The story was pretty much everywhere. I embedded the photo here, sorry, in which the horrible teeth attributed to methamphetamine use look similar to the horrible teeth attributed to diet soda.
Top: "Dentition associated with the methamphetamine abuser." Bottom: "Dentition associated with consumption of diet soda." (Bassiouny, General Dentistry)
This was all based on an interesting article in the journal General Dentistry, in which Dr. Mohamed Bassiouny, a professor in the department of restorative dentistry at Temple University, wrote about three people with severe tooth decay, one of whom drank a lot of diet soda. Specifically she drank two liters every day, and "she did not seek any dental health services for an extended period of time (more than two decades)."
Another person in the article used methamphetamines, and another used crack. They were all described as having comparably advanced tooth decay.
As the American Beverage Association responded to the paper in a statement, though, "To single out diet soda consumption as the unique factor in her tooth decay and erosion -- and to compare it to that from illicit drug use -- is irresponsible."
Soda is acidic, and there's value in knowing that diet soda can be bad for teeth despite its lack of sugar. That's about all to be taken from this extreme case with confounding variables, though. Meanwhile the person in the study who was the example of methamphetamine use ... also drank a lot of soda:
He continuously experienced dryness of the mouth; to restore hydration, he frequently sipped two to three (12 oz.) cans of regular soda every day. He did not recall seeking any routine dental care during that time, except for emergency molar extraction. He came to the university dental clinic to "fix his mouth."
So before you have to fix your mouth, what's reasonable to know about diet soda and teeth?
Researchers at the University of Iowa looked at the acidities of the things we drink, and how acidity correlated with tooth erosion. They soaked molars in various beverages for 25 hours, then measured the changes. (The molars were no longer attached to people.) Gatorade was the worst, followed by Red Bull and Coke, and then Diet Coke and apple juice. All of those drinks are acidic. Here's what the change in just 25 hours looked like microscopically:
Teeth were painted with acrylic nail polish and soaked for 25 hours in Coke, which was replaced every 5 hours. Sections viewed under polarized light microscope showed erosions (arrows) in the root (top) and enamel (bottom). (Ehlen et al., Nutrition Research)
It's not uncommon for people addicted to meth to have unsettling dentition ("meth mouth"). That can be partly because of the acidity of the drug -- as Bassiouny noted, "ingredients used in preparing methamphetamine can include extremely corrosive materials such as battery acid, lantern fuel, antifreeze, hydrochloric acid, drain cleaner, and lye" -- and partly because of the systemic effects and lifestyle that come with it. Meanwhile attributing bad teeth to diet soda alone in moderation has never happened. To that point, Dr. Eugene Antenucci, spokesman for the Academy of General Dentistry, told CBS,
"How much [soda] is too much? I don't know, but if it's your primary drink, and you're drinking more soda than water, I would say that's too much." Meanwhile any amount of lantern fuel is too much.
So, drink more water. Also, as the University of Iowa researchers found, "Practices such as 'swishing' and 'holding' beverages in the mouth prolong acid-tooth contact time and could increase erosion risk." Certainly don't "hold" soda in your mouth for 25 hours.