With the development of dental instruments, such as dental microscopes and cone beam computed tomography, the precision of current dental diagnosis and treatment has greatly improved. However, the observation of deep periodontal pockets, fractures near the root apex, and collaterals of root canals is difficult using these instruments. To solve these problems, we developed two types of micro-image sensors that can be used for the observation of root canals. The first image sensor is an external-irradiation probe that uses an external light source. This probe has high resolution and a wide field of view. The other sensor is an internal-irradiation probe, which can be used to observe an image and transmit the illumination light with a single probe. The external-irradiation probe has an image fiber with a diameter of 600 μm and a gradient index (GRIN) lens. The internal-irradiation probe has an image fiber with a diameter of 300 μm, a GRIN lens, and 40 optical fibers with a diameter of 40 μm each as a light source. Using these probes, we captured the image of a resolution chart; line spaces with the widths of 10-100 μm were observed using both types of probes. The evaluations of the visibility of the captured image showed higher measurement values than those of commercially available endoscopes. We will apply this ultra-compact image sensor to various fields besides dentistry, such as medical and industrial applications.
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