Dental Materials and Pharmacology
What this domain tests
This domain tests material selection, setting reactions, handling and drug safety. Expect calculations and contraindications.
Core rules
- Composite has a resin matrix, filler and silane coupling agent. Polymerisation shrinkage occurs; curing depth depends on shade, thickness and tip distance.
- Glass ionomer sets by an acid-base reaction, releases fluoride and chemically adheres to tooth. It is useful for primary teeth and liners but is moisture-sensitive.
- Amalgam is an alloy with mercury; it needs mechanical retention and has no adhesive bond. Avoid it in known mercury allergy.
- Addition silicone (vinyl polysiloxane) is stable and accurate. Alginate is a hydrocolloid, dimensionally unstable, and should be poured promptly.
- Lidocaine 2% with 1:100,000 epinephrine has a maximum dose of 7 mg/kg, up to 500 mg. Plain lidocaine has a lower maximum, about 4.4 mg/kg. Articaine 4% has a maximum of 7 mg/kg.
- Paracetamol is first-line analgesia. NSAIDs need caution in asthma and renal disease; aspirin is avoided in children.
- Antibiotics are not for pulpitis or dry socket; use them for systemic infection, swelling or fever.
Worked example
A 60-kg patient needs a lower molar extraction. Lidocaine 2% with 1:100,000 epinephrine: 7 mg/kg x 60 kg = 420 mg. Each 1.8-mL cartridge contains 36 mg lidocaine. 420 divided by 36 = 11.6, so the calculated limit is about 11 cartridges, although the absolute cap is 500 mg. The lower calculated limit governs; record the dose.
Traps
- Do not use a vasoconstrictor in uncontrolled hyperthyroidism or pheochromocytoma without specialist advice.
- Do not place composite over eugenol-containing material without a barrier.
- Alginate impressions distort if stored wet or poured late.
- Maximum dose calculations use actual concentration and lean body weight.