Project Topics

Engineering Projects

Published on Feb 10, 2016


Acid is a highly corrosive substance that is in all batteries, many chemicals, and industrial wastes. Surprisingly, it is also on many people's teeth! According to the Mereck Manual of Medical Information, carbohydrates and sugars are the biggest culprits of tooth decay.

It states that "all simple sugars including table sugar (sucrose) and sugars in honey (levulose and dextrose), fruit (fructose), and milk (lactose) have the same effect on the teeth. Whenever sugar comes in contact with plaque, streptococcus mutans bacteria in the plaque produce acid." Interestingly, the bacteria and the sugar do not directly cause the tooth decay. It is really the acid, the byproduct resulting from the bacteria consuming the sugars, that causes tooth decay. Acid demineralizes or dissolves teeth and cause tooth decay. Thus, a tooth with decay should weigh less than a tooth without decay.


The process of this experiment is as follows. 80 teeth were gathered and cleaned of all stains, plaque, and debris by special tools such as hand scalers, EMS (electro-magnetic scalers), and polishers.

The teeth were blotted dry with lint-free Kim-Wipes tissue and weighed on a Sartorius scale to 0.0001 gram.

They were then placed in 10 individual vials in 8 categories and labeled from control (pH7), pH2, pH3, pH4, pH5, pH6, Neutral Sodium Fluoride, and Acidulated Phosphate Fluoride.

The teeth were allowed to decay for about 2 months before reweighing them on the same Sartorius scale in the exact same manner.


According to Dentistry Today (November 2005), "acid pH levels cause tooth surfaces to lose calcium and phosphorous ions" which leads to decay.

Acid is able to start to damage teeth once the pH drops below a 5. Acid essentially chelates and dissolves the teeth. The teeth in solutions with pH4, pH5, and pH6 had very little change.

But, when the pH level dropped below pH4, the demineralization process occured at a much faster rate.

In fact, there is a 4 fold difference between pH2 and pH6. Our study shows that there is a dramatic increase in demineralization at pH under 4.


From my results I came to the conclusion that my hypothesis was correct. The larger solutes exerted more osmotic pressure on the water than the smaller solutes. By researching my project's topic I was able to apply it to the function of the kidneys in the human body.

The nephron in the kidney is where membrane transport to maintain the body fluids and blood concentration occurs. One form of membrane transport is osmosis and diffusion.

This project was to observe acid does affect the decay of teeth. The more acid there is in the solution, the greater is the amount of decay. The greatest destruction occurs when the pH level drops below 4. Fluoride definitely helps in reversing or minimizing the damaging effect of tooth decay!

Science Fair Project done By Stephen M. Tang