ORE Part 1 Pharmacology in Dentistry 1 — Questions and Answers
Question 1: What is the mechanism of action of articaine, the most widely used local anaesthetic in UK dental practice?
- Blocks voltage-gated sodium channels in the neuronal membrane, preventing action potential propagation and nerve conduction (Correct answer)
- Stimulates GABA receptors to inhibit pain transmission
- Blocks calcium channels to reduce neurotransmitter release
- Acts centrally on the thalamus to reduce pain perception
Correct answer: Blocks voltage-gated sodium channels in the neuronal membrane, preventing action potential propagation and nerve conduction
Articaine (like all local anaesthetics) blocks voltage-gated Na+ channels in the axon membrane, preventing depolarisation and action potential propagation, achieving reversible nerve conduction blockade.
Question 2: What concentration of articaine is most commonly used for dental local anaesthesia?
- 4% articaine with 1:100,000 adrenaline (Correct answer)
- 2% lignocaine alone
- 0.5% bupivacaine
- 10% lignocaine topical only
Correct answer: 4% articaine with 1:100,000 adrenaline
4% articaine with 1:100,000 adrenaline (epinephrine) is the most commonly used dental local anaesthetic in the UK for routine procedures. The vasoconstrictor prolongs duration and reduces systemic absorption.
Question 3: Why is adrenaline (epinephrine) added to dental local anaesthetic cartridges?
- To cause vasoconstriction, reducing systemic absorption, prolonging duration of anaesthesia, and providing a bloodless operative field (Correct answer)
- To increase the speed of anaesthetic onset
- To reduce the risk of allergic reaction
- To reduce the pH of the solution
Correct answer: To cause vasoconstriction, reducing systemic absorption, prolonging duration of anaesthesia, and providing a bloodless operative field
Adrenaline (1:80,000 or 1:100,000) causes local vasoconstriction, reducing blood flow at the injection site. This slows systemic absorption, prolongs anaesthetic effect, and reduces bleeding in the surgical field.
Question 4: What is the maximum safe dose of lidocaine (lignocaine) with adrenaline in a healthy adult?
- 7 mg/kg (up to 500 mg maximum) (Correct answer)
- 3 mg/kg (up to 200 mg)
- 10 mg/kg
- 1 mg/kg only
Correct answer: 7 mg/kg (up to 500 mg maximum)
The maximum safe dose of lidocaine with adrenaline (vasoconstrictor) is 7 mg/kg body weight, up to a maximum of 500 mg. Without adrenaline, the limit is 3 mg/kg (up to 200 mg).
Question 5: A patient is taking a non-selective MAOI antidepressant. What dental anaesthetic concern arises?
- Adrenaline should be used with extreme caution or avoided — MAOIs potentiate catecholamine effects, risking severe hypertension (Correct answer)
- MAOIs increase the risk of LA allergy
- MAOIs cause LA to be ineffective
- No concern — MAOIs have no effect on dental anaesthetics
Correct answer: Adrenaline should be used with extreme caution or avoided — MAOIs potentiate catecholamine effects, risking severe hypertension
Non-selective MAOIs (e.g., phenelzine) prevent breakdown of catecholamines. Adding adrenaline may cause exaggerated and prolonged sympathomimetic effects including severe hypertensive crisis.
Question 6: Which local anaesthetic has the longest duration of action, useful for postoperative analgesia?
- Bupivacaine (Marcain) 0.5% (Correct answer)
- Lidocaine
- Mepivacaine
- Articaine
Correct answer: Bupivacaine (Marcain) 0.5%
Bupivacaine has the longest duration among common dental local anaesthetics (up to 7–9 hours). It is used for nerve blocks where prolonged postoperative analgesia is beneficial (e.g., surgical extractions, implant surgery).
ORE Part 1 Pharmacology in Dentistry 1
What is the mechanism of action of articaine, the most widely used local anaesthetic in UK dental practice?