Children usually change their molars around the age of 9-12 years old, and the replacement time of milk molar is affected by many factors. When children often chew tough food, the roots of the milk teeth resorb quickly, and the permanent teeth usually erupt smoothly. Girls develop earlier than boys and usually erupt their first or second bicuspids around the age of 9-10. Boys are a little later, completing molar replacement around 10-11 years of age. If deep caries exists in the molar or a periapical infection develops, hard and soft tissue adhesions can occur, resulting in difficult or ectopic eruption of the bicuspids. A few malnourished children with delayed tooth germ development may have their molar teeth replaced at around 12 years of age.