i think its aspartamine or something that is linked to tons of medical problems.
As for the OP, i dont know. Bacteria in the mouth break down sugar, i dont know if they can break down sugar substitutes.
they probably can but the reason sugar substitutes work is they are 100-1000x sweeter than sugar so you only need 1/100-1/1000 as much of it, so with normal pop you may need 240 grams of sugar in a 2 liter but with diet soda and their super-sweet artifical sugar you may only need 0.240 grams, which is about 1 calorie of sugar in a 2 liter.
So even if the bacteria do break down artifical sugar, there is such a small amount of it in diet soda that it will not matter.
I dont know if the other ingredients can decay teeth though, like the acids.