There are three possible planes in which the patient’s head may be positioned incorrectly: 1) Horizontal, 2) Vertical and 3) Anteroposterior. Incorrect positioning in each plane produces characteristic effects. Of course, there is the possibility of multiple errors in more than one plane – this will produce multiple and sometimes compounding effects and, in this instance, have are referred to as “compound” errors. The analysis of positioning errors therefore involves stepwise recognition of the radiographic features associated with each planar discrepancy.
Horizontal plane discrepancies – Essentially alter the position of the teeth and jaws on one side relative to the path of the effective rotation center and x-ray beam projection. The two possible options are that the patient is a.) twisted with respect to the machine, or b.) that their head is tilted. Both result because the midsagittal plane of the patient is not correctly aligned at the time of exposure. This can occur if the patient “follows” the receptor during exposure and move off-center.
Twisting – The most obvious image effects from the patient “twisting” within the machine are anatomic. Most noticeably:
While the anterior teeth remain relatively normal, there are two secondary effects on the dentition:
Panoramic radiograph (schematic on right) demonstrating the effects of twisting – Elongation of left mandible, reduction in size of teeth on opposite side, occlusal plane canting and pronounced tooth overlap on the same side.
Tilting – The principle effect of tilting the patient is to create artifacts in the dentition and ramus superoinferiorly. The most obvious image effects are also anatomic. Most noticeably:
The effects of tilting on the dentition include:
Vertical plane discrepancies – Essentially alter the relative position of the occlusal plane of the teeth and condyles of the mandible. The possible options are that the patient’s chin positioned too far up, too far down or that it is not positioned on the chin rest (when this is used to position the patient). Vertical errors occur when the patient’s head is incorrectly positioned superiorly inferiorly in the machine. The instructions in the manufacturer’s manual may vary in which plane is used to adjust the patient’s head up or down. Prevention of this error can be accomplished by ensuring that the patient’s horizontal reference line is parallel to the floor or the lateral reference markers.
Panoramic radiograph (cropped and zoomed on right) demonstrating the effects of positioning the head off the chin rest. Note that in addition the patient is positioned too far forward.
Anterioroposterior plane discrepancies – Essentially alter the position of the teeth, especially the anterior teeth in the focal trough. The two possible options are that the patient is positioned either too far forward or too far backward.
Too far forward – Anterior positioning of the patient too far forward occurs either due to patient slipping forward, sucking the bite block or not using a bite block.
Prevention of this error first necessitates that a bite block is used; secondly it requires that the patient’s anterior teeth are placed in an end-to-end position in the bite block. Prevention of subsequent patient movement can be aided by adjustment of the forehead support, when available, to prevent the patient from sliding forward.
The effect of positioning the patient too far forward is to position structures that are normally within the focal trough, like the anterior dentition, further anteriorly and out of focus and to bring more posterior structures, like the spine, nasal fossa and maxillary sinus into the focal trough.
Panoramic radiograph (schematic on right) demonstrating visual effects on image with patient’s head positioned too far forward during exposure: Spine superimposed over the ramus area, nasal fossa and maxillary sinus become clearly evident. Effects on the dentition however are the most noticeable with narrowing and blurring of the anterior teeth.
Prevention of this error, as with anterior positioning errors, necessitates that a bite block is used; secondly it requires that the patient’s anterior teeth are placed in an end-to-end position in the bite block.
The principle effect of positioning the patient too far back is to position structures that are normally within the focal trough, like the anterior dentition, further posteriorly and out of focus.
Panoramic radiograph (schematic on right) showing effects of positioning the patient’s head too far back – widening of the entire image, loss of the posterior ramus of the mandible (right), accentuated ghosting of the mandible, and blurring of the turbinates across the sinus. Note the obvious effects on the dentition with pronounced widening of the anterior teeth.
Panoramic Patient Positioning Errors | ||
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Error Type | Description | Correction |
Midsagittal Plane (Horizontal) | ||
Head Rotated/Twisted/Turned | Error presents with distortion of structures right to left. Structures on one side appear narrow (labial to the focal trough) while structures on the other side appear wide (lingual to the focal tough). | Center the patient’s midline so that it is straight and aligned perpendicular to the floor. |
Head Tilted/Canted | Error presents similar to head rotation in terms of structure distortion. In addition, one side is higher than the other and the occlusal plane is crooked. | Center the patient’s midline so that it is straight and aligned perpendicular to the floor. |
Frankfort/Occlusal Plane (Vertical) | ||
Head/Chin Tilted Too High Up | Distorts superior structures placed lingual to the focal trough like the nasal cavities. Superimposes the hard palate over the maxillary teeth apices. Elongates the maxillary anterior teeth. Moves the condyles off the sides of the image. Occlusal plane appears flat or frowned. |
Lower the patient’s head/chin down until the Frankfort plane is parallel to the floor. The forehead and chin should be in the same vertical plane. |
Head/Chin Tilted Too Far Down | Distorts inferior structures placed lingual to the focal trough like the chin. Superimposes the hyoid bone over the mandible. Foreshortens the anterior teeth. Moves the condyles off the top of the image. Occlusal plane appears like a grin. | Raise the patient’s head/chin up until the Frankfort plane is parallel to the floor. The forehead and chin should be in the same vertical plane. |
Anteroposterior Plane (Forward-Backward) | ||
Head Too Far Forward | Distorts the anterior teeth horizontally appearing blurred and narrowed (labial to focal trough). Superimposition of the spine onto each side of the image. | Ensure patient’s teeth bite end-to-end in bite block groove. Move AP posterior to center structures in the focal trough and align with landmark. |
Head Too Far Backward | Distorts the anterior teeth horizontally appearing blurred and widened (lingual to focal trough). Excessive ghosting of the rami may occur. Condyles and rami often cut off on each side of the image. | Ensure patient’s teeth bite end-to-end in bite block groove. Move AP anterior to center structures in the focal trough and align with landmark. |