Palatoglossal air space

The palatoglossal air space is the air left between the tongue and the palate when the tongue is not held against the roof of the mouth during a panoramic exposure. That air casts a radiolucent shadow over the upper teeth on the radiograph.

Synonyms: palatoglossal airspace; palatoglossal air space shadow; tongue not to palate; air space shadow; radiolucent band over the maxillary apices

What is the palatoglossal air space?

It is one of the most common positioning errors in panoramic radiography, and it happens for a single reason: the tongue is not stuck to the roof of the palate at the moment of the exposure. Incorrect tongue positioning leaves a radiolucent artifact in the palatoglossal air space, and that artifact compromises the quality of the image.

In one dental institution in Riyadh, 2629 panoramic radiographs taken between August 2020 and June 2021 were scored for ten kinds of positioning error. Failure to place the tongue close to the palate was the most common one on the list. That is a single institution, not a population figure — but it matches what the trial literature calls this error when it names it.

Every published description used for this entry describes the finding on a panoramic radiograph rather than on a periapical radiograph. Treat it as a panoramic finding.

What it looks like, and over which teeth

The radiolucency belongs to the air space, not to anything in the teeth or the bone. It sits where that pocket of air sat, between the tongue and the palate, and that puts it across the upper teeth.

That has a consequence worth holding on to. When a 2026 comparative study of 100 adults scored these radiolucencies, it scored them by region of the arch, anterior and posterior, rather than tooth by tooth. The finding is regional. It belongs to a stretch of the radiograph, not to a tooth.

How to tell it from periapical pathology

Start from the other side of the comparison, because that is the side with the crisp signs. Apical periodontitis shows radiographic signs such as widening of the periodontal ligament and a periapical radiolucency, and how far those extend depends on the stage of the lesion. Those signs are tied to a tooth. They sit at an apex, and they involve that apex's own ligament space.

The air space, by contrast, is the regional finding described above — a radiolucency over a stretch of the arch, scored anterior or posterior rather than at a named tooth. Where the darkness follows an arch region and no single apex shows the tooth-level signs, air is the better explanation than disease. That contrast is drawn from two separate descriptions rather than from a study that tested it directly, so treat it as a way of orienting yourself, not as a test.

One study has looked at whether the air space degrades periapical diagnosis. In 2025, in a study of periapical lesion detection on panoramic radiographs by an artificial intelligence system, the presence of the palatoglossal air space did not significantly affect its detection of periapical lesions in the upper teeth. Read that carefully before it reassures you: the reader in that study was software, not a person.

Against it sits what the imaging authors say in passing. Incorrect tongue positioning may mean repeating the study or moving to cone-beam CT, both of which increase radiation exposure, and failure to follow tongue-position instructions is described as resulting in missed pathology or unnecessary further radiation. Neither paper measured that as an outcome. It is the field's working assumption, stated by people who image for a living, and it is not the same thing as evidence.

Why it happens, and what stops it

The cause is the instruction not landing. Telling a patient to put the tongue on the roof of the mouth is easy to say and easy to half-do, and the radiograph records whichever version you got.

Two recent studies put numbers on how far plain instruction gets you.

In the 2026 study of 100 adults, the 50 people who received standard verbal instructions alone showed the posterior artifact half the time, 50%, against 22% in the group who held a piece of unleavened bread against the palate (p = 0.006). Group membership was the only significant independent predictor of the posterior artifact, with an odds ratio of 0.25 (p = 0.003). But the same intervention did not reach statistical significance for the anterior radiolucency. The anterior maxilla — the region this entry is about — is the harder half of the problem, and a physical aid did not solve it there.

A 2024 randomised controlled trial of 270 patients tested three aids placed on the tongue before the usual instruction: fruit leather, chewing gum and celluloid tape. Each group produced significantly more error-free images than the control group (all cases P < 0.05), and the fruit leather group had the highest chance of an error-free image, at 9.57 times.

Where the instruction itself is the barrier, one method reworks the instruction rather than adding an object. Scott and Reed describe a demonstration of "breathe-in, breathe-out, swallow, lips closed and hold still", which never mentions the tongue but uses the tongue positions that occur during breathing and swallowing, to reduce the intensity of both the palatoglossal and pharyngeal air spaces. They developed it for patients who often cannot follow traditional tongue-position instructions, including children and patients with intellectual disabilities.

Does the radiograph need retaking?

There is no published rule for this artifact specifically, so the decision is the ordinary one and the artifact does not change its terms.

The terms are these. The value of a radiograph to a care decision has to be balanced against radiation safety, to minimise exposure to the patient and occupational risk to the people taking it — that is the American Dental Association expert panel's framing of every dental exposure. A repeat is another exposure, and so is moving up to cone-beam CT; the imaging literature names both as consequences of this error rather than as remedies for it.

What the evidence does say is that the fault is correctable at the point of exposure. That is where it is cheapest to fix.

Common errors

• Calling the shadow a lesion. The tooth-level signs of apical periodontitis are at one apex and involve that apex's ligament space. A darkness that runs across a region of the arch is a different kind of finding.
• Assuming the instruction worked. Half of the controls given standard verbal instruction alone still showed the posterior artifact.
• Assuming an aid fixes the front. In that study the aid worked posteriorly and did not reach significance anteriorly.
• Taking the AI result as your own reassurance. The system that was unaffected by the air space was software reading retrospectively, not a clinician reading at a screen.