Usefulness of MR imaging for odontogenic tumors.

MRI has become an invaluable diagnostic tool in all areas of the body. However, it has not been widely used to image odontogenic tumors of the jaw. Major advantages of MRI include excellent soft tissue contrast in the absence of ionizing radiation. Furthermore, diffusion-weighted MRI and dynamic contrast-enhanced MRI can be used as functional imaging techniques for assessing tissue biology. In this review article, we present representative MR images of several types of odontogenic tumors, and discuss MR imaging characteristics useful for differential diagnosis.

Morphological comparison of artificial teeth position utilising denture space in glossectomy patients.

OBJECTIVE: This study aimed to compare the denture space of edentulous glossectomy patients with that of a control group from the perspective of artificial teeth positioning by using three-dimensional techniques. BACKGROUND: It is known that the shape of the denture space may be affected by tongue resection or reconstruction. However, the details of artificial teeth positioning in these patients remain unclear. MATERIALS AND METHODS: Six edentulous glossectomy patients aged 73-83 years and six normal participants aged 74-85 years participated in the study. Piezography was used to elucidate the characteristics of the denture space. For visualisation, piezographic records were scanned using cone beam computed tomography and the data were converted into stereolithographic format. Three-dimensional images of piezographic records were then constructed. Bucco-lingual widths of the mandibular occlusal surface were reproduced, and the camber line of the occlusal surface was set so as to simulate the position of the artificial teeth. The maximum chord of the occlusal surface on the left and right sides was recorded and measured. The discrepancy and ratio of the larger chord to the smaller chord between the right and left sides was calculated and subjected to statistical analyses using the Mann-Whitney U test. RESULTS: There were significant differences in discrepancy and ratio between the left and right in the control group and the glossectomy patients (P Ë‚ .01). The glossectomy patients showed a greater discrepancy and ratio than the control group. CONCLUSIONS: The simulated artificial teeth positions on the occlusal surface between the right and left side were asymmetric in glossectomy patients.

Evaluation of tongue volume and oral cavity capacity using cone-beam computed tomography.

The aims of this study were to reveal the usefulness of a newly developed method for measuring tongue volume (TV) and oral cavity capacity (OCC) and to assess the relationship between them. The tongue was coated with a contrast agent, and the TV and OCC were determined using cone-beam computed tomography (CBCT). We enrolled 20 adults who were scheduled to undergo CBCT to evaluate the relationship of the third molar roots to the alveolar nerve before molar extraction. Each participant's tongue was coated with a contrast agent, and CBCT of the tongue and oral cavity was performed. Using computer software, we evaluated reconstructed 3D images of the TV, oral cavity proper volume (OCPV), and OCC. The mean TV was 47.07 ± 7.08 cm3. The mean OCPV and OCC were 4.40 ± 2.78 cm3 and 51.47 ± 6.46 cm3, respectively. There was a significant correlation between TV and OCC (r = 0.920; p < 0.01) but not between TV and OCPV. The mean TV/OCC ratio was 91 ± 5%. The proposed method produced CBCT images that enabled effective measurement of TV and OCC. This simple method of measuring TV and OCC will be useful in the diagnosis on the tongues with abnormal size.

Incidence of hypercementosis in mandibular third molars determined using cone beam computed tomography.

PURPOSE: This study was conducted to investigate the incidence and predictors of hypercementosis in mandibular third molars using cone beam computed tomography. METHODS: Using a retrospective approach, 1,160 cone beam computed tomography image sets were analyzed. Two oral radiologists independently evaluated the image sets based on four severity grades: 0, no hypercementosis around the root; 1, hypercementosis surrounding less than half of the root surface; 2, hypercementosis surrounding more than half of the root surface; and 3, hypercementosis surrounding the entire root surface. Hypercementosis was identified as a dark or light layer. Statistical analyses of relationships between hypercementosis incidence and possible predictors (e.g. age, sex, impaction, and occlusion) were performed using chi-square test or Fisher's exact test; logistic regression was used for multivariate analysis. RESULTS: The severity of hypercementosis increased with age, and the incidences were as follows: ≤19 years, 0%; 20-24 years, 14.1%; 25-29 years, 57.7%; 30-39 years, 83.0%; 40-49 years, 92.7%; 50-59 years, 93.4%; and ≥60 years, 96.8%. CONCLUSION: The observed incidences of hypercementosis were relatively higher than in previous studies, and the incidence was significantly lower for occluded teeth than for non-occluded teeth.

3D evaluation of the morphological and volumetric changes of the tongue and oral cavity before and after orthognathic surgery for mandibular prognathism: a preliminary study.

BACKGROUND: The volumetric ratio of the tongue to the oral cavity has been recognized to be one of the important factors for the maintenance of stable occlusion. Oral cavity capacity is changed after orthognathic surgery in patients with mandibular prognathism; however, the volumetric changes of the oral cavity including the tongue before and after surgery have not been analyzed. The purpose of this study was to evaluate the morphological and volumetric changes of the tongue and oral cavity following orthognathic surgery using a newly developed vinyl polysiloxane impression method. MATERIALS AND METHODS: The study was performed in fifteen subjects who underwent surgical orthognathic treatment. Impressions of the tongue together with the oral cavity were obtained before orthognathic surgery and 1, 3, and 6 months after orthognathic surgery. These impression patterns were scanned using cone-beam computed tomography (CT), and three-dimensional (3D) images of the oral cavity including the tongue, and the upper and lower dental arches were reconstructed. The morphological and volumetric changes in the oral cavity capacity and the tongue volume were examined. RESULTS: The volume of the tongue with the volume of the oral cavity decreased after orthognathic surgery. There was a correlation between the decrease in the oral cavity capacity and tongue volume. The volumetric ratio of the tongue to the oral cavity seems to be maintained before and after orthognathic surgery. CONCLUSION: VPS method, free from radiation exposure, may be useful for investigating the morphological and volumetric changes of the tongue and oral cavity, which may possibly influence the stability of the dental arch and occlusion during surgical orthodontic treatment.

Morphological observation of the medial pterygoid muscle by the superimposition of images obtained by lateral cephalogram and MRI.

OBJECTIVE: To observe the morphological relationship between the maxillofacial skeleton and medial pterygoid muscle by superimposing images constructed by MRI on a cephalogram. DESIGN: Cross-sectional study. SETTING: The Departments of Maxillofacial Orthognathics and Orthodontics, Tokyo Medical and Dental University. PARTICIPANTS: Sixteen patients (5 males and 11 females, aged between 13.5 and 27.5 years) with various craniofacial skeletal patterns, who were about to start orthodontic treatment. METHODS: Lateral cephalometric radiographs and MRI scans were obtained and their images uploaded to a computer using a digitizer. The area of the medial pterygoid muscle was selected by binarization from the MRI. The mid-sagittal-plane MRI with a complete superimposed sagittal image of the medial pterygoid muscle was superimposed on the cephalogram using anatomical structures situated in the mid-sagittal plane of the head and shapes that could be identified from both the radiograph and the MRI image. RESULTS: These combined images showed various shapes of the medial pterygoid muscle. The inclination axis of the medial pterygoid muscle was correlated with various cephalometric variables including SNB (r=0.658), Facial angle (r=0.601), ramus inclination (r=0.676) and Ba-Po% (r=0.585). The volume of the medial pterygoid muscle was also correlated with cephalometric variables such as ramus inclination (r=0.453), Ba-Nmm (r=0.676), Ba-Po% (depth) (r=0.447), Ar-Go% (depth) (r=0.444) and Ar-Go% (actual length) (r=0.532). CONCLUSIONS: Morphometric analysis using a superimposed image of the medial pterygoid muscle produced from a cephalogram and MRI may help explain the influence of the medial pterygoid muscle inclination axis and volume on the shape of the mandibular bone, especially the shape of the ramus.

The development of new image receptor-holding instruments with appropriate horizontal X-ray beam angulation for periapical radiographs.

OBJECTIVES: This study aimed to develop new image receptor-holding instruments with appropriate horizontal X-ray beam angulation, based on the anatomical data of posterior region interproximal surfaces derived from archived CT images. METHODS: CT images of 92 patients with sound upper and lower dental arches were collected from our CT database and analyzed to determine the angles between the tangential interproximal contact line and the central groove line of posterior teeth. The average angle for each site was calculated and used to modify instruments using a three-dimensional printer. The utilities of the conventional and the modified instruments for viewing proximal surfaces were compared using two dry skulls. RESULTS: The right and left sides of each site, except for the lower second premolar and first molar sites, did not differ significantly. The difference between the sites was 2.0°; hence, we calculated mean values for the two sides at each site. In the maxilla, the angles of the first and second premolar, second premolar and first molar, and first and second molar to the groove line were 83.9° (±5.4°), 84.4° (±3.9°), 81.6° (±5.1°), while those in the mandible were 85.0° (±9.2°), 85.0° (±4.0°), and 90.6° (±4.9°), respectively. The holding instruments modified to 80° demonstrated better proximal viewing ability in the upper molar region than conventional instruments. CONCLUSIONS: The mean angles of the interproximal surfaces were determined from CT data. The image receptor holding-instruments were modified according to these angles to allow appropriate X-ray angulation, which facilitated improved observation of the proximal surfaces of teeth in the posterior region in this pilot in vitro study.

Ability of Cone-beam Computed Tomography to Detect Periapical Lesions That Were Not Detected by Periapical Radiography: A Retrospective Assessment According to Tooth Group.

INTRODUCTION: The detection of periapical lesions by periapical radiography (PR) can be hampered by structural noise, the impact of which differs among tooth groups. The aim of this study was to investigate the ability of cone-beam computed tomographic (CBCT) imaging to detect periapical lesions that could not be detected with PR according to tooth group. METHODS: This study retrospectively evaluated teeth that (1) had previously undergone root canal treatment (178 teeth from 86 patients), (2) had coincidentally been located within the field of view of CBCT scans performed for endodontic reasons, and (3) had also been examined with PR. The teeth of interest for the CBCT examinations were excluded to avoid sampling bias. Two dentists evaluated both the CBCT and PR images for periapical lesions. The McNemar test was used to compare the ability of CBCT imaging and PR to identify periapical lesions (α = 0.05). RESULTS: The overall periapical lesion detection rates of PR and CBCT imaging were 31.5% and 52.2%, respectively (P < .0001). The ability of CBCT imaging to identify periapical lesions that were not detected by PR was statistically significant for the maxillary incisors/canines (P < .0001) and maxillary molars (P < .005). CONCLUSIONS: Within the limitations of this investigation, it can be concluded that CBCT imaging is effective at detecting periapical lesions that cannot be detected on PR, particularly in the maxillary incisors/canines and molars. Our findings suggest that the influence of structural noise in the maxillary anterior region and maxillary posterior region should not be overlooked during the interpretation of PR images.

Non-Hodgkin lymphoma involving the mandible: imaging findings.

OBJECTIVE: The aim of this study was to investigate the imaging findings of non-Hodgkin lymphoma (NHL) involving the mandible. STUDY DESIGN: The imaging studies of 4 patients with NHL involving the mandible were retrospectively reviewed. Panoramic and computerized tomographic (CT) images were available for all patients. Magnetic resonance imaging (MRI) was available for 3 patients. RESULTS: On panoramic images, an apparent radiolucent lesion was found in only 2 of 4 cases. However, in all cases careful observation demonstrated imaging findings suggesting malignancy. On CT and MRI, tumor replaced the bone marrow in all cases and spread to the surrounding soft tissue in 3 cases. Cortical bone destruction tended to be mild for the extent of tumor involvement. CONCLUSIONS: NHL involving the mandible tended to show slight or mild cortical bone destruction relative to the extent of the tumor involvement. Careful observation was considered to be necessary when interpreting conventional images, because they might not clearly demonstrate bone destruction.

Trial of a CAD/CAM system for fabricating complete dentures.

The purpose of this study was to evaluate the fabrication of a complete denture using a CAD/CAM system. Cone beam CT was used to measure the complete denture and the artificial teeth. After a 3D complete denture image was structured using 3D CAD software, we factored out the artificial teeth and obtained a 3D denture base image. A machining center cut an acrylic resin block, and fabricated an acrylic complete denture base. The artificial teeth were bonded to the cut denture base using resin cement. A 3D digitizer digitized the fabricated acrylic denture. We measured the deviations between the master 3D complete denture image and the 3D data of the fabricated acrylic denture. The average deviations from the master 3D image were 0.50 mm for the occlusal surface. This present study indicates that it is possible to fabricate a complete denture using a CAD/CAM system.

Standardization of thresholding for binary conversion of vocal tract modeling in computed tomography.

Postoperative head and neck cancer patients suffer from speech disorders, which are the result of changes in their vocal tracts. Making a solid vocal tract model and measuring its transmission characteristics will provide one of the most useful tools to resolve the problem. In binary conversion of X-ray computed tomographic (CT) images for vocal tract reconstruction, nonobjective methods have been used by many researchers. We hypothesized that a standardized vocal tract model could be reconstructed by adopting the Hounsfield number of fat tissue as a criterion for thresholding of binary conversion, because its Hounsfield number is the nearest to air in the human body. The purpose of this study was to establish a new standardized method for binary conversion in reconstructing three-dimensional (3-D) vocal tract models. CT images for postoperative diagnosis were secondarily obtained from a CT scanner. Each patient's minimum settings of Hounsfield number for the buccal fat-pad regions were measured. Thresholds were set every 50 Hounsfield units (HU) from the bottom line of the buccal fat-pad region to -1024 HU, the images were converted into binary values, and were evaluated according to the three-grade system based on anatomically defined criteria. The optimal threshold between tissue and air was determined by nonlinear multiple regression analyses. Each patient's minimum settings of the buccal fat-pad regions were obtained. The optimal threshold was determined to be -165 HU from each patient's minimum settings of the Hounsfield number for the buccal fat-pad regions. To conclude, a method of 3-D standardized vocal tract modeling was established.

Diagnostic accuracy of cone-beam CT in the assessment of mandibular invasion of lower gingival carcinoma: comparison with conventional panoramic radiography.

PURPOSE: To evaluate the diagnostic accuracy of cone-beam CT in assessing mandibular invasion by lower gingival carcinoma and compare it with that of panoramic radiography. PATIENTS AND METHODS: Fifty patients with squamous cell carcinoma of the lower gingiva who were examined by both panoramic radiography and cone-beam CT before surgery were included in this study. Five radiologists used a 6-point rating scale to independently evaluate cone-beam CT and panoramic images for the presence or absence of alveolar bone and mandibular canal involvement by tumor. Using the histopathogical findings as the gold standard, we calculated and compared the area under the receiver operating characteristic curve (Az value) and the sensitivity and specificity of the two imaging modalities. RESULTS: In evaluations of both alveolar bone and mandibular canal involvement, the mean Az value for cone-beam CT (0.918 and 0.977, respectively) was significantly higher than that for panoramic radiography (0.793 and 0.872, respectively). The mean sensitivity for cone-beam CT (89% and 99%, respectively) was significantly higher than that for panoramic radiography (73% and 56%, respectively). There was no significant difference in the mean specificity. While cone-beam CT could provide high-resolution three-dimensional images, the image quality around the alveolar crest was often hampered by severe dental artifacts and image noise, resulting in difficulties in detecting subtle alveolar invasion. CONCLUSION: Cone-beam CT was significantly superior to panoramic radiography in evaluating mandibular invasion by lower gingival carcinoma. Its diagnostic value in detecting subtle alveolar invasion, however, may be limited by severe dental artifacts and image noise.

A comparative study of cone-beam computed tomography and conventional panoramic radiography in assessing the topographic relationship between the mandibular canal and impacted third molars.

OBJECTIVE: To evaluate the diagnostic accuracy of cone-beam CT compared with panoramic images in predicting neurovascular bundle exposure during extraction of impacted mandibular third molars. STUDY DESIGN: Cone-beam CT and panoramic images of 142 impacted mandibular third molars were prospectively evaluated to assess tooth relationship to the mandibular canal. These interpretations were then correlated with intraoperative findings. The sensitivity and specificity of the 2 modalities in predicting neurovascular bundle exposure at extraction were calculated and compared. The diagnostic criterion for panoramic images was defined using multivariate logistic regression analysis. RESULTS: In predicting the exposure, the sensitivity and specificity were 93% and 77% for cone-beam CT, and 70% and 63% for panoramic images, respectively. Cone-beam CT was significantly superior to panoramic images in both sensitivity and specificity. CONCLUSION: Cone-beam CT was significantly superior to panoramic images in predicting neurovascular bundle exposure during extraction of impacted mandibular third molar teeth.