Oral Radiology - II Lecture 5: Panoramic Radiography PDF

ORAL RADIOLOGY - II LECTURE 5 PANORAMIC RADIOGRAPHY Panoramic radiography is an extra oral radiographic procedure that produces a single image of the facial structures that include maxillary and mandibular arches with their supporting struc...

ORAL RADIOLOGY - II LECTURE 5 PANORAMIC RADIOGRAPHY Panoramic radiography is an extra oral radiographic procedure that produces a single image of the facial structures that include maxillary and mandibular arches with their supporting structures. Historically, the concept of obtaining dental arches on a single film was developed independently by Dr. Numata and Dr. Paatero. Principles of panoramic radiography In the panoramic x-ray machine, the receptor or film is attached to a rotating system and moves in the same direction as the beam from the x-ray tube. This movement of x-ray source and the receptor around the patient’s head creates a curved focal trough - a zone in which the objects are displayed clearly on the resulting radiograph. Dr. Mohammed Nishan   The rate of movement of the receptor is regulated to be the same as that of the x-ray beam sweeping through the dentoalveolar structures on the side of the patient nearest the receptor.  A slit shaped lead collimator is used on the x-ray tube and reduces the size of the beam and is hence known as slit-beam/pencil beam or narrow beam. Another collimator between the object and the film further reduces the scattered radiation from the object to the film. Dr. Mohammed Nishan   Structures on the opposite side of the patient (near the x-ray tube) are distorted and appear out of focus.  Structures near the x-ray source are so magnified that they are not seen as discrete images on the resultant image.  Because of both of these circumstances, only structures near the receptor are captured on the resultant image. Focal trough Focal trough is a three-dimensional curved zone or image layer, where the structures within this zone are reasonably well defined on the final panoramic image. In image shown, the focal trough is an imaginary zone passing through the midline of the mandibular dental arch and body of the mandible Focal trough depends upon: Brand of equipment used and with the imaging protocol selected within each unit. Path and velocity of the receptor and x-ray tube head, alignment of the x-ray beam, and collimator width. Dr. Mohammed Nishan As demonstrated in the image A above shows xray tube head moving from 1 to 3 rotating about a center of rotation on right side while taking radiograph of the left jaw. A it completes its rotation from 1 to 3, half of the jaw or the entire left side of the jaw is radiographed. The computer screen shows image development corresponding to the movement xray tube head makes from 1 to 3. Types of images formed Real Image – Focal trough – objects situated between center of rotation and receptor/film. Double image – region posterior to the center of rotation where the structures are intercepted by x-ray beam twice Ghost image – objects situated between the center of rotation and x-ray source. Dr. Mohammed Nishan Parts of a panoramic machine There are various panoramic units available in market. Although varying in design and appearance, all consist of four main components, namely:  An X-ray tubehead, producing a narrow fan-shaped X-ray beam, angled upwards at approximately 8° to the horizontal.  Control panel  Patient-positioning apparatus: o Chin rest area,head immobilizing supports (temple support), o bite peg (to position the incisors) and o light beam markers (mid-sagittal, canine guidance and Frankfort plane.  An image receptor (digital or film), with or without an associated carriage assembly Advantages of panoramic radiography 1. In one image both the jaws and supporting structures are visualized therefore it gives a broad coverage area. The panoramic image covers an area that includes the entire mandible from condyle to condyle and maxillary region from tuberosity to tuberosity. Superior aspect extending to the middle third of the orbits and inferiorly to the chin and sides of the neck. 2. The anatomical structures are most identifiable and the teeth are oriented in their correct relationship to the adjacent structures and to each other. 3. Relatively simple to perform and require minimal patient effort. 4. It is less time consuming when compared to full mouth radiography with multiple intra-oral projections or other site specific extra oral projections. 5. Panoramic radiograph can be used in cases where patient is unable to open mouth or patients with gag reflex to intra oral films/sensors. 6. It provides for an overview and treatment follow-up. 7. It provides visual aid for case presentation and patient education 8. Comparatively low radiation dose than conventional full mouth intra-oral radiographic evaluation. 9. Fractures are more easily illustrated on panoramic views. 10. In pediatric patients for assessment of mixed dentition status and eruption pattern when child is not willing or have difficulty in placement of intra-oral films. Dr. Mohammed Nishan  11. It demonstrates periodontal disease in a general way manifesting a generalized bone loss. 12. All the parameters are standardized, and repetitive images can be taken on recall visits for comparative and research purposes. Disadvantages: 1. Poor resolution, magnification, poor definition, loss of detail and geometric resolution when compared to intra-oral films. 2. Inherent magnification and distortion of various regions especially when structures are outside the focal trough 3. Areas of diagnostic interest outside the focal trough may be poorly visualized. 4. In severe proclined or retroclined anterior teeth, are poorly visualized on radiograph. 5. Number of radiopaque and radiolucent areas may be present due to the superimposition of real/double or ghost images and because of soft-tissue shadows and air spaces. 6. Due to multiple rotation, patient with facial asymmetry or patients jaws that do not conform to the rotation curvature may give a diagnostically poor panoramic image. 7. In errors of patient positioning, the amount of vertical and horizontal distortion will vary from one part of the film to another part of the film. 8. The ease and convenience of obtaining an OPG may encourage careless evaluation of a patient’s specific radiographic needs. 9. Panoramic imaging has a tendency to produce overlapping of teeth images, most particularly in the premolar area. 10. The ease and convenience in obtaining the panoramic image may lead to indiscriminate use for other projection that might be adequate. This is one of the prime concerns in regard to patient dosage. 11. Setting up a panoramic unit is expensive and therefore an extra investment for practitioners. 12. Artefacts are easily misinterpreted and are more commonly seen. Dr. Mohammed Nishan Indications 1. As a substitute for full mouth intraoral periapical radiographs. 2. For evaluation of developmental anomalies and tooth development for children during the mixed dentition period as well as TMJ dysfunctions. 3. To assess the patient for and during orthodontic treatment 4. To establish the site and size of lesions such as cysts and tumors in the body and ramus of the mandible. 5. For progress of pathology and follow-up of treatment, or postoperative bony healing. 6. Prior to any surgical procedures such as extraction of impacted teeth, enucleation of a cyst, etc. 7. For detection of fractures of the middle third and the mandible following trauma. 8. In case of periodontal disease for an overall view of the alveolar bone levels. 9. Assessment for underlying bone disease before constructing complete or partial dentures. 10. Evaluation of the vertical height of the alveolar bone before inserting implants. Patient preparation Patients should be asked to remove any earrings, jewellery, hair pins, spectacles and dentures or orthodontic appliances. The procedure and equipment movements should be explained, to reassure patients and if necessary a test exposure should be used to show them the machine’s movements. Equipment preparation The cassette containing the phosphor plate or film should be inserted into assembly. Control panel should be covered in cling film The operator should put on suitable protective gloves (e.g. latex or nitrile) The collimation should be set to the size of field required. Dr. Mohammed Nishan The appropriate exposure factors should be selected according to the size of the patient – typically in the range of 70–90 kV and 4–12 mA Patient positioning The patient should be positioned in the unit so that their spine is straight and instructed to hold any stabilizing supports or handles provided The patient should be instructed to bite their upper and lower incisors edge- to-edge on the bite-peg with their chin in good contact with the chin support. The head should be immobilized using the temple supports. The light beam markers should be used so that the midsagittal plane is vertical, the Frankfort plane is horizontal and the canine light lies between the upper lateral incisor and canine. The patient should be instructed to close their lips and press their tongue on the roof of their mouth so that it is in contact with their hard palate and not to move throughout the exposure cycle (approximately 15–18 seconds). Dr. Mohammed Nishan