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Summary Recent advances in orthognathic surgical techniques and orthodontic treatment, such as the use of dental implants for orthodontic anchorage, bone and tooth transplantation, and intraoral distraction for mandibular lengthening, have led to an increased demand for more advanced diagnostic image information than can be supplied by conventional radiography. In this article, the authors have reviewed several 3D imaging techniques that might be useful in this field. Currently, personal computers are equipped with such high processing speeds that it is easy to process interactively the image data of a complex 3D object and portray its dynamic properties in real-time. The powerful image-rendering capabilities of 3D CT may substitute for conventional radiographic examinations in the near future. Reducing the radiation dose to patients in spiral/helical CT scanning without impairing image quality, however, is a goal that must be achieved as soon as possible.14, 19 The limited cone-beam CT system seems to have an advantage because of the reduced radiation dose associated with the image data acquisition in a single rotation of the x-ray tube.1, 38 In the meantime, 3D imaging without any exposure to radiation and based on MR, ultrasound, or laserscanned image data is available to clinicians. The potential clinical applications of 3D imaging in dentistry represent a technologic advance that is rapidly becoming a reality that may far exceed anyone's expectations.

Objective. To observe changes in the pharyngeal airway and the hyoid bone position after mandibular setback osteotomy in 30 patients with mandibular prognathism by means of 3-dimensional computed tomography (3DCT). Study design. Preoperative and postoperative computed tomography (CT) examinations were performed on 17 patients treated by sagittal split ramus osteotomy with rigid osteosynthesis and on 13 patients treated by intraoral vertical ramus osteotomy without osteosynthesis. The amount of mandibular setback was measured by the preoperative to postoperative difference of the mandibular position in axial CT images. The sizes of the preoperative and postoperative pharyngeal airway were evaluated from semitransparent and crosscut 3DCT images. Postoperative displacement of the hyoid bone was evaluated by a technique to superimpose a postoperative hard tissue 3DCT image on the preoperative image. The helical scan technique was used in the CT examination. The volume rendering technique was used to create 3DCT images. Results. The mean mandibular setback was 7.8 ± 2.1 mm with a range of 5 to 11 mm. Three months after surgery, the lateral and frontal widths of the pharyngeal airway had decreased significantly in comparison with the preoperative width. The mean reduction rates of the lateral and frontal width were 23.6% and 11.4%, respectively. The diminished airway did not recover by either 6 months or 1 year after surgery in most cases. Downward and posterior displacement of the hyoid bone was seen postoperatively. There were positive correlations between the amount of mandibular setback and reduction of the lateral width of the pharyngeal airway (r = 0.54) and the amount of hyoid bone displacement (r = 0.42). There were no significant differences between the two surgical techniques. Conclusion. Three-dimensional computed tomography was a practical imaging technique to evaluate the morphologic airway changes. The pharyngeal airway may have irreversible narrowing after mandibular setback surgery. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:278-87)

Solitary bone cyst is a radiolucent lesion classified as a pseudocyst with a variety of reported shapes including round, oval, and irregular. In the long bones, a truncated cone shape has been described, and the fallen trabecula sign is seen in association with pathologic fracture. The purpose of this study was to classify and document the various shapes, to describe the width versus height dimensions of jaw SBCs, to determine the identifying signs of trauma, and to evaluate other reported radiographic features. Radiographs of 44 SBCs in 43 patients were studied. Sixty-four percent demonstrated the cone shape, and four subtypes of this shape were identified. Other shapes included oval (16%), irregular (16%), and round (4%). Radiographic signs of trauma were observed in 28% of the cases. No evidence of the "fallen trabecula sign" was found in this series.

In the present study, new MRI techniques were used to evaluated the pathologic condition of a mucosal cyst in the maxillary sinus. The contrast enhancement technique using Gd-DTPA clearly revealed the cystic nature of the lesion. The diagnostic information about the relationship between the mucosal cyst and periodontal disease, and the precise location of the cyst in relation to the walls of the maxillary sinus were obtained by panoramic MR image and alternate positioning of the patient.

Six cases of solitary (simple) bone cyst with typical clinical, radiographical, and histological findings were examined by bone scintigraphy. Bone scintigraphy using99mTc-HMDP was performed prior to operation. No uptake of99mTc-HMDP in these solitary bone cysts was demonstrated.

The authors present examples of the significantly improved diagnostic imaging for cystic lesions in the jaw bone, floor of the mouth and maxillary sinus with Gadolinium-DTPA (Gd-DTPA) enhanced MRI. Twelve cases of cystic lesions, which were 6 cases of intra-osseous odontogenic cysts and cystic tumors, 2 cases of epidermoid cysts in the floor of the mouth and 4 cases of cystic polyp of the maxillary sinus. Improved MR images provided useful information delineating the thickness of circumscribed soft tissue wall (cystic wall), the location of the intra-cystic substance and the configuration of the tumor masses.

The effects of 1) X-irradiation and 2) hyperthermia at a temperature of 43 degrees C individually and in combination have been investigated using cultured 8-day mouse embryos. B6C3F1 embryos were exposed to 0.3-2.0 Gy of X-rays, 5-20 min of heating, or 5 min of heating and irradiation at 0.3, 0.6, and 0.9 Gy. Irradiation alone at 0.3 Gy showed no apparent effect on embryonic development, but irradiation at 0.6-2.0 Gy caused a dose-dependent increase in malformed embryos. Heating alone for 5 min produced no malformed embryos, while heating for 10-20 min caused malformations as a function of heating time. Combined treatments produced higher frequencies (22.2-100%) of malformations than those of the sum of the separate treatments (0-41.7%). Malformations observed were primarily microphthalmia, microcephaly, and open neural tubes. The results indicate that in cultured mouse embryos irradiation combined with a "nonteratogenic dose" of hyperthermia directly exerts an additive effect on formation of the malformed embryos. In addition, a single occurrence of left-sided tail was produced by hyperthermia alone, while four occurrences were produced in combination with radiation.

Although various panoramic X-ray machines with linear tomographic functions are now frequently applied to diagnosis related to dental implant treatment, the angles of the tomographic objective planes are automatically determined and cannot be adjusted for individual patients. To resolve this problem, a direct laser positioning (DLP) system was developed. In this investigation, the measurement accuracy of images obtained by the DLP system in comparison with those from reformatted computed tomography (CT) was assessed.A rectangular parallel piped phantom was scanned with the system and the height and width were measured on linear tomograms. Ten sites in 3 dried mandibles and 21 mandibular molar sites in 15 patients were examined both with the DLP system and the reformatted CT to compare the measured values on both images.The phantom experiment showed that the difference between the actual and measured heights and widths of the phantom were within 1 mm.The difference between the values obtained by the DLP system and CT was slightly larger in the patients than those in the dried mandibles.The DLP measurement accuracy was deemed sufficient for clinical use.

Muscle oedema, which can be seen as a thickness increment by ultrasonography, is important in provoking pain and fatigue during low-level contraction. Although oedema is related to the balance of inflow and outflow of blood, there are no data on the correlation between muscle thickness change and blood-flow. Blood-flow velocities in the facial artery and the muscle thickness changes were measured by colour Doppler ultrasonography in 30 healthy volunteers during 20 min contraction with 10% of maximum force. Thickness and velocity changes both reached a peak in the initial phase of contraction. The initial change of thickness did not correlate with the velocity in the facial artery, while those immediately after exercise showed a high correlation. The velocity changes in the facial artery might depend on both the general response to contraction and local metabolic or mechanical factors in the contracted masseters.

The authors have presented several 3-D CT imaging techniques that may be useful in dentistry. MPR and dental MPR provides cross-sectional images of the jaws and the dental arches, and its utility in implant treatment planning is widely recognized. SSD allows the clinician to visualize the surface of an anatomic structure that is selected by a threshold value. Volume rendering is a powerful and flexible three-dimensional imaging technique that can create various unique images. MIP may be useful in contrast-enhanced CT examinations, such as sialography. Model production and virtual reality three-dimensional imaging may become major techniques in the near future. Although the increased radiation dose to the patients has to be considered, future imaging demands will bring more access to 3-D CT imaging by dental patients and, with adequate three-dimensional rendering techniques, more accurate diagnosis and treatment planning.

Objective. The purpose of this study was to examine both condylar displacement of the temporomandibular joint after sagittal split ramus osteotomy with rigid osteosynthesis and intraoral vertical ramus osteotomy without osteosynthesis in patients with mandibular prognathism by means of three-dimensional computed tomography. Study design. In this pilot study, five patients treated with sagittal split ramus osteotomy and 5 patients treated with intraoral vertical ramus osteotomy were evaluated. A technique to superimpose a postoperative three-dimensional computed tomography image on its corresponding preoperative image was designed. Postoperative condylar displacement, rotation, and tilting were measured in three-dimensional computed tomography images. Results. Within 3 to 6 months after surgery, changes in the inclination of the condylar axes were distinctly seen, although changes in the position of the condyles within the joints were minimal. In particular, outward rotation of the condylar long axes after intraoral vertical ramus osteotomy was a frequent finding. Conclusions. The three-dimensional computed tomography superimposition technique was a practical method of evaluating post-surgical condylar displacement after mandibular osteotomy.

The combined action of cadmium and X-rays was examined on 8-day mouse embryos using a whole embryo culture system. B6C3F1 mouse embryos were explanted onto the headfold stage and cultured for 40 hrs. To examine the dose-effect relationships of the single treatments, the embryos were exposed to 1.2−2.2 μM cadmium or to 0.82−2.64 Gy of X-rays at 1 hr. after the explantation. In combined treatments, 1.58 μM of cadmium was applied at 1 hr. and X-rays of 0.82 or 1.24 Gy was applied at 1.5 hr. The end-points measured were the yolk sac diameter, crown-rump and head lengths, somite number, protein contents of yolk sac and embryo, and formation of the neural tube defect. Cadmium-induced neural tube defect increased as a function of dose in a highly curvilinear manner. The remaining end-points affected by the single treatments were also indicative to be curvilinear. The combined action of cadmium and X-rays was found to exert an additive effect on the inhibition of embryonic growth and a synergistic effect on the teratogenicity. The form of the dose-effect curves of the single agents was suggested to be responsible for teratogenic synergism. Other possibilities of interaction remain to be resolved.