The big teeth, also known as molars, permanent molars don’t replace teeth, they grow directly out of the mouth, and milk molars will start to be replaced around the age of ten. 1. Permanent molars. At about six years of age the first permanent molar begins to erupt from the back of the last tooth in the mouth without any milk teeth to replace it, and at about twelve years of age, directly behind the first permanent molar, the second permanent molar also erupts without replacement of milk teeth. 2. Milk molar. Molar teeth include the first and second molars. At around 10 years of age, the second molars begin to loosen and the second premolar erupts underneath them, and the first molar is replaced by the first permanent premolar. The first molar will be replaced with the first permanent premolar. It is recommended to pay attention to oral hygiene during tooth replacement and have regular oral checkups to prevent caries.