Midori Yoshida

Numerical Evaluation of Image Contrast for Thicker and Thinner Objects among Current Intraoral Digital Imaging Systems

The purpose is to evaluate the performance of current intraoral digital detectors in detail using a precise phantom and new method. Two aluminum step wedges in 0.5 mm steps were exposed by two photostimulable phosphor plate (PSP) systems—one with automatic exposure compensation (AEC) and the other without AEC—and a CCD sensor. Images were obtained with 3 doses at 60 kV. The effect of metallic material also was evaluated. The contrast-to-noise ratio (CNR) for thinner steps and the low contrast value (LCV) for thicker steps were obtained. The CCD system was the best under all conditions (P < 0.001), although the Gray value was sensitive to the dose, and the Gray value-dose relation varied greatly. The PSP system with AEC was superior to that without AEC for the LCV (P < 0.001) but was inferior to it regarding the CNR (P < 0.001). CNR and LCV in the PSP system without AEC were not affected by the metallic plate. Intraoral digital imaging systems should be chosen according to their diagnostic purpose. PSP system with AEC may be the best for detecting molar proximal caries, whereas the PSP system without AEC may be better for evaluating small bone regeneration in periodontal disease. The CCD system provided the best performance.

Infiltration of trace metal ions in the oral mucosa of a rat analyzed using SRXRF, XAFS, and ICP-MS

Although the accumulation and distribution of metals from metallic orthodontic appliances in the oral mucosa have been studied extensively, they remain unclear because their concentration is quite low. In this study, metal specimens (Ni, Ni-Ti, and Co-Cr) were sutured in the unilateral oral mucosa of rats, and the distribution of the eluted elements in the mucosal tissue was estimated using inductively coupled plasma mass spectrometry (ICP-MS) and synchrotron radiation X-ray fluorescence analysis (SR-XRF). While the infiltrations of Ni, Co, and Cr into the oral mucosal connective tissue were observed with SR-XRF, significant increases were only found in Ni from the pure Ni group and Cr from the Co-Cr group. Furthermore, Ni and Co were estimated as hydrated ions while Cr was estimated in oxide form through X-ray absorption fine structure (XAFS) analysis.

Creation of a dental X-ray unit with a contactless exposure control switch

OBJECTIVE A new dental radiographic unit (DXRU) with a contactless switch for adjusting exposure conditions and a foot-pedal exposure switch was developed to prevent bacterial or viral contamination from patients and was compared with a conventional DXRU with a panel push-button switch with respect to user friendliness. METHODS 45 fourth-year dental school students carried out intraoral radiography using both types of DXRU. Errors regarding dose shortages of X-rays were compared and a questionnaire completed. RESULTS 22 (49%) of the 45 students failed to provide the correct radiographic exposure and the number of errors was 32 for the conventional DXRU, and 4 (9%) students failed to provide the correct radiographic exposure and the number of errors was 4 for our new DXRU, at the first stage (p < 0.001). At the second stage, the number of students who failed to provide the correct radiographic exposure and the number of errors decreased to 12 and 16, respectively, for the conventional DXRU (p < 0.05). 37 (82%) of the 45 students preferred our DXRU because of its contactless switch and the push-pedal exposure switch. CONCLUSIONS These data suggested that our new contactless mechanism should be used for other DXRUs for contamination control.

Dental students’ levels of understanding normal panoramic anatomy

Background/purpose In dentistry, panoramic radiography is an important examination technique. The Faculty of Dentistry at Tokushima University educates students about panoramic radiographic anatomical landmarks. The purpose of this study was to investigate differences in the understanding of each panoramic anatomical landmark among students. Materials and methods This study analyzed the results of 40 fifth- and 79 sixth-year faculty students who had taken a written examination to clarify their knowledge of anatomical landmarks in 28 panoramic radiographic regions. Anatomical landmarks were classified into 3 categories: , , and  to compare correct answer rates. Results The mean overall correct answer rate by the 119 students for the 28 regions was 53%. The rate did not vary between the 2 academic years. On comparison of the 3 categories, significant differences were only observed between  and , as the values for the latter were lower. Among the anatomical landmarks, the rates for the condylar head, hyoid bone, panoramic innominate line, styloid process, and nasopalatine line were higher, and those for ghost images of the contralateral nasopalatine line, the cervical vertebrae, mandibular foramen, mastoid air cell, and posterior pharyngeal wall were lower. The values for , such as the dorsum of tongue, middle and inferior nasal conche, and middle and inferior nasal meatuses, were also lower. Conclusion These results indicate the necessity of improving educational approaches for regions with lower rates of correct answers.

History of Digital Detectors in Intraoral Radiography

The first digital sensor used in intraoral radiography, RadioVisioGraphy was introduced in 1987. It was based on the activity of a charged-Coupled Device (CCD) sensor. Later on, other digital sensors became commercially available, including the Digora featuring an imaging plate coated with photostimulable phosphor (PSP) in 1994 and the complementary metal-oxide semiconductorbased sensor, CDR active pixel sensor, in 1998. These technologies have recently undergone considerable improvement, and several dental clinics have switched from film-based systems to digital imaging. In the early days, digital sensors were considered inferior to film in clinical diagnostics, but according to recent research results, there is no longer any significant difference because of the improvement in performance. However, our latest research using a new evaluation method and a precise phantom model indicated some differences between the performance of CCD and PSP systems and further differences between PSP systems of different function and performance.

1/F Noise-Fluctuated Cozy Lighting System for Concentration Improvement

The power spectrum of human heart rate measured over 24 h exhibits “power-law” 1/f alpha-type spectral behavior with alpha approximately 1. This may be one of the reasons why 1/f noise help people make relaxed, or feel comfortable. As a result, people feel relaxed by looking at a candle light, listening to the sound of ocean wave, or feeling the breezing wind because all of these natural phenomenon is based on the 1/f noise fluctuation. Considering this feature, a technical approach of 1/f noise fluctuation has been applied to various industry products, ranging from light illumination, fan control, temperature control, etc. to implement cozy products. For example, one typical example would be a lighting product mimicking a candle light, which illuminate just like a true candle. A candle light provides a cozy atmosphere to relax our mind by forgetting severe business issues, which is because of the nature of 1/f noise fluctuation as mentioned above. However, it is not suitable to do something important by concentration under a candle light because of the changes of brightness and the blinking nature of candles. This study designs and develops 1/f noise-fluctuated cozy lighting system with stable brightness and chromaticity without blinking so that people unconsciously feel relaxed under this lighting system without noticing the 1/f noise fluctuation and concentrate on work or operation. In order to implement this lighting system, combination of two types of white LED lights were used. White LED lights are manufactured by the combination of different colors having different spectrum. For example, Blue with YAG fluorophore, Blue with RG fluorophore, UV with RGB fluorophore, etc. provide all white LED lights. This means that it is possible to make two different types of LED lights which have the same white color with different combination of spectrums. If the two white colors of the two LED are the same, nobody cannot notice when the two LEDs are switching over each other, periodically or randomly. People only think that the white color is constantly provided by the white LED light. However, if the switching is based on 1/f noise fluctuation, some positive effect can be expected under this lighting system. This paper shows the overview of the idea of 1/f noise-fluctuated cozy lighting system, and then presents the two basic challenges of the idea towards concentration improvement; Combination of two types of white LED and 1/f noise-fluctuated switching system. These two challenges are presented using a prototype lighting systems developed in this study.Copyright