Panoramic positioning errors

A panoramic positioning error is a fault in how the patient was placed in the machine, and it distorts the image rather than the anatomy. The focal trough is shallow, so small errors show up as unequal magnification, overlap and lost sharpness. The shape of the occlusal plane and the width of the anterior teeth tell you which error occurred.

Synonyms: reverse smile line; patient too far forward; chin tipped; pano positioning

What is a panoramic positioning error?

Many of the radiographic artefacts you meet on a panoramic radiograph come from something in the beam — a denture, an earring, the cervical spine. A positioning error comes from the patient's own head being in the wrong place relative to the image layer.

That distinction matters because it makes the errors readable. The focal trough has limited dimensions, so a head that sits a few millimetres forward, or a chin lifted a few degrees, produces unequal vertical and horizontal magnification, overlapping teeth and lost sharpness. Rondon and colleagues describe this in their review of the panoramic literature, and Dhillon and colleagues report the same mechanism independently.

The consequence is that each fault deforms the image in its own direction. You do not have to remember a list. You have to look at two things — the curve of the occlusal plane, and how wide the front teeth are — and work backwards.

What does each common positioning error look like?

The UK guidance — from Public Health England and the Faculty of General Dental Practice — sets out a fault table that pairs each positioning fault with what it does to the image.

Rondon and colleagues add detail that helps you separate the two anteroposterior faults when the width change is subtle. Too far forward also shortens and blurs the arches, and the premolar region overlaps the ramus. Too far back blurs them too but expands them horizontally, and pushes the condyles out to the lateral edges of the image.

The two chin faults have their own extra tells. With the chin up, the intercondylar distance increases and the condyles are projected out of the imaged area altogether. With the chin down, the teeth overlap, the symphysis may not be visible, and both condyles can appear to run off the top edge.

Rotation and lateral tilt are different errors and they look different. A turned head elongates the teeth on one side of the midline and shortens them on the other, and one ascending ramus is projected much larger than the other, with condyles of unequal size. A head tilted sideways makes the imaged structures asymmetrical — the side toward the tilt appears smaller — with heavy proximal overlap.

How do you read the occlusal plane to identify the error?

Start with the curve, because it separates the vertical faults from everything else. In a correctly positioned patient the occlusal plane sits at roughly 20 to 30 degrees below horizontal, according to Rondon and colleagues. Lift the chin and that curve flattens or turns upward — the appearance clinicians call a reverse smile line. Drop the chin and the curve deepens.

Then look across the arch. If the curve is normal but the anterior teeth are the wrong width, the fault is anteroposterior: narrow means too far forward, wide means too far back. If the width is wrong on one side only, the head was turned.

This is not a shortcut invented for teaching. In one study of 480 panoramic radiographs, an experienced oral radiologist classified head positioning errors on occlusal plane orientation alone.

What it's confused with

The tongue fault is worth separating for a practical reason: it is correctable at the chairside. In a comparative study of 100 people, a physical aid held against the palate cut the posterior artefact from 50% in the control group to 22%, though it made no significant difference to the anterior radiolucency.

One case sits in both families and is worth knowing as such. The exaggerated cervical spine shadow over the anterior teeth is a ghost image, and the UK guidance lists it as a positioning fault — the patient was not standing up straight. If you have ruled out a radiopaque object and the shadow is spinal, look at the posture.

Which errors make the radiograph non-diagnostic?

There is no list, and that is the answer rather than a gap in it. The UK guidance grades every dental radiograph on a two-point scale: an image is diagnostically acceptable when it has "no errors or minimal errors in either patient preparation, exposure, positioning, image (receptor) processing or image reconstruction and of sufficient image quality to answer the clinical question", and not acceptable when errors "render the image diagnostically unacceptable". The test is functional, and it is the same test that governs any decision to retake. The same flattened occlusal plane can be acceptable for a third molar assessment and useless for maxillary apices — which is why the question a radiograph is taken to answer belongs in your search pattern before you judge its quality.

The performance targets attached to that scale are for not-acceptable images to run at no more than 5% with digital imaging and no more than 10% with film. Both are UK targets, described in the guidance as what is achievable in the majority of well-managed practices, with an explicit acknowledgement that practices serving patients with additional needs may not reach them.

Published series sit some way from that, and how far depends on what is being counted. In one Indian dental college series of 1,782 radiographs graded on the older three-point scale, 24.9% were unacceptable. In a Swedish county's public dental service, across all 1,904 panoramic examinations taken during 2011, 3% had errors severe enough to make correct diagnosis impossible. In a Brazilian service, 69 of 1,088 radiographs were retaken for a tongue positioning error. Those are three different definitions of what an error costs, not three measurements of the same thing.

How common are they?

Common enough that the error-free radiograph is the exception. Across four published series, the proportion carrying at least one positioning error runs from about two-thirds to 95%: 89.0% of 1,782 radiographs at one Indian dental college, adults only, read by a single observer; 79% of 1,904 radiographs covering a Swedish county's whole year; 66.1% to 78.8% of 947 archived radiographs at a Turkish university, depending on which of four observers was reading; and 95% of 500 radiographs at another Indian institution.

Look at the Turkish figure again. The spread is not only between populations — it appears inside a single set of images. Four observers scored the same 947 radiographs and returned rates from 66.1% to 78.8%, with only fair agreement between them on quality overall.

For the same reason, be wary of any page that tells you which error is the most common one. Failure to hold the tongue against the palate leads in the Indian dental college series, at 55.7%, and in the Swedish county series. Head turned to one side leads at another Indian institution, at 33.8%. Movement leads in a study of 100 children, half of them with special needs. And in the Turkish study, each of the four observers named a different error. A 2024 systematic review of studies that trained models on panoramic datasets found the criteria for judging panoramic image quality varied widely between studies and were prone to bias, which is the same problem seen from another angle.

No meta-analysis pools these figures. Treat the range as unsettled, and quote a number only with the population it came from.

Population does move the result, though. In that study of 100 paediatric patients, images of children with special needs carried significantly more errors and were rated lower quality than matched controls, and younger patients in both groups showed more movement and positioning errors. That is the same population the UK guidance exempts from its targets.

How to be sure

Read the plane before you read the teeth. A flat or inverted curve tells you the maxillary apices are the region you cannot trust; an exaggerated curve tells you the same about the lower incisors. Deciding that first stops you calling a positioning artefact a lesion.

Then treat it as a measurable process rather than a matter of care. The UK guidance asks for image quality to be analysed at least every six months, on a sample of no fewer than 100 images, with panoramic reported separately from intra-oral, and the underlying reason recorded every time an image is rated not acceptable.

That audit is worth doing because the faults respond. A cluster randomised trial across 40 English dental practices, examining 800 panoramic radiographs, found that regular feedback on image quality significantly reduced technical faults, and the effect was still present eight weeks after the feedback stopped.