Light Blitzes Plaque

Fast forward a decade and imagine what a drugstore shelf might hold. A pill containing an entire day’s nutrients? A gadget that confers the benefits of aerobic exercise as you sit in your armchair? Among such items it’s possible, even likely, that you’ll find a little blue light that you pop briefly into your mouth each day to prevent gum disease. Two researchers at the Harvard-affiliated Forsyth Institute have developed a prototype of just such a device after discovering, wholly by accident, that blue light kills the bacteria that are the prime cause of periodontal disease.

Associate clinical professor of periodontal medicine J. Max Goodson, the institute’s director of clinical research, was using intense blue light (its wavelength falling within the blue segment of the visible light spectrum) to whiten patients’ teeth, the same way sunlight bleaches laundry hanging in a backyard. Because he expected the light to cause a sunburn-like reaction as a side effect, he measured the inflammation of the patients’ gums. “Much to our surprise,” he says, “rather than an irritating effect, we actually found a diminution of inflammation.”

One prototype of a blue-light-emitting device proposed by Harvard researchers resembles an electric toothbrush. Using it inside the mouth for 30 seconds daily might help prevent much periodontal disease.
Photograph by Jim Harrison

Goodson had stumbled on a discovery with important implications for preventing and treating periodontal disease, which affects 30 percent of Americans to a degree that threatens tooth loss. After a single one-hour treatment with blue light, patients’ gingival index scores—which measure inflammation, a symptom of gum disease—not only dropped, but stayed down for six months. On a scale of zero (normal, healthy gums) to three (spontaneous bleeding, without any probing), the average patient’s score went from 0.64 before the whitening treatment to 0.33 three months later, and 0.28 six months later.

Upon reflection, the finding made sense. Several species of bacteria that cause periodontal disease, known as black-pigmented bacteria, transport hemoglobin into their bodies as an iron source (this is thought to be why they make the gums bleed, by using enzymes that weaken blood vessels), and store the hemoglobin’s dark-colored, photosensitive porphyrin. Light directed at these bacteria is absorbed by the porphyrin and, through a chemical reaction, produces substances that are toxic within the bacterial cell.

Because the whitening treatment used peroxide, an antibiotic, as well as light, Goodson—working with instructor in dermatology Nikolaos S. Soukos, who directs the Forsyth Institute’s applied molecular photomedicine lab—tested the finding using light alone. Their results, reported recently in Antimicrobial Agents and Chemotherapy, showed that in the mouths of control-group members, who were told they were receiving light therapy, black-pigmented bacteria constituted 6 percent of all oral bacteria. In the mouths of people who received the blue-light treatment, just 1 percent of the bacteria were black-pigmented. (The researchers’ goal is not to banish all bacteria from the mouth, but to get rid of the most harmful types—Soukos speaks of restoring “balance and harmony in dental plaque.”) Goodson and Soukos also experimented with other colors of light and found that blue worked best. At this point, they aren’t sure why.

Goodson and Soukos envision an over-the-counter device, available at drug stores, that people could use for 30 seconds a day. Their electric-toothbrush-like prototype resembles a glow-in-the-dark popsicle; another design concept would run on batteries and fit fully within the mouth. Because the light frequency used lies within the visible range, users wouldn’t even need protective eyewear. The scientists are seeking a corporate investor to manufacture and promote the product.

Will light therapy replace flossing? Not likely. Of the 700 species of bacteria that live in human mouths around the world, blue light works only on the black-pigmented group. (Periodontal disease and tooth decay are caused by two different groups of bacteria that tend to be mutually exclusive: if you’ve got gum disease, you probably won’t get cavities, and vice versa.) Blue light has no effect on the bacteria that cause tooth decay (chiefly oral streptococci), whereas flossing gets at the cavity causers that nestle between the teeth and under the gums.

One product that light therapy might replace is the breath mint. Black-pigmented bacteria are also to blame for halitosis, and light therapy gets at its root cause by killing the bacteria, rather than simply masking their odor as mints and mouthwashes do. Goodson isn’t optimistic that U.S. consumers will buy a product designed to prevent a disease they don’t care much about until it strikes, especially a product that adds one more task to the hectic morning list of shower, shave, brush, and floss. But he does think they might respond to a marketing approach that targets their vanity: they spent $300 million last year on Crest Whitestrips tooth-whitening kits. A one-hour whitening treatment, of the type Goodson was performing in his initial study, costs $600. “People will go out and pay incredible amounts of money for whiter teeth, but to cure their disease, they won’t,” Goodson says. “Bad breath, they care about.”             

             ~Elizabeth Gudrais

Max Goodson e-mail address: [email protected]

Nikolaos Soukos e-mail address: [email protected]

Read more articles by: Elizabeth Gudrais

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