Integrated Basic Medical Sciences
Integrated basic medical sciences: this section tests anatomy, physiology, biochemistry, pathology, microbiology and pharmacology through single-best-answer vignettes rather than recall lists. Expect a nerve at risk during a surgical extraction, a drug interaction to spot before you prescribe, or a healing process that has gone wrong.
Core rules to hold
- Muscles of mastication: masseter, temporalis and medial pterygoid elevate; lateral pterygoid protrudes and, with the suprahyoids, opens.
- The lingual nerve lies immediately lingual to the mandibular third molar crown; the inferior alveolar nerve enters the mandibular canal at the mandibular foramen.
- All three trigeminal divisions are sensory; only V3 carries motor fibres - to the muscles of mastication, mylohyoid, anterior digastric and tensor veli palatini.
- Facial nerve branches run superficially within the parotid; deep cheek lacerations risk the marginal mandibular branch.
- Calcium balance is a PTH–vitamin D–calcitonin axis; RANKL from osteoblasts drives osteoclast differentiation and resorption.
- Lidocaine 2% with 1:100,000 adrenaline contains 20 mg/mL; maximum 7 mg/kg with vasoconstrictor (4.4 mg/kg without) and an absolute ceiling of about 500 mg.
Worked example
A 60 kg adult needs an inferior alveolar nerve block; the cartridge is 2% lidocaine with 1:100,000 adrenaline. Two per cent means 2 g per 100 mL, so 20 mg/mL. The limit is 7 × 60 = 420 mg, below the 500 mg ceiling. Volume = 420 ÷ 20 = 21 mL, roughly ten 2 mL cartridges. A standard block uses 1.5–1.8 mL, so it is comfortably safe - the calculation exists so you can recognise overdose, not so you use the full limit.
Traps
- Mixing V2 and V3 territories in questions about post-extraction numbness.
- Ignoring cautions for adrenaline-containing solutions in uncontrolled hyperthyroidism, phaeochromocytoma and severe cardiac disease.
- Adding metronidazole or a macrolide to a warfarin patient without checking INR.
- Choosing antibiotics instead of incision and drainage for a fluctuant abscess.