Say Cheese: Dental Analysis

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Objective

SWBAT analyze dental impressions to identify a crime suspect. SWBAT describe the work of a forensic dentist.

Big Idea

Teeth can be a crucial piece of evidence when solving a crime. How can something so small provide such big clues?

Engage

5 minutes

I start each class period in this unit with a warm-up activity that targets forensic science concepts and other skills (observation, problem-solving, etc.) Not only does this get the students in the frame of mind necessary to address the field of forensics, but it also introduces key vocabulary they will use throughout the unit in a more relevant way. In addition, this activity allows students to refine their research skills as they perform quick internet searches to find the correct answers. By using the attached weekly Answer Sheet* and passing it out as they enter the classroom every Monday morning, not only can I save paper, but I can also provide a routine that allows students to begin without prompting, waiting for paper, or asking things such as, "What do we do?" and, "Where do we write our answers?"

For this particular lesson, I have decided to utilize a Video Challenge titled, Underwater Detectives" in which students watch a short video clip about forensics and follow up by answering an assortment of trivia questions.


After providing about 2-3 minutes to choose the correct answers, we go over them together and discuss the information provided. I help students to define key terms and providing background knowledge necessary to help students understand the questions. However, I do not spend as extended period of time on this portion, as it is just meant to be an activator and not necessary to understanding the core of the lesson at this time.

*Challenges and answer sheet courtesy of http://sciencespot.net/Pages/classforscistarters.html

Explore

15 minutes

I explain to the students that forensic dentists assist in crime solving by studying teeth and teeth impressions. Dental records are often used to identify people. Because teeth are one of the hardest substances in the human body, they are frequently well preserved. Dental x-rays or records showing fillings, position of teeth, etc. can help forensic dentists find a match of teeth to the individual. In fact, I explain that eighty percent of all cases,  teeth impressions are used to identify unknown victims. I provide more information and build background knowledge by playing the How is odontology used to solve crimes? video.

In order to hold students accountable for watching the video, to assess the students' understanding of the video and to encourage communication between students, I ask them to share one thing they learned from the video with their shoulder partner.

Next, I pass out the Student Bitemark Impression Lab and page 3 only* of the Bite Mark ID Lab to the students. We read through the procedures together, and I call on a student volunteer to help me model the process for making a bite mark impression. After fielding any clarifying questions (usually there aren't many), I have my Materials Managers (one student delegated from each table group) collect the required materials and set them to work on part 1, in which they create bite mark impressions using styrofoam plates.

*Page 1 & 2 are designed to help the teacher prepare for and implement the lesson. Students will not need these documents.

Explain

10 minutes

Before moving on to section 2, I have students work with their table groups to compile a list of all the factors that may differ among bite mark impressions.  Some ideas may include braces vs. no braces, number of teeth, tooth placement, etc. I perform a quick Whip Around, having students provide responses until there are no new or unique ideas left. We talk about how teeth can differ within these factors. For example, how could tooth placement be different? (Some could angle in, out, be straight, stick out further than others, etc.)

Elaborate

10 minutes

Now that students are familiar with basic bite mark analysis, it is time for them to apply their learning in the form of an investigation. I direct students to Part 2 (Identification) on their labs.

In this section, students leave dental impressions on several pieces of candy, and study each other's candy to determine who made the bite marks.

Students read and follow procedures as they are listed. I monitor the room as they work, helping them to clarify instructions and asking questions to help assess understanding and challenge students' thinking, such as:

  • Why do you think your bite mark will be easy (or hard) to identify?
  • What skills does an odontologist need to have to be successful in an instigation like this?
  • What events or factors could have caused this (point to something on the impression)?
  • How could you make it harder for someone to identify your impression?

Page 2 of the Bite Mark ID Lab provides a key for teachers to record the names of each student and their corresponding piece of candy. The Student Bite Mark Impression Lab (included in the resources section) will contain a table for students to record their observations and inferences.

*For sanitary reasons, all candies are placed in Ziploc baggies prior to being handled by students.

Evaluate

5 minutes

After completing the identification portion of the lab, I facilitate a class discussion, allowing students to share their ideas as to who created each impression. I hold up a numbered baggie and ask each table group to share who they thought it belongs to, providing evidence from their investigation.

Just for fun, I make a game out of it. If a group guesses correctly and has sound evidence to justify their thinking, I give their group 3 points. If a group If a group does not guess correctly, but still has sound evidence to justify their thinking, I give their group 1 point. If a group guesses incorrectly, they receive 0 points. After going through each sample impression, I calculate the points. The groups that receives the most points gets a few extra candies to actually eat! for more information about games in the classroom, please see my reflection.

In order to assess the learning that has taken place, students respond in writing to a series of reflection questions, including the following:

  • Write a paragraph to summarize what you have learned about bite mark impressions from this activity.
  • What do you think are the benefits of dental analysis for forensics investigators?
  • What do you think are the drawbacks of dental analysis for forensics investigators?
  • What have you learned about the work of forensic dentists?
  • Select another area of forensics that we have studied. Compare and contrast this method to dental analysis, using a Venn diagram.