Shinji Yoshii

Fabrication of Two Different Probe Architectures for Ultra-Compact Image Sensors for Root Canal Observations

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.

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.u3000Our 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.

Development of Novel Image Sensor for Root Canal Observation

The development of dental instruments such as dental microscope and cone-beam computed tomography has greatly improved the precision of current dental treatments. However, observation of fractures near the apex collateral of the root canal remains difficult when using these instruments. In this study, we developed two types of probes: an ‘external-irradiation system’ and an ‘internal-irradiation system’. The external-irradiation probe is composed of an image fibre with a diameter of 500 μm and a gradient-index lens (GRIN lens) with the same diameter as the image fibre. The internal-irradiation probe is composed of an image fibre, GRIN lens, and five optical fibres for illumination, with diameters of 300, 250, and 65 μm, respectively. In an observation experiment of the resolution chart using these probes, both probes could observe lines and spaces of 10–100 μm using an external light source. To evaluate resolution, visibility was measured for each image, and higher visibility was observed as the lines and spaces were increased. We attempted to illuminate the observation area with optical fibres inside the probe; however, it was difficult because of the low intensity of the light. Furthermore, we observed the actual root canal of an extracted tooth. In future, we would like to redesign the GRIN lens and a suitable offset of the optical fibres.

Two-year clinical comparison of a flowable-type nano-hybrid composite and a paste-type composite in posterior restoration.

AIMnThe purpose of the present study was to compare the clinical efficacy between a flowable-type nano-hybrid composite and a paste-type composite for posterior restoration.nnnMETHODSnOf 62 posterior teeth in 33 patients (mean age: 34.1 years), 31 were filled with a paste-type composite (Heliomolar [HM] group), and another 31 with a flowable nano-hybrid composite (MI FIL [MI] group). Clinical efficacy was evaluated at 2 years after the restoration.nnnRESULTSnThere were no differences for retention, surface texture deterioration, anatomical form change, deterioration of marginal adaptation, and secondary caries, while a statistical difference was found for marginal discoloration, which was significantly greater in the HM group (P < 0.05). Furthermore, color matching in the MI group was superior to that in the HM group immediately after the restoration throughout the study period.nnnCONCLUSIONSnThe present 2-year clinical evaluation of different composites showed that the flowable nano-hybrid composite could be an effective esthetic material for posterior restoration.

Fabrication and evaluation of dental endoscopic instruments using fiber-optic system

The entrance of a tooth root canal is very small to the naked eye, and in most cases, dentists operate blindly to perform the treatment using an instrument. Particularly, the observation of fractures near the root apex and collaterals of root canals is difficult even using the latest dental instrument. To solve these problems, we attempted to develop a novel dental endoscope. In this study, we developed micro image sensors that can be used for observation of root canals and evaluation of the image sensor visibility. Previous methods have only single line visibility; however, the new method enables evaluation of the sectional visibility in the screen area. Compared with commercially available image sensors, the new image sensor has more than two times higher sectional visibility. Hence, the most focusing area can be analyzed and the aforementioned problems can be solved to improve image sensors. Moreover, not only the micro image sensors but also other sensors can be evaluated quantitatively using this new method.

Optical-based diagnostic technique for detection of tooth caries using laser-induced breakdown spectroscopy

A laser-based emission-type diagnostic technique using laser-induced breakdown spectroscopy (LIBS) for the in vivo analysis of tooth enamel is described. The system aims to improve the promptness of laser dental treatment and accuracy of identifying early caries from healthy teeth. Our research group has been developing the LIBS system for various applications. In addition to the research on the LIBS system, a novel microdental endoscope to observe fractures near the root apex has been developed in a recent study. The LIBS system for dentistry presented in this paper is the first attempt to combine the techniques of the microdental endoscope and the spectroscopic measurement from our group. In the LIBS operation, not only the elemental information is obtained, but also the pulse-operated-condensed laser generates microsized plasma on the surface of the materials when it removes trace substances. The combination technique using LIBS with the microdental endoscope allows noncontact dental diagnosis with chemical analysis and dental treatment at the same time.