Basic Dental Sciences (Anatomy, Histology, Physiology, Biochemistry, Microbiology, Pharmacology)
Basic science questions in this exam are applied: which nerve supplies this area, which organism drives this disease, why a local anaesthetic fails in inflamed tissue, and what dose is safe. Learn the mechanisms, not isolated lists.
Anatomy and histology
- Trigeminal divisions: ophthalmic, maxillary and mandibular. The inferior alveolar nerve, lingual nerve, mylohyoid nerve and long buccal nerve are commonly tested, as is the mylohyoid nerve's role in anomalous innervation of mandibular molars.
- Muscles of mastication: masseter, temporalis, medial pterygoid elevate; lateral pterygoid opens and protrudes.
- Enamel is about 96% mineral and cannot regenerate because ameloblasts are lost after eruption; dentine contains tubules that transmit stimuli and permit fluid movement.
- Oral mucosa is masticatory (keratinised), lining, or specialised (dorsal tongue).
Microbiology and biochemistry
- Caries: Streptococcus mutans initiates, lactobacilli propagate in acid; fluoride acts topically, forming fluorapatite and inhibiting enolase.
- Periodontal red complex: Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia; Aggregatibacter actinomycetemcomitans is associated with rapid attachment loss in young patients.
- Saliva buffers with bicarbonate, contains amylase and IgA, and its flow falls with anticholinergic drugs and radiotherapy.
Pharmacology of local anaesthetics
- Local anaesthetics are weak bases: the uncharged form crosses the nerve membrane and the charged form blocks the sodium channel from inside.
- A higher pKa means a slower onset; inflammation lowers tissue pH, reducing the uncharged fraction and explaining failure in acute infection.
- Maximum doses: lidocaine 4.4 mg/kg (300 mg), mepivacaine 4.4 mg/kg, prilocaine 8 mg/kg (risk of methaemoglobinaemia), articaine 7 mg/kg (500 mg).
Worked example
A 20 kg child needs lidocaine 2% with 1:100,000. Two per cent means 20 mg/mL. The limit is 4.4 x 20 = 88 mg, so the maximum volume is 88/20 = 4.4 mL, well above one 1.8 mL cartridge but a figure that must be calculated rather than guessed.
Traps
- Confusing milligrams with millilitres when calculating a maximum dose.
- Assuming a local anaesthetic will work normally in acute cellulitis.
- Mixing up the elevating and opening muscles of mastication.