PANORAMIC RADIOGRAPHY DA 105

Dental Radiography Questions What equipment is used in panoramic radiography? What is the focal trough? What are the advantages and disadvantages of panoramic radiography?

Introduction Purpose To present basic concepts of panoramic radiography To describe the patient preparation, equipment preparation, and patient positioning procedures needed to perform this procedure

Basic Concepts Purpose and Use Fundamentals Equipment Basic Concepts Rotation center Focal trough Equipment Basic Concepts

Basic Concepts Panoramic film Panoramic radiography Shows a wide view of the upper and lower jaws Panoramic radiography Used to examine the upper and lower jaws on a single film

A, Panoramic radiograph. B, Panoramic anatomy

Purpose and Use An overall image of the maxilla and mandible Often used to supplement bite-wing and selected periapical films Images seen on a panoramic film are not as defined or sharp as the images seen on intraoral films

Fundamentals In panoramic radiography, the film and x-ray tubehead move around the patient The x-ray tube rotates around the patient’s head in one direction while the film rotates in the opposite direction The patient may stand or sit in a stationary position

The film and x-ray tubehead move around the patient in opposite directions in panoramic radiography

Fundamentals The movement of the film and the tubehead produces an image through the process known as tomography Tomography A radiographic technique that allows the imaging of one layer or section of the body while blurring images from structures in other planes

Rotation Center The pivotal point, or axis, around which the cassette carrier and x-ray tubehead rotate There are three basic rotation centers depending on the manufacturer Double-center rotation Triple-center rotation Moving-center rotation

Types of panoramic x-ray machines Types of panoramic x-ray machines. A, Double-center rotation machines have two rotational centers, one for the right and one for the left side of the jaws. B, Triple-center rotation machines have three centers of rotation and create an uninterrupted radiographic image of the jaws. C, Moving-center rotation machines rotate around a continuously moving center that is similar to the arches, creating an uninterrupted image of the jaws

Focal Trough Can be defined as a three-dimensional curved zone in which structures are clearly demonstrated on a panoramic radiograph

Example of an “image layer” or “focal trough

Equipment Panoramic x-ray units Film Intensifying screens Cassette

Panoramic X-ray Units There are a number of different panoramic x-ray units All have similar components X-ray tubehead Head positioner Exposure controls

A, Orthophos XG Plus extraoral x-ray machine A, Orthophos XG Plus extraoral x-ray machine. B, Orthoralix 8500 extraoral x-ray machine. C, Example of a digital panoramic system

Main components of the Orthophos XG 5: A, x-ray tubehead; B, head positioner; C, exposure controls

Panoramic X-ray Units X-ray Tubehead Collimator Similar to an intraoral x-ray tubehead Collimator Differs from the collimator used in the intraoral x-ray tube head The collimator used in the panoramic x-ray machine is a lead plate with an opening in the shape of a narrow vertical slit

The collimater on the Orthophos XG 5 has a narrow slit opening

Panoramic X-ray Units The x-ray beam emerges from the panoramic tubehead through the collimator as a narrow band It passes through the patient and exposes the film through another vertical slit in the cassette carrier The vertical angulation is fixed so that the x-ray beam is directed slightly upward

Head Positioner A chin rest, notched bite-block, forehead rest, and lateral head supports or guides Used to align the patient’s teeth as accurately as possible

The head positioner (notched bite-block, forehead rest, and lateral head supports) is used to align the patients teeth in the focal trough

Exposure Controls Suggested exposure factors for milliamperage and kilovoltage are provided by the manufacturer and can be varied to accommodate patients of different sizes Exposure time is fixed

   Exposure controls on the Orthophos XG 5 can be used to adjust exposure factors

Film Screen film is used in panoramic radiography It is sensitive to the light from an intensifying screen It is placed between two intensifying screens in a cassette holder

Intensifying Screens Calcium tungstate Rare earth Emit blue light Emit green light Require less x-ray exposure than calcium tungstate screens

Cassette A device used to hold the extraoral film and intensifying screens May be rigid or flexible, curved or straight Must be light-tight Must be marked to orient the finished radiograph

Film cassettes. A and B, Rigid cassettes Film cassettes. A and B, Rigid cassettes. Intensifying screens are attached to the inside cover and base of a rigid cassette. When the panoramic film is placed in the cassette, it lies between the screens. C, Flexible cassette has an opening at one end, creating a pouch. The panoramic film is placed between two removable, flexible intensifying screens, which are then slid into the pouch

This panoramic film is labeled with two metal letters indicating the patients right (R) and left (L) sides

Step-by-Step Procedures Equipment Preparation Patient Preparation Patient Positioning

Equipment Preparation Load the panoramic cassette in the darkroom under safelight conditions Cover the bite-block with a disposable plastic coverslip or sterilize between patients Set the exposure factors

Patient Preparation Explain the radiographic procedures Place a lead apron without a thyroid collar on the patient and secure it A double-sided lead apron is recommended Remove all objects from the head and neck area that may interfere with film exposure

A double-sided lead apron is recommended for use during exposure of a panoramic film

Patient Positioning Instruct the patient to sit or stand “as tall as possible” with the back straight and erect Instruct the patient to bite on the plastic bite-block Position the midsagittal plane perpendicular to the floor

The patients teeth must be positioned in the grooves on the bite-block

Frankfort and midsagittal planes Frankfort and midsagittal planes. The Frankfort plane passes through the floor of the orbit and the external auditory meatus. The midsagittal plane divides the body in half into right and left sides

The patients Frankfort plane must be positioned so that it is parallel to the floor

Patient Positioning Position the Frankfort plane parallel with the floor Instruct the patient to position the tongue on the roof of the mouth and keep the tongue in that position during exposure of the film Instruct the patient to close the lips around the bite-block Instruct the patient to remain still while the machine is rotating during exposure Expose the film and proceed with film processing

Common Errors Patient Preparation Errors Patient Positioning Errors

Patient Preparation Errors Ghost Images Lead Apron Artifact

Ghost Images A radiographic artifact seen on a panoramic film that is produced when a radiodense object is penetrated twice by the x-ray beam It is found on the opposite side of the film It appears indistinct, larger, and higher than its actual counterpart

Large hoop earrings (1) and ghost images (2) Large hoop earrings (1) and ghost images (2). The ghost image of the earring appears on the opposite side of the film and is enlarged and laterally distorted

Ghost Images Problem Solution If all metallic or radiodense objects are not removed before exposure, a ghost image results that obscures diagnostic information Solution The dental radiographer must instruct the patient to remove all radiodense objects in the head and neck region prior to positioning the patient

Lead Apron Artifact Problem Solution A radiopaque cone-shaped artifact that obscures diagnostic information results if the lead apron is incorrectly placed, or if a lead apron with a thyroid collar is used Solution The dental radiographer must always use a lead apron without a thyroid collar when exposing a panoramic film

On a panoramic radiograph, a lead apron artifact appears as a large cone-shaped radiopacity obscuring the mandible

Patient Positioning Errors Positioning of the lips and tongue Positioning of the Frankfort Plane – Upward Positioning of the Frankfort Plane – Downward Positioning of the Teeth – Anterior to the Focal Trough Positioning of the Teeth – Posterior to the Focal Trough Positioning of the Midsagittal Plane Positioning of the Spine

Positioning of the Lips and Tongue Problem If the patient’s lips are not closed on the bite-block during the exposure of a panoramic film, a dark radiolucent shadow results that obscures the anterior teeth If the tongue is not in contact with the palate during exposure of a panoramic film, a dark radiolucent shadow results that obscures the apices of the maxillary teeth Solution Instruct the patient to close the lips around the bite-block and swallow and raise the tongue up to the palate during the exposure of the film

  If the tongue is not placed on the roof of the mouth, a radiolucent shadow will be superimposed over the apices of the maxillary teeth

Positioning of the Frankfort Plane Upward Problem If the patient’s chin is positioned too high a “reverse smile line” is apparent on the radiograph Solution Position the patient so the Frankfort plane is parallel with the floor

The patients head is incorrectly positioned; the chin is tipped up

A “reverse smile line” is seen on a panoramic film when the patients chin is tipped up

Positioning of the Frankfort Plane Downward Problem If the patient’s chin is positioned too low or is tipped down an “exaggerated smile line” is apparent on the radiograph Solution Position the patient so that the Frankfort plane is parallel with the floor

The patients head is incorrectly positioned; the chin is tipped down

An “exaggerated smile line” is seen on a panoramic film when the patients chin is tipped down

Positioning of the Teeth – Anterior to the Focal Trough Problem If the patient’s teeth are positioned too far forward on the bite-block or anterior to the focal trough, the anterior teeth appear “skinny” and out of focus Solution Position the patient so that the anterior teeth are placed in an end-to-end position in the groove on the bite-block

The patient is incorrectly positioned; the teeth are too far forward on the bite-block

The anterior teeth appear narrowed and blurred on a panoramic film when the patient is positioned too far forward on the bite-block

Positioning of the Teeth – Posterior to the Focal Trough Problem If the patient’s teeth are positioned too far back on the bite-block or posterior to the focal trough, the anterior teeth appear “fat” and out of focus Solution Position the patient so that the anterior teeth are placed in an end-to-end position in the groove on the bite-block

The patient is incorrectly positioned; the teeth are too far back and not on the bite-block

The anterior teeth appear widened and blurred on a panoramic film when the patient is positioned too far back on the bite-block.

Positioning of the Midsagittal Plane Problem If the patient’s head is not centered the ramus and posterior teeth appear unequally magnified on the panoramic radiograph The side farthest from the film appears magnified Solution Position the patient’s head so that the midsagittal plane is perpendicular to the floor while the midline is centered on the bite-block

The patient is incorrectly positioned; the head is not centered

The patients posterior teeth and ramus appear to be magnified on a panoramic film when the head is not centered

Positioning of the Spine Problem If the patient is not standing or sitting with a straight spine, the cervical spine appears as a radiopacity in the center of the film and obscures diagnostic information Solution Instruct the patient to stand or sit “as tall as possible” with a straight back

If the patient is not standing erect, superimposition of the cervical spine (arrows) may be seen on the center of the panoramic film

Advantages of Panoramic Radiography Field size Simplicity Patient cooperation Minimal exposure

Panoramic radiograph of a pediatric patient

Disadvantages of Panoramic Radiography Image quality Focal trough limitations Distortion Equipment cost