Permanent teeth that come in after the age of 6 are usually not replaced. In infants, milk teeth begin to erupt around 6 months after birth, and 20 milk teeth erupt around 2.5 years of age. 6 to 13 years of age is the replacement period, during which 20 milk teeth are replaced by permanent teeth. Permanent teeth are teeth that stay with us for the rest of our lives and are not replaced. At around 6 years of age, at the end of the milk teeth row, the first permanent molar starts to erupt, which is usually called the “six-year-old tooth”, and this is the earliest permanent tooth in the mouth, and will not be replaced once it erupts, and all the permanent teeth that erupt after 6 years of age, including the second and third molars (wisdom teeth), will not be replaced either. Since the eruption of milk teeth, and especially after the replacement of permanent teeth, it is important to maintain good oral hygiene, have regular oral checkups, and seek medical attention when caries and other discomforts are detected.