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.
- 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.
- 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.
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.
- 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.
- 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.