Making Toothpaste is Easy, Modeling Decay Bacteria Harder

For the last several years, we’ve made toothpaste with my class and they’ve always had fun doing it.  Part of the excitement comes from the idea that they are actually making something that is usually bought in a store.  It is cool to show them how to make things they are familiar with, but never thought about doing themselves.  I call it the Chemistry of Everyday Things – which always reminds me of Don Norman’s classic of cognitive science, The Psychology of Everyday Things.  The GEMS guide Secret Formulas from Lawrence Hall of Science has projects making paste, a cola-like beverage, and ice cream, as well as toothpaste.  As always, I change the basic activity around to tune it for my class and whatever seems interesting that year.

When asking them about what was the basic purpose of toothpaste, I’m sometimes surprised when it takes several responses before getting to “cleaning our teeth.”  Modern marketing is doing wonders with selling taste, tooth whitening, colored gels, and stripes.  This year just before we started on our toothpaste project, I had just been re-reading the section on mouth bacteria and tooth decay from Natalie Angier’s The Canon: A Whirligig Tour of the Beautiful Basics of Science and was captivated by her description of over 600 species of bacteria at work in our mouth to cause cavities.  After some more background reading, I felt I needed to do more with helping them get a better picture of the massive ecosystem at work in our mouths.  Just telling never works well, so I started looking for some kind of model to illustrate.   

My first thought was that some teacher must have made a good quality, scientifically accurate video that was hopefully a bit less terrifying than Texas Chainsaw Massacre.  But I didn’t find what I wanted.  There were lots videos of dentists in white coats just talking about film on teeth.  Also, there were lots of really gross videos and photos of mouths of rotting teeth.  One video intended for college students had fascinating content about how the various bacteria had different functions and how they communicated with each other.  Unfortunately, the animation was too abstract and the content level and the cognitive load were too much for elementary students. 

I’ve started thinking about getting a model tooth, like the ones in the dentist videos, and seeing if I can find a way for something more or less like bacteria to grow on it fairly easily and quickly.  Or alternatively, to find some kind of highly visible coloring or film we could brush off as a way to model the growth of bacteria.