Normal human beings have 20 milk teeth and 28-30 permanent teeth.The first milk teeth begin to erupt at the age of 5-6 months, and at around 2 years of age, all the milk teeth grow to form a milk jaw.At the age of 5.5-6 years old, the milk mesial incisors begin to loosen, and the inherited permanent teeth erupt, and the first permanent molar, also known as the six-age tooth, is exposed to the oral cavity.At around the age of 11-12 years old, the second permanent molar begins to grow to form a permanent jaw.At around the age of 17-18 years old, the wisdom teeth begin to erupt, as there are large variations in wisdom teeth which do not necessarily grow symmetrically. Around 17-18 years old, wisdom teeth begin to erupt. Due to the large variation of wisdom teeth, they do not necessarily grow symmetrically, and some people are even born without wisdom teeth, resulting in the appearance of 28-32 permanent teeth in the mouth.