Indiana University      Research & Creative Activity      April 1998 Volume XXI Number 2

Early Detection of Dental Caries:

Quantitative Laser Flouorescence

With the advent of fluoridated water supplies and tooth pastes beginning in the late 1950s, the rate of tooth decay in the American population stabilized. But widespread fluoridation has failed to eradicate dental caries. Figures released by the Oral Health Research Institute (OHRI) at the Indiana University School of Dentistry show that:

The average teenager develops at least one new carious lesion yearly.
The average young adult develops about 0.9 new carious surfaces each year.
An adult beyond the age of 65 typically develops 0.87 new carious surfaces yearly.

George Stookey, Professor of Preventive/Community Dentistry and Director of the Oral Health Research Institute at the Indiana University School of Dentistry, holds the wand used to induce enamel fluorescence during a dental examination. Images of the teeth are recorded and appear on the computer monitor. Image comparisons determine tooth decay progression between exams. --credit

OHRI, under the leadership of its director, George Stookey, a professor of preventive/community dentistry and an associate dean for academic and student affairs at the School of Dentistry, continues to seek ways to eradicate this costly and sometimes painful disease. Drawing upon pioneering work done in Sweden, Stookey has embarked OHRI on a project to develop an early detection system for dental caries by using fluorescence illumination.

Human teeth are coated by a layer of enamel that is about 1 to 1.5 millimeters in thickness, depending on location. Research shows that dental decay begins because of a shift in the oral equilibrium that stimulates demineralization. Healthy teeth have a balance between demineralization and remineralization, so there is always slight degeneration of the enamel taking place in some areas, and restoration of the enamel surface in other areas. In an incipient carious lesion, however, the balance is lost over the long term, and only demineralization occurs. Examinations of these incipient cavities reveal a thin outer layer of partially demineralized enamel covering a large demineralized area.

Currently, the standard detection method is oral examination using a mirror and an explorer--the metal stick with a slightly curved probe on it familiar to anyone who has visited a dentist. Dentists run the explorer over dental surfaces to find these early demineralized areas. The only chance for recovery at this stage is if the thin layer of enamel on the outside can remain intact; unfortunately, the metal tip of the explorer often ruptures that fragile layer of enamel covering the incipient lesion.

By the time the dentist can detect the incipient lesion with the visual-tactile methods of the mirror and explorer, demineralization has usually progressed to a depth of 300 to 500 microns, or about one-third to one-half of the total thickness of the enamel. It will take two or three more years for that area, if unchecked, to develop into a lesion. Stookey and his team at OHRI are studying a way to detect incipient lesions earlier and without using the invasive explorer. If dentists can catch the process soon enough, treatment can be developed to reverse the loss of enamel and restore the surface to normal.

The experimental method involves quantification of the light-induced fluorescence level of enamel. Sound, healthy enamel shows a higher fluorescence than demineralized enamel; demineralized areas appear relatively darker under light that excites the fluorescence. To capture and quantify the extent of demineralization, Stookey and his staff use a miniature intra-oral camera and an arc-lamp. The arc-lamp is prefiltered to limit its wavelength so the energy it emits will excite the natural fluorescence of human teeth. The fluorescence image is captured by the small intra-oral camera, fitted with a high-pass filter to capture only the wavelengths emitted by the fluorescence. Once the image is captured and stored digitally on a computer, it must be analyzed. "The real challenge," Stookey explains, "is to find which areas are heading into extended demineralization. Only those will need treatment. The rest will naturally remineralize."

In a laboratory at OHRI, Stookey and his staff of postdoctoral researchers show the challenges they face in perfecting the fluorescence measurement system. They call up computer images of subjects' teeth that have been put under ultraviolet light and digitally photographed. A computer program called QLF--quantitative light fluorescence--then allows the staff to mark the darkest areas on the computer screen. Once the staff has set the parameters, the computer calculates both the bounded area and the depth of the demineralization, then stores the data. Some months later, subjects return and researchers again illuminate and photograph their teeth, and darkened areas are again measured. "The difficulty is in the quantification. We need to measure progression over time," Stookey explains. "The changes can be minute, so we continue to develop our imaging and measurement software. That's the key to success."

The OHRI project's on-screen imaging techniques are aided by collaboration with Mostafa Analoui, an assistant professor of stomatology and an electrical engineer, who is director of the Oral Maxillo-Facial Imaging Research Facility at the School of Dentistry. If the team can successfully meet the software and imaging challenges, the fluorescence quantification method offers great promise. "Ultimately," Stookey says, "we hope to detect incipient caries one or two years earlier than with conventional methods. If this works, some day we may be able to treat dental caries before they breach the enamel and becomes actual lesions." --William Rozycki

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