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How Forensic Dentistry Works

Types of Teeth
2008 HowStuffWorks

Teeth aren't fingerprints; they aren't inherently unique from birth. When teeth grow in, or erupt, they do so differently in each person. Teeth grow an average of 4 micrometers per day, so it's possible to give a rough age estimate based on teeth. It can also be possible to distinguish ethnicity from the teeth. Some Asians and Native Americans have incisors with scooped-out backs.

­The patterns of tooth wear also vary and can chan­ge over time. Not only can people be identified by their teeth, you can also learn a lot about their lifestyles and habits by the state of their teeth.

Although each type of tooth has a different name, we have multiples of some types of teeth. For example, a full set of adult teeth includes two upper central incisors and two upper lateral incisors. Therefore, each individual tooth needs its own designation. There are dozens of methods for labeling teeth in use, but the three most popular methods are the Universal System, the Palmer Method and the FDI (Fédération Dentaire Internationale) World Dental Federation notation.

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In the United States, most dentists use the Universal System. In this system, each of the 32 adult teeth is assigned a number. Number one is the upper right third molar, while number 32 is the lower right third molar. The 20 deciduous, or baby teeth, are designated by the letters A through K or the number-letter combination of 1d through 20d.

Some teeth, like molars, have multiple surfaces too. Each of these surfaces has a name. The center of the tooth is the biting surface, known as the occlusal. This surface has two elements: the cusps, or raised parts, and the grooves, or indentions. The mesial surface of the tooth is toward the front of the mouth, while the distal is toward the back. The side toward the inside of the mouth is the palatal surface on the upper jaw (lingual on the lower jaw). The tooth surface facing the cheek is the buccal. So if you get a filling on the distal of number 15, you'll know that means it's on the surface facing the back of the mouth on your upper second molar (or 12-year molar).

When you visit the dentist for a checkup, he or she uses a Universal System chart and makes a notation on each tooth to show variations such as chips and dental work such as fillings, crowns and bridges. The dentist also includes observations about the health of your teeth, like receding gums or signs of periodontal disease. Most dental visits involve taking sets of X-rays, which can also show work not easily seen, like root canals.

In the next section, we'll look at how forensic dentists use these records to identify teeth.