Teeth Impressions

Teeth and teeth impressions can be used in an investigation to identify an unknown person and to learn information about him or her. Try the following activity to learn more about what teeth can tell you.

Materials

- scissors
- Styrofoam plate
- Marking pen

Procedure

1. Cut the Styrofoam plate into six equal wedges.
2. Stack two of wedges together, and cut 1 inch (2.5 cm) from the pointed end of both. Throw away the pieces that you cut off.
3. Slip the cut ends of the two wedges into your mouth. Push them in as far as possible while still being comfortable.
4. Bite down on the wedges firmly, then remove them.
5. Label the top wedge Impression of the Top Teeth and the bottom wedge Impression of the Bottom Teeth.
6. Examine the teeth impressions. How many teeth made marks in the top impressions? How many made marks in the bottom impressions? What features of the impressions are useful in telling the top teeth from the bottom teeth? How are the teeth different?

More Fun Stuff to Do

Collect teeth impressions from several helpers. Be sure to label each impression with the person’s name whether it is the top or bottom teeth. Leave the room, then have one helper take a bite from a piece of cheese or hard chocolate. Can you identify who took the bite by comparing the impression in the cheese or chocolate to the set of impressions?

Explanation

Humans are provided with two sets of teeth, which appear at different times in life. The first set, called deciduous teeth, appear when we are children. The second and final set, the permanent teeth, appear later and replace the deciduous teeth.

This process of replacement begins at about age six, when we lose our front incisor teeth, and continues to about age eighteen, when we get our third set molars, commonly called our wisdom teeth. We have twenty deciduous teeth: four incisors and two canines (which cut or tear food) and four molars (which chew and grind food) in each jaw. We have thirty-two permanent teeth: four incisors, two canines, four premolars, and six in each jaw.
The arrangement of each person’s teeth is unique and can be easily used to help identify a person. The number and type of teeth are valuable in determining the age of the individual. Forensic dentists can compare teeth impressions to dental records. Eighty percent of time, teeth impressions are used to identify unknown victims.

Detective Science in Action

Teeth impressions have used to identify many criminals. One hungry burglar was caught because of a half-eaten piece of cheese he left at the scene of the crime. The burglar became hungry during a break-in and took a piece of cheese out of the refrigerator. He had just taken one bite from the cheese when he heard a noise. Startled, be dropped the cheese and ran out of the house. When police arrived, they found the cheese. They matched the teeth impressions of the suspect to the bite marks in the cheese.