Making an impression

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Math II Unit 1: statistics And data Analysis bite mark analysis

Making an impression

Bite-mark study could bolster use as evidence

By Brandy Benedict

Originally published in the Milwaukee Journal Sentinel

It's commonly believed that no two sets of human teeth are alike. Chips, jagged edges, crooked teeth and gaps all contribute to a person's unique smile.

It seems reasonable, then, that bite patterns made by those teeth should be as unique as the teeth themselves, though this has not been scientifically proven.

Now, a team of researchers at Marquette University has gotten one step closer.

By measuring the position and rotation of individual teeth from hundreds of bite samples collected from volunteers, the researchers can statistically estimate how often the characteristics of a particular bite pattern occur in the population and determine the probability of someone else having the same characteristics.

The researchers ultimately hope that the scientific analysis of the patterns will provide a more objective basis for analysis and comparison of bite-mark evidence in criminal trials.

"This project will put science behind the impression that a person's pattern of bites is unique," said Thomas Radmer, assistant professor and director of oral and maxillofacial surgery at Marquette.

L. Thomas Johnson, adjunct professor at Marquette University's School of Dentistry, explained that while intuition may say that each set of teeth would make a distinct bite pattern, there is no scientific database proving it.

So Johnson and Radmer decided to create one.

During a two-year period they collected more than 400 bite patterns from male volunteers ages 18 to 44, the demographic most likely to be the aggressors in violent crimes involving biting.

Each subject bit down on a copper-coated wax wafer, simultaneously capturing the indentations of his top and bottom teeth. The copper coating on the wafer ensured that the bite marks would show up clearly when scanned into a computer.

For each sample they measured six characteristics: tooth width; degree of rotation of a tooth; inward or outward displacement; arch width; spaces between teeth; and any missing or extra teeth.

Measurements of each bite mark pattern initially were taken by hand and had to be checked for consistency.

"This is not an exact science; it's a bit subjective," Johnson said. "There has to be a human mind and eye to compare."

Now, a computer can do all the hard work and get it right every time.

Thomas Wirtz, director of the dental informatics program at Marquette, developed a computer program to measure the bite pattern characteristics automatically, eliminating any errors in measurement.

His program looks at every pixel in the image to locate the positions of all the teeth, and then uses formulas to calculate distances and angles.

It takes 15 to 20 minutes to measure a sample by hand, but Wirtz's computer program can do it in about 10 seconds, a huge improvement considering the researchers ultimately would like to build a database of tens of thousands of samples. "Without the automated program it would be a monumental task," Radmer said.

Controversial as evidence

Bite marks have a controversial history as evidence in criminal trials. First brought up as forensic evidence in 1870, bite marks did not formally gain legal credibility in the U.S. courts until 1954. Since then, bite-mark evidence has been used in a number of cases, most famously to convict serial killer Ted Bundy.

But occasionally forensic dentists have been known to make some costly mistakes.

In April 2002, DNA evidence freed Ray Krone, dubbed the "snaggletooth killer," who spent 10 years in an Arizona prison, including two on death row, based solely on incorrectly analyzed bite marks.

Bite-mark patterns can vary wildly in clarity, and like a bruise, they can change over time. The quality of a bite mark also depends on the substance a person has bitten, as bite marks on gum or Styrofoam cups can be more defined than bite marks on skin. The force of the bite, the angle of the bite and the area bitten can all affect the appearance of a bite mark.

Forensic dentists apply their expertise to formulate an opinion on whether the accused could have made the particular bite mark patterns.

But the subjective nature of bite-mark analysis and interpretation has been the focus of harsh criticism, and forensic dentistry has been called a "junk science."

"False convictions leave bite marks with a black eye," said Donald Simley, a certified forensic dentist based in Madison. The study "should help the whole science of bite-mark evidence."

Radmer agreed: "The defense attorneys have been taking aim at this type of evidence in jury trials as being subjective, not objective."

'Worthwhile' study

With statistics to back up professional opinion, the researchers hope to make bite-mark forensics more scientifically sound.

"What the Marquette study is trying to do is provide an objective, reliable basis to answer the critics," said Daniel Blinka, a professor in the Marquette Law School and legal consultant for the study. "It has a broader significance in providing a template for other areas of forensic expertise, like fingerprint and handwriting analysis, to look to and follow."

Wirtz's computer program could be adapted to measure the width of tire treads, or width of ridges in a fingerprint. "There are multiple applications throughout the field of forensics," Radmer said.

The study was funded with a nearly $110,000 grant from the National Institute of Justice through the Midwest Forensic Resource Center, part of the Ames Laboratory Research Center at Iowa State University. The researchers expect to complete their study by Sept. 30 and will present results in February at the annual meeting of the American Academy of Forensic Science in Washington, D.C.

The researchers agreed that the pilot study shows there is some predictability and provides a basis for further studies.

"We've shown with a very high confidence level that the (bite) pattern is unique," Radmer said.

Johnson, too, is pleased with the results: "I think it was worthwhile."

Through the use of statistics, and using our class as a sample, we will perform our own bite mark analysis.

Bite Marks

  • Firmly bite into your Styrofoam piece leaving an impression of your teeth. Be sure to label your piece with your name.

  • Take each of the following measurements in cm using your ruler. Round any decimals to the nearest tenth of a centimeter. Record your measurements in the table.

    • Measure the distance between the canine teeth in cm. Measure from the center of the tooth mark.

    • Measure the distance between the 2nd molars in cm. Measure from the center of the tooth mark.

    • Measure the distance, in cm, from between the front incisors to the line connecting the 2nd molars. Measure from the center of the tooth mark.

  • Assign someone in your group to enter your data into the online spreadsheet.



Student / Adult



Incisor to Molar

  • Pool the class data. Find the mean and standard deviation of each dot plot. Make 6 dot plots of the class distribution. Put your mean in the middle of the distribution. Describe the shape of the distribution.

Construct each of the dot plots below.

Distance between canines (males) Distance between canines (females)

Mean: _________ Standard Deviation: ____________ Mean: _________ Standard Deviation:____________

Distance between molars (males) Distance between molars (females)

Mean: _________ Standard Deviation: ____________ Mean: _________ Standard Deviation:____________

Distance between incisors and molars (males) Distance between incisors and molars (females)

Mean: _________ Standard Deviation: ____________ Mean: _________ Standard Deviation:____________

The dot plots can be created using Fathom or TI-Nspire or a frequency histogram can be created using TI-83/84. Refer to your data in your table.


  1. First it will be helpful to turn on additional diagnostic information in your calculator.




  1. Press. (This just resets the list menus)

  1. Press

To clear out OLD data, first highlight L1 and press CLEAR, ENTER.
If there is OLD data already in the lists that needs to be cleared press the up arrow, , to highlight L1 and then press to clear out the old data. Do the same for L2 if it has OLD data that needs to be cleared.

  1. Enter the ratios of each member of your class in L1.

  1. Go to the STAT PLOT menu by pressing . Move the cursor to the and press . Move the cursor to and press .

  1. Finally press and then press .


  1. Start a New Document and Select “Add Lists & Spreadsheet”

  1. Title the first column “MS” (male student) and type in all of the data in the first column.

  1. Next, press the button and select Data►6:Quick Graph.

  1. You may need to drag the x-axis a bit to see the distribution appropriately.

  • In either of the distributions what seems to be the ‘center’ of the data?


Each student should gather impressions from at least two adults (21 and older) and return to class with the data measurements. If possible, gather data from a male and a female.

As a class, the adult data will be pooled and compared with the student data.

Distance between canines (males) Distance between canines (females)

Mean: _________ Standard Deviation: ____________ Mean: _________ Standard Deviation:____________

Distance between molars (males) Distance between molars (females)

Mean: _________ Standard Deviation: ____________ Mean: _________ Standard Deviation:____________

Distance between incisors to molars (males) Distance between incisors to molars (females)

Mean: _________ Standard Deviation: ____________ Mean: _________ Standard Deviation:____________


  1. Compare the means and standard deviations of the following groups:

  1. What overall conclusions can you make from the above comparisons?

Comparing Random Samples: Now, collect data from other Math II classes completing the same activity.

  1. How do the means and standard deviations compare between all of the random samples?

  1. What factors might contribute to a difference in the results?


Retrieved from: On-line Study Guides – Bitemarks (Originally published in Forensic Dentistry On-line)

Teeth are often used as weapons when one person attacks another or when a victim tries to ward off an assailant. It is relatively simple to record the evidence from the injury and the teeth for comparison of the shapes, sizes and pattern that are present. However, this comparative analysis is often very difficult, especially since human skin is curved, elastic, and distortable. In many cases, though, conclusions can be reached about any role a suspect may have played in a crime. Forensic odontologists can learn a lot about the victims and suspects by analyzing any bite marks that were discovered as evidence. Bite marks can be helpful in excluding someone as a suspect, or determining that the suspect could be the one who inflicted the bite.

At a crime scene, the victim was found with a distinct bite mark on his forearm. A bite mark sample was collected from 5 possible suspects. The primary suspect is a female because of the measurements that were taken. Can you decide which of the possible suspects are females? What factors could contribute to a more specific conclusion?

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