Specialized Types of extra oral radiographs

Dr. Ghassan Ali

Specialized Types of extra oral radiographs

• Dental Panoramic Tomography (OPG, OPT)
• Cephalometry
• Lateral Obliques (Bimolars)
• Sialography
• Soft Tissue Lips

THE MANDIBLE

• Lower jaw bone comprising a body and rami, condylar and coronoid processes
• The mandible articulates with the temporal bone at the tempero-mandibularjoint (TMJ)
• Synovial condylar joint with articular disc

SALIVARY GLANDS :        3 sets of salivary glands

Parotid salivary glands : situated at the lateral aspects of the rami of the mandible. Parotid duct opens adjacent to the upper 2nd Molar(Stensen’s duct).

Submandibular salivary glands : are situated adjacent to the submandibular fossae on the medial aspects of the body of the mandible. Ducts (Wharton’s) open beneath the tongue.

Sublingual salivary gland : lie beneath the tongue.

Dental Panoramic tomography equipment:

       Specialised units capable of panoramic views of the whole jaw or parts of jaw, Some systems can perform localised coronal/sagittal tomograms through the dental arch and some can be converted for use in cephalometry.

Dental Panoramic Tomography

•Sometimes referred to as DPT, OPT, OPG
•Uses the principle of tomography to produce a radiograph of both dental arches on one film
•The x-ray tube and film move around the head as the exposure is made
•Only the structures within the focal plane (focal trough) are projected sharply onto the film everything else is blurred out
•Useful when overall evaluation of the dentition and/or jaws is required.
•Positioning important to ensure optimum image quality
•Head should not be rotated(causes asymmetry in image)
•Frankfurt plane horizontal
•Important to remove ear ringsand necklaces, braces and dentures

Indication, Uses of Dental Panoramic Tomography

1. gross caries
2. pain related to a whole quadrant
3. orthodontic assessment
4. pre-operative assessment
5. prior to dental surgery  under G.A.
6. mandibular fractures
7. cysts, tumours, developmental anomalies
8. assessment of TMJ’s
9. periodontal disease
10. 8’s (wisdom teeth)
11. Implantology

Advantages

1. A large area is imaged.
2. The image is easy for patient to understand.
3. Positioning is relatively simple.
4. The overall view of the jaws allow rapid assessment of any underlying possibly unsuspected disease.
5. The view of both sides of the mandible on one film.
6. The radiation effective dose is about one third of the dose from a full moth survey of intraoral films.
7. Performed on patients who are unable to open their mouth.
8. Can used as a visual aid in case of presentation and patient education.

Disadvantages

1. Represent only a section of the patient
2. Soft tissues and air shadows can overlie the required hard tissue structures.
3. Ghost shadow can overlie the structures in the focal trough.
4. The tomography movement toghether with distance between the focal trough and film produce distortion and magnification of the final image.
5. The use of the indirect action film and intensifying screen result in some loss of image quality.
6. The tech. is not suitable for children under 5 years or on some disabled patients because of the length of the exposure cycle.
7. Some patients do not conform to shape of the focal trough and some structure will be out of focus.

Focal trough :

                         It is a three dimensional curved zone or image layer in which the structures well defined on panoramic radiographs.

Cephalometry

•Cephalometric lateral - a lateral radiograph of thewhole face to show the relationship of the upperand lower jaws, the soft tissue profile of the face,and various bony landmarks.

•Assessment and follow-up of facial deformity

Lateral Obliques

•Radiographs of molars and premolars using film positioned beside the face
•Useful in difficult, uncooperative patients
–small children, mentally/physically handicapped
–extraoral film is better tolerated
–short exposure time
–some distortion of teeth and loss of definition

Technique of Lateral Oblique:

•Patient may hold cassette or in children a parent.
•Neck is extended to bring mandible away from cervical spine.
•The central ray is directed between the C spine and the angle of mandible.
•The teeth and jaw adjacent to the cassette are imaged.

Sialography technique

•Duct orifice cannulated
•Contrast injected
•Niopam 200
•Preliminary films to exclude radiopacities -intraductal calculi
•Plain films or digital fluoroscopy
–   +/- subtraction

Soft Tissue Lips

Radiographs of lips to identify foreign bodies e.g. tooth fragments, glass

Radiation Protection

•Good technique
•Good processing
•Lead rubber aprons
•pregnancy - risk is negligible, but most practitioners avoid if possible
•ONLY X-RAY IF NECESSARY!