October/November 2015 Teacher's Guide for Tooth Decay: a delicate Balance Table of Contents



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In-Class Activities


(lesson ideas, including labs & demonstrations)

  1. The following experiments/demonstrations can be used to investigate dissolution of solids, as in demineralization of tooth enamel. All the following use either egg shell or bone to represent teeth (although some use actual teeth):

    1. Dissolve CaCO3 in HCl or vinegar—egg shell, limestone or even marble dissolving in the acid. Although tooth enamel is not exactly analogous to CaCO3, you could use this as an example of what happens to a calcium-based mineral when it is exposed to acid secretions. Put an egg into vinegar and observe it over several days. The acid will dissolve the shell, similar to what happens when acid attacks tooth enamel, although that is a much slower process.

    2. This simple experiment uses chicken bones (allegedly akin to tooth material) and vinegar to show erosion. It misses the chance to use soda as the acid. Students could check pKas of relevant acids (acetic, phosphoric, citric, malic, carbonic) to predict effects on bones and do the experiment to test their hypothesis. (http://healthyteeth.org/acid-attack/) (perhaps they can also draft revised experiment with improved procedure)

    3. You could have students design an experiment using actual citric and phosphoric acids in varying concentrations acting on extracted teeth (obtained from a local dentist, perhaps?) to test their effects. (See this site for a science fair experiment, as an example: http://www.selah.k12.wa.us/SOAR/SciProj99/ElisaSciProj.html#TOP.)

    4. Here’s a simple demonstration to show fluoride’s protective effect on teeth (or similar substance, at least): http://healthyteeth.org/power-of-fluoride/.

    5. This student science fair project tests various liquids, mostly sodas, to see their effect on the decay of egg shells, chosen to represent real teeth: http://mwvsciencefair.wikispaces.com/Teeth+Decay+in+Liquids. You could have students evaluate the project in terms of how well it simulates tooth decay, and how well it was designed/executed, to test their understanding of the process of science.

  2. You can show examples of precipitation to simulate the remineralization of hydroxyapatite on tooth surfaces using solutions of 0.1 M CaCl2 in Na2CO3 or CaCl2 & NaOH.

  3. To show students how an equilibrium works, you could do the standard equilibrium demonstration or lab activity involving iron(III) nitrate (KNO3) and potassium thiocyanate (KSCN). This site presents a nice visual description of the very simple lab showing the effects of stresses on this equilibrium: http://www.chem.uiuc.edu/chem103/equilibrium/iron.htm. And this one provides some nice questions as follow-up to the activity: http://www.chalkbored.com/lessons/chemistry-12/Le-Chatelier-lab.pdf.

And this one provides a bit more chemistry at a slightly higher academic level: http://faculty.scf.edu/GambinC/CHM%202046/CHM%202046%20Lab/Le%20Chatelier%27s.doc

This 7:40 YouTube video clip shows various stresses on the iron-thiocyanate equilibrium: https://www.youtube.com/watch?v=xT43fdoT_4w



  1. Or you can do one of many other demonstrations of equilibrium, such as this one:

    1. This 3:04 YouTube video clip shows an instructor simulating a chemical equilibrium system using a “reaction” (water being transferred between two aquaria) approaching and reaching equilibrium: https://www.youtube.com/watch?feature=player_embedded&v=_QnRt7PYzeY

    2. This 14:51 Flinn video has Irwin Talesnick teaching teachers how to do the equilibrium demonstration discussed in a: https://www.youtube.com/watch?feature=player_embedded&v=ksGWvU8KaGE.

    3. You could also do this demonstration using clear cups as the reservoirs and straws (of differing diameters) to transfer the water between the cups. Remember to color the water to make it more obvious to your audience and be sure you have a one-color background behind the cups—or the aquaria.

  2. You can show pH change using Universal indicator in the reaction of baking soda (NaHCO3) in HCl or vinegar; or test the pH of a colorless soda, like 7 Up or Sprite.

  3. Almost all of the acidity of soda pop comes from the phosphoric acid and not from the carbonic acid from the dissolved CO2. You can verify this by measuring the pH of fresh and flat soda pop (minus the CO2 and, hence the carbonic acid); there's very little difference in pH. The phosphoric acid is corrosive, but actually the acid concentration in soda pop is lower than that in orange juice or lemonade. Try submerging identical strips of magnesium (or iron staples) in each of these beverages overnight, including soda pop. Which beverage dissolves more metal? Which dissolves the metal fastest? (http://antoine.frostburg.edu/chem/senese/101/consumer/faq/why-phosphoric-acid-in-soda-pop.shtml)

  4. Vernier Software’s “Chemistry with Vernier” lab manual, experiment 35 has students determine the phosphoric acid content of various sodas. This site provides an evaluation copy of the activity, but it includes a statement that it is an incomplete document, lacking safety instructions, preparation of materials, etc.; they provide the link for you to buy the lab manual. (http://www2.vernier.com/sample_labs/CWV-35-COMP-phosphoric_acid.pdf)

  5. Show pH change—e.g., Universal indicator, baking soda & HCl or vinegar

  6. If you teach an AP or second-year level class, this lab that describes using infrared spectroscopy (830 nm) to experimentally determine the amount of phosphorus (from phosphoric acid) in cola soft drinks may be of interest: Lozano-Calero, D.; Martin-Palomeque, P. Determination of Phosphorus in Cola Drinks. J. Chem. Educ., 1996, 73 (12), p 1173. The abstract of the article is available online at http://pubs.acs.org/doi/abs/10.1021/ed073p1173. The pdf is available to subscribers only at this same URL.

  7. Have kids design an experiment to test the acidity of various sour candies. Here’s a sample from Mensa for Kids: http://www.mensaforkids.org/teach/activity-plans/the-science-of-candy/. Students can review this procedure to determine its efficacy. After discussion of this test, they can devise their own, hopefully improved procedure. (You can download a pdf of the activity for classroom distribution.) This is a list of candy products and their corresponding pH levels: http://www.drokeefe.com/pages/candy-ph.htm.

  8. Here’s another science experiment testing sugar and dental erosion: http://scijourner.org/index.php?option=com_content&view=article&id=236:experiment-sports-drinks-possible-cause-of-tooth-erosion.

  9. Have students make their own toothpaste. Here’s an article from J. Chem. Educ. that provides the student and teacher versions of the lab activity: Trantow, A. JCE Classroom Activity #47: Brushing Up on Chemistry. J. Chem. Educ., 2002, 79 (10), pp 1168A–1168B; abstract available online at http://pubs.acs.org/doi/abs/10.1021/ed079p1168A, pdf of entire article available only to subscribers, at this same URL.

  10. This Journal of Chemical Education article provides five questions (and answers) that students of AP, second year or IB courses could be asked to solve regarding fluoride in dental applications, to give them applications of chemistry to the real world. Chemistry topics included in these questions are: “stoichiometry, concentration units, resonance in polyatomic ions, bond order, bond length, geometry of polyatomic ions, and treatment of water.” (Resources for Student Assessment. Pinto, G. Fluorine Compounds and Dental Health: Applications of General Chemistry Topics. J. Chem. Educ., 2009, 86 (2), p 185; abstract available at http://pubs.acs.org/doi/abs/10.1021/ed086p185; the pdf of the article is also available to subscribers at this same URL)

  11. You can have students research and debate the water fluoridation controversy. “Pros” can start with information from the Fluoride Information Network, http://fluorideinfo.org/, while “cons” can begin with information from the Fluoride Alert Network, this source: http://fluoridealert.org/. Perhaps a more balanced view can be found at the Centers for Disease Control (CDC) Web site, here: http://www.cdc.gov/fluoridation/benefits/index.htm

  12. As mentioned in the “More on saliva and equilibrium in the mouth” section, amylase is one of the enzymes in saliva that helps digest starches.

  1. There is a standard activity that shows amylase activity on starch. The student chews on a carbohydrate and tests the result with tincture of iodine. (simple: http://www.coolscience.org/CoolScience/KidScientists/IodineStarch.htm) and

(a bit more complex: http://www.juliantrubin.com/encyclopedia/biochemistry/saliva_amylase.html)

  1. Or you can use amylase by itself. Here’s a YouTube video clip (7:13) that shows the process in detail, and then the result after several minutes: https://www.youtube.com/watch?v=cZyq4koUCNM.

  2. And here is an inquiry-based student activity from The Science Teacher, “Enzyme Inquiry”, to take the previous student activity a step further: http://science.kennesaw.edu/~mdias/SCED%204415/Biology%20Teaching%20Resources/Enzyme%20Inquiry.pdf.

  1. Another activity showing saliva’s effects is to test mouth pH before and after eating. “Wait at least two hours after eating or drinking to ensure that the food consumed does not alter test results. Cleanse the mouth by filling the mouth with saliva and then swallowing or spitting. Fill the mouth again with saliva and place a small amount on a pH strip. The strip will change colors based on the results.” http://www.livestrong.com/article/192281-what-is-ph-of-saliva/

  2. In this student activity (college-level, but not that difficult), students measure the “amylase number”, a relative value that reflects the individual’s amount of amylase and its ability to break down starch. They then compare class results. (https://www.apsu.edu/sites/apsu.edu/files/chemistry/SP11_1021_BREAKING_DOWN_STARCH_USING_SALIVARY_ENZYMES.pdf)

  3. You may want to use the idea of the photo-initiated catalysts to begin the polymerization process in materials used for composite fillings as an example of light’s effects on chemical reactions. The light used in this process is usually a blue, or even ultraviolet light. You can ask students why a blue light is used, rather than a red or green light, for example.

  4. Depending on the level of your students, you might want to have them do the following calculations to show the difference in solubility between hydroxyapatite and fluoroapatite.

Exercise: SOLUBILITY and SOLUBILITY PRODUCT


Tooth enamel is composed of the mineral hydroxyapatite, Ca5(PO4)3OH
(Ksp = 6.8 x 10-37). The presence of acids, i.e. acidic fruits and fruit juices or acids that are formed when various sugars are metabolized by bacteria, will react with the hydroxyapatite, thus leading to tooth decay. Fluoride is often added to toothpaste and water treatment plants in some communities add fluoride to drinking water to prevent tooth decay. The fluoride reacts with the Ca5(PO4)3OH to form the more decay resistant fluorapatite, Ca5(PO4)3F (Ksp = 1.0 x 10-60). These measures have resulted in a dramatic decrease in the number of cavities among children. Calculate the solubility of Ca5(PO4)3OH and Ca5(PO4)3F in water.
1. Write a chemical equation for the reaction of hydroxyapatite with acids (H+):
2. Calculate the solubility of Ca5(PO4)3OH in water
[ICE tables—samples are given on the site below to show how to solve this problem]




Ca5(PO4)3OH

Ca2+

PO43-

OH-

Initial

 

 

 

 

Change

 

 

 

 

Equilibrium

 

 

 

 

3. Calculate the solubility of Ca5(PO4)3F in water







Ca5(PO4)3F

Ca2+

PO43-

F-

Initial

 

 

 

 

Change

 

 

 

 

Equilibrium

 

 

 

 

(http://wc.pima.edu/~skolchens/C152OL/Ch19/Ksp.htm)



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