NZDREX common mistakes
NZDREX · Understand the traps and how to avoid them.
Choosing an irreversible treatment (extraction, endodontic treatment, or a crown) in a scenario where the history and clinical findings support a reversible or more conservative option, without documenting why the conservative path was rejected.
Candidates pattern-match the most dramatic finding in the vignette (a deep pocket, a radiolucency, a cracked cusp) and jump to the definitive treatment, forgetting that NZDREX-style scenarios test the decision hierarchy: prevention and minimal intervention first, then reversible care, then irreversible care. Time pressure pushes candidates to commit early rather than weigh alternatives.
What to do instead
For every treatment-planning item, write a one-line justification for the chosen option and a one-line reason each less invasive option was excluded. If you cannot articulate why the conservative option fails, it probably does not. Practise ranking options on an invasiveness ladder before selecting.
Building a treatment plan that ignores the patient's stated chief complaint, medical history, or financial and time constraints, producing a technically ideal but unworkable sequence.
Candidates treat planning as a list of ideal procedures and forget that the plan must be sequenced (emergency phase, disease control, reassessment, definitive care, maintenance) and must fit the patient. Medical factors such as anticoagulants, bisphosphonates, uncontrolled diabetes, or smoking status are noted but not acted on.
What to do instead
Use a fixed planning template: chief complaint, medical and social history with implications, disease-control phase, reassessment point, definitive phase, maintenance. For each medical finding, state the concrete modification it forces (for example, timing of extraction relative to anticoagulant management, or deferring implants until glycaemic control is confirmed).
Preparing a cavity that is deeper or wider than the caries requires, or failing to remove all infected dentine at the enamel-dentine junction while over-preparing the pulpal floor.
Candidates confuse 'remove all caries' with 'remove all stained dentine', and they lack a clear rule for when residual affected dentine is acceptable. Without a structured excavation endpoint, they either leave soft infected tissue peripherally (risking failure and sensitivity) or chase stained dentine to the pulp.
What to do instead
State the endpoint explicitly: infected, soft, wet, leathery dentine removed; firm, dry, stained affected dentine may remain on the pulpal floor in a vital tooth. Excavate peripherally first to establish the enamel-dentine junction, then work centrally. Check with a sharp excavator and consider caries-detector dye only as an adjunct, not a substitute for tactile assessment.
Selecting and placing a restorative material without matching it to the cavity classification, moisture control achievable, and occlusal load, and without correct adhesive protocol (etch pattern, primer/solvent, rubbing, air-thinning, curing).
Candidates memorise material properties in isolation but do not connect them to the clinical situation (for example, a universal adhesive used in the wrong mode, or resin composite placed in a load-bearing posterior region without adequate thickness). Adhesive steps are rushed and air-thinning is skipped, leaving solvent and a weak bond.
What to do instead
Before choosing a material, name the cavity class, the isolation achievable, and the expected load. Then state the adhesive mode and justify it. Rehearse the sequence aloud: etch time, rinse, moisture state, primer application with agitation, air-thin until no movement, cure time and intensity. For posterior composites, confirm minimum thickness and cuspal coverage decisions.
Committing to a diagnosis of pulpal and periapical status from a single test or radiograph, rather than integrating cold/EPT results, percussion, palpation, probing, and radiographic findings, and failing to distinguish pulpal from periapical diagnoses.
Candidates conflate the two diagnosis axes and treat a positive percussion test as proof of irreversible pulpitis, or treat a radiolucency as proof of a non-vital pulp. They also misread false negatives (calcified canal, recent trauma, immature apex) as evidence of necrosis.
What to do instead
Always record two separate diagnoses: pulpal (normal, reversible pulpitis, irreversible pulpitis, necrosis, previously treated) and periapical (normal, symptomatic apical periodontitis, asymptomatic apical periodontitis, acute apical abscess, chronic apical abscess, condensing osteitis). Justify each with the specific test that supports it and note any test you consider unreliable and why.
Describing canal preparation and obturation in vague terms ('clean and shape, then fill') without specifying working length determination, apical limit, irrigation protocol, patency, and the obturation endpoint and technique.
Candidates learn the concept of cleaning and shaping but not the operational details that determine success, and they underestimate the effect of the apical limit and irrigant activation on outcomes. Under exam pressure they default to generalities.
What to do instead
For any endodontic item, state: working length method (apex locator confirmed radiographically), apical preparation size rationale, irrigant type, concentration, volume and activation, use of a chelator, patency file use, and obturation technique with the acceptable limit (for example, 0.5 to 1 mm short of the radiographic apex) and the criteria for a satisfactory fill.
Classifying periodontal disease by pocket depth alone, omitting clinical attachment loss, bleeding on probing, plaque/calculus distribution, and risk factors, and then proposing a maintenance interval without reference to risk.
Candidates equate deep pockets with severe disease and shallow pockets with health, ignoring attachment loss, recession, and the staging/grading logic that depends on interdental attachment loss, tooth loss from periodontitis, complexity factors, and risk progression.
What to do instead
Record a full six-point chart with probing depths, recession, attachment loss, bleeding on probing, mobility, furcation involvement, and plaque scores. Then state stage (severity and complexity) and grade (rate of progression and risk) with the specific data supporting each. Set the maintenance interval from the risk profile, not from a default.
Designing a removable partial denture or fixed prosthesis without first assessing the remaining dentition's prognosis, abutment suitability, occlusal scheme, and the need for a surveyor-style path of insertion analysis.
Candidates focus on the missing teeth and the prosthesis itself, treating the remaining teeth as passive supports. They omit rest seat design, clasp selection, major connector choice, and the consequences for the abutments, or they plan a bridge across teeth of poor prognosis.
What to do instead
Before designing, list each remaining tooth with its prognosis and its role (abutment, strategic, extract). Then state the path of insertion, rest seat locations and form, clasp type and rationale, major connector choice with justification, and the occlusal scheme. For fixed work, confirm the abutment teeth can tolerate the load and that the design permits cleaning and repair.
Planning an implant without assessing bone volume and density, soft tissue quality, occlusal load, and the patient's medical and smoking risk, and without considering the restorative-driven position or the surgical guide.
Candidates treat implants as a default replacement and skip the diagnostic sequence that determines whether an implant is appropriate and where it must sit. They consider only the surgical site and not the prosthetic outcome, and they underestimate the effect of smoking, uncontrolled diabetes, or a history of periodontitis on survival.
What to do instead
Work backwards from the planned crown: define the ideal implant position, then check whether bone and soft tissue allow it. State bone volume and density assessment method, the need for grafting or a staged approach, the surgical guide plan, and the medical and behavioural risk factors with their management. Include a maintenance plan and a contingency if the site proves inadequate.
Selecting an aesthetic material or shade without considering optical properties, translucency, thickness, and the underlying substrate, or placing an aesthetic restoration without verifying occlusion and margins.
Candidates choose shade by eye alone and ignore that final appearance depends on substrate colour, material thickness, opacity, and the presence of a bonding layer. They also treat aesthetics and function as separate, finishing the aesthetic work without checking contacts and excursive movements.
What to do instead
For aesthetic items, state the substrate, the planned material with its thickness and translucency, the shade-taking method and lighting conditions, and how the substrate will be masked if needed. After placement, verify margins, contacts, and excursive clearance before polishing, and document the occlusal check.
Answering ethics or professionalism items with a general statement about doing the right thing, rather than naming the specific obligation, the correct process, and the required documentation and disclosure.
Candidates know the ethical principles but not how they translate into action in a concrete scenario: informed consent, confidentiality limits, managing a mistake, dealing with an impaired colleague, or a conflict of interest. They give principled-sounding answers that do not resolve the scenario.
What to do instead
For each ethics item, identify the competing obligations, name the governing principle or professional standard, then state the concrete action, who must be informed, what must be documented, and the timeframe. Where a mistake has occurred, state the duty of candour: disclose to the patient, document, and follow the practice's adverse-event process.
Describing infection control in general terms ('follow standard precautions') without specifying the correct sequence for hand hygiene, PPE donning and doffing, instrument reprocessing, or the distinction between single-use and reusable items.
Candidates learn infection control as background knowledge and do not rehearse the operational sequence, so they cannot identify the specific breach in a scenario or the correct corrective step. They also confuse cleaning, disinfection, and sterilisation.
What to do instead
Memorise and rehearse the sequences: hand hygiene moments, PPE order, instrument transport, cleaning, inspection, packaging, sterilisation cycle parameters, and storage. Be able to state the classification of an item (critical, semi-critical, non-critical) and the minimum reprocessing it requires, and identify the exact step where a described breach occurred.