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Healthy teeth are essential for chewing, speech, and a confident smile. Because tooth decay can jeopardize these functions, a science fair project can vividly illustrate how decay occurs and how it can be prevented. Eggshells, composed mainly of calcium carbonate, make an excellent stand‑in for human enamel and are easy to acquire in large quantities.
While sweet foods are commonly cited as culprits, the real question is whether sugar itself or the acids produced by bacteria are responsible. To investigate, immerse eggshells in a series of solutions that represent common beverages and everyday liquids. Include pure sugar water to test the sugar hypothesis, and also test cola, mineral water, lemonade, milk, and vinegar.
Place one eggshell in each mason jar filled with the chosen liquid, seal the jars, and let them sit for one week. After the incubation period, record the condition of each shell—did it soften, dissolve, or remain intact?
Typically, eggshells exposed to cola and vinegar show the greatest degradation, sometimes disappearing entirely. In contrast, shells in sugar water and mineral water remain largely unchanged, while those in lemonade and milk may display variable damage.
Dental professionals explain that sugar fuels plaque bacteria, which metabolize the sugar and produce acids that erode enamel. Cola contains phosphoric acid, and vinegar contains acetic acid—both strong enough to dissolve calcium carbonate. Lemonade’s citric acid and milk’s lactic acid are milder, so their impact depends on concentration and exposure time.
For a deeper look, extend the immersion time for the lemonade and milk samples and observe when decay becomes apparent.
Beyond regular brushing, fluoride is a key preventive agent. To test its effectiveness, coat one eggshell entirely with a fluoride toothpaste gel and place it in a vinegar jar. Leave another eggshell uncoated in a second vinegar jar. Monitor both shells for signs of decay.
If fluoride is protective, the coated shell should remain intact longer than the uncoated one. After initial observations, keep the coated shell in vinegar to determine the duration of its protection.
