What Lies Beneath

Urban legend has it that a can of Coke will strip the rust off a nail or clean the tarnish off a penny. We’ll leave those experiments to the MythBusters, but one thing is certain: colas, sodas, sports drinks, wine and even fruit juices can damage teeth.

It’s not just the copious amounts of sugar in these drinks that cause problems. Most sodas contain phosphoric acid, a preservative, or citric acid, for flavor. These chemicals lower the pH levels in soft drinks to about 2.5 (on a scale where 7 is neutral and lower numbers indicate increasing acidity). Vinegar and wine score almost as low as soda, while lemon and lime juice, with a pH of less than 2, are nearly as corrosive as battery acid.

That’s bad news for tooth enamel, which begins to dissolve in just slightly acidic conditions. Repeated exposure to acids will strip the teeth of their protective enamel, leaving them vulnerable to cavity-causing bacteria.

It’s not clear how many people suffer from acid erosion, but it could be as high as 20 percent and is likely increasing, says Athena Papas, J66, professor of public health and community service and cohead of the Division of Geriatric Dentistry at Tufts School of Dental Medicine. “We are getting better at defining erosion, and it’s becoming much more obvious,” she says.

Extra shiny amalgamate fillings or fillings that stand up higher than the tooth are just two telltale signs of acid erosion, she says. Eventually, the yellow tint of the dentin layer that lies beneath enamel may begin to show through, or the tooth may change shape, losing its structural integrity.

“The way to avoid acid erosion is to avoid frequent contact of teeth with acid,” says Carole Palmer, G69, who heads the Division of Nutrition and Oral Health Promotion at the dental school.

Avoiding low pH products, such as soft drinks and sour candies—and even chewable vitamin C tablets—is definitely a step in the right direction, says Palmer. But many acidic foods, including fruits and vegetables, are part of a healthy diet. So researchers suggest, for example, using a straw to minimize contact between acidic beverages and tooth surfaces. Chasing acidic drinks or meals with plain water or milk also will help restore the pH balance in the mouth. And not eating in between meals can help, too, because it allows saliva to neutralize acids in the mouth.

For some people, health issues can compound the damage done by acidic foods and beverages. Because saliva serves as a natural anti-bacterial rinse, patients who experience dry mouth are at increased risk for acid erosion, says Papas. Many prescription medications, including those for high blood pressure and depression, decrease salivary flow.

A relatively rare autoimmune disorder that affects the salivary glands, Sjögren’s disease, also causes severe dry mouth. Papas, who conducts research on Sjögren’s and works with elders who often take multiple medications, estimates as many as 60 percent of patients she treats suffer from some degree of acid erosion.

Dentists should be on the lookout for erosion, Papas says, because specific wear patterns may be an indicator of other health problems. Erosion on the tongue side of the front teeth may indicate frequent vomiting and is sometimes seen in bulimics. Deep craters, known as cupping, on the chewing surfaces of molars could signal gastroesophageal reflux disease (GERD), in which the digestive juices surge into the throat and mouth, bathing the back teeth in hydrochloric acid. Because many GERD patients are asymptomatic, dentists are often the first to diagnose the condition, Papas says.

Addressing any medical issues in your patients is the first step in preventing further erosion, says Papas. Prescription-strength fluoride rinses and remineralizing solutions can help reverse erosion, while varnish applied during a dental visit can protect the teeth from acid and cavities alike.

And that often-dispensed advice to brush after every meal might not be so wise. Using a toothbrush in a low pH mouth may do more harm than good, spreading enamel-eating acid throughout the mouth. A 2006 study in the journal Caries Research suggests that waiting 30 to 60 minutes after a meal to brush will give saliva a chance to do its job.

This article first appeared in the Spring 2012 issue of the Tufts Dental Medicine magazine.

Jacqueline Mitchell can be reached at jacqueline.mitchell@tufts.edu.