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Development of an Image Sensor for Dentistry - Fiber Connecting Technique with the Gradient Index (GRIN) Rod Lens

In dentistry, endodontic treatment becomes necessary when dental caries progresses deep into the tooth and reaches the dental pulp or the periapical tissue. A large part of this treatment is performed without direct observation of the root canals. Previously, we reported a prototype of a dental endoscope. In this study, we attempted to develop a novel image sensor for dental endodontic diagnosis and treatment that allows capturing an image of the fine constructions inside the root canals.　Our fabricated probe contains an image fiber, a GRIN lens, and optical fibers as light sources. These materials are encased inside a stainless steel tube to ensure the durability. In previous experiments, we attempted to connect all materials in one step. However, the captured images had deviations along the center axis between the image fiber and GRIN lens. To solve this problem, we considered a new, two-step method for connecting the two materials. In this method, an image fiber and a GRIN lens with the same diameter were placed on stages capable of three-dimensional fine positional adjustments at a resolution of 0.01 mm. The surfaces of the materials were connected under observation through a microscope. An evaluation of the captured images showed that the deviations in the previous images were 22.4 μm along the X-axis and 45.7 μm along the Y-axis. In contrast, the deviations with the new method were 16.7 μm and 8.9 μm along the X-axis and Y-axis, respectively. Therefore, the new method greatly improved precision along each axis. With this method, our fabricated probe could capture and evaluate images more efficiently. We are now trying to fabricate and evaluate a new image sensor.