Imaging system captures dental data with near-IR light
Improving the accuracy and efficiency of dental examinations is the aim of a new optical dental imaging system developed by Dr. William Colston and his colleagues in the Medical Technology Program at Lawrence Livermore National Laboratory (Livermore, CA). Built in collaboration with the University of Connecticut Health Center (Farmington, CT), the imaging system uses near-infrared (IR) light to capture information about teeth and tissue microstructures that are presently unobtainable by mechanical probing, visual inspection, or x-ray imaging.
"Using dental optical coherence tomography (OCT), the imaging system can diagnose gum disease more accurately, detect the extent of decay in a tooth, and evaluate dental restorations and implants," says Colston. Better still, the system is noninvasive and does not expose a patient to ionizing radiation, as does x-ray imaging. Providing cross-sectional images of dental microstructures at a resolution of 10 μm, OCT can stack these images to form three-dimensional tomograms. These tomograms provide quantitative information about deteriorating connective soft tissue and the structural integrity of dental implants.
During OCT, which is based on a polarization-sensitive, Michelson white-light interferometer, circularly polarized low-coherence light is focused on the biological tissue of a sample. To obtain a cross-sectional image of the tissue, backscattered light intensity and polarization are measured as a function of the axial depth and the transverse location of the tooth. A scanning retroreflector is used to vary the path length of the interferometer`s reference arm for each transverse location of the sample. Interferometric signals are then detected when the distance to the reference and sample reflections are matched to the source coherence length. Lastly, the return light is split into orthogonal polarizations before being detected.
To detect such images, Colston and his colleagues have developed a hand-held scanner that focuses light from a low-coherence diode-light source onto the tissue being examined. Moving its reference arm enables the interferometer to scan different points throughout the depth of the tissue. 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 the cross sections.
Such images can show features relevant for diagnosing periodontal diseases, the plaque-induced disorders that result in deterioration of connective tissue. Using these images, dentists can determine tissue states and how well the tissue is attached. Imaging the hard tissue structure also provides a safe and noninvasive alternative method for locating sites of potential and actual cavities, making possible the early treatment that could prevent or stop further tooth deterioration.
"OCT images also show such structural restoration defects before leakage occurs. Because techniques currently used for evaluating restorations are inadequate, the OCT technique minimizes tooth loss and decreases unnecessary replacement of restorations," says Colston. At present, Colston and the other team members are engineering the system to simplify operation and reduce costs.
