The baby (deciduous) teeth begin to appear (erupt) at about 4-5 weeks of age and are completely in by 6-8 weeks. Puppies begin to lose their baby teeth at about 4 1/2 months of age, just before the permanent teeth begin to appear. By 6 to 7 months of age, all the permanent teeth will have erupted. The types of teeth are incisors, canines (fangs), premolars and molars. Dogs have 28 baby teeth and 42 permanent teeth.