DANB RHS study guide, domain by domain

On images of an 8-year-old with mixed dentition, which finding indicates normal development?

Pick the option you would mark on test day. The choice stays fixed, and every option then explains itself.

1. No primary teeth remaining in either arch

   Primary molars and canines are normally still present at 8; their absence would point to early loss, not normal development.
2. Permanent tooth buds below primary roots

   In mixed dentition the developing permanent teeth sit beneath the roots of the primary teeth they will replace, which is the expected picture at age 8.
3. Fully formed third molar crowns

   Third molar crowns only begin to calcify around ages 8 to 10 and finish years later, so complete crowns at 8 would be unusual.
4. Complete root formation on all permanent teeth

   Complete root formation on all permanent teeth comes in the teen years; at 8 even the first molars and incisors are still finishing their roots.

Why must imaging software keep each digital image exactly as it was captured?

1. Edited copies lose the patient ID

   Edited copies keep the patient data attached in imaging software, so losing the ID is not the reason.
2. PSP plates are erased from the saved file

   PSP plates are erased by bright light in the scanner after they are read, independent of the saved file.
3. Unaltered files form the legal record

   Unaltered files form the legal record of the examination; enhanced copies are fine for viewing, but the captured image itself must not be overwritten.
4. Enhanced copies print poorly on paper

   Enhanced copies print and share like any other image; print quality is not why the captured version is kept.

After a maxillary molar extraction, a root tip may be displaced into the sinus. Which image best localizes it in three dimensions?

1. Repeat periapical of the extraction site

   A repeat periapical is a two-dimensional view; it can show the fragment but not its depth relative to the sinus floor.
2. Panoramic image of both jaws

   A panoramic image is two-dimensional and distorted in the sinus region, so it does not show the fragment's depth relative to the sinus floor.
3. Maxillary topographic occlusal image

   An occlusal view adds a different angle but is still a flat projection, not a three-dimensional localization.
4. Limited-field CBCT of the region

   A limited-field CBCT shows the root tip in three planes, so its position relative to the sinus floor can be located with the smallest field that answers the question.

With a tungsten target, characteristic radiation from the K shell is produced only when the operating voltage exceeds approximately:

1. 70 kVp

   Tungsten's K-shell electrons are bound at about 69.5 keV, so K-shell characteristic radiation appears only once the tube runs at roughly 70 kVp or higher.
2. 50 kVp

   At 50 kVp the electrons lack the energy to eject tungsten K-shell electrons, so the useful beam is braking (bremsstrahlung) radiation.
3. 90 kVp

   90 kVp is above the threshold, but characteristic radiation already begins near 70 kVp, so 90 is not the point where it starts.
4. 100 kVp

   100 kVp is far above the K-shell binding energy; choosing it confuses the usual upper range of dental units with the threshold.

Radiation is detected coming through the tubehead housing rather than out of the PID opening. Which type of radiation is this?

1. Scatter radiation

   Scatter radiation is deflected from its path when the beam strikes the patient's tissues; it does not come from inside the housing.
2. Primary radiation

   Primary radiation is the useful beam that exits through the PID opening, not radiation passing through the housing walls.
3. Leakage radiation

   Leakage radiation is any radiation escaping through the tubehead housing other than the useful beam; 21 CFR 1020.30(k) caps it at 0.88 mGy air kerma in 1 hour at 1 meter, and a reading above that means the unit needs service.
4. Secondary radiation

   Secondary radiation is created when the primary beam interacts with matter such as the patient's tissues, not inside the tubehead.

While a digital series is being exposed, which practice best keeps the computer free of contamination?

1. Clicking the mouse with contaminated gloves, then wiping it at noon

   Touching the mouse with gloves from the mouth contaminates it for every patient seen before the midday wipe.
2. Touching the keyboard only with the gloved little finger

   Touching the keyboard with the gloved little finger still carries saliva from the mouth onto the keys.
3. Running the software with a foot pedal or a clean-handed helper

   A foot pedal or a helper with clean hands keeps gloves that touched the mouth away from the mouse and keyboard altogether.
4. Disinfecting the mouse and keyboard once at the end of the day

   A single end-of-day disinfection leaves the computer contaminated between patients all day.

When imaging a bedridden patient in a nursing facility with a handheld unit, infection control precautions should be:

1. Identical to those used in the dental office

   Identical precautions apply because standard precautions cover every patient in every setting: a bedside handheld exam uses the same barriers, gloves and disinfection as the office.
2. Limited to hand hygiene between residents

   Hand hygiene is necessary but leaves the sensor, holder and handheld unit unprotected between residents.
3. Lighter than in the dental office

   Lighter precautions than in the dental office ignore that saliva and contaminated receptors spread infection the same way at a bedside.
4. Left to facility housekeeping staff

   Leaving it to facility housekeeping staff covers the room, but the radiographer is responsible for the barriers and equipment used on the patient.

Placing a latex finger cot over a digital sensor before its barrier sleeve has been shown to:

1. Eliminate the need for disinfecting the sensor

   Sleeves can fail, so the sensor is still cleaned and disinfected after each patient even with a finger cot underneath.
2. Lower the exposure time the sensor needs

   A thin latex layer has no effect on the exposure the sensor requires.
3. Improve the contrast of the digital image

   Contrast depends on exposure settings and image processing, not on the barrier around the sensor.
4. Reduce leakage of saliva onto the sensor

   A finger cot under the sleeve adds a second layer, which has been shown to reduce saliva reaching the sensor through tears or the opening of the sleeve.

The quantity of x-rays in the beam is controlled mainly by:

1. Filtration and collimation

   Filtration removes weak photons and collimation trims the beam size; neither is the main control of how many photons are produced.
2. Milliamperage and exposure time

   Milliamperage sets how many electrons cross the tube per second and time sets for how long, so together they determine the number of x-ray photons.
3. Collimation and PID length

   Collimation and PID length shape and direct the beam; they do not set how many photons the tube produces.
4. Kilovoltage peak and filtration

   Kilovoltage peak mainly sets photon energy, and filtration removes weak photons; neither is the main control of beam quantity.