I really can't say that Mountain Dew rots teeth.  My son (16) eats junk and drinks soda (mountain dew included) and hates to brush his teeth....He has 0 cavities.  His teeth are perfect except for a slight overbite.  The dentist attributes that to the water he drank when he was a little kid.  We lived in a city that had floride in the water.  And yes, he drank water.  I am a junk food junkie and did not fix the best meals when he lived with me.  But the youngin had great teeth.  And, in response to any criticisim (however spelled) of his diet, he moved to his dads at age 12...couldn't take the country!)
We moved to WV when my daughter was 10 months old, she's now 6.  She (at the last dentist visit) has 13 cavities and will have to undergo dental surgery to fix all of them.  We have well water.  I have started buying the nursery water w/floride to give her to drink, to cook with, and to make koolaid with.  She eats more nutritious meals, as I have really buckled down to make sure she gets the food she should eat.  She also does not like a lot of sweets.
I live in a very rural, impoverished area of WV.  Diane Sawyer needs to come up here and check the kids teeth.  My daughter's best friend only drinks Mt. Dew, no water or anything else.  She has perfect teeth.  She brushes them everyday and is on town water (has floride).  I suggest the main problem with the children's teeth rotting is NOT Mountain Dew, but the fact they have well water and no access to floride.
And I do wonder at times how some of the people here in WV that are on government assistance can afford their cigarettes and alcohol but still live in such deplorable conditions.