Puppies and kittens have baby teeth that erupt on a predictable schedule. Usually by 2-3 months of age, a puppy will have all of its baby teeth in place for a total of 28. A kitten will have its 26 baby teeth erupted by 2-3 months also. There is some variability in this between dog breeds and size of the adult dog.
The permanent teeth can have a more varied eruption schedule, but the approximate time for adult incisors to start coming in is 3-4 months for both cats and dogs. The adult canines come in between 4-6 months for dogs and 4-5 months for cats. Molars and premolars are usually in by 7 months in dogs and 6 in cats.
Dogs have 42 adult teeth and cats have 30.
There are things that can go wrong with baby teeth and the adult teeth to follow. Therefore, it is good to start getting your pet used to you handling its mouth when it is little so that you can monitor the mouth for problems.
One thing that can go wrong is a failure of a baby tooth to fall out when the adult tooth is coming in. Normally an erupting adult tooth presses on the baby tooth root, causing the root to start dissolving. The baby tooth is shed as just a cap of a crown before the adult tooth comes in.
An exception is the upper canine baby tooth, which can persist for a few days to weeks before falling out. But for all others, the presence of two teeth together causes damage to gum tissues and often makes the adult tooth take a different direction as it comes in. This leads to infection along tooth roots and pain on chewing. Removal of persistent baby teeth is needed and can be a delicate procedure as the root is for times longer than the crown.
Other things to watch for are broken puppy and kitten canine teeth. Puppies and kittens can be hard on their teeth as they play. If a baby tooth breaks, it can become infected. The infection can spread to the developing adult tooth. A pet is not going to alert you to a toothache.
Sometimes an adult tooth fails to appear, in which case dental X-rays are used to see if it is beneath the gum line. If a puppy has a tooth close to the surface, gum tissue can sometimes be opened to allow it to erupt. Otherwise, deeply buried adult teeth are usually removed via oral surgery to prevent them from causing damage in the jaw.