It is not normal for an 11 year old boy to have only 4 teeth replaced, most children have almost all of their milk teeth replaced by the age of 11. Possible causes include congenital absence of permanent tooth germs, abnormal position of permanent tooth germs, bad dietary habits, calcium deficiency and so on. 1. Congenital absence of permanent embryo: If the child is born with absence of permanent embryo, the roots of milk teeth cannot be absorbed, and the milk teeth will be retained. 2. Abnormal position of permanent embryo: If the permanent embryo is in abnormal position, it will be difficult to erupt out of the oral cavity. 3. Bad dietary habits: If the diet is too fine, the roots of the milk teeth will not be absorbed, which will also affect the replacement of normal teeth. 4. Calcium deficiency: Calcium deficiency during growth and development can also affect the eruption of permanent teeth. There may be other reasons for late replacement of milk teeth. It is recommended to go to the hospital stomatology department in time to take surface tomograms, and follow the doctor’s advice to take the best treatment.