Numbering systems have been developed in order to have a standard way of referring to particular teeth (there are more than 32 different systems). Two are commonly in use in the US today:
The Universal Numbering System has been adopted by the American Dental Association and is in use by most general dentists today, and the Palmer Notation Method is used by some orthodontists, pedodontists (child dental specialist), and oral surgeons (originally called the Zsigmondy system after an Austrian dentist of that name who developed the idea in 1861). Internationally the two-digit FDI* World Dental Federation ISO-3950 notation is widely used.
* Federation Dentaire Internationale
Tooth number 1 is the tooth farthest back on the right side of your mouth in the upper (maxillary) jaw.
Numbering continues along your upper teeth toward the front and across to the tooth farthest back on the top left side (which is number 16).
The numbers continue by dropping down to the lower (mandibular) jaw. Number 17 is the tooth farthest back on the left side of your mouth on the bottom.
Numbering continues again toward the front and across to the tooth farthest back on the bottom right side of your mouth (which is number 32).
In this system, the teeth that should be there are numbered. If you are missing your wisdom teeth, your first number will be 2 instead of 1, acknowledging the missing tooth. If you've had teeth removed or teeth are missing, the missing teeth will be numbered as well.
In the original system, children's 20 primary teeth are numbered in the same order, except that a small letter "d" follows each number to indicate deciduous (primary) teeth. 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 number 1 through 20. So, a child's first tooth on the upper right would be A and 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 "L" is right side up for the teeth in the upper right. The teeth in the upper left use a backward "L." For the bottom quadrants, the "L" is upside-down. The quadrants may also be identified by letters, such as "UR" or "URQ" for 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.