There are 20 deciduous teeth, which usually erupt at about 6 months, and grow at 2-3 years old, and 28-32 permanent teeth (the number of wisdom teeth is 0-4), which generally grow at about 6 years old, and 28 teeth 12- 13 years old (wisdom teeth vary from person to person), so the tooth replacement period is generally 6-650. There are certain rules for changing teeth. It's simple.