Radiographic Errors: Cause, Appearance, and Correction

Core Review

Technique Errors

Technique errors are caused by incorrect positioning of the patient, film/sensor, PID, or exposure settings. They are the most common errors and are preventable with proper technique.

Horizontal Angulation Errors

Definition: Horizontal angulation refers to the direction of the central ray in the horizontal plane (side-to-side). Correct horizontal angulation directs the X-ray beam through the interproximal contacts, producing open contacts on the radiograph.

Incorrect Horizontal Angulation → Overlapped Contacts

• Appearance: Interproximal contacts are overlapped — tooth structures superimpose on each other. The overlapping appears as dark bands where one tooth's enamel overlaps the adjacent tooth. It is most noticeable in bitewing and anterior periapical radiographs.
• Cause: The PID was directed at an angle that did not pass directly through the interproximal contacts. The central ray was aimed either too far mesially or too far distally.
• Correction: Redirect the PID so the central ray passes directly through the interproximal contacts of the teeth being imaged. For bitewings, align the PID parallel with the curve of the arch at the interproximal contact points.
• NBDHE tip: If you see overlapping contacts on a bitewing, think "incorrect horizontal angulation."

Vertical Angulation Errors

Definition: Vertical angulation refers to the angle of the central ray in the vertical plane (up-and-down). With the paralleling technique, the ideal vertical angulation is 0 degrees (PID perpendicular to the image receptor). With the bisecting angle technique, the vertical angulation is determined by the bisecting angle rule.

Incorrect Vertical Angulation → Foreshortening

• Appearance: Teeth appear shorter than their actual length. Roots appear compressed. The image looks "squished." Bitewings may show distorted occlusal surfaces.
• Cause: Excessive vertical angulation — the PID was angled too steeply (too much positive or negative angulation).
• Correction: Decrease the vertical angulation so the central ray is closer to perpendicular to the image receptor (paralleling technique) or the bisector (bisecting technique).

Incorrect Vertical Angulation → Elongation

• Appearance: Teeth appear longer than their actual length. Roots appear stretched. The teeth look unnaturally elongated and narrow.
• Cause: Insufficient vertical angulation — the PID was not angled steeply enough.
• Correction: Increase the vertical angulation.

NBDHE Memory Aid:

• Foreshortening = Too Steep (excessive angulation)
• Elongation = Too Flat (insufficient angulation)
• Think: "Short = Steep, Long = Low"

Incorrect Vertical Angulation on Bitewings:

• Excessive vertical angulation (+10° or more): Occlusal surfaces distorted, contacts overlapped (even with correct horizontal angulation), alveolar bone appears more radiolucent (darker), appearing as "burnout" which is actually a projection artifact
• Insufficient vertical angulation (too flat): Minimal occlusal surface distortion; however, too little vertical angulation may prevent the beam from passing through contacts adequately

PID Alignment Errors

Cone Cut (Partial Image)

• Appearance: A clear (unexposed) area on the radiograph, often with a curved border, where no radiation reached the image receptor. The shape depends on the PID shape (round for round PID, rectangular for rectangular PID).
• Cause: The PID was not aligned with the image receptor — the X-ray beam missed part of the film or sensor. This occurs when the PID is not centered on the aiming ring or when the PID drifts during exposure.
• Correction: Ensure the PID is centered over the image receptor and aligned with the aiming ring before exposure. Check that the PID is fully seated against the aiming ring if using a positioning system.
• NBDHE distinction: If the entire film is blank = the machine did not produce radiation (machine malfunction), not a cone cut. Cone cut = PART of the image is missing with a distinct curved or straight border.

Double Exposure

• Appearance: Two superimposed images on a single film. Teeth appear "doubled" or ghosted.
• Cause: The same film was exposed twice. In digital radiography, this is essentially impossible with most systems, as each image is stored as a separate file.
• Correction: Track exposed and unexposed films carefully. In digital, ensure you are acquiring a new image, not overwriting an existing one.

Film/Sensor Placement Errors

Inadequate Coverage (Missing Apices)

• Appearance: The apices of the teeth are not visible on the image. Typically, 2-3 mm of periapical bone beyond the apex should be visible.
• Cause: The image receptor was not positioned far enough apically. The bite block was placed too occlusally, or the receptor edge was not positioned beyond the occlusal plane by the appropriate amount.
• Correction: Position the image receptor so it extends approximately 1/4 inch beyond the occlusal or incisal edge, ensuring the receptor edge covers 2-3 mm beyond the expected apex.

Inadequate Coverage (Missing Coronal)

• Appearance: The occlusal or incisal surfaces are not visible.
• Cause: The image receptor was not positioned far enough coronally. The bite block was placed too apically.
• Correction: Ensure the receptor edge extends 1/8-1/4 inch beyond the occlusal/incisal surface.

Reversed Film

• Appearance: A lighter image overall with a herringbone or tire-track pattern visible. The image has reduced contrast and density.
• Cause: The film packet was placed backward in the mouth — the white (tube) side faced away from the PID, and the lead foil backing faced the PID. The lead foil absorbed most of the X-ray beam before it could reach the film emulsion, but the foil pattern is imprinted.
• Correction: Always place the white (plain, non-embossed) side of the film packet toward the PID, facing the teeth. The embossed dot should face the PID.
• NBDHE note: This error is unique to film-based radiography. Digital sensors do not have a lead foil backing.

Film Bending

• Appearance: Distorted, stretched, or warped image. Teeth and anatomical structures appear distorted in a non-uniform way.
• Cause: The film was bent to accommodate the patient's anatomy (palatal vault, floor of mouth) rather than using an appropriately sized receptor or modifying the technique.
• Correction: Do not bend the film. Use smaller receptor sizes for anatomical limitations (size #0 or #1 for narrow arches), or modify the technique (e.g., bisecting angle for shallow palates).

Incorrect Film Placement for Bitewings

• Appearance: The bitewing image shows incorrect anatomical coverage. Missing distal of canine or mesial of third molar areas.
• Cause: The image receptor was placed too far anteriorly or posteriorly.
• Correction: For posterior bitewings, the anterior edge of the receptor should cover the distal half of the mandibular canine.

Motion Errors

Patient Movement

• Appearance: Blurred image with evidence of motion. Structures lack sharp margins. Overall ghosting or blur.
• Cause: The patient moved during the exposure. This is more common with longer exposure times (slower film, older AC units).
• Correction: Instruct the patient to remain completely still during the exposure. Use the shortest possible exposure time. Immobilize the patient's head with headrest.

Film/Sensor Movement

• Appearance: Blurred image, often with distortion. Movement may produce localized blur distinct from patient movement.
• Cause: The patient released bite pressure on the film/sensor holder, or the holder shifted. The tongue pushed against the receptor.
• Correction: Instruct the patient to bite firmly on the bite block and not to release until instructed. Ensure the holder is stable.

Receptor Placement and Anatomy

Palatal-Glossal Air Space Shadow

• Appearance: A dark (radiolucent) shadow over the apices of the maxillary teeth on periapical radiographs, often obscuring the apices.
• Cause: The tongue was not held against the palate during exposure, or the patient was not breathing through the nose. The air space between the tongue and palate creates the radiolucent shadow.
• Correction: Instruct the patient to hold the tongue against the palate or to close the mouth and breathe through the nose during the exposure.

Film-Sensor Angulation (Bisecting Technique) For the bisecting angle technique, there are specific error patterns related to the incorrect bisector angle:

• The central ray must be directed perpendicular to the imaginary bisector between the long axis of the tooth and the long axis of the film
• If the angle is too steep, foreshortening results
• If the angle is too flat, elongation results

Exposure Errors

Underexposed Image

• Appearance: Light, low-density image. Structures are difficult to see. Minimal contrast.
• Cause: Insufficient mAs (mA or exposure time too low), kVp too low, or source-to-receptor distance too great.
• Correction: Increase mA, exposure time, or kVp. For digital sensors, increase exposure time in small increments.

Overexposed Image

• Appearance: Dark, high-density image. Structures are difficult to differentiate. In film, the image appears black with loss of detail. In digital, the image may appear "burnt out" with areas of saturation.
• Cause: Excessive mAs, kVp too high, or source-to-receptor distance too short.
• Correction: Decrease mA, exposure time, or kVp.

Important Digital Distinction: Digital sensors have a wider dynamic range (latitude) than film. This means digital imaging is more forgiving of exposure errors — an underexposed or overexposed digital image can often be adjusted using software. However, this does not mean exposure factors should be ignored. Excessive dose is still a radiation safety concern even if the image is salvageable.

Processing Errors (Film-Based Only)

While digital radiography has largely replaced film, the NBDHE still tests film processing errors.

Dark Film (Overdevelopment)

• Appearance: Uniformly dark radiograph
• Causes: Developer temperature too high, development time too long, developer solution too concentrated

Light Film (Underdevelopment)

• Appearance: Uniformly light radiograph
• Causes: Developer temperature too low, development time too short, depleted developer solution

Yellow-Brown Stains

• Appearance: Yellowish or brownish discoloration of the radiograph
• Causes: Insufficient fixing (fixer depleted or fixing time too short), inadequate washing

Fogged Film

• Appearance: Overall gray appearance with reduced contrast
• Causes: Film exposed to light (darkroom light leak), improper safelight, expired film, film exposed to heat or chemical fumes

Developer Cutoff

• Appearance: A straight dark line across the film
• Cause: The developer level in the automatic processor was too low — the top portion of the film was not immersed in the developer

Reticulation

• Appearance: Cracked or net-like pattern on the film surface
• Cause: Extreme temperature changes between processing solutions (e.g., hot developer to cold fixer)

Clinical Application

You take a posterior bitewing and notice that the contacts between teeth #2-3, #3-4, and #4-5 are overlapped — you cannot see clearly between the teeth to evaluate for interproximal caries. The image is otherwise properly exposed and covers the correct area. The diagnosis: incorrect horizontal angulation. The PID was aimed too far mesially or distally relative to the interproximal contacts. The correction: identify the interproximal contact points between the posterior teeth. Align the PID so the central ray passes directly through these contacts. Use the aiming ring as a guide — the PID should be centered and parallel with the ring.

Common Traps

• TRAP: Confusing foreshortening and elongation. Foreshortening = steep vertical angulation (think "getting shorter" → too steep); Elongation = flat vertical angulation (think "getting longer" → too flat).
• TRAP: Thinking overlapped contacts are caused by vertical angulation. Overlap is primarily a horizontal angulation error.
• TRAP: Confusing cone cut with underexposure. Cone cut has a distinct border; underexposure affects the entire image uniformly.
• TRAP: Forgetting that digital sensors are more forgiving of exposure errors than film but dose reduction is still the goal. Never intentionally overexpose just because software can correct it.