ and Cats’ Age by Their Teeth

For Puppies and kittens: In dogs and cats, using teeth to determine age works best when they are younger. Puppies and kittens have small, sharp deciduous teeth (baby teeth) that start erupting through the gums around 2-3 weeks of age. At approximately 16 weeks, they lose the first set of deciduous incisors (the teeth at the very front of the mouth) and permanent teeth (adult teeth) erupt. Over the next 8 weeks, they will continue to lose their deciduous incisors, and the permanent incisors will grow in. At six months, the permanent canine teeth (fangs) should be in place. By eight months, they should have a full mouth of permanent teeth. This timeline can vary somewhat depending on the size and breed of the animal. Toy breeds’ teeth may come in a little slower and some kittens start to lose their deciduous teeth around 12 weeks of age, but it gives us a good approximation.

Young dogs and cats: Between eight months and two years, most dogs and cats have shiny glossy teeth with minimal staining or plaque buildup.

Mature dogs and cats: After about two years, the teeth start to wear more, become stained, and tartar forms on the teeth. How quickly tartar builds up and the general wear on the teeth varies from animal to animal, based on a number of factors. Some of these factors include how much they chew, what they chew on, diet, whether the pet parent brushes the teeth, the shape of the mouth, and the breed.

How to Estimate Your Horse’s Age by Their Teeth

Horses are a different story. Have you wondered what the idiom “Don’t look a gift horse in the mouth” means?

You can get a pretty accurate estimate of a horse’s age by looking in their mouth, but it would be an insult to the giver of the horse if you examined the teeth to see if it was a young horse with lots of years left in him or an older horse who should be put to pasture.

The Science of Horse Teeth

Like dogs and cats, we can look at when permanent teeth erupt to estimate the age of a young horse. However, horses’ permanent teeth come in much later than dogs and cats.

The first permanent incisors (the ones in the very center of the six incisor teeth) are present at approximately 2 ½ years of age. The next set is present at 3 ½ years and the final outer most set erupts around 4 ½ years of age.

The horse’s incisor teeth developed to cut grass when grazing and therefore they are constantly being worn down. The incisor teeth have very long roots with a curved shape. As they wear down their teeth, the body slowly pushes the teeth upward. These teeth wear and erupt in a predictable pattern, helping us to estimate a horse’s age.

Anatomy of Horse Teeth

The shape and wear of the incisor teeth is better understood by looking at an illustration* (a picture is worth a thousand words) but I will do my best to describe the shape and wear on the teeth.

Look at the top surface of the teeth. At first, the incisor teeth have an oval shape. As they wear down over time, the tooth becomes more rectangular.  The tops of the teeth also start to lose enamel and reveal the underlying tissue, called dentin. Dentin is light brown in color and becomes visible approximately six months after the tooth erupts. For the first set of incisors, you will see it around 3 years, the middle incisors around 4 years, and the outer most incisors around five years.

As the teeth continue to wear, you will see a “cup” shape appear in the center of the tooth.

• In the lower incisors, the cup wears off the first incisor set at six years, seven years for the middle incisor set, and 8 years for the outermost incisor set.
• For the upper incisors, the first set usually wears down around 9 years, 10 years for the middle incisors, and 11 years for the outermost incisors.

Teeth in Older Horses

Once the cup is gone, you will see an enamel spot in its place. The enamel spot usually disappears around 13-16 years of age.

At 16-17 years of age the incisors wear down to a triangular shape, then start to become rectangular again starting at 18 years of age. Once all the incisor teeth have a rectangular shape with no visible cups or enamel spot, the horse is at least 20 years of age. After 20 years, there is usually no change in the appearance of the teeth and aging needs to be based on other factors.

Additional Tips

You can also get a rough estimate of a horse’s age by looking at the angle of the incisor teeth from the side. When they first erupt, the incisors line up almost on top of each other. As the teeth wear, the angle of the teeth becomes much sharper. By around 20 years of age, the upper and lower incisors meet at almost a 90-degree angle.

Remember that these are general rules of thumb to help estimate the age of a horse. Tooth wear is also affected by diet, breed, and lifestyle. But if you want to break the old adage and look your gift horse in the mouth, these tips will help determine if you were given a young, middle aged, or old horse. If you want a more accurate estimate of age, ask your favorite equine veterinarian to examine your new horse.

*You can find many illustrations on aging horses by their teeth in an online search. The site I found especially helpful is: https://myseniorhorse.com/diseases-and-conditions/teeth/horse-teeth-by-age/