Metal artifacts from posterior mandibular implants as seen in CBCT.

PURPOSE: Metal artifacts from dental implants have not been clarified in cone-beam computed tomography (CBCT) images in previous studies. Hence, only mesiodistal metal artifacts from dental implants in the posterior mandibular region were assessed using CBCT. MATERIALS AND METHODS: Twenty-two patients with a total of 61 dental implants in posterior mandibular sites were enrolled. The pixel values surrounding dental implants were measured using CBCT and rotational panoramic radiography, and then the means were calculated. RESULTS: The mean pixel values between dental implants, between dental implants and neighboring teeth, and posterior to dental implants were significantly lower than between neighboring teeth in CBCT. In addition, the mean pixel value between dental implants did not significantly differ from that between neighboring teeth in rotational panoramic radiography. CONCLUSIONS: It was concluded that mesiodistal metal artifacts surrounding dental implants are demonstrated on CBCT.

Demonstration of the accessory mental foramen using rotational panoramic radiography compared with cone-beam computed tomography.

OBJECTIVE: Rotational panoramic radiography is routinely used in dental practice. It has not been clarified, however, whether an accessory mental foramen can be demonstrated using this technique. The visibility of accessory mental foramina on rotational panoramic radiographs was compared with those on para-panoramic images reconstructed from cone-beam computed tomographic (CBCT) images. MATERIALS AND METHODS: A total of 365 patients (130 males and 235 females) were retrospectively analyzed. Para-panoramic images were reconstructed from CBCT images with the accessory mental foramen/foramina using three-dimensional visualization and measurement software, and then the accessory mental foramen on rotational panoramic images was compared with that on para-panoramic images. RESULTS: A total of 37 accessory mental foramina were observed in 28 patients on CBCT images. The rate of being able to visualize the accessory mental foramen or bony canal between the point of bifurcation from the mandibular canal and the accessory mental foramen on rotational panoramic radiographs was 48.6% (18 of 37 accessory mental foramina). CONCLUSION: Approximately half of the accessory mental foramina-positive CBCT images demonstrated the accessory mental foramen, or bony canal between the point of bifurcation from the mandibular canal and accessory mental foramen on rotational panoramic radiographs.

Detection and classification of unilateral cleft alveolus with and without cleft palate on panoramic radiographs using a deep learning system.

Although panoramic radiography has a role in the examination of patients with cleft alveolus (CA), its appearances is sometimes difficult to interpret. The aims of this study were to develop a computer-aided diagnosis system for diagnosing the CA status on panoramic radiographs using a deep learning object detection technique with and without normal data in the learning process, to verify its performance in comparison to human observers, and to clarify some characteristic appearances probably related to the performance. The panoramic radiographs of 383 CA patients with cleft palate (CA with CP) or without cleft palate (CA only) and 210 patients without CA (normal) were used to create two models on the DetectNet. The models 1 and 2 were developed based on the data without and with normal subjects, respectively, to detect the CAs and classify them into with or without CP. The model 2 reduced the false positive rate (1/30) compared to the model 1 (12/30). The overall accuracy of Model 2 was higher than Model 1 and human observers. The model created in this study appeared to have the potential to detect and classify CAs on panoramic radiographs, and might be useful to assist the human observers.

Observation of maxillary sinus septa and bony bridges using dry skulls between Hellman's dental age of IA and IIIC.

Maxillary sinus septa and bony bridges were observed using dry skulls in childhood, classified based on Hellman's dental age, to clarify maxillary sinus septum formation. Eighty-eight maxillary sinuses of 44 dry skulls and a cone-beam computed tomography (CBCT) unit were used. The locations of the septum, defined as a pointed bony structure originating from the inferior wall, and bony bridge, defined as a bony structure between the maxillary sinus wall and dental germ, were antero-posteriorly recorded, and the superoinferior distance, distance from the bony palate, and angle to the median palatine suture were measured. The rate of septum presence in the maxillary sinus was high (41.7%) in IIIC, and the septa were located in the deciduous molars, premolars, and molars. Also, all bony bridges were related to the median maxillary sinus wall, and the rate of the maxillary sinus showing a bony bridge was high in IIA and IIIA. Septum presence in the maxillary sinus was observed in IIA, IIC, IIIA, IIIB, and IIIC of Hellman's dental age. Also, bony bridges were observed in IC, IIA, IIC, IIIA, IIIB, and IIIC of Hellman's dental age.

[Case of bronchiolitis obliterans with rapidly progressive bronchiectasis after allogeneic peripheral blood-derived stem cell transplantation].

A 64-year-old woman underwent allogeneic peripheral blood-derived stem cell transplantation for acute lymphocytic leukemia. She complained of dyspnea and was admitted to hospital 116 days after transplantation. Because of positive serum testing for the Aspergillus antigen and antibody, and ground-glass opacity in the right upper lobe on high-resolution computed tomography (HRCT), we made a diagnosis of pulmonary aspergillosis and administered an antifungal agent. Although tests for the Aspergillus antibody became negative and the ground-glass opacities disappeared, her dyspnea persisted. Progressive bronchiectasis was seen on HRCT, predominantly in the lower lobes. A pulmonary function test showed mixed impairment. We made a diagnosis of bronchiolitis obliterans after chronic graft versus host disease (GVHD). Prednisolone and an increased dose of tacrolimus (FK506) were administered, but type II respiratory failure progressed and she died 2 months after admission. On HRCT, each lobe was graded for bronchiectasis using a scale: 0 = normal, 1 = less than 2 x the diameter of an adjacent pulmonary artery, 2 = 2 - 3 x the diameter of an adjacent pulmonary artery, and 3 = more than 3 x the diameter of an adjacent pulmonary artery. A total score was calculated by summing the scores of all the lobes (maximum 15). In this case, the total score increased rapidly from 0 to 13 in 2 months.

Observation of buccal foramen in mandibular body using cone-beam computed tomography.

The location and course of the mandibular canal and multiple mental foramina are important in dental implant insertion and any surgical procedures involving the mandible. The purpose of the present investigation was to assess buccal foramen presence in the mandible using cone-beam computed tomography (CBCT) images. A total of 84 patients were enrolled in this investigation. Buccal foramen presence in the mandibular body, which was defined as a buccal bone defect of the bony canal penetrating through the buccal cortical bone, was assessed using two- and three-dimensional CBCT images. Buccal foramen presence, located from the median to molar regions, was observed in 44% of patients. There was no significant difference among gender and age. Also, a buccal foramen showing continuity with the mandibular canal was observed in 7.1% of patients. Buccal foramen presence in the mandibular body could be assessed in detail using CBCT images.

[Estimation of effective dose to salivary glands at examination of the oral and maxillofacial region].

The salivary glands and the oral mucosa were included in the determination of effective doses of radiography in the new ICRP (International Commission on Radiological Protection) recommendations. These changes will likely result in an upward reassessment of the effective dose during oral and maxillofacial radiographic examination. We measured the dose received by many organs and calculated the effective doses using the guidelines in ICRP Publications 103 and 60. For this study, we used intraoral radiography (incisor, canine, premolar, molar, maxillary, and mandibular areas) and panoramic radiography. The two levels of effective doses were compared. As a result, exposure during intraoral radiography ranged from 4 to 8 microSv and that during panoramic radiography ranged from 16 microSv in Publication 103. Effective doses in Publication 103 were higher than those in Publication 60. The dose was 1.6-4.5 times higher in intraoral radiography and 2.2 times higher in panoramic radiography. In conclusion, the salivary glands markedly influenced the value of the effective doses of radiography in this study.

Use of tungsten sheet as an alternative for reducing the radiation dose behind the digital imaging plate during intra-oral radiography.

OBJECTIVES: To verify the use of tungsten sheet as an alternative to lead foil for reducing the radiation dose behind storage phosphor plates (SPPs). METHODS: At six sites (incisor, canine, and molar sites in both the maxilla and mandible) in a head phantom, radiation doses were initially measured behind conventional film packets containing two films and a lead foil. At the same sites, radiation doses were also measured behind packets containing only SPPs. Thereafter, the same dose measurements were performed with shielding materials (lead foil or tungsten sheet) within the packets. These doses were defined as behind doses. RESULTS: There were no differences in the mean behind doses between the conventional film packets and the SPP packets without shielding materials for any of the six sites examined. The behind doses were reduced by both lead foil and tungsten sheet, with significant differences in all sites when compared with no shielding. Lead foil reduced the behind dose of the SPP packet to 37.6% on average, while tungsten sheet reduced the behind dose to less than 20% in all of the sites examined, with an average of 14.7%. CONCLUSIONS: Tungsten sheet appeared to be effective as an alternative shielding material, sufficiently reducing the doses behind the SPP packets to less than 20% when compared with sheetless packets in all of the six sites examined.

Depression of the maxillary sinus anterior wall and its influence on panoramic radiography appearance.

OBJECTIVES: To clarify the depression aspect of the maxillary sinus anterior wall and to investigate its relationship with the panoramic image appearance of a diagonal line from the inferior part of the so-called panoramic innominate line to the medial portion of the orbital floor line. METHODS: Based on CT data, panoramic images were simulated for two typical cases with and without anterior wall depression. Next, on axial CT images of 1689 subjects (3378 sinuses) stored in our image database, the wall depths were measured and analyzed for their relationships with the panoramic appearances of the diagonal line, classified into invisible, obscure and clear patterns. RESULTS: Based on the simulation study, visualization of the diagonal line was verified to alter depending on the morphology of the anterior wall and the position of the panoramic image layer. In 408 (12.1%) sinuses, the diagonal line (clear and obscure patterns) could be seen on the panoramic image. The incidences of the obscure and clear patterns increased with increasing age groups. The mean wall depths were 2.91, 4.80 and 7.28 mm for the invisible, obscure and clear patterns, respectively. The clear pattern showed the highest value for the wall depth, followed by the obscure pattern. CONCLUSIONS: The diagonal line on a panoramic image was verified to be related to depression of the maxillary sinus anterior wall, and its panoramic image appearance can be altered depending on the position of the tomographic image layer.

Longitudinal observation of maxillary sinus bony bridges and septa in childhood.

The rate of septum presence in the maxillary sinus has been reported to be over 30%. It was considered that a bony bridge might change to a maxillary sinus septum with growth in a previous study using dry child skulls. In the present investigation, maxillary sinus bony bridges and septa were longitudinally observed using computed tomography (CT). Multislice CT was performed in three patients. A bony bridge was defined as a bony structure between the maxillary sinus wall and dental germ. Also, a septum was defined as a pointed bony structure in the inferior wall of the maxillary sinus. The height and angle of the bony bridge/septum and the distance between the base of the bony bridge/septum and bony palate were measured. In three patients, the bony bridge in the maxillary sinus floor was observed in the second molar on the first CT, and the maxillary sinus septum was observed on the second CT at the same site. In conclusion, it was longitudinally observed that a bony bridge changed to a maxillary sinus septum with growth, such as root formation and tooth eruption.

Optimizing the reconstruction filter in cone-beam CT to improve periodontal ligament space visualization: An in vitro study.

PURPOSE: Evaluation of alveolar bone is important in the diagnosis of dental diseases. The periodontal ligament space is difficult to clearly depict in cone-beam computed tomography images because the reconstruction filter conditions during image processing cause image blurring, resulting in decreased spatial resolution. We examined different reconstruction filters to assess their ability to improve spatial resolution and allow for a clearer visualization of the periodontal ligament space. MATERIALS AND METHODS: Cone-beam computed tomography projections of 2 skull phantoms were reconstructed using 6 reconstruction conditions and then compared using the Thurstone paired comparison method. Physical evaluations, including the modulation transfer function and the Wiener spectrum, as well as an assessment of space visibility, were undertaken using experimental phantoms. RESULTS: Image reconstruction using a modified Shepp-Logan filter resulted in better sensory, physical, and quantitative evaluations. The reconstruction conditions substantially improved the spatial resolution and visualization of the periodontal ligament space. The difference in sensitivity was obtained by altering the reconstruction filter. CONCLUSION: Modifying the characteristics of a reconstruction filter can generate significant improvement in assessments of the periodontal ligament space. A high-frequency enhancement filter improves the visualization of thin structures and will be useful when accurate assessment of the periodontal ligament space is necessary.

Observation of maxillary incisive canal using dry skulls between Hellman's dental age IA and IIIC.

The maxillary incisive canals were observed in childhood from infancy to school-aged children to clarify their development. Cone-beam computed tomography was performed to investigate 44 dry child skulls. Two-dimensional images of various planes in the maxillary incisive canal were reconstructed on a computer using 3-dimensional visualization and measurement software. Then, antero-posterior angulation, and antero-posterior and lateral axes of the maxillary incisive canal were measured at the inferior and middle levels. The mean difference of angulation between the inferior and middle levels was 2.3 degrees in IIC, and 11.1 degrees in IIIC. The mean ratio of the lateral axis to antero-posterior axis at the middle level was 2.54 in IIC, and 1.93 in IIIC. In conclusion, it was antero-posteriorly straight from IA to IIC, and, after IIIA, it curved at the middle level. The cross-sectional shape in IIC was depressed with a larger lateral axis.

Cone-beam computed tomography images of phantoms with simulating trabecular bone structure fabricated using micro-stereolithography.

OBJECTIVE: Phantoms with simulating mandibular trabecular bone structure fabricated using micro-stereolithography were applied for a quantitative evaluation of cone-beam computed tomography (CT) images. MATERIALS AND METHODS: Phantoms with a three-dimensional lattice, in which a square pillar was set at 0.10, 0.20, 0.30 and 0.40 mm at the edge, spaced at 0.60 mm, were made of an acrylic resin using micro-stereolithography. Cone-beam CT with a 0.1 mm-cubic voxel was then performed, and a plot profile of voxel values was analyzed. RESULTS: The plot profiles of seven peaks corresponding to pillars in phantoms with 0.20, 0.30 and 0.40 mm-pillars were visually observed in cone-beam CT images. However, peaks of corresponding pillars in the 0.10 mm-pillar phantom could not be distinguished. The differences between average measured and designed distance were very small. CONCLUSION: Cone-beam CT images of phantoms with 0.20, 0.30 and 0.40 mm-pillars fabricated using microstereolithography were obtained.

[Comparison of absorbed and effective dose from two dental cone beam computed tomography scanners].

OBJECTIVE: This research compared the field of view with the tissue absorbed dose and effective doses using the two dental cone beam computed tomography (CBCT) scanners. MATERIALS AND METHODS: Two CBCT devices, an Alphard VEGA and 3DX multi-image micro CT MCT-1, were used. Measurements were made using an Alderson RANDO phantom and thermoluminescence dosimeters (TLDs). The calculation of the effective dose was carried out according to ICRP Publication 60 and 103. RESULTS: The effective doses for Alphard VEGA D mode, I mode, P mode, and C mode were 86, 238, 413, and 323 µSv, respectively. The effective doses using 3DX for the maxillary incisor, maxillary molar, mandibular incisor, mandibular molar, TMJ, and mandibular molar scout images were 27, 30, 48, 60, 14, and 1 µSv, respectively. CONCLUSIONS: Both Alphard VEGA and 3DX values revealed salivary gland and oral mucosa doses much higher than those required for other tissues. It is necessary to select a small mode suitable in order to realize optimization.

[Absorbed dose and the effective dose of panoramic temporo mandibular joint radiography].

PURPOSE: This study measured the radiation doses absorbed by the patient during Panoramic temporo mandibular joint radiography (Panoramic TMJ), Schüllers method and Orbitoramus projection. The dose of the frontal view in Panoramic TMJ was compared to that with Orbitoramus projection and the lateral view in Panoramic TMJ was compared to that with Schüllers method. METHODS: We measured the doses received by various organs and calculated the effective doses using the guidelines of the International Commission on Radiological Protection in Publication 103. Organ absorbed doses were measured using an anthropomorphic phantom, loaded with thermoluminescent dosimeters (TLD), located at 160 sensitive sites. The dose shows the sum value of irradiation on both the right and left sides. In addition, we set a few different exposure field sizes. RESULT: The effective dose for a frontal view in Panoramic TMJ was 11 µSv, and that for the lateral view was 14 µSv. CONCLUSION: The lens of the Orbitoramus projection was 40 times higher than the frontal view in Panoramic TMJ. Although the effective dose of the lateral view in Panoramic TMJ was 3 times higher than that of the small exposure field (10×10 cm on film) in Schüller's method, it was the same as that of a mid-sized exposure field. When the exposure field in the inferior 1/3 was reduced during panoramic TMJ, the effective doses could be decreased. Therefore we recommend that the size of the exposure field in Panoramic TMJ be decreased.

Comparison between cone-beam and multislice computed tomography depicting mandibular neurovascular canal structures.

OBJECTIVE: The most common diagnostic imaging modalities for cross-sectional imaging in dental implant planning are currently cone-beam computed tomography (CBCT) and multislice CT (MSCT). However, clinical differences between CBCT and MSCT in this task have not been fully clarified. In this investigation, the detection of fine anatomical structures in the mandible was assessed and compared between CBCT and MSCT images. STUDY DESIGN: The sample consisted of 28 patients who had undergone CBCT and MSCT. The bifid mandibular canal in the mandibular ramus, accessory mental and buccal foramina, and median and lateral lingual bony canals were observed in 2-D images, and the findings were compared between CBCT and MSCT. RESULTS: Four of 19 canals observed in CBCT were not observed in MSCT images. Three accessory mental foramina in 2 patients and 28 lateral lingual bony canals in 18 patients were observed consistently using the two methods. CONCLUSION: Depiction of fine anatomic features in the mandible associated with neurovascular structures is consistent between CBCT and MSCT images.

Assessment of maxillary sinus septa using cone-beam computed tomography: etiological consideration.

BACKGROUND: Septum presence in the maxillary sinus complicates sinus floor elevation surgery, and so it is important that septa are accurately diagnosed on preoperative imaging. PURPOSE: Septa were observed regarding their relationship with the bony palate using cone-beam computed tomography (CT). MATERIALS AND METHODS: Thirty maxillary sinuses with dentate jaws of 15 dry skulls and a cone-beam CT unit were used. A septum was defined as a pointed bone structure, and an exostosis was defined as a rounded bone structure. The occurrence and locations of maxillary sinus septa and exostoses of more than 2 mm in height were evaluated. Also, angles between the direction of septum and median palatine suture were measured on axial images. RESULTS: Twelve septa of 11 maxillary sinuses (37%) and nine exostoses of nine maxillary sinuses (30%) were observed. Also, 42% of septa and 67% of exostoses were antero-posteriorly aligned according to the transverse palatine suture. Moreover, the mean septum angle was 57.9 degrees in the anterior maxillary sinus region, and 101.8 degrees in the transverse palatine suture region, and significant differences were noted between them. CONCLUSION: Maxillary sinus septa and exostoses could be clarified regarding their relationship with the bony palate using cone-beam CT.

Accessory mental foramen assessment using cone-beam computed tomography.

OBJECTIVE: The purpose of the present study was to assess the accessory mental foramen using cone-beam computed tomography (CBCT) images. STUDY DESIGN: A total of 157 patients were enrolled in this investigation. The mental and accessory mental foramina, which show continuity with the mandibular canal, were assessed using axial and cross-sectional, 2-dimensional CBCT images. The sizes of the mental and accessory mental foramina were measured and statistically analyzed. Also, the distance between the mental and accessory mental foramina was measured. RESULTS: The accessory mental foramen was observed in 7% of patients. There was no significant difference regarding the sizes of the mental foramen between accessory mental foramen presence and absence. Also, the mean distance between the mental and accessory mental foramina was 6.3 mm (SD: 1.5 mm). CONCLUSION: The accessory mental foramen, which shows continuity with the mandibular canal, could be observed in 7% of the subjects using CBCT.