Infection Control, Occupational Safety and Laboratory Management: Disinfection, Sterilization, Waste and Quality Assurance
Infection Control, Occupational Safety and Laboratory Management
This domain tests the boundary between the clinic and the laboratory: how items are classified, which method actually kills what, how staff are protected from dust and monomers, and how a laboratory proves its processes are working.
Core rules
- Spaulding classification: critical items (penetrate tissue - sterilise), semi-critical (contact mucosa - high-level disinfection or sterilization), non-critical (contact intact skin - low-level disinfection).
- Impressions and prostheses are semi-critical. Rinse off blood and saliva, disinfect with a method compatible with the material (immersion or spray per the disinfectant's label), rinse, then pour. Alginate cannot be heat-sterilised and deforms if soaked too long; addition silicone tolerates many disinfectants better.
- Sterilization parameters: steam autoclave at 121 °C for 15–20 minutes, or 134 °C for 3–4 minutes; dry heat at 160 °C for 2 hours; unsaturated chemical vapour and 2% glutaraldehyde immersion (around 10 hours) for heat-sensitive items.
- Monitoring is layered: mechanical (gauge, printout), chemical (indicator tape, internal strips) and biological (Geobacillus stearothermophilus spores for steam). Biological indicators are run at least weekly and after any repair.
- Occupational hazards: silica and plaster dust from trimming (use water-cooled, local exhaust ventilation), methyl methacrylate monomer (sensitisation, dermatitis, vapour extraction), beryllium and nickel in base-metal dust, noise from lathes, and eye or hand injury. PPE includes eye protection, mask, gloves and a laboratory coat.
- Waste segregation: sharps into rigid containers, infectious waste into yellow-coded bags, chemical waste such as waste monomer and used glutaraldehyde kept separate.
Worked example
A used irreversible hydrocolloid impression arrives from a patient with a blood-borne infection. Correct sequence: wear gloves and eye protection, rinse under running water to remove visible bioburden, immerse or spray with a disinfectant for the labelled contact time, rinse again, then pour promptly so the alginate does not dry and distort. Do not autoclave the impression and do not pour it undisinified - the stone model becomes a contaminated surface for everyone downstream.
Traps that cost marks
Calling disinfection sterilization; relying only on indicator tape; and assuming the model is safe because the impression was rinsed.