While your puppy doesn't place his baby teeth under his pillow and wait for the tooth fairy to trade them for some nice bones, he loses his primary teeth just like human children do. One major difference between the primary and permanent teeth is the number. Puppies have 28 baby teeth and 42 permanent teeth.
Born toothless, a puppy's deciduous, or baby, teeth start erupting about the age of 3 weeks; his entire set of primary teeth is in his mouth at 6 weeks. The exact schedule depends on the breed and the individual puppy. The baby teeth are smaller and darker than the permanent teeth that follow. The incisors or "fangs" arrive first, between the ages of 3 and 6 weeks. They're followed by the canines, at 5 to 6 weeks of age, and the premolars at 6 weeks. Puppies don't have molars -- they're part of those additional, permanent teeth.
When your puppy starts chewing on everything in sight, his permanent teeth are coming in and teething has begun. The chewing helps relieve the discomfort of tooth eruption. Because the baby teeth are softer than the permanent teeth, he's more likely to fracture one during vigorous chewing or while playing with littermates or his human family. No matter whether it's deciduous or permanent, a fractured tooth causes painful abscessing, so any broken baby tooth should be extracted by your vet.
Besides being whiter, the permanent teeth are stronger than the baby teeth. The incisors are also the first permanent teeth to erupt, between the ages of 3 and 5 months. The canines appear between the ages of 4 and 6 months, with the premolars coming between 4 and 6 months. Last to arrive are the molars, between 5 and 7 months. When all of the puppy's permanent dentition is in, he should have 42 teeth, although some dogs might be missing one or two. Those 42 consist of 22 in the lower jaw and 20 in the upper jaw. Each jaw has two canines, six incisors and eight premolars. The lower jaw has six molars, while the upper jaw contains four.
Sometimes, a deciduous teeth doesn't fall out and the permanent tooth has already erupted, leaving two teeth where only one should be. As you bring your puppy to the vet for his shots and well visits, your vet will check his teeth on every visit. If she notices a retained tooth, she'll make arrangements to have it removed if it doesn't fall out on its own. If the retained tooth isn't removed, the permanent tooth grows at an odd angle, or the teeth crowd, causing maloccusion or a problematic bite. Since vets often remove retained teeth when a puppy is about 6 months of age, you might want to schedule the surgery to coincide with spaying or neutering, since both require anesthesia.