1. The Infection Control Boundary: Legal & Regulatory Framework
Every impression, bite registration, try-in appliance, and articulatory record arriving in the laboratory has been in intimate contact with patient saliva, blood, and mucosal biofilms. Pathogens including Hepatitis B, Hepatitis C, HIV, Mycobacterium tuberculosis, and respiratory viruses can survive on impression surfaces for hours or days if left untreated.
Under GDC Standards (Principle 1.5: You must find out about and follow the law and regulations that govern your work), UK Health Technical Memorandum 01-05 (HTM 01-05), and Scottish Dental Clinical Effectiveness Programme (SDCEP) guidance, both the dental surgery and the dental laboratory hold shared responsibility for cross-infection control.
The primary statutory rule states that all items must be cleaned and disinfected by the surgery before dispatch. However, the laboratory must operate on the assumption of potential bioburden, establishing a documented standard operating procedure (SOP) for incoming verification and decontamination prior to bench handling.
2. Material-Specific Disinfection Chemistry & Dimensional Stability
Disinfectant efficacy must be balanced against the physical and chemical properties of the restorative material to prevent dimensional distortion or compromised plaster surface reproduction:
• **Hydrocolloids (Alginate):** Highly susceptible to both imbibition (absorption of water leading to swelling) and syneresis (exudation of fluid causing shrinkage). Alginate impressions should never be soaked in long-immersion baths. Protocol: Rinse under running water to eliminate gross bioburden, immerse in a validated biocide (e.g., dual-chain quaternary ammonium or hypochlorite) for the manufacturer-specified short contact time (typically 3–5 minutes), rinse, and seal in a damp gauze bag.
• **Polyethers (e.g., Impregum):** Hydrophilic polymers that swell and distort if immersed for prolonged periods. Require specialised fast-acting immersion disinfectants or validated biocidal sprays with strict contact timing.
• **Addition-Cure Silicones (Polyvinyl Siloxane / PVS) & Polysulphides:** Hydrophobic and highly dimensionally stable. Can withstand complete immersion in EN-certified glutaraldehyde-free, aldehyde-free, or sodium hypochlorite solutions (1,000 ppm available chlorine) for 10 minutes without structural compromise.
• **Digital Scanners & Hardware:** Intraoral scanner wand tips, calibration targets, and digital transfer hardware must be processed according to manufacturer instructions using high-level disinfectant wipes (EN 14476 virucidal rating) or autoclaved if validated.
3. Laboratory Pumice, Polishing Lathes & Aerosol Biosecurity
The laboratory polishing lathe and pumice trough represent one of the most heavily contaminated microbial reservoirs in the dental technology environment if not rigorously controlled.
When polishing acrylic dentures after try-in or repair, bacteria and fungal spores (including Candida albicans and Staphylococcus aureus) are aerosolised into the breathing zone by high-speed rag wheels (2,800 RPM).
Compliant polishing protocols require: (1) Replacing pumice slurry daily or using single-patient aliquots of disinfectant pumice solution (e.g., mixing pumice powder with 1:10 biocidal concentrate rather than plain water); (2) Disinfecting rag wheels, brushes, and splash guards daily via autoclaving (134°C) or chemical immersion; and (3) Operating local exhaust ventilation (LEV) hoods with adequate face velocity to capture airborne particulates.
4. The Work Ticket Decontamination Audit Trail
A robust quality assurance system under DAMAS requires full traceability of the decontamination status across the clinical-laboratory interface.
The incoming laboratory work ticket must feature a specific checkbox indicating: "I certify that this impression / device has been cleaned and disinfected according to HTM 01-05 guidelines" signed by the clinical registrant. If an impression arrives unlabelled, wet with blood, or lacking confirmation, the laboratory must quarantine the package and contact the practice.
Similarly, the outgoing laboratory delivery ticket must state that the finished custom-made prosthesis has undergone final laboratory decontamination (e.g., immersion in chlorhexidine or biocidal solution) before packaging in a sealed, tamper-evident bag marked: "Decontaminated — Ready for Clinical Try-In / Insertion".