Their function 10^(5.5-pH) * (mg/cl sugar + 1) does seem to imply that sugar and acidity have a synergistic effect, where the +1 in the sugar term is a hack to keep the result from being 0 if the sugar is 0. This doesn't make sense, as a modest increase in sugar, say from 0 to 1 would double the result regardless of the pH.
What the equation says to me is that acidity sets the stage for tooth damage, but as bad as that is, once you start feeding the bacteria in that set stage, you are in real trouble.
However, the entire article is a hypothesis. It is a best guess by somebody with scientific knowledge, but there is no reason to believe the real formula shouldn't be 10^(5.5-ph)+10(mg/cl sugar) or something completely different.
However, my son and daughter both need a science fair project soon. I wonder if there is a way to formalize this a little.
Their function also improves the results if the drink is more basic. A drink with a pH of 13 would have an amazing score on here.
If you normalize the pH above 5.5 since it has "little to no effect" things on the lower end of the results are better, with milk being worse than water, and chocolate milk being worse than milk.
This shows how bogus it is - you can put lots of sugar in a basic drink and it would score well.
The key point for me is why is concentration of sugar in mg/cl? Why not mg/l, or g/l, or oz/gallon? Each one would give a different answer, and all are equally justifiable. (There is also the weird idea that a decrease in pH of 1, which is 10 times the concentration of H+, would therefore be 10 times as bad.)
