When Doctor's Orders Lead to Cavities: Many Common Drugs Promote Tooth Decay

May 26, 2000

For teeth constantly on the mend from the effects of acid-producing bacteria that set up housekeeping in our mouths, saliva is a fabulous fluid. Saliva protects and helps repair our teeth from the constant assaults that bacteria and our diet together mount against our tooth enamel. But more than 600 medications cause dry mouth, reducing saliva flow or even turning off the spigot and leaving millions of people at increased risk for tooth decay.

A visit to dentist Gene Watson, D.D.S., Ph.D., is often the last stop for such patients. Watson, director of the Salivary Dysfunction Center at the University of Rochester Medical Center, gave up a thriving dental practice to devote his career to discovering new knowledge about our oral health. His latest discovery appears in the March-April issue of Caries Research. In a recent experiment with clonidine, a medicine for treating high blood pressure in adults and often used to treat attention deficit hyperactivity disorder in children, Watson's dental research team showed that rats receiving clonidine developed 84 percent more cavities on the smooth surfaces of their teeth than rats not on the medicine.

Watson's group is one of just a handful in the world to study the effects of drugs on cavities. In previous studies he has shown that the drugs atropine and propranolol also boost the cavity rate in rats. The researchers found that propranolol, commonly used to treat heart patients, alters the composition of saliva and makes it less effective, while atropine lessens saliva flow. Drugs that behave like atropine include antihistamines like Benadryl, anti-depressants such as Elavil and Aventyl, and Detrol, which is used to treat incontinence.

Anything that stems the flow of saliva is a concern to dentists, many of whom regard the substance with a kind of wonder. "Our saliva washes away sugars and other substances that help promote cavities. It neutralizes the acids in our mouths," says Watson. "And it's concentrated with minerals like calcium and phosphate. When you eat sugar, bacteria on your teeth produce acid that demineralizes the teeth a little bit, but then the saliva flows in and replaces the layer that has been removed."

The effect of a dry mouth on tooth decay is not as well known as it should be, Watson says. "Most patients and doctors are not aware of the problem." Dental researchers say millions of people are at heightened risk for tooth decay because of the medicines they take. Watson says the problem is particularly common among the elderly, many of whom take several medications that stem the flow of saliva.

"A dry mouth can start an unfortunate cycle. To make his mouth feel better, the person starts drinking liquids constantly, oftentimes juices or colas that contain sugar and are acidic. That just promotes tooth decay. If you start sipping those all day, you end up in trouble."

In addition to medication, an autoimmune disease known as Sjögren's syndrome as well as radiation treatment for cancers of the head or neck can also knock out saliva flow by damaging the salivary glands. Watson says that doctors who treat patients who have Sjögren's or cancer, as well as physicians who treat the elderly, are among the health-care professionals who should be especially aware of the dental effects of dry mouth.

Dentists like Watson take a variety of steps when they encounter patients whose medications cause dry mouth. Oftentimes Watson speaks with the patient's physician about switching to another medicine, reducing the dose, or changing the timing of the dose. Other suggestions can include more vigilant brushing, a change in diet, and less frequent snacking. Or he might recommend a mouthwash with fluoride, or even a prescription fluoride gel.

Watson urges patients on medications to be vigilant in brushing their teeth and having their teeth checked and cleaned every six months. "If there is evidence that there's a problem, then the medication might be playing a role, and they should speak to their dentist or physician."

For its latest research, the team chose to study clonidine because half of adults who take the medicine for high blood pressure complain of dry mouth. The medicine is also being used more and more by doctors to treat children who have attention deficit hyperactivity disorder. The drug tricks the body into releasing less of the neurotransmitters acetylcholine and norepinephrine, which stimulate the salivary glands.

Watson's group compared cavities in 56 rats, including some on the medication and some that weren't. The control rats had an average of 30 cavities on their smooth tooth surfaces, while their counterparts on clonidine had an average of more than 55 cavities, an 84-percent jump. The discrepancy was less but still notable on the teeth's chewing surfaces.

Since rodents develop cavities similar to humans, researchers often turn to rats to understand the tooth decay in human patients. "What promotes cavities in rats promotes cavities in humans, and what prevents or controls cavities in rats controls them in humans," says Watson, who is also assistant professor in the Eastman Department of Dentistry. Watson was joined in the research, funded by the National Institutes of Health, by technical associate Sylvia Pearson and William Bowen, B.D.S., Ph.D., Welcher Professor of Dentistry.

Watson and Bowen have worked closely together since Watson decided to give up his practice in his hometown of Charleston, W.Va., and go back to school to learn to do research. "I felt like I could do more to contribute to the welfare of patients," he says. Watson joined the University of Rochester, home to the nation's first research center devoted to the study of cavities. Soon he became interested in saliva and the medications that affect it and eventually earned his doctorate in pharmacology and physiology, becoming an expert in the workings of certain molecules involved in saliva production.

Growing up with an innate interest in how things worked, Watson took a dental course simply to fulfill a requirement as an engineering graduate student at West Virginia University in Morgantown, W.Va., He did well, and a friend in the course suggested he go to dental school, setting him off on a whole new direction. "I applied, got accepted, and decided to go. Until that moment I had absolutely no intention of becoming a dentist. It just happened."

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