Science Buddies: "Ask an Expert"

I'm planning on doing a project on finding a safe and effective teeth whitening product. I want to test for both the efficiency and abrasiveness of products such as activated charcoal, hydrogen peroxide, baking soda, whitening toothpaste, etc. To test the efficiency, I can just stain egg shells and compare the effects of the different products, but I'm unsure of how to test for the abrasiveness. Should I just use the same egg shells and measure the mass before and after the experiment? Or is there a more accurate way to represent damage to the enamel (it has to be measurable)? What other materials can I use other than egg shells? Also, I'm not sure about how long the experiment should be. I was thinking about using the products on the "teeth" everyday for a month. If I were to use the egg shells, would I have to remove the insides of the egg (and if so how would I do that?)

I think that your suggestion about mass before and after is a good one, as long as you are sure that the egg shell is not wet or still contaminated with your whitening agent after (which would alter the mass). Another way, if you have access to the equipment, would be to look under a microscope before and after whitening to see if you can measure any difference in the texture.
As for how long, I would look at the typical product for whitening (since this is what you are trying to compare your new product to) and use a similar timeline.

For removing the inside of an egg, I have seen people puncture two small holes in the egg with a needle and use air to blow the insides out of one of he holes (this was during egg dying as a craft but I'm sure it would work for this application as well!)

Best of luck, let me know if you have further questions!