Local Anaesthesia
Core Concepts
Local anaesthesia is essential for pain-free dental treatment. Candidates must understand the pharmacology of local anaesthetics (e.g., lidocaine, articaine), vasoconstrictors (epinephrine), and the techniques of administration (infiltration, nerve blocks). Key concepts include maximum safe doses, contraindications, and management of complications (e.g., syncope, toxicity, needle breakage). Also, knowledge of anatomical landmarks for nerve blocks is crucial.
Common Traps
Questions often test the calculation of maximum safe dose: for lidocaine 2% with 1:100,000 epinephrine, max dose is 4.4 mg/kg (or 300 mg absolute). Another trap is the difference between infiltration and block anesthesia: infiltration is for localized areas; blocks for larger regions. Also, be clear on the signs of local anaesthetic toxicity (e.g., tinnitus, metallic taste, seizures) and the management of anaphylaxis.
Worked Example / Rule of Thumb
A 70 kg patient requires extraction of a lower molar. Use an inferior alveolar nerve block with 2% lidocaine with 1:100,000 epinephrine. Max dose = 4.4 mg/kg × 70 kg = 308 mg, but absolute max is 300 mg. Each cartridge (1.8 mL) contains 36 mg lidocaine, so max is about 8 cartridges. Rule of thumb: always aspirate before injecting to avoid intravascular injection.