Incorrect Head Orientation

Incorrect Head Orientation – There are three possible planes in which the patient’s head may be positioned incorrectly: 1) Anteroposterior, 2) Vertical and 3) Horizontal. 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.

  • Anterior 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.
Figure 105.
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  • 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 and therefore more in focus.
  • The most obvious effects however are those on the dentition, which include:
    • Blurring of the anterior teeth
    • Narrowing of the anterior teeth
    • Unsharpness
    • Pronounced premolars overlap
Figure 106.
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Figure 107.
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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.
Figure 108.
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Panoramic radiograph demonstrating visual effects on image with patient’s head positioned too far forward during exposure: In this instance a bite block was not used and most probably contributed to poor patient positioning.
  • Too far backward – Posterior positioning of the patient too far back usually occurs when the patient’s teeth are not biting on the bite block. The patient may suck the bite block rather than bite it.
  • Figure 109.
    fig109
    • 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. The principal visual anatomic effects are widening of the entire image, ghosting of the mandible, and blurring of the turbinates (nasal conchae) across the sinus.
    • Another effect is to bring part of the molar dentition into the crossover region of the panoramic x-ray beam and increase the possibility of ghost artifacts from the mandibular angle and ramus.
    • The most obvious effects however are those on the dentition, which include:
      • Wide, unsharp image of the anterior teeth with the teeth more difficult to see
      • Widened crowns
      • Roots cut off (fuzzed out)
    Figure 110.
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    Figure 111.
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    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.
  • 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. It may also result from patient movement during exposure. This can occur more often with children as they may have a tendency to “follow” the cassette during exposure and hence move.
  • Figure 112.
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    Tilted
    Figure 113.
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    Twisted
    • This error can be prevented by ensuring the midsagittal reference line of the panoramic unit coincides with the patient’s midline and that this line is perpendicular to the floor. Prevention of patient movement can be facilitated by adjustment of the lateral head supports to stabilize the patient and prevent movement during exposure.
    • The principle effect of mal-positioning the patient is to off set more lateral and posterior structures, like the posterior dentition and ramus, with respect to the focal trough and x-ray beam projection.
      1. Twisting – The most obvious image effects from the patient “twisting” within the machine are anatomic. Most noticeably:
        • The width of ramus on one side reduces (closer to the film) and becomes closer to the spine.
        • The width of the ramus on other side increases (farther away) and is further away from the spine – it may also be off the image.
        • The conchae on the side opposite the twisting are more pronounced.
        • The maxillary sinus and nasal fossa of the same side as the twisting become more noticeable.

        While the anterior teeth remain relatively normal, there are two secondary effects on the dentition:

        • The first is that tooth size increases posteriorly on the side opposite to the direction of head tilt and,
        • Secondly, there appears to be increased overlapping of contacts on the opposite side of the tilt.
    Figure 114.
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    Figure 115.
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    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.

    Twisting not only produces a distorted image that may be more difficult to interpret, this error can create pseudo-pathology. An interesting feature sometimes visualized on radiographs is a triangular radiopacity apparently located within the maxillary sinus.

    Figure 116.
    fig116
    Panoramic radiograph showing triangular radiopacity within left maxillary sinus. Note a large discrepancy between the mandibular ramus width with the left side and the side with the pathology, being much wider than the right. This object within the sinus is merely another representation of the left zygomatic process of the maxilla. This structure assumes this appearance, due to the twisting of the patient’s head, because is now at right angles to the projected x-ray beam.
    1. 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 lower border of the mandible slopes markedly on the side to which the head is tilted.
      • The mandible also appears elongated and tilted up.

      The effects of tilting on the dentition include:

      • A reduction in the size of the teeth on the tilted side.
      • A greater overlap of the teeth on the opposite side.
      • Canting (sloping) of the occlusal plane towards the tilted side.
    Figure 117.
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    Figure 118.
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    Panoramic radiograph (schematic on right) demonstrating the effects of tilting.
    • 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. Some suggest using the ala-tragal line (a line between the side of the nose and the tragus of the ear); some use the cantho-meatal line (a line between the outer part of the eye and the tragus); others use the Frankfort horizontal (a line between the lower part of the eye and the tragus). Even some use the occlusal plane as a reference.

      Practically vertical errors result from non-alignment of the lateral reference plane of the patient’s head parallel to the lateral side indicator.

      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. Alignment markers are either located on the lateral side indicator (as is indicated in this example) or may be present as thin light markers. Prevention of patient movement can also be aided by adjustment of the lateral head supports to stabilize the patient and prevent movement during exposure.
      • Head tilted too high – The first possibility is that the patient’s head is positioned too high or tilted up.
    Figure 119.
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    Figure 120.
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    Figure 121.
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    Panoramic radiograph (schematic on right) demonstrating the effects of positioning the head too far up.
  • Head tilted too low – The second possibility is that the patient’s head is positioned tilted too far down. The principle effect of tilting the chin down is to position more of the maxillae into the focal trough, align the maxillary teeth and to bring less of the lower anterior mandibular area into the focal trough. The anatomic effects of positioning the head too far down can be severe and may necessitate retaking the radiograph.
  • Figure 122.
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    • Most noticeably, the TMJs are positioned higher and in many cases off the image.
    • Secondly the hyoid bone comes into the doubling diamond and forms a single widened line
    • Finally the anterior mandible is usually unsharp or fuzzy

    Dentition effects are probably the most visually obvious and include:

    • Severe curvature of the occlusal plane producing a “Jack-O-Lantern” effect and,
    • Lack of definition of the lower incisors and pronounced foreshortening of the roots of these teeth.
    Figure 123.
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    Figure 124.
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    Panoramic radiograph (schematic on right) demonstrating the effects of positioning the head too far down.
    • Chin not on chin rest – The third possibility is that the patient’s chin is lifted from the chin rest. This is usually because the initial height at which the machine is set is lower than the height required. Often a patient will stoop to enter a panoramic machine but once they are positioned and immediately before exposure will straighten themselves up.

      The main visual effect of the chin being lifted from the chin rest is to create an image with a shift of anatomic structures superiorly. This may result in the top of the sinus and the condyles being cut off.

      There are usually minimal effects of this positioning error on the dentition, however the possibility of movement and horizontal or vertical errors as previously described increases because the chin is no longer stabilized by the lower support. This leads to the possibility of distortion, overlapping and unsharpness of the anterior teeth in particular.
    Figure 125.
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    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.