OCT partners with spectroscopy for better caries detection

By Kathy Kincade, Editor in Chief

September 26, 2008 -- Optical coherence tomography (OCT) won't be commercially available to dentists until sometime next year, but researchers and commercial developers are already working to improve its ability to detect dental decay sooner and diagnose it more accurately.

While OCT can probe more deeply into tissue than x-rays and thus help pinpoint where a suspected caries lesion is taking root -- plus quantify the extent of demineralization over time -- it cannot provide the biochemical information that would further enhance diagnostic specificity.

So some researchers are combining OCT with another optical imaging technique: spectroscopy. Their goal is to leverage the strengths of both approaches to overcome the sensitivity and specificity limitations of existing caries-detection products such as Diagnodent, D-Carie, and DIFOTI.

"Although technologies such as the Diagnodent and DIFOTI can be very useful for detecting caries in terms of serving as a warning sign, studies have shown they have low specificity and sensitivity," said Lin-P'ing Choo-Smith, principal investigator at the National Research Council Canada's Institute for Biodiagnostics. "Our goal is to use OCT and Raman spectroscopy as a way of overcoming the sensitivity issue and give dentists the ability to distinguish demineralization from stains, pigmentation, and hypocalcification."

Choo-Smith and her colleagues from the department of restorative dentistry at the University of Manitoba and the department of dental clinic sciences at Dalhousie University have developed a fiber-optic-coupled polarization-resolved Raman spectroscopic system for early caries detection. Working with extracted teeth, they have been able to detect tiny cavities by using Raman spectroscopy in conjunction with OCT to search for slight decreases in calcium hydroxyapatite (Optics Express, April 28, 2008, Vol. 16:9, pp. 6274-6284). They presented their findings at a meeting in June sponsored by the European Organisation for Caries Research and again in July at the International Association for Dental Research meeting in Toronto.

Researchers at the National Research Council Canada's Institute for Biodiagnostics have developed a Raman spectroscopy dental probe that can enhance early caries detection by gathering biochemical information.

Their next step is to refine the system and its handheld contact probe and begin preclinical studies early next year. An actual clinical device is still at least five years away, Choo-Smith said. But that device will be designed to produce both an OCT image that illustrates the location of potential decay and provides a "yes/no/maybe" signal, similar to the Diagnodent, with a quantitative value attached to it that indicates the degree to which caries exists and, over time, progresses.

"If we use OCT as the initial screen to look for early lesions and pinpoint where they are, then we can bring in the Raman to get the biochemical information about proteins and chemical composition," she said. "We've done a lot of OCT samples that have been very successful. But if you have hypocalcification, where there is extra scattering that is similar to what we see in caries, to the untrained eye this could be misinterpreted as caries. If you bring in the Raman to enhance the specificity of the initial OCT finding, the dentist can have much more confidence."

Near-infrared vs. Raman

Using NIR transillumination to detect demineralization and occlusal lesions, researchers at the University of California, San Francisco shine 1,310-nm light at the base of the tooth and then image the tooth from the top down. Image courtesy of Daniel Fried, University of California, San Francisco.
Daniel Fried, Ph.D., a leading researcher in the department of preventive and restorative dental sciences at the University of California, San Francisco (UCSF), says that while the Canadian research is interesting, near-infrared (NIR) spectroscopy -- both by itself and in conjunction with OCT -- is a better option than Raman for detecting dental decay.

"Raman is similar to fluorescence in that you can see changes in the surface, but it is not capable of giving any depth-resolved information," he said. "But NIR images show high contrast between healthy and demineralized areas, and demineralization is easily differentiated from stains, pigmentation, and hypomineralization."

The clinical PS-OCT system at the University of California, San Francisco. Here the system is imaging a sound premolar scanned from the root to the crown. Note the resolution of the dentinal-enamel junction. Image courtesy of Daniel Fried, University of California, San Francisco.
Following a number of studies of NIR transillumination, Fried's group at UCSF has concluded that this technique is useful for detecting early interproximal and occlusal caries because enamel is highly transparent at 1,310 nm (Optics Express, January 24, 2005, Vol. 13:2, pp. 573-582).

"The big thing with the NIR is you get an image of the lesions, which you don't get with Diagnodent and the other optical caries-detection devices," he said. "In addition, stains don't absorb light in the NIR. They become invisible."

Despite the many studies that have demonstrated the effectiveness of NIR transillumination, however, the technology is still a ways away from clinical reality.

"NIR imaging [for caries detection] has the potential to be a standalone device but the biggest hurdle right now is the high cost of the technology," Fried said. "But if the cost can get lower, I could see every dentist using this because you can look right through the enamel of the tooth. And it is easy to use."

In the mean time, Fried's group has spearheaded a number of OCT studies demonstrating the ability of OCT to image the effects of fluoride-enhanced remineralization of mild and severe early artificial in vitro caries (Journal of Biomedical Optics, January/February 2006, Vol. 11:1). They are now working to develop a caries detection system that combines OCT and NIR.

"The greatest advantage of PS-OCT [polarization sensitive OCT] is that it allows you to quantify the extent of demineralization and get an image that is depth resolved," Fried said. "It allows you to take nondestructive images of decay and watch it progress. NIR doesn't give you depth-resolved information, or at least not as quantitative information as PS-OCT. The idea is to use NIR to screen and look for lesions, and then use OCT to quantify the severity."

Copyright © 2008 DrBicuspid.com

To read this and get access to all of the exclusive content on DrBicuspid.com create a free account or sign-in now.

Member Sign In:
MemberID or email address:  
Do you have a DrBicuspid.com password?
No, I want a free membership.
Yes, I have a password:  
Forgot your password?
Sign in using your social networking account:
Sign in using your social networking