UNDERSTANDABLY, many patients equate visiting the dentist with pain and suffering. Even those with perfectly healthy teeth and gums sometimes suffer discomfort while the insides of their mouths are probed with sharp, wickedly curved instruments that convey visions of medieval torture. Dental exams and procedures now are less scary than in the past, but they still can be painful and certainly are no fun.
The day of pain-free dentistry may arrive sooner because of an invention that improves the accuracy and efficiency of dental examinations. Bill Colston and colleagues in the Medical Technology Program at Lawrence Livermore, in collaboration with the University of Connecticut Health Center, have developed an Optical Dental Imaging System using near-infrared light. It captures information about teeth and tissue microstructures that has been unobtainable through mechanical probing, visual inspection, or x-ray imaging. Using this imaging system in lieu of the other methods, dentists will be able to diagnose gum disease much more accurately, detect the extent of decay in a tooth--something that they can only estimate today, in part by using the dreaded dental drill--and closely evaluate dental restorations and implants.
The system is noninvasive, painless, and safe. It does not expose a patient to ionizing radiation, as does x-ray imaging. It provides cross-sectional images of dental microstructures at a resolution of 10 micrometers, supplying more detailed diagnostic information. The cross sections can be stacked to form three-dimensional tomograms that provide quantitative information about deteriorating connective soft tissue as well as the structural integrity of dental implants. No other system can image both hard (e.g., enamel and dentin) and soft (e.g., gingival) tissue.

Shining a Light on Tissues
Near-infrared light is directed deeply into the internal structures of teeth and gums. The complication with this method is that as the light interacts with dense biological tissue, it becomes highly scattered. For imaging applications, this means blurred images. Colston likens the effect to what you see by shining a flashlight on your hand to look at its internal structure--not much. There is, however, a component of the reflected light that remains unscattered and thus contains good quantitative and structural image information. Finding a way to extract this information from the noise generated by scattered light was what Colston and the project team did to devise an effective optical imaging system for dental evaluations. Their approach uses a new, proprietary technological advancement in optical imaging that maps the changing intensities of reflections from dental tissue samples and microstructures.

Scanning with Finer Detail
The dental imaging system includes a scanner (Figure 1a), interferometer, and demodulation electronics. To detect an image, a handheld scanner focuses light from a low-coherence diode light source on the tissue being examined. Different points through the axis (depth) of the tissue can be scanned by moving the reference arm of the interferometer. When the arm is moved in parallel motions across the sample, transverse scans are produced that can be combined with axial information to create two-dimensional plots or images of cross sections.
An image can show, for example, features relevant for diagnosing periodontal diseases (Figure 1b and c), the plaque-induced disorders that result in deterioration of connective tissue and resorption of alveolar bone. The imaging system provides in vivo images that allow a dentist to determine with great accuracy the state of the tissue and how well it is attached. Imaging the hard tissue structure can also provide a safe and noninvasive alternative for locating sites of potential and actual cavities, making possible the early treatment that will prevent or stop their progress.
Inadequate seals between restorations and the gingival margin can result in infection, dissemination of bacteria, and loss of supporting tooth structure. OCT images, for example, can also show such structural restoration defects before significant leakage occurs. Because techniques currently used for evaluating restorations are inadequate, the OCT technique can help minimize tooth loss and decrease unnecessary replacement of restorations.
Colston and the other team members (Figure 2) are engineering the system to make it small enough for dentists to handle, easily usable without additional training, and inexpensive to produce.
--Gloria Wilt

Key Words: dental diagnostics, Optical Dental Imaging System, optical imaging.

For further information contact Bill W. Colston, Jr. (925) 424-5854 (colston1@llnl.gov).

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