CDA common mistakes
CDA · Understand the traps and how to avoid them.
Answers water-to-powder questions by a general rule ('more water = sets faster') without separating alginate from gypsum, so items about setting time, setting expansion, and spatulation are answered backwards.
Candidates memorize 'spatulate faster to make it set faster' and then over-apply it, because both materials are powders mixed with water and the two systems are studied in the same sitting.
What to do instead
Build a four-column table (material | what speeds setting | what slows setting | what the water ratio actually controls) and fill in alginate (cooler water, thicker mix, faster gelation; more water = weaker, slower set) versus gypsum (spatulation, water ratio, slurry water, accelerators/retarders; more water = longer set, less strength, less expansion). Recite the two rows from memory before answering any mixing item.
Identifies instruments by picture recognition only and then mixes up look-alike pairs - explorer vs. periodontal probe, sickle scaler vs. universal curette, spoon excavator vs. hatchet, amalgam carrier vs. condenser - selecting the wrong name for a described function.
Study time is spent flipping flashcards of instrument photos, so the visual shape is stored without the function, working-end design, or the task it performs.
What to do instead
Study function-first: for each instrument write one sentence on what it does and one distinguishing design feature (probe has millimeter markings and a blunt tip; explorer has a sharp flexible point; curette has a rounded back and two cutting edges). Then cover the names and identify from the written function, not the picture.
Puts the steps of a Class II restorative procedure out of order - placing etchant after the bonding agent, seating the wedge or matrix after material placement, or light-curing before the material is condensed - when asked to sequence a procedure.
Candidates know each step exists but learn them as a list of vocabulary words rather than as a dependent sequence, so any distractor that names a real step looks plausible.
What to do instead
Write out three procedures (amalgam Class II, composite Class II, crown seat) as numbered flows with the reason for each order (etch creates micromechanical retention before bonding; wedge protects the adjacent tooth and holds the matrix; cure after condensing). Practice by explaining the sequence aloud and justifying each step to yourself.
Chooses the saliva ejector for procedures that need high-volume evacuation, and cannot state where the HVE tip is positioned relative to the tooth being treated.
Both devices are 'the suction' in casual clinic talk, so the distinction between removing pooled fluids at low volume and removing water spray, saliva, and aerosols at high volume never gets encoded.
What to do instead
Learn the pair as a contrast: saliva ejector = low volume, patient comfort, pooled fluid, does not handle handpiece coolant or aerosol; HVE = high volume, used with the water-cooled handpiece, tip placed on the surface adjacent to the operating site. Rehearse two clinical scenarios (long crown prep, sealing a lower molar) and name the device and tip position for each.
Treats kVp and mA as interchangeable 'exposure knobs' - for example stating that increasing mA increases subject contrast, or that raising kVp only makes the film darker.
Both are described as exposure settings on the control panel, and the candidate never separates the quality of the beam from the quantity of photons.
What to do instead
Fix two sentences in memory: mA controls quantity of x-rays and therefore overall density/blackening; kVp controls penetrating power and therefore the scale of contrast (higher kVp = more grays, lower contrast). Then practice two-step reasoning: 'which knob changes contrast?' and 'which knob changes the number of photons?' before answering.
Reverses elongation and foreshortening, or matches them to the wrong angulation error, when asked what caused a distorted image.
The words sound like the image appearance rather than the tooth, and both distortions come from the same vertical angulation variable, so they are stored as one blurry concept.
What to do instead
Reason from geometry rather than memorizing labels: too little vertical angulation (or the receptor not parallel to the long axis) stretches the image, so the tooth looks long = elongation; too much vertical angulation compresses it, so the tooth looks short = foreshortening. Link each word to its first letter: too little angulation -> long image; too much -> short image, then apply it to a described error.
Misreads receptor orientation and mounting cues - calling a herringbone pattern an exposure error instead of a receptor placed backwards, or mounting so the embossed dot ends up concave/away from the occlusal edge.
The embossed dot and the herringbone artifact are taught as trivia facts once, without a rule the candidate can re-derive at the exam.
What to do instead
Attach the cause to each image sign: herringbone/tire-track pattern = receptor placed backwards (tube side away from the beam), so re-expose with the correct side; double image = double exposure; clear/blank = no exposure. For mounting, state the rule as 'dot convex and toward the occlusal/incisal edge as the patient would view it,' and check every mount question against that rule.
Applies the wrong level of disinfection because items are classified by what they are made of rather than by how they are used - wiping a semicritical item with a low-level or intermediate-level disinfectant, or soaking a housekeeping surface in glutaraldehyde.
The Spaulding categories are learned as a list of example items instead of a decision rule, so anything that looks like 'just a surface' gets a disinfectant wipe regardless of contact with mucosa or blood.
What to do instead
Use the three-question rule on every item: does it enter tissue or the bloodstream (critical -> sterilize), does it touch intact mucous membrane (semicritical -> sterilize or high-level disinfect), does it only touch intact skin or environmental surfaces (noncritical -> low/intermediate disinfectant or a barrier). Sort ten items with the rule and note the disinfectant level you selected and why.
Sends handpieces and burs to the sterilizer without cleaning debris out of the chuck or flutes, or leaves them soaking in a chemical disinfectant instead of processing them for sterilization between patients.
The candidate focuses on 'autoclave = sterile' and forgets that steam cannot penetrate blood, composite, or amalgam debris, and treats handpieces as delicate equipment that should be chemically wiped rather than heat-sterilized.
What to do instead
Memorize the chain as clean -> lubricate/flush per manufacturer -> bag -> sterilize, and state that debris left in a bur block or chuck protects microorganisms from steam. Practice explaining in one sentence why cleaning must precede sterilization, and note that heat-tolerant handpieces and all burs are sterilized between patients.
Gets biological monitoring facts wrong - states that a spore test is run daily or per load, or fails to say what happens to loads already released when a spore test comes back positive.
Spore testing is filed under 'quality assurance' trivia, so the interval and the follow-up action are memorized loosely or not at all.
What to do instead
Fix one sentence: spore test at least weekly with a control, and a positive result means the sterilizer is taken out of service, the loads since the last negative test are recalled and reprocessed (or the exposure evaluated), and the cause is corrected before reuse. Say that sentence through once, then answer any monitoring item by checking it against those three elements: interval, control, and recall action.