Milk teeth normally begin to change around the age of 5~7 years old, and around the age of 12~14 years old, all 28 permanent teeth, except wisdom teeth, erupt. Babies are born toothless and start to erupt their milk teeth at around 6 months of age. There are 20 teeth in the milk tooth row, which usually erupt completely at around 2 and a half years of age. The milk teeth are normally replaced by permanent teeth, which may start at around 5 years of age for females and 6 years of age for males. The mesial incisors begin to be replaced at 5 to 8 years of age; the lateral incisors at 5 to 9 years of age; the cuspids at 8 to 11 years of age; the first premolars at 9 to 12 years of age; and the second premolars around 9 to 13 years of age; the first molar at 5 to 7 years of age; and the second molar at 11 to 13 years of age.