HARVARD GAZETTE ARCHIVES

Nikos Soukos (left), director of the Forsyth Laboratory, and Max Goodson, Forsyth's director of clinical research, have found certain pathogens sensitive to light. (Staff photo Stephanie Mitchell/Harvard News Office)

The research, published in the April Journal of Antimicrobial Agents and Chemotherapy, suggests that light in the blue region of the visible spectrum might be useful in preventing, controlling, or treating periodontitis - an oral infection that can lead to loss of bone and teeth.

"Some of the key bacterial pathogens associated with periodontitis produce and accumulate compounds that are sensitive to light," said Nikos Soukos, director of the Forsyth Laboratory of Applied Molecular Photomedicine and the principal investigator. "We found that, when exposed to particular wavelengths of light, a percentage of those pathogens was eradicated within seconds."

Another important finding was that when the proportion of such pathogens was reduced, the proportion of other, potentially helpful, bacteria increased. "This suggests that it might one day be feasible to use light to restore a healthy bacterial balance in the mouth," Soukos said.

The current research stemmed from an observation by Max Goodson, director of clinical research at Forsyth, that the blue light used in a tooth-whitening procedure appeared to decrease inflammation of the gums.

"Technology employing blue light to improve oral ecology could be the most important advance in maintaining periodontal health since the invention of the toothbrush," said Goodson, an associate clinical professor of periodontology at Harvard Medical School and Harvard School of Dental Medicine.

Background on bacteria

Previous Forsyth research had shown that as many as 700 different types of oral bacteria may be found in dental plaque that accumulates on teeth. While some bacteria appear to be benign or even helpful, others may invade and destroy gum tissue and bone, leading to loss of teeth, and, possibly, to infection elsewhere in the body.

Among the more destructive bacteria are the so-called "black-pigmented bacteria" (BPB), which have been implicated as pathogens associated with periodontitis. Such bacteria accumulate black pigment consisting mainly of organic compounds called porphyrins. Some porphyrins are photosensitive, and, when activated by visible light, induce a photodynamic reaction that kills the microorganism within seconds.

In embarking on their research, Soukos and Goodson knew that other researchers had used lasers to deliver red or green light, which partially inactivated certain oral bacteria. The Forsyth team also knew, from published reports, that porphyrins absorb blue light more readily than light that is red or green.

The team employed a halogen lamp source commonly used for tooth whitening to shine broadband light composed mainly of blue and a small percentage of green light (wavelengths ranged from 380 to 520 nanometers) on pure cultures of BPB and on dental plaque samples obtained from individuals with chronic periodontitis.

They found that the light rapidly killed BPB in pure cultures and that it selectively eliminated BPB in plaque samples containing 500 to 600 different bacteria. They also found that certain species were more readily inactivated by the light than others and that varying the intensity and exposure time had different impacts on different species.

The researchers concluded that intraoral light exposure can selectively reduce pathogens in dental plaque.

If proved effective in clinical studies, the findings could lead to new methods for preventing or controlling periodontal disease. Such methods would be rapid, noninvasive, and nontoxic, Soukos said.

The team is currently developing a handheld, light-based device that might one day be used by consumers to help combat periodontal disease.

The research was funded in part by the National Institute of Dental and Craniofacial Research, and BriteSmile Development.

The Forsyth Institute is an independent, nonprofit research organization focused on oral, craniofacial, and related biomedical science.