Evidence, and a Patient Irradiated Ten Years Ago

Correct answer: B. Refer to an oral and maxillofacial surgeon for management, with consideration of hyperbaric oxygen or antibiotic protocols

• A. There is no basis for a six-month interval, and delay simply allows the infection to progress.
• B. CORRECT. Radiation-induced changes in bone are PERMANENT and do not resolve with time. The irradiated mandible is hypocellular, hypovascular and hypoxic, so any surgical wound risks OSTEORADIONECROSIS. At a dose above 60 Gy to the posterior mandible the risk is substantial and lifelong. The correct step is specialist referral for atraumatic surgical technique, primary closure, prophylactic antibiotics, and consideration of hyperbaric oxygen or the alternative pentoxifylline-tocopherol protocol.
• C. The passage of time does NOT restore the vascularity of irradiated bone. Ten years does not make routine extraction safe — this is the central misconception the item is testing.
• D. Non-restorable teeth with periapical lesions cannot be maintained on antibiotics. Chronic infection in irradiated bone is itself a trigger for osteoradionecrosis.

Note: The rule for irradiated patients is that dental extractions should ideally be completed at least 2–3 weeks BEFORE radiotherapy begins. Afterwards, prevention becomes everything: daily 5000 ppm fluoride, meticulous hygiene, saliva management, and avoiding elective surgery in the field for life. ORN affects the posterior MANDIBLE overwhelmingly, because it receives the highest dose and has the poorest collateral supply.

Correct answer: C. Case-control study

• A. A systematic review with meta-analysis sits at the TOP of the evidence hierarchy — a comprehensive, pre-specified synthesis of all eligible studies.
• B. The RCT is the strongest primary design. Randomization distributes confounders, known and unknown, between groups.
• C. CORRECT of the designs listed. A CASE-CONTROL study is RETROSPECTIVE and observational: it identifies people who already have the outcome, matches them with controls, and looks backwards for exposure. It is therefore highly vulnerable to RECALL BIAS and SELECTION BIAS, cannot establish temporal sequence with confidence, and yields an odds ratio rather than a true risk. It is efficient for rare diseases and long latency periods, but it sits low in the hierarchy.
• D. A prospective cohort follows exposed and unexposed groups FORWARD to the outcome. It establishes temporality and calculates true relative risk, making it stronger than case-control.

Note: The hierarchy, top to bottom: systematic review and meta-analysis > randomized controlled trial > cohort > case-control > case series and case reports > expert opinion. Note that CASE REPORTS and EXPERT OPINION are weaker still than case-control — if they appear as options, they take the bottom place.

Correct answer: D. Population or patient problem

• A. Probability is not a PICO element.
• B. Prognosis is one of the question TYPES a PICO can address, alongside therapy, diagnosis, aetiology and harm — but it is not what the P stands for.
• C. Prevalence is an epidemiological measure, not a PICO element.
• D. CORRECT. P is the POPULATION, patient or problem — who the question is about. The full framework is P (population or problem), I (intervention), C (comparison), O (outcome). A well-formed PICO turns a vague clinical question into a searchable one. Applied here: in irradiated patients requiring mandibular extraction (P), does hyperbaric oxygen (I) compared with antibiotic prophylaxis alone (C) reduce the incidence of osteoradionecrosis (O)?

Note: Some versions add a T for Time or Type of study, giving PICOT. The value of the framework is that it forces you to specify the comparison, which is the element most often left vague.

Correct answer: B. The test indicates disease is present when the patient does not actually have it

• A. That describes a TRUE NEGATIVE.
• B. CORRECT. A FALSE POSITIVE is a positive test result in a person who does NOT have the condition. Its consequences are unnecessary anxiety, further investigation, and sometimes unnecessary treatment — a false positive on a caries-detection device leads to a restoration in sound enamel.
• C. That describes a TRUE POSITIVE.
• D. That describes a FALSE NEGATIVE — the more dangerous error in most clinical settings, because disease goes undetected and untreated.

Note: The formulas, which are worth writing out rather than memorising as strings: SENSITIVITY = TP / (TP + FN) — the proportion of DISEASED people the test correctly identifies, so a sensitive test rules disease OUT when negative (SnNout). SPECIFICITY = TN / (TN + FP) — the proportion of HEALTHY people correctly identified, so a specific test rules disease IN when positive (SpPin). ⚑ Sensitivity is TP/(TP+FN), NOT TN/(TN+FN) — that miswriting circulates in several files in this series.