17 Errors & Troubleshooting Practice Questions & Answers

1. 1. An operator exposes a periapical with a solid-state CMOS sensor. The unit completed its cycle and the exposure indicator sounded normally, but the software displays an essentially blank image with no tooth structure at all. Which explanation fits best?

   • A.The sensor was seated with its active surface turned away from the tubehead, so almost no beam reached it.✓ Answer
   • B.The sensor cable was coiled tightly around the holder, which reversed the polarity of the image signal.
   • C.The kilovoltage was set far too high, and the extra penetration wiped out all of the contrast between structures.
   • D.The patient moved throughout the exposure, and the motion smeared every tooth outline out of the image.

   A rigid CCD or CMOS sensor has a dense, shielded backing behind its active surface. If the sensor is placed backward, that backing absorbs the radiation and virtually no signal reaches the detector, so the result is a blank or near-blank image rather than a merely light one. Movement blurs an image but does not erase it, and no cable position can reverse an image signal.

   Source: Iannucci & Howerton, Dental Radiography: Principles and Techniques — digital receptor placement errorsReport a problem with this question

2. 2. A digital periapical looks pale and washed out: enamel and dentin are barely separated from the background, and raising the brightness in the software only makes the image grainier. What is the correct assessment and action?

   • A.The monitor's brightness has drifted; the display is recalibrated and the same image is reviewed again.
   • B.The image is diagnostically acceptable; graininess is expected with digital receptors at this setting.
   • C.The receptor was overexposed; the density exceeds the display range, so the contrast curve is adjusted.
   • D.The receptor was underexposed; the lost signal is unrecoverable in software, so the image is retaken.✓ Answer

   Overall density is governed by milliamperage and exposure time. An overexposed digital image usually still contains the diagnostic signal and can be rescued by adjusting display density, but an underexposed receptor never recorded enough signal, so amplifying it in software only amplifies noise. The exposure factors must be corrected and the image repeated.

   Source: Iannucci & Howerton, Dental Radiography: Principles and Techniques — exposure factors and digital image densityReport a problem with this question

3. 3. After switching to rectangular collimation with a beam-alignment ring, an assistant obtains a molar bitewing with a sharply defined white, unexposed band running the full length of one border of the image. What is the appropriate correction?

   • A.Raise the exposure setting one step to fill in the pale band, then reprocess the image in the software.
   • B.Re-seat the ring on the indicator rod and center the position-indicating device on the receptor, then retake.✓ Answer
   • C.Shift the horizontal angulation so the central ray passes through the contacts, then expose the region again.
   • D.Increase the vertical angulation of the tubehead a few degrees and expose the same receptor a second time.

   A cone cut is a centering error: part of the receptor lay outside the beam and received no radiation, which on a digital image appears as a clear white area with an edge matching the collimator shape. Rectangular collimation leaves very little margin, so the correction is to align the position-indicating device with the beam-alignment ring over the receptor. Changing vertical or horizontal angulation corrects a different fault and will not fill the band.

   Source: Iannucci & Howerton, Dental Radiography: Principles and Techniques — cone cut and beam alignment devicesReport a problem with this question

4. 4. A periapical of the mandibular anterior teeth shows the incisors stretched and disproportionately long, with the apical regions running off the edge of the image. What error occurred and how is it corrected?

   • A.Horizontal angulation was off, so the central ray is redirected through the open contacts before retaking.
   • B.The receptor was too close to the teeth, so it is moved toward the midline before it is exposed again.
   • C.Vertical angulation was too great, so it is decreased before the receptor is exposed a second time.
   • D.Vertical angulation was too small, so it is increased before the receptor is exposed a second time.✓ Answer

   Elongation is a vertical angulation error in which the central ray is directed too flat, closer to the long axis of the teeth than to the bisector, so the projected image is stretched. Increasing the vertical angulation restores true length; decreasing it would produce the opposite fault, foreshortening. Horizontal angulation controls the proximal contacts, not tooth length.

   Source: Iannucci & Howerton, Dental Radiography: Principles and Techniques — vertical angulation errors (elongation and foreshortening)Report a problem with this question

5. 5. A maxillary molar periapical shows the crowns and most of the roots, but the apices are cut off along the top edge, while a wide strip of the opposing mandibular teeth appears along the bottom. What is the correction?

   • A.Slide the receptor forward toward the anterior teeth so that more of the arch is captured on it.
   • B.Decrease the vertical angulation several degrees so the apices are projected onto the receptor.
   • C.Increase the exposure time so that the thin apical bone registers on the receptor during the retake.
   • D.Move the receptor deeper toward the palate and re-seat the bite block on the teeth being imaged.✓ Answer

   Missing apices with an excess of the opposing arch on the image means the receptor was not carried far enough into the palate or the bite block was resting on the opposing teeth, so the receptor did not extend beyond the apices. A diagnostic periapical must show the apices with a margin of surrounding bone, and that is achieved by repositioning the receptor and holder rather than by changing angulation or exposure.

   Source: Iannucci & Howerton, Dental Radiography: Principles and Techniques — receptor placement criteria for periapical imagesReport a problem with this question

6. 6. In a maxillary premolar periapical taken with a paralleling holder, the occlusal plane slants steeply across the image and the crowns are bunched into one corner. The patient has a shallow palate. What should the operator do?

   • A.Move the receptor away from the teeth toward the midline of the palate so it parallels their long axes.✓ Answer
   • B.Press the receptor firmly against the palatal surfaces so it cannot shift while the patient bites down.
   • C.Raise the vertical angulation until the occlusal plane looks level, leaving the receptor where it is.
   • D.Bend the upper corner of the receptor away from the palate so the patient can close on the bite block comfortably.

   In the paralleling technique the receptor must stand parallel to the long axes of the teeth. A shallow palate makes the receptor contact the palatal vault and tip, which tilts the occlusal plane on the image; moving the receptor toward the midline of the palate gives it room to stand upright. Bending a phosphor plate creases it permanently and distorts the image, and angulation changes do not restore parallelism.

   Source: Iannucci & Howerton, Dental Radiography: Principles and Techniques — paralleling technique and receptor placementReport a problem with this question

7. 7. A patient bites down hard on a phosphor plate. The resulting image shows distorted anatomy plus a sharp thin white line, and the same line reappears in the identical position on every later image made with that plate. What is the correct action?

   • A.Take the plate out of use and replace it, because the crease permanently damaged the phosphor layer.✓ Answer
   • B.Rescan the plate at a higher resolution setting, since the scanner's optics produced the white line.
   • C.Erase the plate through two full light-box cycles, which clears the retained artifact from the phosphor.
   • D.Clean the plate with an alcohol-soaked gauze square, which lifts the debris causing the white line.

   A crease or scratch physically breaks the phosphor layer, so no signal is recorded along that line. Because the defect is in the receptor itself, it reproduces on every image made with that plate and cannot be removed by rescanning, erasing or cleaning; the plate is discarded and replaced, and the affected image is retaken.

   Source: Imaging Science in Dentistry (2019) classification of photostimulable phosphor plate artifacts — plate defectsReport a problem with this question

8. 8. Several exposed phosphor plates are left on the counter in a lighted operatory for a while before scanning. The resulting images look washed out and faded, with density lost most heavily along the edges. What explains this?

   • A.The plates were exposed at too low a milliamperage, so little signal was stored in the phosphor.
   • B.The plates sat in room light, which released part of the stored latent image before scanning.✓ Answer
   • C.The scanner's erasing lamp failed, so signal from an earlier patient remained on the plates.
   • D.The plates were wiped with a disinfectant whose residue blocked the laser during the readout.

   The latent image on a phosphor plate is stored energy that is released by light, which is exactly how the scanner reads and erases it. Ambient room light between exposure and scanning bleeds that energy off, giving faded, washed-out images with the greatest loss where light reached the plate first. Exposed plates are kept in light-tight containers and scanned promptly.

   Source: Imaging Science in Dentistry (2019) classification of photostimulable phosphor plate artifacts — ambient light artifactsReport a problem with this question

9. 9. Every image scanned this morning, on several different plates and from several different patients, shows the same thin white line in the same position across the image. What does this pattern indicate?

   • A.The x-ray unit's timer is failing and interrupts the beam at the same point each time.
   • B.The plates are underexposed, and the software inserts a line where data are missing.
   • C.A fault in the scanner itself, such as debris or damage in its optical path, is marking each image.✓ Answer
   • D.A scratch in the phosphor of one plate is reproduced whenever that same plate is used.

   Localizing an artifact means asking what all the affected images have in common. A defect confined to one receptor follows only that receptor, but an artifact that repeats in the same place across different plates and different patients comes from the shared readout device, so the scanner's optical path is cleaned or serviced according to the manufacturer's instructions.

   Source: Imaging Science in Dentistry (2019) classification of photostimulable phosphor plate artifacts — scanner errorsReport a problem with this question

10. 10. A newly exposed phosphor plate image shows the expected periapical anatomy plus a faint second set of tooth outlines from a different region that does not belong to this patient. The plate was exposed only once. What caused this?

    • A.The plate was placed backward, and the pattern comes from behind its lead foil backing.
    • B.The plate was scanned twice, and the scanner merged the two readings into a single file.
    • C.The plate was stored beside another exposed plate, and signal transferred between them.
    • D.The plate was not erased after its previous scan, so residual signal from that earlier image remained.✓ Answer

    A phosphor plate retains its latent image until the stored energy is released by light, so plates are erased with a light source or the scanner's erase cycle after every reading. If that step is skipped or the erase setting is too weak, residual signal from the previous exposure remains and superimposes on the next image as a faint ghost. Signal does not migrate between plates.

    Source: Imaging Science in Dentistry (2019) classification of photostimulable phosphor plate artifacts — incomplete erasure and residual imagesReport a problem with this question

11. 11. A maxillary anterior periapical shows a dense, smoothly outlined radiopaque shadow superimposed over the incisor crowns, hiding the incisal edges. The patient is still wearing eyeglasses and a lip piercing. What is the correct response?

    • A.Change the horizontal angulation to project the shadow clear of the crowns, and retake.
    • B.Adjust the software contrast until the shadow fades, and read the incisal edges through it.
    • C.Remove the eyewear and the lip piercing, note the reason for the retake, and expose the region again.✓ Answer
    • D.Lower the exposure setting so the metal appears less dense, and expose the region again.

    Metal and other dense objects in the path of the beam absorb radiation and cast radiopaque shadows that hide the anatomy beneath them; because no signal was recorded there, no software adjustment or exposure change can recover it. Eyewear, jewelry, piercings and removable appliances in the field are taken out before exposure, and the retake and its reason are entered in the record.

    Source: Iannucci & Howerton, Dental Radiography: Principles and Techniques — patient preparation and radiopaque foreign-object artifactsReport a problem with this question

12. 12. Two phosphor plates from one full-mouth series come back as a pair: one carries two superimposed sets of teeth from different regions, and the other is completely blank. What happened, and how is it prevented?

    • A.One plate was fogged by room light while another was erased; plates are stored in a light-tight container.
    • B.One plate was exposed twice while another was never exposed; exposed and unexposed plates are kept apart.✓ Answer
    • C.One plate was bent during placement while another cracked; damaged plates are pulled from the set daily.
    • D.One plate was scanned twice while another was never scanned; the scanner queue is cleared between patients.

    Unlike a corded solid-state sensor, a phosphor plate can be re-inserted and exposed a second time, which produces one plate with two superimposed images and leaves a second plate unexposed and blank. The fault always appears as this pair, and it is prevented by keeping exposed receptors physically separated from unexposed ones during the series; both regions must then be retaken.

    Source: Iannucci & Howerton, Dental Radiography: Principles and Techniques — double exposure and receptor handling during a seriesReport a problem with this question

13. 13. A periapical is blurred throughout: the trabecular pattern and the outlines of the restorations are indistinct. The tubehead was checked and holds its position without drifting. What is the appropriate corrective step?

    • A.Shorten the exposure time by one step and expose again, since the blur comes from excess density.
    • B.Re-instruct the patient to hold completely still, confirm the holder is secure, and expose again.✓ Answer
    • C.Sharpen the image with the software filter, since the anatomy recorded on the receptor is intact.
    • D.Increase the vertical angulation slightly and expose again, since the blur is an angle distortion.

    Generalized blurring means the receptor and the anatomy moved relative to each other during the exposure. With the tubehead verified as stable, the source is patient or receptor movement, so the patient is re-instructed and the receptor is stabilized in a holder before the retake. Sharpening filters cannot restore detail the receptor never recorded, and blur is neither a density nor an angulation fault.

    Source: Iannucci & Howerton, Dental Radiography: Principles and Techniques — movement (blurred image) errorsReport a problem with this question

14. 14. A CMOS sensor has begun producing intermittent dropouts and streaked images, and the failures grow more frequent as the day goes on. Staff routinely coil the cable tightly around the sensor for storage. What is the best explanation and remedy?

    • A.Strain at the cable-to-sensor junction damages the conductors; the cable is stored loosely coiled.✓ Answer
    • B.The sensor overheats inside its barrier; it is left uncovered between patients so it cools.
    • C.The imaging software needs reinstalling; the workstation is restarted between patients.
    • D.Static builds in the coiled cable and adds streaks; it is wiped with a damp cloth before use.

    The cable and the point where it enters the sensor housing are the most fragile part of a corded receptor, and repeated kinking, pulling or tight coiling breaks conductors, which shows up as intermittent dropouts and streaking. Cables are handled gently, never wrapped tightly, and stored loosely coiled as directed by the manufacturer's instructions for use.

    Source: White & Pharoah, Oral Radiology: Principles and Interpretation — care and handling of solid-state digital receptorsReport a problem with this question

15. 15. At the end of an intraoral series, the assistant must reprocess the solid-state sensor and the plastic beam-alignment holders used with it. Which handling is correct?

    • A.Immerse the sensor and the holders in a high-level disinfectant, then rinse and dry them.
    • B.Wipe the sensor and the holders with a surface disinfectant, since both are noncritical items.
    • C.Barrier and surface-disinfect the sensor per its instructions, and heat-sterilize the holders.✓ Answer
    • D.Heat-sterilize the sensor along with the holders, since both contacted mucous membranes today.

    Digital sensors and phosphor plates contact mucous membranes but cannot withstand heat sterilization or immersion, so they are covered with an FDA-cleared barrier during use and then cleaned and disinfected according to the manufacturer's instructions for use. Holders, bite blocks and alignment rings are heat-tolerant semicritical items and must be heat-sterilized between patients.

    Source: CDC Guidelines for Infection Control in Dental Health-Care Settings (2003) — digital radiography sensors and semicritical instrumentsReport a problem with this question

16. 16. The imaging workstation's keyboard and mouse sit at chairside and are touched with gloved hands during the imaging appointment. Which approach to these surfaces is correct?

    • A.Spray them with an intermediate-level disinfectant after each patient and let the solution air-dry.
    • B.Leave them uncovered and have the assistant remove one glove before touching them during exposures.
    • C.Cover them with barriers, change the barriers between patients, and disinfect if a barrier is breached.✓ Answer
    • D.Send them for heat sterilization at the end of each clinical day, since gloved hands touch them.

    Keyboards and mice are clinical contact surfaces: they are touched with contaminated gloves but are irregular, hard to clean and easily damaged by liquid, so barrier protection that is changed between patients is the preferred method. Cleaning and disinfection is reserved for when a barrier is breached or the surface becomes visibly contaminated, and electronic devices are never heat-sterilized.

    Source: CDC Summary of Infection Prevention Practices in Dental Settings (2016) — clinical contact surfaces and surface barriersReport a problem with this question

17. 17. Between patients, the tubehead, the position-indicating device, the extension arm and the exposure control panel must be reprocessed. How are these surfaces correctly handled?

    • A.They are clinical contact surfaces: barriers are replaced, or the surfaces are cleaned and disinfected.✓ Answer
    • B.They are semicritical items: each is pouched and heat-sterilized at the end of the clinical day.
    • C.They are housekeeping surfaces: a detergent wash at the end of the day is enough, not cleaning between patients.
    • D.They are critical items: each is scrubbed and then immersed in a chemical sterilant between patients.

    The tubehead, position-indicating device, extension arm, control panel and exposure button are touched by gloved hands or contacted by spatter during imaging, which makes them clinical contact surfaces rather than housekeeping surfaces. They are managed either with barriers replaced between patients or by cleaning followed by an EPA-registered hospital disinfectant, because these fixed components cannot be heat-sterilized or immersed.

    Source: CDC Summary of Infection Prevention Practices in Dental Settings (2016) — environmental infection prevention and control of dental radiography equipmentReport a problem with this question

Practice questions only — not real exam items, and not affiliated with or endorsed by the Dental Assisting National Board. Questions are written to the domains published in DANB's current RHS and ICE exam outlines, and cover digital radiography only, matching DANB's statement that film-based concepts are no longer tested. This bank does not cover the chairside assisting or dental anatomy component exams. What a dental assistant is legally allowed to do — including who may expose radiographs and what training a state requires first — is set by each state's dental board and is deliberately out of scope here. Exam format, eligibility, and scoring are set by DANB and change from time to time; confirm the current requirements with DANB and your state board before you register. Official DANB exam outlines →