In the original system, children's 20 primary teeth are numbered in the same order, except that a small letter "d" follows each number. This letter indicates that it is a deciduous (primary or "baby") tooth. So, a child's first tooth on the upper right would be 1d and the last tooth on the lower right would be 20d.
However, most dentists and insurance companies now use a modified version of the Universal Numbering System for children. This version uses the letters A through T instead of the numbers 1 through 20. So, a child's first tooth on the upper right would be A. The last tooth on the lower right would be T.
In this system, the mouth is divided into four sections called quadrants. The numbers 1 through 8 and a unique symbol are used to identify the teeth in each quadrant. The numbering runs from the center of the mouth to the back.
In the upper right section of the mouth, for example, tooth number 1 is the incisor (flat, front tooth) just to the right of the center of the mouth. The numbers continue to the right and back to tooth number 8, which is the wisdom tooth (third molar.)
The numbers sit inside an L-shaped symbol used to identify the quadrant. The quadrants may also be identified by letters. For example, "UR" or "URQ" would mean the upper right quadrant.
In children, the Palmer Notation System uses uppercase letters instead of numbers. Following the same order as for adult's teeth, children's 20 primary teeth are lettered "A" through "E" in each quadrant. The same symbol is used to identify the quadrants.