Oral and Maxillofacial Surgery: Anaesthesia, Impactions and Trauma
Oral and Maxillofacial Surgery
This domain tests local anaesthetic pharmacology and technique, third molar assessment, odontogenic infection management, maxillofacial trauma patterns and medically complex surgery.
Core rules
- Lidocaine 2% = 20 mg/mL; a 1.8 mL cartridge holds 36 mg. Maximum dose with vasoconstrictor is 7 mg/kg (absolute cap 500 mg); without vasoconstrictor 4.4 mg/kg.
- Inferior alveolar nerve block targets the mandibular foramen in the pterygomandibular space, with the barrel parallel to the occlusal plane on the opposite side; aspirate before depositing to avoid intravascular injection.
- Third molar assessment uses Pell and Gregory (depth and ramus relationship) and Winter's classification (mesioangular is commonest in the mandible).
- Odontogenic infections follow fascial planes; Ludwig's angina is bilateral submandibular, sublingual and submental involvement with tongue elevation - secure the airway, give intravenous antibiotics and perform incision and drainage.
- Mandible is the commonest facial fracture, with the angle most frequently involved; Champy's line of ideal osteosynthesis runs along the external oblique ridge. Le Fort I is low transverse, II pyramidal, III craniofacial dysjunction.
Worked example
A 60 kg patient needs two cartridges of 2% lidocaine with 1:100,000 adrenaline. Dose delivered = 2 × 1.8 mL × 20 mg/mL = 72 mg, or 1.2 mg/kg. The permitted maximum is 7 × 60 = 420 mg, so this is well within limits. If the same patient required surgery under 4.4 mg/kg without vasoconstrictor, the ceiling would be 264 mg - still adequate for three cartridges, showing why vasoconstrictor choice, not cartridge count alone, governs safety.
Traps
- Quoting lidocaine concentration as a weight rather than as mg/mL.
- Forgetting that aspiration is mandatory in nerve blocks.
- Treating trismus after a block as infection when it is often needle trauma or haematoma.
- Describing Le Fort levels in the wrong order.