Dental local anesthesia practice questions
Fifteen questions on how local anesthetics work, the drugs you will meet in clinic, cartridge calculations and early signs of toxicity. Pick an answer to see the explanation.
Written by the Quizard team. Last updated
Local anesthesia sits between pharmacology and clinic, so exams tend to mix mechanism questions with short calculations. Maximum doses vary between sources and countries, so this set leaves them out. Learn the limits your own school teaches.
| Written as | Means | In a 1.8 mL cartridge |
|---|---|---|
| 2% lidocaine | 20 mg/mL | 36 mg |
| 4% articaine | 40 mg/mL | 72 mg |
| Epinephrine 1:100,000 | 0.01 mg/mL | 0.018 mg |
| Epinephrine 1:200,000 | 0.005 mg/mL | 0.009 mg |
Questions
0 of 15 answered
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1. How do local anesthetics block nerve conduction?
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Answer: They block voltage-gated sodium channels. Blocking voltage-gated sodium channels stops the sodium influx an action potential needs.
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2. Which of these is an ester local anesthetic?
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Answer: Benzocaine. Benzocaine is an ester. The other three are amides.
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3. Where are amide local anesthetics mainly metabolized?
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Answer: Liver. Amides are mainly metabolized by liver enzymes, while esters are mainly hydrolyzed in plasma.
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4. Why is articaine broken down largely in plasma, although it is classed as an amide?
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Answer: It also carries an ester side chain. Its ester group is hydrolyzed by plasma esterases.
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5. How many milligrams of lidocaine are in 1.8 mL of a 2% solution?
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Answer: 36 mg. 2% means 20 mg/mL, and 20 × 1.8 = 36 mg.
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6. What is the concentration of epinephrine 1:100,000?
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Answer: 0.01 mg/mL. 1 g in 100,000 mL equals 1,000 mg in 100,000 mL, which is 0.01 mg/mL.
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7. Which is a reason to add a vasoconstrictor?
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Answer: It slows absorption and prolongs the block. Slower absorption keeps the drug at the nerve for longer and lowers the systemic peak. It also reduces bleeding at the site.
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8. Why are local anesthetics often less effective in infected tissue?
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Answer: Low tissue pH leaves more drug ionized. Acidic tissue shifts the drug toward its ionized form, and less of it can cross the nerve membrane.
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9. Generally, how does a lower pKa affect a local anesthetic?
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Answer: Faster onset. At tissue pH more of the drug is in the un-ionized form that crosses the membrane, so onset tends to be faster.
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10. Prilocaine is particularly linked with which adverse effect?
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Answer: Methemoglobinemia. Its metabolite o-toluidine can oxidize hemoglobin to methemoglobin.
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11. Which local anesthetic is often chosen for long-lasting postoperative pain control?
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Answer: Bupivacaine. Bupivacaine is long acting, which helps with pain after a long procedure.
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12. What is the main purpose of aspirating before injecting?
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Answer: To reduce the risk of intravascular injection. Blood in the cartridge suggests the needle tip is in a vessel, so the needle should be repositioned.
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13. Which nerve needs a separate injection for buccal soft tissue anesthesia of the mandibular molars?
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Answer: Long buccal. An inferior alveolar block does not reliably cover this tissue, so the long buccal nerve is often blocked as well.
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14. Which is an early sign of local anesthetic systemic toxicity?
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Answer: Numbness around the mouth and tinnitus. Early CNS signs include circumoral numbness, tinnitus and lightheadedness, and they can progress to seizures.
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15. True allergy is more often associated with which group, partly because of a PABA metabolite?
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Answer: Esters. Ester metabolism produces para-aminobenzoic acid. True allergy to amides is considered rare.
For exam study only, not clinical guidance. Doses, reference ranges and protocols vary, so follow your course, your local policy and current references. Spotted a mistake? Tell us.
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