The A to Z of OPGs. Sarah Constantine MBBS, FRANZCR Dental Radiologist International Teleradiology Corporation Clinical Senior Lecturer University of Adelaide Don Chorley Radiation Safety Manager and Education Radiography South Australian Dental Service Clinical Lecturer

Introduction The orthopantomogram (OPG) is a commonly requested examination, referred by both medical practitioners and dentists. Despite its frequency in practice, there is a reluctance by many radiologists to provide a detailed radiological report, due to a lack of familiarity with the normal anatomy and artifacts seen on the OPG. This presentation demonstrates the normal anatomy seen on the OPG, as well as artifacts produced by the tomographic technique, and incorrect patient positioning.

Normal Anatomy The normal anatomy of the OPG is complicated as a result of the tomographic technique. The image is produced by both the film and the x-ray source rotating around the stationary patient. This tomographic technique results in a panoramic image of the dental arches and surrounding bone, soft tissue structures and air cavities. Each image has a "focal trough" where the structures are sharply projected, and outside this plane the structures appear blurred. This also produces a number of images artifacts.

The BONY ANATOMY seen on an OPG includes the bones of the mandible, maxilla, zygoma, and temporal bones. The film quality will determine if all features are clearly visible. MANDIBLE CORONOID NOTCH CONDYLE CORONOID PROCESS NECK ALVEOLAR BONE RAMUS ANGLE SYMPHYSIS MENTI BODY MANDIBULAR CANAL MENTAL FORAMEN

MAXILLA, ZYGOMA, TEMPORAL BONE The BONY ANATOMY seen on an OPG includes the bones of the mandible, maxilla, zygoma, and temporal bones. The film quality will determine if all features are clearly visible. NASAL SEPTUM EAC LATERAL NASAL WALL ORBITAL FLOOR HARD PALATE GLENOID FOSSA INTERMAXILLARY SUTURE ZYGOMATIC ARCH ALVEOLAR BONE MAXILLARY SINUS WALL MAXILLA, ZYGOMA, TEMPORAL BONE STYLOID PROCESS

The SOFT TISSUE ANATOMY includes the superficial facial structures, the soft palate, pharynx, tongue and nasal passages. INFERIOR TURBINATE SOFT PALATE TONGUE PINNA EPIGLOTTIS POSTERIOR PHARYNX

The AIR CAVITIES are demarcated by the soft tissues and bones The AIR CAVITIES are demarcated by the soft tissues and bones. These include the pharynx, and nasal cavities. NASAL CAVITY NASOPHARYNX ORAL CAVITY OROPHARYNX HYPOPHARYNX LARYNX

Calcifications are also important, as they can indicate the position of many structures including the submandibular duct, the palatine tonsils and the carotid arteries.

Submandibular calculus

Carotid artery calcification.

Artifacts Produced by the Tomographic Technique. DOUBLE IMAGES occur when an object or anatomical structure is between the x-ray tube and the film twice, and is the same distance from the film on both occasions. This generally means a structure in, or close to, the midline. Common double images seen on an OPG are those of the cervical spine and hyoid bone.

Artifacts Produced by the Tomographic Technique. CERVICAL SPINE HYOID BONE

Artifacts Produced by the Tomographic Technique. GHOST IMAGES occur when an object or anatomic structure that is outside the focal plane, is dense enough to attenuate the x-ray beam and project an image. The image is projected on the opposite side to the real bony structure, and is blurred and magnified because it is not in the focal plane. As the x-ray tube is angulated up, the ghost image is also higher than the real image. Many bony ghost images are visible on an OPG.

Artifacts Produced by the Tomographic Technique. POSTERIOR MANDIBLE CERVICAL SPINE

The concept of GHOST IMAGES can be best demonstrated by a patient wearing jewellery: the earring in the right ear has a sharply demarcated true image, the blurred ghost image is seen projected over the left maxillary sinus which is higher than the pinna of the ear.

Radiographic Technique and its Relationship to Diagnostic Quality. PATIENT POSITIONING is crucial to obtaining a good quality OPG. There are a number of positioning errors that can produce film artifacts, and awareness of these can prevent reporting errors. The focal trough is spatially located and fixed in positioned to image the mandible and maxilla when the patient is in the true anatomical position. All errors occur due the patient not being positioned with the upper and lower arches in the focal trough with the patient head in the anatomical position.

Radiographic Technique and its Relationship to Diagnostic Quality. The focal trough is fixed in its relationship to the x-ray tube and detector, the patient is positioned to the focal trough with their central incisors positioned in bite grooves located in the bite block. Patients biting in front or behind the bite groove or not standing in the anatomical position will create image problems. When the patient is in the anatomical position the occlusal plane rises a few degrees from the anterior teeth to the posterior teeth. The Frankfurt Horizontal Line is parallel to the floor. This slight rise of the occlusal plane is critical to achieve the optimum OPG.

Radiographic Technique and its Relationship to Diagnostic Quality. Four critical visual effects, created by patient positioning:   Axial rotation about the mid-sagittal line, magnification of the side furthest from the receptor minification of the side closest to the receptor during rotation. Forehead tilted forward or back (chin tilted up or down), occlusal plane over smiley or grimacing Incisal edge of anterior teeth few mm forward or behind the biting groove, central anterior teeth magnified or minified with loss of root detail. Tongue not positioned to the hard palate, overexposure of the upper teeth root structures, due to air chamber below the hard palate.

Axial Rotation. Answer: Symmetrical placement of the patient within the head support structure will solve this problem. In this situation the patient was rotated so their left side was closer to the receptor as it passed (minified) and the right side further from the receptor as it passed (magnified).

Forehead Tilted Forward (chin down) Answer: Tilt patient’s head back by raising head support until anatomical position achieved. Overcrowding of upper teeth and loss of detail of the anteriors as they are projected out of the focal trough

Forehead tilted back (chin up) Answer: Tilt patient’s head forward by lowering head support until anatomical position achieved. Loss of detail upper and lower teeth as they are projected out of the focal trough

Incisal edge of anterior teeth a few mm in front of the biting groove Answer: Position the incisal edge of the anterior teeth within the bite groove, in older OPG units position the canine guide light to the centre of the canine. Loss of detail upper and lower anteriors due to minification

Incisal edge of anterior teeth a few mm behind the biting groove Loss of detail upper and lower anteriors due to magnification The arrows indicate ghosting from the cervical spine Answer: Position the incisal edge of the anterior teeth within the bite groove, in older OPG units position the canine guide light to the centre of the canine.

Tongue not positioned to the hard palate Answer: Ask the patient to place their tongue to the top of their mouth and to keep it there during machine rotation. Loss of detail upper anterior roots due to over exposure

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The Good OPG. Identifies as clearly as possible the detail of the anatomy and any visible pathology in an unequivocal fashion. The quality of an OPG is dependent on good positioning, and very dependent on the habitus and the oral anatomy of the patient in question.

Conclusion A better understanding of the normal OPG will help the general radiologist to provide a more accurate and comprehensive report of studies referred by both dentists and medical practitioners.

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