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Lesson 3-Explore: Let's Investigate Tooth Decay!



Activity 1: The Apple Investigation

The purpose of this activity is to involve students in the processes of scientific inquiry.

assessment iconAssessment:
This is a good time to assess your students' prior knowledge. The purpose of this discussion is to find out what students know, or think they know, about tooth decay and what causes it.

1. Ask the students if anyone has ever had a cavity in a tooth. As students raise their hands, ask them where the cavity happened, to describe what they think a cavity is, and to explain how they think they got a cavity. Record students' responses on the board or flip chart paper.

By age six or seven, some students probably have experienced tooth decay and have had a dentist fill a cavity. If not, students probably know of a family member who has. Ask them to describe what they know about cavities and how a person might get a cavity in a tooth.

2. Show students an apple. Ask them to compare the apple with a tooth. How is the apple like a tooth? How is it different from a tooth?

During this discussion, focus students on the apple as a model of a tooth. Scientists often use models in scientific investigations to find out about things when they cannot or should not experiment with the real object. We know that an apple is not exactly like a tooth, but we can use the apple to conduct an investigation on tooth decay that we would not want to conduct on our own teeth. The apple is shaped somewhat like the crown of a molar tooth and has a covering, the peel or skin, that protects the inside of the apple. We will consider this outer covering of the apple comparable to the enamel that covers and protects the inside of the tooth.

3. Set the stage for investigating tooth decay by asking students what they think would happen inside the apple if someone used a pencil to poke a hole in its skin. At this point, accept all answers and record students' ideas on the board or flip chart paper.

If students have not mentioned it before, indicate that tooth decay happens when something makes a hole in the enamel of a tooth (see Background Information: Using a Model for a discussion of this process). They will use the apple to model what might happen to a tooth if something makes a hole in it.

4. Tell students they will conduct a scientific investigation about an apple with a hole in it. Help students understand how to conduct a scientific investigation by asking questions similar to these:

What would happen if

Remind students that the environment of the mouth is wet, warm, and dark. You may want to display the chart made in Lesson 2, What the Inside of the Mouth Feels Like. What if the apple were in an environment that is similar to that of the mouth? Would the results be the same or different? How could you find out?

Tip from the field test: Some students poked holes into their apple and placed pieces of candy in it. Other students poked holes into their apple and placed it in a plastic bag full of soft drink.

5. Help the students prepare by explaining the steps they will need to do to complete the investigation.

National Science Education Standards iconContent Standard A:
Abilities necessary to do scientific inquiry.

6. After teams have confirmed their scientific question and decided who will perform the tasks, distribute one apple per team. Allow them time to set up their experiment.

7. As a class, determine where to place the control apple (the apple that has not been changed). Make sure students know that they should observe the control apple as well as their experimental apple each time they make observations.

8. Distribute Master 3.1, Apple Record Page, one to each student. Discuss the record page and make sure students know how to complete each section. Allow students time to complete the first three questions and to record their beginning observation.

9. Discuss the teams' answers for question 3 on the record page: What do we think will happen to our apple? Record students' ideas on flip chart paper and save the paper. In a few days, they will compare their results with their initial ideas.

Many times in science class, we ask students to express their initial ideas about something and refer to those ideas as their predictions. Often, however, their initial ideas are merely guesses because they have no experience or existing data on which to base their ideas. Predictions in science usually are based on some prior information or knowledge from previous work. (The dictionary definition of "predict" is "to foretell on the basis of observation, experience, or scientific reason.") Consequently, we don't refer to students' initial ideas as their predictions. If students conduct a second investigation based on the results from the first, then they can make predictions based on their previous experience.

10. Reserve time every day for students to observe their experimental apples and the control apple. Because the change is gradual, require students to record their observations only once at the beginning, once in the middle, and once at the end of the investigation. Encourage students to use hand lenses, thermometers, and the balance to record data about their apple or the environment of the apple.

Every time students observe their apples, ask them to explain why they are doing the apple investigation. Remind them that the apple is a model of a tooth and that they are investigating tooth decay.

You might put up a banner that asks the question, What is tooth decay? and point to that as a daily reminder of the purpose of the investigation.

11. Continue with Lessons 4 and 5. Return to Activity 2 of this lesson in five to seven days.

The information about oral bacteria and decay in Lessons 4 and 5 will help students interpret the results from their apple investigation.

Activity 2: Completing the Apple Investigation

The purpose of this activity is to help students analyze and interpret their scientific investigation.

1. After several days (whatever time you designate for the investigation) cut open each team's apple and the control apple. Instruct teams to observe their own apple and to record the results on their record page. Encourage them to use hand lenses and the balance to make their observations.

The inside of the apples will turn brown quite quickly after you cut them open. You might wait to cut open the control apple until students have recorded the results from their experimental apple.

one half of an apple the other half of the apple

2. Display all the team apples and the control apple. Label each apple according to its variables: number of holes, size of holes, in a plastic bag, in the refrigerator, in a closet, and so on. Invite students to observe the results from all the apples. Discuss the results and help students answer their original question based on what they can observe.

3. Review the teams' responses to Question 3 on their record page.
Discuss whether their responses were accurate and why initial ideas are not always accurate.

Often scientists do not have enough experimental data to make accurate guesses or predictions. The more data they gather, the better their predictions become. (Refer to the note about guesses versus predictions.)

4. Discuss the results of their investigation based on what they learned in Lesson 4 by asking questions such as these:

Remember that the apple is not a perfect model of a tooth. The decay process is not the same, although the appearance might be similar. The inside of the apple will turn brown upon exposure to the air. Tooth decay requires acids produced by oral bacteria.

National Science Education Standards iconContent Standard A:
Abilities necessary to do scientific inquiry.

5. Review the processes that students used to answer their initial question about the apple. Help students compare what they did to what scientists do when they conduct investigations or experiments. Help students realize that they can be scientists.

6. To end the activity, ask students what they would do differently if they repeated their investigation.

How would the students change their question? How would they set up their investigation? What do they predict would happen? This time, the students would be making predictions, not guesses, because they have results upon which to base their predictions.

7. Ask students if they think scientists repeat their investigations and, if so, why.

Scientists often repeat their investigations or ask a new question based on their results. In fact, some scientists study the same (or a similar) question for many years.

8. Congratulate the students on their work as scientists.

Take-home Activity: So You Want to Be an Eggs-pert Scientist!

Exee juggling eggsIn this lesson, we continue with the second of the three take-home activities. As mentioned in Lesson 2, the take-home activities are designed to engage children and their parents in oral health activities at home. The procedure for doing the activity is on one side of the page and the other side contains important background information for the parent.

You might want to complete this activity as an extension activity in class. However, allow time for students to do the activity at home first and then offer it in class for those who did not have the experience at home.

1. Introduce the activity to the students and review the directions. Do not complete the activity in class at this time. Allow students to experience the fun at home first.

This take-home activity engages children and parents in a scientific investigation that models the tooth decay process. This experience demonstrates the effect of an acid on a hard surface like an eggshell and models how acids on teeth can cause tooth decay. It also allows the students to model for their parents the inquiry process they put into practice with the apple investigation.

2. Once again, point out the Certificate of Completion and inform students that you would like their parent or guardian to send the completed form back to school. The parent and child should keep the activity page at home.

3. Send 1 copy of Master 3.2, Take-home Activity 2: So You Want to Be an Eggs-pert Scientist!, home with each student and wait for results.

4. If students are interested, complete the activity at school and discuss the results.

Ask students how an egg is like a tooth and how an egg is not like a tooth. Ask students if they think an egg is a good model for a tooth. Then, discuss students' observations and their explanations of what they think happened. Relate the results to what students have learned about the acid that bacteria produce in their mouths. How might the acids in their mouths act on their teeth like the vinegar, which also is an acid, acted on the eggshell?

Exee writing
assessment iconAssessment:
This is a good time to collect the Mouth Journals to see if students were able to link the apple in the investigation with a model of a tooth. Can they use their observations from the apple investigation to propose explanations for tooth decay?


Instruct the students to use their Mouth Journals to write or draw about what they learned in Lesson 3. Encourage them not only to include information that will help Exee understand about the mouth and tooth decay, but also information about what it means to be a scientist. What are some things scientists do to answer questions like those that Exee asks about the mouth?

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