Expert: Jeff Dalin DDS - 2/11/2005

Question
I am a 3rd grader.My mom helped me type this email so that you can understand what questions i need answered better.I have to turn in my project on february 16th.Thank you very much for helping me.

I am doing a project on tooth enamel and acids in the food we eat. so, first of all i don't know how to explain the words LACTIC, ACID, ACETIC, PHOSPHORIC, and CITRIC to a bunch of 3rd graders. Any suggestions? I know that acid eats calcium. I know that tooth enamel and eggshells are mostly calcium. My hypothesis is lactic acid eats tooth enamel faster than acetic, phosphoric, and citric acid because lactic acid is what is made by the s.mutans in your mouth. is it true that s mutans mix with saliva and glucose (i think that its your blood sugar) to make plaque and then the plaque uses even more sugar from your food to turn it into lactic acid? Is that the only acid that plaque turns sugar into? And what is the deal with weak and strong acids? is it the weaker the acid the more calcium it eats and opposite for the strong acid? I looked on the internet and found that I couldn't use my baby teeth for the experiement but i could use eggs. The eggshell is the tooth enamel and I put the eggs in 8oz of yogurt (Lactic acid), 8oz of pickle juice (Acetic acid), 8oz coca-cola (Phosphoric acid), and 8oz freshly squeezed orange juice (Citric acid). I also have one in water to show what no acid will do to your enamel. I'm keeping them at room temperature because i cant get the house as hot as our mouth. They really smell. What is the temperature of our mouth? I can see which one started damaging the egg first (the pickle juice) but how can i measure/compare the changes? I used the measuring tape to measure the size before the test began but eggshell is not that thick so I think i might need another way of measureing the damage. I guess I am comparing time by taking pictures at the first sign of any changes (4 hours later) and everyday after that. can you please help? I don't know if i am doing this right.

Answer
Victoria,
Wow...what great questions. Let me see what i can do to help you out. First off, all of these acids can dissolve tooth enamel. The factor that is the most important is concentration of the acid and the length of time it is in contact with the tooth surface. The mineral in tooth enamel is called calcium hydroxyapatite. The strep mutans join together to form colonies called dental plaque. They make the sticky part of the plaque to hold themselves on the tooth surface. The strep mutans eat sugars and as a byproduct make acid. This acid then dissolves the enamel on the tooth surface.
As far as your experiment goes, it sounds excellent. What you need to do is leave the egg shells in the different solutions (acids) and see what it looks like at 1 hour, 3 hours, 6 hours, 12 hours, and 24 hours (and longer if you want). Mouth temperature is slightly cooler than body temperature so it is in the 90's.
As far as testing how much the eggshell is dissolving, it will be something subjective. You can measure size and thickness of the shell. Pictures will help.
Maybe go into Google and search under "acid dissolving tooth enamel" or "acid dissolving egg shells" and see what comes up. Another place to find details about this experiment is to search sites that discuss science fair projects. One final place to search for help is to call the American Dental Association in Chicago and ask for the Library. They have excellent librarians there who should be able to help you.
Keep up the good work. You are doing a great job so far!!!

Jeff Dalin, DDS