Materials Included In Kit

Additional Materials Required

Safety Precautions

Toothpaste is considered a non-hazardous material; however, any material that has been in the lab should not be put in the mouth. Zirconyl chloride solution contains hydrochloric acid which is toxic by ingestion or inhalation and corrosive to body tissue. Alizarin red solution is a body tissue irritant. Use these chemicals in a fume hood and avoid all contact with eyes, skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All solutions may be flushed down the drain with water according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• This kit contains ample materials for a class of 24 students working in pairs.
• When choosing toothpaste samples for the testing, try to choose five very different samples (in terms of cost, color, consistency like paste vs. gel and special formulations, such as baking soda, tartar control, sensitive and denture formulas).
• A sample data table is provided with toothpastes that offer a range of results. Keep in mind, however, that even if you choose some of these toothpastes to test, data may vary from that in the sample data table as toothpaste formulations are constantly changing.

Answers to Questions

1. Answers will vary.
2. Answers will vary.
3. Answers will vary.
4. Answers may vary; however, the toothpastes with baking soda will likely have larger crystals.
5. Answers will vary.
6. Steps 1–4 in Test 2 were the control. This was to be sure the act of rubbing the cotton swab on plain water was not causing the scratches or abrasion.
7. The abrasive is the active ingredient necessary to remove food residue, pellicle, plaque and tartar.
8. Too harsh of an abrasive may scratch or damage the enamel.
9. Answers will vary, although it would be expected that the tartar control samples will show a higher abrasion. This would remove plaque before it forms into tartar.
10. Answers will vary, although the toothpastes with baking soda will likely be more basic.
11. Answers will vary, although it is likely that none will be out of the acceptable pH range.
12. Those samples with a pH higher than 7 will taste more bitter.
13. Those samples with a pH lower than 7 will taste more sour.
14. Answers will vary; however, students may attribute taste to the water used, foods or drinks recently consumed and other additives, such as sweeteners.
15. Fluoride is added to toothpaste in order to fight tooth decay by helping to strengthen the enamel.
16. Fluoride acts by replacing some of the mineral on the enamel and by suppressing the bacteria’s ability to generate acids.
17. Answers will vary; however, it is likely that some of the sensitive or whitening toothpastes may not contain adequate fluoride.
18. Answers will vary.
19. Answers will vary.
20. Surfactants aid in the removal of plaque and loose debris from the mouth.
21. Answers will vary.
22. Answers will vary.
23. Answers will vary.
24. Answers will vary; however, students may find that the lowest cost paste is not necessarily the best value because it does not contain the qualities needed of a good toothpaste.
25. Answers will vary; however, students may find that the highest cost paste is not necessarily the best.
26. Results with tap water would vary depending on the region and quality of water. Student answers will vary; however, they may hypothesize that there would be less foaming, different pH, different amount of fluoride (if the tap water contained some) or perhaps a different fragrance.
27. Answers will vary. Toothpaste manufacturers may increase the size of the toothpaste tube opening.

Teacher Handouts

12790_Teacher1.pdf

References

Consumer Reports, September 1992; pp 602–606.

Fong, E.; Scott, A. S.; Ferrus, E. B.; Skelly, E. G. Body Structures and Functions, 8th ed.; Delmar Publishers: New York, 1993; pp 187–189.

Hole, J. W. Human Anatomy and Physiology; William C. Brown: Dubuque, IA, 1990; Fifth Edition; pp 521–522.

Russo, T. Consumer Microchemistry; Theta Technologies: Southgate, KY, 1996; p 37–38.

Selinger, B. Chemistry in the Marketplace; Harcourt Brace: Sydney, Australia, 1989, Fourth Edition; pp 117–118.

Snyder, Carl H. The Extraordinary Chemistry of Ordinary Things, John Wiley & Sons, Inc.: New York, 1992; pp 584–586.

Svehla, G. Vogel’s Qualitative Inorganic Analysis; John Wiley and Sons: New York, 1987, Sixth Edition; pp 181–182.

The Visual Dictionary of Human Anatomy, DK Publishing, Inc.: New York, 1996; p 23.

Introduction

Whitens teeth! Freshens breath! Fights cavities! Removes plaque! Toothpaste ads make all sorts of promises, but are these claims true? Is one toothpaste really superior to another? Does it make sense to buy the more expensive brand? These questions will be answered as you learn about the tooth and tooth decay as well as about the role of toothpaste in maintaining healthy teeth.

Concepts

• Chemical function
• Oral health
• pH

Background

In order to appreciate the function of toothpaste, an understanding of the parts of the tooth, how tooth decay occurs, and how it can be prevented is important.

Let’s start by looking at the structure of the tooth. The tooth is composed of three primary parts: the crown, the neck, and the root (see Figure 1). The crown portion is the visible part of the tooth which projects above the gum; the neck is the area where the tooth enters the gumline; and the root is anchored in the alveolar bone of the jaw.

The crown is covered by a glossy, white, hard coating called enamel. Enamel is composed primarily of calcium salts and is the hardest substance in the body. Enamel, in spite of its toughness, can be damaged or worn down by abrasive action, injury or acids.

The main mass of a tooth is located beneath the protective enamel. This bone-like calcified tissue is called dentin. Dentin is not as hard as the enamel, which makes it more susceptible to tooth decay. In a healthy tooth, this is not a cause for worry because there is only a shallow crevice between the enamel and the firm, pink gum, exposing little or no dentin. However, in a tooth with receding gums, a pocket forms around the tooth where the gum has pulled away from the tooth. Thus, dentin is exposed and is much more likely to decay (see Figure 2).

The dentin surrounds the tooth’s soft central cavity called the pulp cavity. This cavity contains blood vessels, nerves and connective tissue (pulp). The blood vessels and nerves reach this cavity through tubular root canals which extend upward into the root.

So why does tooth decay occur? Less than one minute after the teeth receive a thorough cleaning, a thin, transparent film called the pellicle begins to coat the teeth, tongue and gums. This film, derived from proteins in saliva, anchors bacteria and collects stains from food, drink and tobacco. The pellicle is swarming with bacteria which reproduce and then live in the sticky, gel-like substance known as plaque. The bacteria in the plaque ferment the sugars in foods to produce acids, which attack the tooth enamel. When enough erosion of the enamel has occurred, microorganisms can pass through the weakened barrier to begin the decay process on the interior dentin. The result is dental caries, better known as tooth decay or cavities.

Over time, plaque deposits bond with minerals in saliva to form tartar, also called calculus, a calcified or hardened deposit that only professional cleaning can remove. Calcification can start within 2 to 14 days of plaque formation. Plaque can also seep below the gumline and cause gingivitis, a mild gum disease causing gum inflammation. With more extreme gum recession and prolonged neglect, plaque can form in the periodontal pockets and can attack the deeper tissue and bone causing periodontitis, a severe gum disease.

So what is the key to keeping the teeth free of cavities and disease? The key lies in the frequent removal of the accumulated plaque. This feat depends mainly on grinding it away with a good dental abrasive. With daily removal of plaque, the minerals normally present in saliva replace those on the teeth that may have been removed by mouth acids. To be effective as a dental abrasive, the grinding agent must be harsh enough to remove food residue, pellicle, accumulated plaque and tartar, yet not so harsh as to grind away at the enamel itself. Typical abrasives include salts of calcium, magnesium, aluminum or titanium (see Table 1).

The Food and Drug Administration considers the abrasive to be the active ingredient in toothpaste and it is usually present at ~27%. Toothpaste also has other ingredients in specific proportions, each with its own important function (see Table 2). Water, which is a solvent and filler, is the most abundant ingredient at 37%. The second most abundant ingredient at ~32% is a humectant which helps maintain the consistency and moisture content of the paste. Glycerin is a common humectant. A common standard for toothpaste states that when it is heated to 45 °C and kept there for 28 days, toothpaste should not form a gas, separate, or ferment. It must not run out of the tube if the cap is left off and the tube is on its side, nor should it sink into the bristles of the toothbrush as soon as it is applied. On the other hand, it should not be so firm as to roll off the brush under normal use.

A small amount of detergent, or surfactant, is added to most toothpaste formulations as a foaming agent. While this detergent is not a principal protection against tooth decay, it aids in the removal of plaque and loose debris from the mouth and also gives the sense of cleanliness.

Fluoride is included at about 0.1 percent concentration in most brands to fight decay by helping to maintain the strength of the enamel. The fluoride seems to act in two ways. First it speeds the replacement of some of the mineral on the enamel, converting it to a harder mineral more resistant to corrosion by acids. Second, it suppresses the bacteria’s ability to generate acids.

Other toothpaste additives include preservatives, thickeners, colors, flavors and sweeteners.

In this laboratory activity, abrasive power, pH, fluoride ion content and foaming ability will be measured. After gathering data from various toothpaste samples, results will be analyzed and judgments will be made about the different toothpastes.

Materials

Safety Precautions

Toothpaste is considered a non-hazardous material; however, any material that has been in the lab is now considered a chemical and should not be consumed. Zirconyl chloride solution contains hydrochloric acid which is toxic by ingestion or inhalation and corrosive to body tissue. Alizarin red solution is a body tissue irritant. Use these chemicals in a fume hood and avoid all contact with eyes, skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Test 1. Appearance

1. Assign each of the five toothpastes a number from 1 to 5 and fill in the toothpaste names on the data table.
2. Using a permanent marker, number five plastic slides from 1 to 5.
3. Smear a pea-size dab of each toothpaste onto the corresponding slide.
4. First, use the naked eye to make observations on the toothpaste’s appearance (e.g., color, scent, consistency). Record your descriptions in Table 3.
5. Next, place each slide under the microscope and make observations about particles or crystals in the toothpaste (e.g., size, quantity, color). Record your data in Table 3. Note: For a better view of solid crystals under the microscope, observe the toothpaste where it is in a thin layer.
6. Do not rinse off the slides. Save the slides for use in Test 2.

Test 2. Abrasiveness

Control

1. Add 1–2 drops of distilled water onto one of the microscope slides but away from the dab of toothpaste.
2. Obtain a cotton swab and, applying a consistent pressure, rub the swab back and forth through the water 25 times.
3. Pat the area dry and observe any scratches on that end of the slide under the microscope.
4. Rate the amount of scratches (0 = none to 5 = high degree of scratching). Record the ratings in Table 3.

Test Samples: This test will be done using the 5 slides already containing toothpaste from Test 1.

1. Use a cotton swab to flatten the toothpaste sample on the microscope slide.
2. Add 1–2 drops of distilled water to the toothpaste sample.
3. Using consistent pressure, rub the cotton swab back and forth 25 times through the toothpaste sample on the slide. Note: Rub in short (1 cm) strokes rather than across the entire length of the slide.
4. Repeat steps 1–3 for the remaining toothpaste samples using a fresh cotton swab each time.
5. Rinse the slides using tap water and pat them dry.
6. Use a microscope to observe any scratches on the surface of the plastic slide. Rate the amount of scratches (0 = none to 5 = high degree of scratching).
7. Record the rating in Table 3.

Test 3. pH

Control

The pH of pure distilled water cannot accurately be measured using pH test paper due to the low ion count and the rapid absorption of carbon dioxide. For the purposes of this lab, assume the water has a neutral pH of 7.

Test Samples

1. Obtain and label five 250-mL beakers.
2. Add approximately 2 g of the corresponding toothpaste to each beaker. Note: This can be done by placing the beaker on an electronic balance and adding 2 g of the sample or by measuring a 2-cm length of toothpaste into the beaker.
3. Add 80 mL distilled water to each beaker.
4. Stir the toothpaste/water mixture with a stirring rod until a suspension is formed.
5. Obtain five small strips of pH paper (~2 cm long).
6. Dip one strip of paper into the first sample.
7. Immediately compare the color on the pH strip to the color chart and estimate the pH of the toothpaste.
8. Record the value in Table 3.
9. Repeat steps 6–8 for the other samples.
10. Save the five toothpaste/water mixtures for use in Tests 4 and 5.

Test 4. Fluoride

Control

1. Using a Beral-type pipet, add 4 drops of zirconyl chloride solution to a small test tube.
2. Using a fresh pipet, add 4 drops alizarin red solution to the test tube.
3. Add distilled water dropwise (while counting drops) to the test tube, tapping and rotating the test tube to stir.
4. If fluoride is present, the deep red color will change to a yellow-orange. (Assume negligible fluoride in the sample after 50 drops.)

Test Samples: This test will be done using the five toothpaste/water mixtures prepared in Test 3.

1. Obtain and label five small test tubes.
2. Using a Beral-type pipet, add 4 drops zirconyl chloride solution to each test tube.
3. Using a fresh pipet, add 4 drops alizarin red solution to each test tube.
4. Add dropwise (while counting drops) the first toothpaste/water mixture to the corresponding test tube.
5. Tap and rotate the test tube to stir.
6. If fluoride is present, the deep red color will change to a yellow-orange. Note: If fluoride is absent, the deep red color will remain. The yellow color may not be noticeable immediately due to suspended material.
7. Record your data in Table 3.
8. Repeat steps 4–7 for the other samples.
9. Save the five toothpaste/water mixtures for use in Test 5.

Test 5. Foaming Ability

Control

1. Obtain a 100-mL graduated cylinder.
2. Add 20 mL of distilled water to the cylinder.
3. Cover the opening of the cylinder with the palm of your hand or with a stopper and vigorously shake the cylinder 25 times.
4. Did any foaming occur? Record your observations in Table 1 and empty out the cylinder.

Test Samples: This test will be done using the five toothpaste/water mixtures prepared in Test 3.

1. Stir the contents of the first toothpaste/water mixture in the beaker to evenly disperse all of the contents.
2. Quickly pour ~20 mL of the mixture into a 100-mL graduated cylinder.
3. Cover the opening of the cylinder with the palm of your hand or with a stopper and vigorously shake the cylinder 25 times.
4. Use a metric ruler to measure (in cm) the level of the foam above the water and record your measurement in Table 3.
5. Rinse out the cylinder and repeat steps 1–4 for the other toothpaste samples.

Test 6. Value

1. Record the cost and tube size (in oz.) of each toothpaste sample in Table 3.
2. Calculate the cost per ounce for each sample.
3. Also record any other information given on the label regarding specific claims or special formulations.

Student Worksheet PDF

12790_Student1.pdf