Puppies begin to lose their first set of teeth at approximately 3 months of age. By 9 months, this process is complete. Occasionally, a puppy's milk teeth don't fall out on their own and need to be removed by a veterinarian to make room for the adult set.
A dog's first set of teeth are very small and sharp and usually come to the surface of the gums three to four weeks after birth. This prompts the weaning process. The second set of teeth are whiter, larger and much stronger. Constant chewing is often an indication that a puppy is teething.