Preservatives commonly found in diet soda, frozen foods, juices, and many other foods appear to help prevent cavities, dental researchers said this weekend at the annual meeting of the International Association of Dental Research.
The surprising message comes from researchers at the University of Rochester Medical Center, which is home to one of the world's leading programs in dental research. William Bowen, D.D.S., Ph.D., Welcher Professor of Dental Research and a member of the Institute of Medicine, presented findings which demonstrate that common preservatives such as benzoates and sorbates appear to enhance the cavity-protecting action of fluoride.
"This is a serendipitous benefit of our diet today," says Bowen. "But you can't rely on serendipity to protect your teeth. There may be a more structured way to take advantage of this, such as putting these preservatives into toothpaste. In the meantime, people would do best to avoid high-sugar foods, including most soft drinks, and maintain good brushing habits."
The recent work picks up on a series of studies by another Rochester team led by microbiologist Robert Marquis, Ph.D., who has shown that, in the test tube, many preservatives seem to mimic fluoride. Bowen took Marquis' research one step further, conducting studies in rats of the effects of fluoride and food preservatives. Rats get cavities almost exactly like humans do, and the same substances that prevent cavities in rats stop them in humans.
In one study the team measured the number of cavities in rats from several groups: some received fluoride, some received benzoates, some received neither, and some received both.
Across the board, animals who had fluoride in their diets had far fewer cavities than those that did not. But fluoride's protective effect was especially strong in animals that also received benzoates. Rats that received neither fluoride nor benzoate had an average of about 16 cavities on their smooth surfaces after three weeks. That compares to two cavities in rats that received fluoride, less than one cavity on average in rats that received fluoride and 0.1-percent benzoate, and no cavities at all in rats that received fluoride and 0.2-percent benzoate.
Benzoates are used in a huge range of foods to help keep the food supply safe from bacteria and other toxins. They commonly make up a tiny proportion, just 0.1 or 0.2 percent of foods like diet soda, ice cream, fruit salads, margarine, and fruit drinks. Most people also get benzoates from natural sources, including cranberries, prunes, and cinnamon. Another preservative that the team studied, sorbate, is common in items like candy bars, lunch meats, mayonnaise and dried fruits.
Bowen and other researchers are confident that the widespread use of fluoride in dental products, food, and drinking water deserves the lion's share of credit for bringing down the rate of tooth decay nationwide after World War II and into the 1980s. But, Bowen notes, "During that same time frame, there's been a huge increase in the use of food preservatives. The decline in tooth decay seen over much of the latter half of the 20th century pretty well matches the increase in soft-drink consumption. In the United States, soda consumption is up to an average of two cans a day per person. That's a lot of benzoate, more than half a gram each day."
Though fluoride and food preservatives are common in the diet of most Americans, Bowen is quick to repeat the age-old adage that without sugar-rich foods, bacteria wouldn't have the meals they rely on to produce the acids that cause tooth decay. The best way to avoid cavities, he says, is to avoid foods high in sugar, brush and floss regularly, and undergo regular dental checkups.
The new research reflects a coming of age of the understanding of how fluoride protects tooth enamel, says Marquis. Fifty years ago Rochester researcher Basil Bibby suggested that fluoride inhibits the bacteria that feed on sugars and secrete the acid that eats through tooth enamel and causes cavities. But many other researchers discarded that hypothesis, instead relying on evidence that fluoride allows teeth to remineralize, helping to fill in small cavities a little bit like a road crew fills in potholes, before they grow even bigger.
Now, Marquis and others have vindicated Bibby by showing that fluoride does affect bacteria directly. In his laboratory, Marquis has shown that fluoride and food preservatives knock out bacteria by pushing them to exhaustion. Though bacteria like streptococcus mutans thrive in the high-acid environment that they create along the surface of teeth and in dental plaque, the bacteria must maintain a lower acidity level within themselves. But fluoride and food preservatives make this difficult. Both take molecular actions that lower the pH within bacteria by continually bringing protons into the cells. Bacteria pump these protons back out, but like an athlete who continually must toss a heavy medicine ball over a fence, the cell soon uses up all its energy pumping the protons back out. Without energy, the cell shuts down and stops producing acid.
"The acid from these bacteria is what causes enamel to dissolve," says Marquis, professor of microbiology and immunology. "Fluoride and preservatives like benzoate prevent the bacteria from acidifying the plaque and causing cavities. The bacteria are still there -- you have to take a tooth brush to get rid of them -- but they're not causing damage."
In his laboratory, Marquis has also shown that the common medicine ibuprofen, a non-steroidal anti-inflammatory drug (NSAID), also acts like fluoride and food preservatives in the way it inhibits bacteria. Again picking up on that basic research, Bowen's team has just published results showing that ibuprofen also enhances fluoride's action, dramatically reducing the number of cavities in rats.
The work by both Bowen's and Marquis' groups has been supported by the National Institutes of Health.