ORE Part 1 Pharmacology in Dentistry 4 — Questions and Answers
Question 1: What is the mechanism of action of bisphosphonates and why are they relevant in dental practice?
- Inhibit osteoclast function by blocking the mevalonate pathway, reducing bone resorption — dental relevance: MRONJ (medication-related osteonecrosis of the jaw) is a rare but serious complication after extractions (Correct answer)
- Bisphosphonates have no dental relevance
- Bisphosphonates prevent all bone healing in the jaw
- They cause jaw bone overgrowth
Correct answer: Inhibit osteoclast function by blocking the mevalonate pathway, reducing bone resorption — dental relevance: MRONJ (medication-related osteonecrosis of the jaw) is a rare but serious complication after extractions
Bisphosphonates inhibit osteoclasts, reducing bone turnover. MRONJ (medication-related osteonecrosis of the jaw) is a rare but serious complication, especially with IV bisphosphonates (used in metastatic cancer), manifesting as exposed, necrotic jaw bone, often triggered by extractions.
Question 2: Which antibiotic can reduce the efficacy of the combined oral contraceptive pill?
- Current evidence suggests ONLY enzyme-inducing antibiotics (e.g., rifampicin) reduce OCP efficacy — broad-spectrum antibiotics no longer considered to do so per FSRH 2019 guidance (Correct answer)
- All antibiotics reduce OCP efficacy
- Only metronidazole reduces OCP efficacy
- Amoxicillin reliably reduces OCP efficacy
Correct answer: Current evidence suggests ONLY enzyme-inducing antibiotics (e.g., rifampicin) reduce OCP efficacy — broad-spectrum antibiotics no longer considered to do so per FSRH 2019 guidance
FSRH updated guidance (2019): non-enzyme-inducing antibiotics (amoxicillin, metronidazole, etc.) do not significantly reduce OCP efficacy. Only enzyme inducers (rifampicin, some anticonvulsants) require additional contraceptive precautions.
Question 3: What is chlorhexidine's mechanism of action and why is it used in dentistry?
- Cationic bisbiguanide that binds to bacterial cell membranes, disrupting integrity at bactericidal concentrations — used as antimicrobial mouthwash, irrigation, and periodontal gel (Correct answer)
- Kills bacteria by inhibiting cell wall synthesis like penicillins
- Provides fluoride remineralisation
- Acts as a pH buffer to neutralise plaque acids
Correct answer: Cationic bisbiguanide that binds to bacterial cell membranes, disrupting integrity at bactericidal concentrations — used as antimicrobial mouthwash, irrigation, and periodontal gel
Chlorhexidine binds to negatively charged bacterial cell walls, disrupting membrane permeability. At low concentrations it is bacteriostatic; at higher concentrations bactericidal. It has broad-spectrum activity and substantivity (binds to oral surfaces, releasing slowly).
Question 4: A patient with a known penicillin allergy (anaphylaxis) requires a dental antibiotic. Which antibiotic should be avoided?
- All cephalosporins (due to cross-reactivity risk — approximately 1–2% with true anaphylaxis history, though generally amoxicillin is clearly contraindicated) (Correct answer)
- Metronidazole only
- Erythromycin — safe alternatives include clindamycin or metronidazole
- Doxycycline — contraindicated in all allergies
Correct answer: All cephalosporins (due to cross-reactivity risk — approximately 1–2% with true anaphylaxis history, though generally amoxicillin is clearly contraindicated)
In a patient with confirmed anaphylactic penicillin allergy: amoxicillin (penicillin) and cephalosporins (cross-reactivity ~1–2%) should be avoided. Safe alternatives for dental infections include metronidazole, clarithromycin, or clindamycin.
Question 5: What is the rationale for prescribing dexamethasone before lower third molar surgery?
- Prophylactic corticosteroid reduces post-operative trismus, swelling, and pain by suppressing inflammatory mediators before surgical trauma occurs (Correct answer)
- To treat infection preoperatively
- To reduce anaesthetic requirements
- To prevent dry socket
Correct answer: Prophylactic corticosteroid reduces post-operative trismus, swelling, and pain by suppressing inflammatory mediators before surgical trauma occurs
Pre-operative dexamethasone (4–8 mg IM or IV) reduces post-surgical trismus, facial swelling, and pain by pre-emptively suppressing the inflammatory cascade. It is used in third molar surgery and other oral surgical procedures.
Question 6: What is the dental significance of long-term steroid therapy?
- Adrenal suppression may cause an 'adrenal crisis' under surgical stress — doubling of steroid dose ('steroid cover') or consultation with medical team required before invasive procedures (Correct answer)
- No dental significance
- Steroids only affect healing, not emergency risk
- Only relevant if steroids are given intravenously
Correct answer: Adrenal suppression may cause an 'adrenal crisis' under surgical stress — doubling of steroid dose ('steroid cover') or consultation with medical team required before invasive procedures
Long-term systemic steroids suppress the HPA axis (adrenal suppression). Surgical stress cannot trigger the normal cortisol surge, risking Addisonian crisis (hypotension, collapse). Historically, 'steroid cover' was applied; current guidance is more nuanced and patient-specific.
ORE Part 1 Pharmacology in Dentistry 4
What is the mechanism of action of bisphosphonates and why are they relevant in dental practice?