Teething: Your baby's first teeth
If your baby develops teeth early, she may get her first tooth as soon as 3 months. (Very rarely, a baby's first tooth is already visible at birth.) In other cases, you may have to wait until she's a year or older. Whenever your baby's first tooth makes its appearance, celebrate the milestone by taking pictures and noting the date in your child's baby book. Teeth actually start developing while your baby is in the womb and tooth buds form in the gums. Teeth come in over a period of months, and they often appear in this order: the bottom two middle teeth first, then the top two middle ones,...
Source: babycenter.com