DRINKING diet soda might help your waistline, but it won't do any favors for your teeth.
Although mineral-rich enamel is the hardest surface in the human body, it's not a match for the old-fashioned American soft drink - including the sugar-free kind.
In a study to be published next month, researchers found that the regular and diet versions of popular drinks such as Pepsi and Coke caused the same amount of dental erosion.
"I was always convinced that there was going to be a difference in the way diet drinks and regular drinks affect teeth," said J. Anthony von Fraunhofer, professor of biomaterials science at the University of Maryland Dental School and lead author of the study. "I was wrong."
Dental erosion isn't the same as tooth decay, but the result is: Teeth that aren't sufficiently protected from cavity-causing invaders can wind up needing the dreaded root canal - or worse.
Decay is usually caused by plaque, the sticky, whitish film composed of saliva, food particles and bacteria. As the bacteria feed on the sugars and starches found in food, they create an acid that first destroys the tooth's hard outer surface (the enamel), then digs deeper into the soft inner layer (the dentin), or further still into the nerve.
Erosion, by contrast, is a direct chemical attack on the enamel.
"Bacteria aren't involved," said von Fraunhofer, who, thankfully for his pearly whites, doesn't have much of a taste for either diet or regular colas. "The acid in the drink itself dissolves the tooth directly. You literally dissolve the enamel and then the dentin away."
Dr. Joel Goodman, a dentist in private practice in Glenelg, recalls an experiment in which an extracted tooth placed in a can of Coke would disappear in a matter of days. He suspects the same would be true of a tooth in Diet Coke - which is what he drinks.
"The key is that you're creating an acid environment," he said.
Soft drink consumption has increased sharply in the United States. In 1947 the average person consumed the equivalent of a hundred 12-ounce soft drinks in a year, which meant about two a week. Fifty years later, that number has climbed to nearly 600 annually, or just under two a day.
Diet beverages have also become more popular. By 1997, the artificially sweetened versions of soda standards accounted for nearly a quarter of all soft-drink sales, up from 16 percent in 1970.
To conduct his experiment, von Fraunhofer carved out 40 chunks of enamel from 20 cavity-free teeth extracted during oral surgery. He and his colleague, dentist Matthew Rogers, soaked the specimens in a variety of beverages poured into small plastic jars. They weighed them at the start and again at 24- to 48-hour intervals.
After 14 days, they found virtually no difference in the amount of tooth enamel lost from the regular and diet versions of Coke, Pepsi, Dr Pepper and Mountain Dew.
The researchers went a step further, examining how aggressive non-colas were on tooth enamel compared with their cola counterparts. The answer, in short: much more so.
Overall, enamel loss was two to five times greater with non-cola beverages. The worst offender, the researchers found, was Mountain Dew (diet or regular), followed by Arizona iced tea, Sprite, Diet Sprite and Canada Dry ginger ale.
When it comes to enamel attack, what seems to matter more than sugar content is a beverage's overall ingredient list. Many soft drinks contain a range of acids, including phosphoric, citric and tartaric acid as well as carbonic acid, which gives drinks their fizz.
In anticipation of the study's publication in General Dentistry, the National Soft Drink Association issued a news release last month calling the study's design "elementary" and "archaic."
One of the group's main sticking points (no pun intended): No one keeps a liquid in his or her mouth 24 hours a day for two weeks straight.
"You couldn't extrapolate this to real-life situations," said Richard H. Adamson, a pharmacologist and toxicologist who is vice president for science at the soft drink association. "If they would have taken other beverages - for example, wine, grapefruit juice, the juice from pickles - they undoubtedly would have found the same effects."
The study, he said, also fails to take into account the protective effects of saliva and good oral hygiene, including regular brushing.
What's more, the association pointed out, numerous factors can contribute to dental erosion, including some chewable medicines, oral hygiene products or even chlorine in a swimming pool.
If you're still leery, though, the researchers did find a few beverages that were relatively enamel-friendly, including root beer, brewed tea and coffee.
If only coffee didn't stain the teeth.