Kenji Seki

Absorbed and effective doses from cone beam volumetric imaging for implant planning

OBJECTIVES Volumetric CT using a cone beam has been developed by several manufacturers for dentomaxillofacial imaging. The purpose of this study was to measure doses for implant planning with cone beam volumetric imaging (CBVI) in comparison with conventional multidetector CT (MDCT). METHODS The two CBVI systems used were a 3D Accuitomo (J. Morita), including an image-intensifier type (II) and a flat-panel type (FPD), and a CB MercuRay (Hitachi). The 3D Accuitomo operated at 80 kV, 5 mA and 18 s. The CB MercuRay operated at 120 kV, 15 mA, 9.8 s. The MDCT used was a HiSpeed QX/i (GE), operated at 120 kV, 100 mA and 0.7 s, and its scan length was 77 mm for both jaws. Measurement of the absorbed tissue and organ doses was performed with an Alderson phantom, embedding the radiophotoluminescence glass dosemeter into the organs/tissues. The values obtained were converted into the absorbed dose. The effective dose as defined by the International Commission on Radiological Protection was then calculated. RESULTS The absorbed doses of the 3D Accuitomo of the organs in the primary beam ranged from 1-5 mGy, and were several to ten times lower than other doses. The effective dose of the 3D Accuitomo ranged from 18 muSv to 66 muSv, and was an order of magnitude smaller than the others. In conclusion, these results show that the dose in the 3D Accuitomo is lower than the CB MercuRay and much less than MDCT.

Assessment of the blood supply to the lingual surface of the mandible for reduction of bleeding during implant surgery

OBJECTIVES The aim of this study was to assess the frequency of the foramina and their canals on the lingual surface of the mandible using computed tomography (CT), which was carried out for dental implant planning. MATERIAL AND METHODS First, the visibility of the lingual canals of the CT image was verified by dissecting five cadavers. CT images of 200 patients, who had decided on implant treatment, were used in this study. The visibility of the foramina and their canals on the lingual surface of the mandible were assessed. RESULTS The foramina were divided into two groups by the positions of the mandible, the medial lingual foramen and the lateral lingual foramen. At least one foramen was found in all patients. In the medial group, a higher level of mental spine was seen in 190 patients, the same level of mental spine was observed in 99 patients and a lower level of mental spine was observed in 114 patients. The lateral lingual foramina were found in 160/200 patients and 88/200 patients presented bilaterally. CT can predict the position and the size of the foramina and their canals on the lingual surface of the mandible. All the patients had more than one foramen in the middle of the lingual surface of the mandible on the CT image. CONCLUSION The frequency of the lingual foramina in the medial region was 100% and that in the lateral region was 80%. It would also be useful to emphasize the significant variation in the precise location of these lingual foramina, and that these can only be visualized presurgically with volumetric imaging modalities, such as CT or Cone beam 3D systems.

Effects of tube current on cone-beam computerized tomography image quality for presurgical implant planning in vitro

OBJECTIVE The purpose of this study was to evaluate the effect of tube current reduction on the quality of cone-beam computerized tomography (CBCT) images of the maxilla and mandible for presurgical implant planning. STUDY DESIGN Six cadaver heads were imaged with a CBCT (3D Accuitomo) operated at 80 kVp and variable tube current (8, 4, 2, or 1 mA) in full-scan mode. For the posterior region of maxilla and mandible, half-scans were also performed at similar settings. The images were evaluated independently by 5 oral radiologists for 15 anatomic landmarks regarding presurgical implant planning. The quality of images were compared with their respective reference images at 8 mA and ranked on a 4-point rating scale as excellent, good, fair, or nondiagnostic. The scores of all observers were averaged for each landmark at every exposure condition, and Bonferroni test (P<.05) was performed. RESULTS The 4 mA images at full-scan mode could visualize each landmark of maxilla and mandible and were evaluated to be the same or almost equivalent in quality as the 8 mA images. Even 2 mA images in full-scan mode and 4 mA in half-scan mode could be used for implant planning. The 1 mA images were unacceptable owing to the substantial degradation in image quality. CONCLUSION Significant dose reduction can be achieved by reducing tube current without substantial loss of image quality for presurgical implant planning in CBCT.

Effects of exposure reduction on the accuracy of an intraoral photostimulable-phosphor imaging system in detecting incipient proximal caries

Digital imaging systems for use in intraoral radiography are becoming common in clinical practice, although its physical properties such as resolution and available dynamic range may be inferior to conventional film systems. The purpose of this study was to determine the diagnostic accuracy in detecting incipient proximal caries using a digital system with storage phosphor plate (Digora®) in comparison with a conventional intraoral film (Kodak Ektaspeed Plus®). Thirty-one extracted upper premolars were selected. Of the 62 surfaces, 33 had proximal caries with discoloration or incipient lesions, and the rest showed no evidence of caries verified on strict inspection using fiber-optic transillumination. All teeth were radiographed following the paralleling technique (60 kV, 40 cm focus-to-film distance). Exposure was adjusted to Ektaspeed Plus film, while reduced to 1/2, 1/4, and 1/8 on Digora®. The films and digital images were evaluated by three observers, using a confidence rating for the presence of caries. On Digora®, the observers could control contrast and brightness. The results showed that Digora® had better performance in detecting caries than the film, even when the exposure was used for the film, although there were no statistically significant differences. The results suggest that the storage phosphor plate system may be used clinically to diagnose incipient proximal caries, while reducing the exposure to the patient.

Composition of the blood supply in the sublingual and submandibular spaces and its relationship to the lateral lingual foramen of the mandible

OBJECTIVE The purpose of this research was to contribute to minimizing arterial disruption during mandibular surgical procedures by clarifying the course of the arteries supplying the sublingual and submental regions. STUDY DESIGN Heads of 75 human cadavers were dissected to identify the arterial supply of the sublingual and submental regions. Computed tomography scans were performed to visualize the lateral lingual foramina of the mandibles. RESULTS The facial artery was found to contribute to the composition of almost half of the sublingual arteries studied. Furthermore, it was demonstrated that the arterial supply to an incisor tooth is often from the submental artery. CONCLUSIONS Our data provide important information for coping with bleeding or hematoma occurring during surgical procedures in the mandibular region.

Development of a new dental panoramic radiographic system based on a tomosynthesis method.

The objective of this study was to develop a new practical method to reconstruct a high-quality panoramic image in which radiographers would be free from the onerous task of correctly locating the patients jaws within the image layer of the panoramic unit. In addition, dentists would be able to freely select any panoramic plane to be reconstructed after the acquisition of the raw scan data. A high-speed data acquisition device was used with a CdTe (cadmium telluride) semiconductor detector and a sophisticated digital signal-processing technique based on tomosynthesis was developed. The system processes many vertical strip images acquired with the detector and generates a high-resolution and high-contrast image. To apply the tomosynthesis technique to the acquired strip images correctly, the actual movement of the panoramic unit was measured, including the X-ray tube and detector, in a scan using a calibration phantom and the authors generated a shift amount table needed for the shift-and-add tomosynthesis operation. The results of the experiments with a PanoACT-1000 panoramic unit, which was a PC-1000 panoramic unit fitted with a high frame rate semiconductor detector SCAN-300FPC, demonstrated the capability of a tomosynthesis technique which, when applied to the strip images of a dry skull phantom, could change the location and inclination of an imaging plane. This system allowed the extraction of an optimum-quality panoramic image regardless of irregularities in patient positioning. Moreover, the authors could freely reconstruct a fine image of an arbitrary plane with different parameters from those used in the original data acquisition to study fine anatomical details in specific locations.

Effect of computer assistance on observer performance of approximal caries diagnosis using intraoral digital radiography

Logicon Caries Detector™ (LDDC) is the only commercially available computer-assisted diagnostic system for caries diagnosis. The object of this study is to elucidate the efficacy of LDDC when used by inexperienced dentists. Fifty extracted teeth were imaged using an RVG6000. Seven dentists who had just passed the Japanese National Dental Board Examination observed those images without LDDC (woLDDC) and assessed the probability that caries lesions were present, then re-assessed the same teeth using LDDC (wLDDC). The areas under the receiver operating characteristic curves (Az) were compared. No statistically significant difference was found between woLDDC Az values and wLDDC Az values when caries lesions of all depths were considered. When positive cases were restricted to caries lesions in the inner half of the enamel or to dentine caries lesions, however, wLDDC Az values were significantly larger than woLDDC (p = 0.043 and 0.018, respectively).

Effects of dose reduction on multi-detector computed tomographic images in evaluating the maxilla and mandible for pre-surgical implant planning: a cadaveric study

OBJECTIVE To assess effects of dose reduction on image quality in evaluating maxilla and mandible for pre-surgical implant planning using cadavers. MATERIALS AND METHODS Six cadavers were used for the study using multi-detector computed tomography (CT) operated at 120 kV and the variable tube current of 80, 40, 20 and 10 mA. A slice thickness of 0.625 mm and pitch 1 were used. Multi-planar images perpendicular and parallel to dentitions were created. The images were evaluated by five oral radiologists in terms of visibility of the anatomical landmarks including alveolar crest, mandibular canal, floors of the maxillary sinus and nasal cavity, contours/cortical layer of jaw bones and the details of trabecular bone. Observers were asked to determine the quality of the images in comparison with 80 mA images based on the criteria: excellent, good, fair or non-diagnostic. The average scores of all observers were calculated for each specimen in all exposure conditions. RESULTS The 40 mA images could visualize such landmarks and were evaluated to be same or almost equivalent in quality to the 80 mA images. Even the 20 mA images could be accepted just for diagnostic purpose for implant with substantial deterioration of the image quality. The 10 mA images may not be accepted because of the obscured contour caused by image noise. CONCLUSION Significant dose reduction by lowering mA can be utilized for pre-surgical implant planning in multi-detector CT.

Comparison between RVG UI sensor and Kodak InSight film for detection of incipient proximal caries

ObjectThe purpose of this study was to compare the efficacy of the four combination modes of Trophy RadioVisioGraphy UI sensor (Trex-Trophy Radiology Inc., Marne-la-Valee, France) and Kodak InSight film (Eastman Kodak Co., Rochester, NY) for detecting proximal dental caries.Materials and MethodsThirty extracted human upper premolars were selected. Of 60 surfaces, 25 had carious lesions in the form of small cavities, and the rest showed no evidence of caries as verified by a micro computed tomogram (micro CT; XCT Research SA+, Stratec Medizintechnik GmbH, Pforzheim, Germany). All teeth were radiographed with the paralleling technique (60kV, 40 cm focus-to-sensor distance). Four combination modes (high-resolution caries mode—HRC; high-sensitivity caries mode—HSC; high-resolution periodontal mode—HRP; and high-resolution endo mode—HRE) were used. Exposure was set at 0.12 sec for HRC, 0.08 sec for HSC, 0.16 sec for HRP, 0.12 sec for HRE, and 0.16 sec for the Kodak InSight film. The resulting images were evaluated by three oral radiologists. The same three observers evaluated the digital images, and were allowed to use the contrast and brightness controls in doing so. Possible differences in ROC curve areas among image modalities were assessed by the Friedman test.ResultsThe mean ROC curve areas were 0.66±0.11 for HRC, 0.78±0.02 for HSC, 0.76±0.04 for HRE, 0.77±0.04 for HRP, and 0.71±0.09 for the Kodak InSight film. There were no statistically significant differences between HRC, HSC, HRE, HRP and the Kodak InSight film in terms of proximal caries detection.ConclusionThe four modes of RVG UI system are each a viable alternative to intraoral film for the detection of incipient dental caries.

Accuracy of Digora System in Detecting Artificial Peri-implant Bone Defects

This study was done to compare the diagnostic accuracy in detecting simulated intrabony defects around fixtures using Digora (DIG; Sordex Orion Corporation, Helsinki, Finland) compared with Ektaspeed Plus film (PLS; Eastman Kodak Co., Rochester, NY). Three titanium implant fixtures were placed in molar areas of three cadavers. Bone defects were created in the interproximal alveolar crest. Exposure time was adjusted to a PLS film and reduced to 1/5 only for DIG (1/5 DIG). The results of four observers were assessed. Sensitivity, specificity, accuracy, and under the receiver operator char-acteristic curve (ROC) area were evaluated. Statistical analyses were performed by using Friedman test and one-way ANOVA test. Mean sensitivity/specificity were 0.60/0.85 (DIG), 0.54/0.81 (1/5 DIG), and 0.64/0.58 (PLS). There were no statistically significant differences in the diagnostic accuracies. Digora had an equivalent performance to radiographic film in detecting intrabony defects adjacent to the implants, notwithstanding the amount of 1/5 of the exposure time.