Sensor dropout

Sensor dropout is a mark on a radiograph produced by damage to the receptor rather than by anything in the patient. On a phosphor plate it is usually a scratch, and damage to the phosphor layer is permanent. Because the mark belongs to the plate, it can fall anywhere on the radiograph, over any anatomy.

Synonyms: dead pixel; PSP plate scratch; digital receptor artifact; line artifact

What is sensor dropout?

You will hear this called a dead pixel or a scratched plate far more often than you will hear it called dropout, and those are the words worth knowing. What sits underneath both is the same thing: a fault in the receptor — the phosphor plate or the digital sensor that records the image. It is a radiographic artifact, and the dental literature files it that way, under the plate rather than under the patient.

The scale is small but not negligible. A two-year audit of 50,000 intraoral radiographs at one university clinic found 3,550 of them — 7.1% — retaken because of artifacts, with plate faults accounting for 1.37% of every radiograph taken.

What does receptor damage look like on the image?

A line. A 2019 classification study of 5,000 intraoral radiographs describes physical deformation of a phosphor plate as showing up as irregular or straight radiopaque lines anywhere on the radiograph, and a 2017 classification paper describes scratches specifically as small, smooth linear opacities anywhere on the image. A 2024 review of 814 phosphor plate radiographs found cracks or scratches were the most common plate-related artifact by a wide margin, at 418 of them.

Note the density word in both: it prints light, not dark. A scratch is damage to the plate's phosphor layer, and the resulting line is radiopaque. That is the opposite of what most people expect from something whose name suggests signal going missing, and it is the first thing to get straight.

Bending gives you a variation on the same theme. Bending a plate to make it more comfortable produces a line along the bend, plus distortion and a density difference across the bent area.

The other half of the appearance is where it sits. It sits wherever the damage sits on the plate. That means it can run through the crown of a molar, out across the alveolar bone and off the edge of the image, ignoring every border that anatomy would respect.

How do you tell it from a fracture line or a real radiolucency?

By testing the receptor, not the image.

Anything inside the patient leaves with the patient. Damage to a phosphor plate does not. The 2019 classification study calls the scratching that handling produces permanent, and the 2017 paper describes excessive bending and rough manipulation as generating irreversible damage to both the phosphor layer and the polyester base underneath it. The plate goes back into its barrier and takes the next radiograph carrying the same fault.

So take the plate out and expose it on its own. The 2019 study's own recommendation is to check plates daily for scratches and, where any are found, to take a test image before deciding whether the plate stays in service. A mark that is still there on a test exposure was never in the patient.

What causes it in sensors and in phosphor plates?

On the plate side, everything is handling. The 2019 classification study lists careless manipulation while positioning the plate in the mouth, excessive bending, the patient biting it, force used to load it into the scanner, and the mechanical stress of the scanner's rollers and holders. The 2017 paper adds friction against the foil cassette as the cause of the border peeling you see on older plates, and attributes crescent-shaped bends to tension on the sheath when a patient bites the bite block badly. Manufacturers recommend protective covers to limit the mechanical damage.

None of this is new or surprising. A 2010 systematic review of digital intraoral workflow lists damage to the receptor among the disadvantages the field did not foresee when it moved off film, and notes plainly that the phosphor plate may be scratched in clinical use.

The solid-state side is less well described in dentistry. The general radiography literature is clearer: a 2018 pictorial review of digital radiography artifacts classifies a whole group of them as equipment defects arising from accident or mishandling, with dropped flat-panel detectors named directly. That is general radiography, not intraoral sensors, and it should not be read as a measurement of what happens to the sensor in your surgery. The one intraoral study to hand is a 2023 conference abstract from a single university clinic, which tested 25 sensors and found small delamination artifacts on 13 of them.

When does a receptor need replacing?

The studies that have tried disagree, because they measure different things on different systems. A 2009 study of five plates stated outright that plate longevity in practice was not established, and concluded that a plate could be used up to 200 times. A 2017 quality assurance study of 20 plates found spatial resolution decreased after 48 clinical uses, and closed by calling for replacement-interval guidelines to be established. A 2020 study of two plates ran 1,800 exposures and measured gradual grey value loss. Different plate systems, different metrics, small samples — the disagreement is as much about what is being measured as about the answer. A 2020 method paper described itself as the first in the literature to assess when dentists should discard their plates, which tells you how open the question still is.

Judging by eye does not close it. A preliminary study of 60 plates compared those discarded by direct visual inspection against an objective artifact score and found poor correlation: many of the plates taken out of circulation scored lower for artifact than plates still in use.

A 2024 quality assurance position paper for general X-ray imaging asks for no clinically significant clusters of defective detector elements, and for the number of defective elements to stay within the manufacturer's specification. That is a general radiography document, not a dental one, and the number it points at belongs to whoever made your receptor.

So the working answer is the test exposure, not a use count. Check the receptor, expose it on its own, and replace it when the mark is there and it matters. One study of 25 general dentists is worth weighing here: reading images carrying severe superimposed plate artifacts, they showed no statistically significant change in how they interpreted periapical inflammatory disease, but their confidence fell and they were more likely to say the plate should be discarded. That is one disease task in one study, so hold it loosely — but it suggests the plate you throw away may be costing you confidence more than accuracy.

Common errors

Calling it a radiolucency. Plate damage prints light. If you have caught yourself looking for a dark streak, you are looking for the wrong thing.

Retaking the radiograph. A second exposure on the same plate reproduces the same fault, because the fault is permanent and it is in the plate. Test the receptor instead.

Reading it as pathology. This is the whole reason the artifact matters, and the difference between an artifact and a finding is worth having straight before you are looking at a line you cannot explain.

Binning plates on a glance. Visual inspection correlated poorly with objective artifact scores in the one study that checked, in both directions — good plates thrown out, marked plates left in circulation.