In this quarter of a century, endodontic treatment has made great advances, where cone beam computed tomography （CBCT） has contributed greatly in regard to the improvement of diagnostic accuracy. This article aimed to summarize the application and effectiveness of CBCT in various aspects of endodontic treatment. Currently, international guidelines on the use of CBCT to endodontic diagnosis state that CBCT is recommended in complex, difficult-to-diagnose cases where conventional 2-dimensional radiography does not provide sufficient diagnostic yield. Our study on the diagnostic impact of CBCT imaging, involving 634 cases, revealed that CBCT was effective in the diagnosis and decision-making of complex endodontic cases. Our recent studies have also demonstrated that root fracture can be diagnosed accurately by means of analyzing the morphology of lesions 3-dimensionally reconstructed from CBCT images, and that CBCT imaging is effective at detecting periapical lesions that are undetectable on periapical radiography, particularly in the maxillary incisors and molars. Clinical cases in which CBCT imaging was useful in determining the number of canals, detecting root resorption, root perforation and root fracture and making presurgical planning are presented. It was concluded that CBCT is extremely effective for endodontic diagnosis.

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Objectives: The purpose of this study was to develop a method for evaluating the image quality of multi-detector computed tomography （MDCT） protocols for dental implant treatment planning. 　Methods: In experiment 1, an aluminum phantom composed of 12 steps, with 7 holes in each step, was scanned with two CT units. The numbers of undetectable holes on superimposed images were counted after the optimal threshold grey value had been determined using the just-noticeable difference （JND） method. The results were compared with those obtained by 7 observers. In experiment 2, we used two 12-step phantoms, with 7 holes in each step. One was made of aluminum, and the other was made of Teflon （polytetrafluoroethylene）. They were scanned with a CT scanner at a tube voltage of 120kV, and the tube current was set at 200, 150, 100, 50, or 10mA. 　Results: On superimposed CT images, the numbers of undetectable holes according to the aforementioned method exhibited predictable relationships with the values obtained by the observers. The number of undetectable holes decreased as the tube current increased up to 150mA in both the aluminum and Teflon phantoms. There was no significant difference in the number of undetectable holes between 150mA and 200mA. Considering the administered radiation dose, a tube current of 150mA was considered appropriate for use in our hospital. 　Conclusions: Our JND-based method can be used to evaluate the image quality of MDCT. This technique, which involves aluminum and Teflon phantoms, is expected to be an effective way of determining the optimal MDCT protocol.

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Objective: During intraoral radiography, the extent to which fingers are exposed to radiation should be reduced as much as possible. We compared the exposure doses between two image receptor-holding methods, a finger-based method and a method involving special devices. Then, we verified the usefulness of the devices. 　Materials and Methods: The maxillary right first molar of a dental x-ray simulator mannequin was chosen as the target tooth for the intraoral x-ray examinations. Irradiation （60kV, 6mA, 0.32s） was performed using a short cone-type x-ray head. Small （10×10×2mm） OSL （optically stimulated luminescence） dosimeter tips were used to measure the radiation doses. In addition to the conventional finger-based method, two types of devices were used to hold the image receptors: the “Smart-grip”, a toothbrush-type device, and the “Smart-wing” system, which combines an occlusion holding device and a rectangular iris. We measured the radiation dose delivered to the back of the receptor when the fingers, “Smart-grip”, and “Smart-wing” were used. In addition to the back of the receptor, the radiation doses at two distant points were also measured. The reverse-side radiation doses of different image receptors （analog film, imaging plates） were also compared. 　Results and Discussion: The radiation dose delivered to the fingertips was 0.178mGy/exposure when the image receptor was held with the fingers, whereas it was 0.072mGy/exposure when an x-ray film was used with a sheet of lead foil. The radiation dose delivered to the reverse side of the image receptor was 0.018mGy/exposure when the “Smart-grip” was used. The radiation dose delivered to the handle of the “Smart-grip” was 0.006mGy/exposure, which was almost the same as the background level. When the “Smart-wing” was used, the dose delivered to the back of the image receptor was 0.024mGy/exposure. 　Conclusion: It was suggested that the radiation dose delivered to the fingers during intraoral radiography can be markedly reduced by using the “Smart-grip” or “Smart-wing”.

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In this study, we investigated the clinical and imaging findings of 14 patients with subcutaneous emphysema, who were examined at our department between 2012 and 2017. 　Patients with subcutaneous redness, swelling, and crepitation that were suspected to be associated with subcutaneous emphysema were examined using computed tomography （CT）. The age, sex, affected region, administered treatment, time to the examination after onset, and whether the emphysema had spread into various tissue spaces were analyzed in these patients. The tissue spaces that were examined for subcutaneous emphysema were chosen based on the anatomical tissue space definitions produced by H. Ric Harnsberger16, and included the temporal, buccal, masticatory muscle, submandibular, parapharyngeal, posterior pharyngeal, parotid gland, submental, anterior and posterior cervical, and mediastinal spaces. These tissue spaces were examined for foamy structures and honeycomb or irregularly shaped regions of aeration, exhibiting homogeneously low signal intensity, which were considered to be indicative of the spread of subcutaneous emphysema. 　Clinical images are presented. Case 1 involved a patient with a maxillary alveolar fracture. Subcutaneous emphysema caused by a CO2 dental laser was noted in case 2. 　Regarding sex and age, the incidence of subcutaneous emphysema was significantly higher among females and patients in their 20s, and the most common site of occurrence was the lower jaw, especially the molar region. The most frequent cause was an air turbine used for tooth extraction. Regarding spread to tissue spaces, foamy structures and irregular regions of aeration with low signal intensity were noted in the masticatory muscle, submandibular, and parapharyngeal tissue spaces in 12 of the 14 patients. 　When a lower impacted wisdom tooth is extracted using an air turbine, compressed air-based dental treatment devices should be used very carefully, and when subcutaneous emphysema is suspected based on clinical findings it is necessary to immediately examine it using CT and determine its extent. It was suggested that CT is useful for diagnosing subcutaneous emphysema.

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Objectives: Video fluoroscopy （VF） is the most commonly used imaging method for evaluating swallowing motions. Other methods include video endoscopy （VE） and ultrasonography （US）. While VF provides clear images of the entire swallowing process, it involves exposure to X-rays and captures 3D movements on 2D images. VE is primarily used for imaging the pharyngeal phase of swallowing, and it is not suitable for evaluating the oral phase. On the other hand, US does not involve radiation exposure and can be used for both 3D and 4D imaging. Some studies have demonstrated that US systems can be used to evaluate swallowing functions in 3D and 4D, which is not possible with conventional VF. However, the image quality of US is affected by the image acquisition settings, the function and shape of the probe, and the texture of the food being swallowed during the examination. In the present study, we aimed to determine the efficacy of US for evaluating tongue movement. Specifically, we sought to determine the optimal image acquisition settings and types of food for evaluating tongue and bolus movements. We also examined the utility of novel software, which was specifically designed for analyzing tongue movement. 　Methods: The Voluson 730 US system （GE Healthcare Japan） and RABA4-8L 3D/4D convex US probe were used. One healthy volunteer was imaged using various image acquisition settings to assess image quality. In addition, the following types of food, which were considered safe and convenient for the purposes of swallowing examinations, were tested: liquids: tea or carbonated water; jelly: agar, agar＋baking soda, or agar＋soft drink; solids: a steamed bun, a pie, udon noodles, a cracker, or Mousse-UpⓇ＋soft drink）. The images were evaluated visually by an oral radiologist. Selected images that were of sufficient quality were saved in BMP format and analyzed using an analytical platform （Ratoc System Engineering Co., Ltd.）, comprised of an existing 4D fast image viewer and 3D image analysis software, and novel software （“Tongue Movement MOVIE software”）, which was specifically designed for delineating tongue and bolus movements. 　Results and Discussion: We demonstrated that use of the 3D/4D US system and novel analytical software designed for analyzing tongue movements was effective at delineating tongue movements and bolus movements at the back of the tongue. The images were of higher quality than the original images, and could be acquired in any direction. Although further evaluations are required to allow this method to be used in routine clinical practice, our findings suggest that it was useful for assessing tongue and bolus movements during the oral phase of swallowing. 　This study received a Grant-in-Aid for Scientific Research （25462931）.

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Multidetector computed tomography （MDCT） was introduced to Nihon University School of Dentistry at Matsudo Hospital in April 2006. Supernumerary teeth are anomalous extra teeth. They are often encountered in daily clinical practice and can cause dental alignment problems, depending on the impaction position, and so dental extraction is sometimes necessary. It is important to accurately assess the position and form of supernumerary teeth and their relationships with the adjacent tissues on CT examinations. Furthermore, CT is required to make decisions regarding tooth extraction and the timing of treatment in the clinical setting. 　The objective of this study was to investigate the characteristic clinical findings of supernumerary teeth by analyzing a large number of MDCT images. 　Of the 34,002 patients who underwent MDCT examinations at our radiology department between April 2006 and March 2016, the subjects were 855 patients with impacted supernumerary teeth （1,081 teeth）. 　The following results were obtained: 　1. The 855 patients consisted of 579 males （67.7%） and 276 females （32.3%）. 　2. The patients’ ages ranged from 4 to 87 years old, and their median age was 9 years old. Most cases （499, 58.4%） involved patients aged <10 years old. 　3. Four hundred and forty-three （51.8%）, 293 （34.3%）, and 93 （10.9%） MDCT scans were ordered by the Division of Oral Surgery, the Division of Pediatric Dentistry, and other divisions at our hospital, respectively, and 26 （3.0%） were ordered by another hospital. 　4. The total number of impacted supernumerary teeth was 1,081, with the highest number （652 teeth, 60.4%） seen in the median maxillary region （mesiodens）. 　5. Forty-five （4.2%） and 1,036 （95.8%） teeth were impacted on the labial and palatal side, respectively. 　6. As for the direction of the tooth crown and root, 248 （22.9%）, 146 （13.5%）, and 687 （63.6%） teeth were classified as normal, horizontal, and inverted, respectively. 　It was confirmed that the optimal treatment policy for impacted supernumerary teeth can be determined by confirming the exact position of each impacted tooth on MDCT.

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