Canine dentition, what’s the big deal? A dog is born with no teeth in his mouth at all. Just as with human dentition, dogs have two sets of teeth in their lifetime. The first set of 28 deciduous puppy teeth (often called milk teeth because they erupt between 3-6 weeks while the pups are still nursing) does not contain molars as there is no need for them while pups are nursing. (See Figure 1.) These tiny, sharp teeth with a small root are all in place by two months of age and are 28 in number. Normal eruption times for the deciduous teeth are as follows:
- Incisors 4-6 weeks;
- Canines 3-5 weeks;
- Premolars 5-6 weeks.
Puppy teeth are usually shed easily around four months of age. However, sometimes a pup’s deciduous teeth don’t shed properly, with the most common problem being the retention of a puppy tooth. This causes the permanent tooth to erupt next to the retained puppy tooth, which can cause the permanent tooth to be positioned incorrectly and the puppy tooth to be surgically removed. On occasion, a deciduous tooth is retained simply because there is no permanent tooth to take its place. This tooth can remain functional for a fairly long time.
The permanent teeth begin to erupt at three months of age. As these permanent teeth develop within the jaws, the roots of the deciduous teeth are absorbed by the surrounding tissues and are shed. By six months of age, the deciduous teeth have been replaced by a full set of permanent adult teeth, so “teething” in a pup is generally most common between three and six months of age. Normal eruption times for permanent teeth are as follows:
- Incisors 12-16 weeks;
- Canines 12-16 weeks;
- Premolars 16-20 weeks;
- Molars 20-24 weeks of age.
In the upper jaw, there are six incisors, two canines, eight pre-molars, and four molars. The lower jaw has six incisors, two canines, eight premolars, and six molars for a total count of 42 (20 upper, 22 lower) teeth. (See Figure 2.) More on how to count teeth later.
What role does canine dentition serve in the function of the dog? The 12 incisors (six upper and six lower) consist of two central incisors, two intermediate incisors, and two lateral incisors. (See Figure 3.) Incisors share a single, common root. The incisors are used to rip and scrape food from bones as well as to remove detritus/insects/irritants from the coat, and to help pick up and carry objects.
The incisors are also used as a landmark in determining the bite of the dog. To simplify: When incisors meet tooth-to-tooth, this is a level bite. (See Figure 4.) When the upper incisors overlap the lower, but are touching or in very close proximity to the lower incisors, this is considered a scissors bite. (See Figure 5.)
An overshot dog is one in which the upper incisors have a noticeable forward gap ahead of the lower incisors, and if a scissors bite is called for, the severity of the fault is determined by the size of the gap. (See Figure 6.)
When the bottom incisors are in front of the upper incisors, but either touching or in very close proximity to the lower incisors, this is considered a reverse scissors; but is considered undershot when there is a slight (or more) gap. Again, a noticeable forward gap of the lower incisors from the upper incisors is considered a fault if a scissors bite is called for in the standard of the breed. The severity of the fault is determined by the size of the gap. (See Figure 7.)
The canine dentition are often referred to as fangs, and they reside right next to the incisors in the upper and lower jaws of the dog. When the dog’s mouth is closed, to form the scissors bite, the canine teeth should intersect and not conflict with the teeth of the opposite jaw. Canines are sharp and come to a point, and they are single-rooted teeth. The canine teeth serve the dog as a defense mechanism—those pointed teeth can cause severe puncture wounds to ward off other dogs or larger predatory animals. They also help the dog bite and hold on to a toy or bone as well as serve the dog well to bring down game. The canines help in holding prey once caught and they are an aid in tearing the prey apart for consumption. The Herding breeds use the teeth to nip at the heels of their livestock and to threaten them from the front when turning and heading stock. Each pair of canines is separated by a set of incisors. (See Figure 8.)
The premolar teeth are located in the jaw behind the dog’s canine teeth. They are irregular and closely spaced. As they approach the molars, they become larger and more complex. The first premolar has one root, the second and third have two roots, and the fourth (Carnassial tooth) has three roots. The premolars are necessary for chewing, and the Carnassial tooth is adapted for shearing flesh. A dog will take a treat from you with his canines and incisors and then move it over to the side of his mouth to chew the meat off the bone. There are 16 premolars; four on either side of the upper and lower jaws, just behind the canine teeth. (See Figure 9.)
The molars are the last teeth at the back of the dog’s mouth. There are four (2-2) molars in the upper jaw and six (3-3) molars in the lower jaw. (See Figure 9.) The two largest teeth in the jaws on each side are the P4 and M1. These are called the Carnassial teeth. (See figure 9.)
The molars at the back of the mouth, with their flatter surfaces, are used to grind food and to crush bones. Dams will use their molars to sever the umbilical cords when whelping their pups. (See figure 9.)
When doing my recent research on canine dentition, I came across a wonderful image at the Online Veterinary Anatomy Museum that demonstrates why it is so important for a Herding dog to have full dentition. Not only do the teeth help in all the ways listed above, but the roots of the teeth serve the purpose of reinforcement and strengthening the jaws of the dog by their density and size. (In Figure 10, this is fully demonstrated by showing the teeth imbedded in the clear skeletal formation of the head.) I was even surprised by the size of the roots of the canine teeth as I had never seen them demonstrated in such a manner.
It is plain to see that a missing tooth not only hampers a dog in daily chores, but it can endanger a dog with a weak spot in the jaw (especially the lower jaw). A well-placed kick from livestock can snap the jaw in half at the point of a missing tooth. This was brought to my attention early in my judging career when I was thanked by an exhibitor for checking for full dentition in his breed. His dogs were used as working cattle dogs, and they were usually far from a motor vehicle—and well over 100 miles away from veterinary care—when gathering the cattle to bring them in closer to the ranch from their far-ranging pastures for the winter. He’d had a dog, missing bilateral P4s on the lower jaws, have just such an accident, and he was distressed that he had to destroy his dog because his jaw snapped when kicked for just the reason stated above. (See Figure 11.)
The first illustration “A” in Figure 11 shows a dog will full dentition. The second illustration “B” shows the dog missing one premolar on the upper jaw and one on the lower jaw. What do you think would happen if this dog took a kick right to the area of the missing lower jaw premolar?
When judging a breed that calls for counting teeth, I was taught to do it in groups when checking the bite: 6 incisors (both up and down) and 4 canines, and then 4 (premolars) and 2 (molars) on the upper jaw and 4 (premolars) and 3 (molars) on the bottom jaw on each side. Thus, reaching the total of 42 teeth. (See Figure 12.)
The last thing one must consider when discussing canine dentition is the owner’s care of the dog’s teeth. While there is little evidence of a tooth decay problem in the canine mouth, there is a lot of evidence that dogs are prone to gum disease if their teeth are not kept clean. Medical studies have proven that there is a connection between gum disease and heart disease in dogs (as well as in people)! If you allow tartar to accumulate on the teeth, it opens up a direct line into the dog’s bloodstream for invasion by anaerobic bacteria that thrives in the tartar of the teeth. Pockets can form around the roots of the teeth and, as they grow larger, the teeth can actually fall out. From the tooth and into the bloodstream, the bacteria finds a home in the dog’s heart where it builds up as plaque and develops into heart disease. If left unchecked, it will lead to the death of the dog.
The amount of tartar that accumulates on a dog’s teeth varies from dog to dog. Some dogs need little tooth care and keep their teeth clean by chewing on bones and treats that are created to scrape the tartar from the gum line. On the other hand, there are some dogs that are very much more likely to have a tartar build-up, even if you give treats to help keep the teeth clean. Many breeders have found that adding organic Norwegian kelp to the dog’s daily diet really does help to keep the teeth clean and tartar free. I order my kelp from Nature’s Farmacy as it is MUCH more inexpensive than others that I used to use. I also like the texture of their product—more like sand instead of powder, though it is not the kelp itself that cleans the teeth but the chemical reaction that occurs when the dog ingests it. (I have used these supplements for years, but I do not benefit from mentioning their product nor do I own stock in the company!) Others learn that they must brush their dog’s teeth on a routine basis. There are good suggestions for routine tooth care on the web, and a simple search on tooth care in the dog should bring up several ideas. This is one area of care that must not be neglected.
For questions about canine dentition or comments, or to schedule a seminar on structure and movement, I may be reached via e-mail – jimanie@welshcorgi.com
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