The cat milk teeth start to come in when the kitten is about 4 weeks old. The all 26 milk teeth appear when the kitten is 6 weeks old. They begin to fall out between the age of 11 weeks until the age of 30 weeks. During the time when the milk teeth are falling out, new permanent teeth are coming in until all 30 of them replace the milk teeth. It happens when the cat is 8-9 months. Occasionally, one or more of the milk teeth don't fall out, or extra teeth are present, which is "a case" for the vet to solve.