Disinfection of Dental Impression for Labs - XDENT LAB

Key Points

• Dental impressions are a high-risk but highly preventable source of cross-contamination in dental labs.

• Rinsing isn’t enough: water alone removes only part of the microbial load; disinfection is non-negotiable.

• Disinfection must be material-driven: silicones tolerate immersion; alginate and polyether should be spray-only to avoid distortion.

• Labs need to choose the right mix of chemical and physical methods based on safety + dimensional stability.

• A step-by-step cleaning and disinfection workflow is now a core quality and biosafety benchmark for dental laboratories.

Introduction

Dentistry constantly exposes people and materials to saliva, blood, and other potentially infectious fluids. Just 1 ml of saliva from a healthy person can contain around 750 million microorganisms, and roughly 280 bacterial species have been isolated from the oral cavity. In patients wearing prosthetic or removable orthodontic appliances, common colonizers include Staphylococcus, Streptococcus, Lactobacillus, Actinomyces, and Candida species.

This microbial burden makes oral health-care professionals and dental technicians particularly vulnerable to cross-infection, as dental materials often go directly from the patient’s mouth to the dental laboratory. A review by Chidambaranathan AS et al. (2019) reported that 67% of items received in laboratories were contaminated with organisms such as Streptococci, Staphylococci, Candida spp., methicillin-resistant S. aureus (MRSA), and P. aeruginosa. In addition, another study said that dental personnel are estimated to have a 5 –10-fold higher risk of acquiring Hepatitis B than the general population, and both Tuberculosis and Hepatitis B pathogens can survive for seven days or longer at room temperature.

For lab owners and dental technicians, these realities highlight that infection control and standardized disinfection of dental materials are not optional; they are fundamental to preventing cross-contamination and ensuring a safe laboratory environment. 

Understanding Cross-Contamination Risks in Dental Laboratories

Cross-contamination in dental environments can occur through multiple interconnected pathways, including:

• Between patients

• From patients to dental professionals

• From dental professionals back to patients

• Between clinical and laboratory teams, especially through shared tools, impression materials, prostheses, and transport systems

• From laboratory personnel to dentists and subsequently to other patients, when contaminated casts or prosthetic components are handled and returned to the clinic

In the laboratory setting, this risk becomes even more pronounced. When technicians work on contaminated impressions, casts, or prosthetic components, microorganisms from one patient’s case can easily be transferred to another. Over time, this contamination can travel full circle: from the patient → to the dentist → to the laboratory → back to the dentist → and ultimately to new patients.

For dental labs, where multiple cases are processed simultaneously and materials frequently move between workstations, cross-contamination is not an isolated event but a systemic vulnerability.

Dental Impression – A Possible source of cross-contamination

As we map out complex transmission pathways, one category of material consistently emerges as a critical control point in every dental laboratory workflow: the dental impression.

Impression making is a fundamental part of dental treatment, used to create a replica of the oral structures. During this procedure, impression materials are heavily exposed to saliva and blood, which may contain infectious agents such as HIV, herpes, hepatitis, or tuberculosis. If not properly managed, these contaminated impressions can transfer microorganisms to stone casts and become a direct source of infection for anyone handling them.

Rinsing impressions under running water is a helpful first step, but studies show it removes only about 40% of microorganisms. Therefore, proper disinfection is mandatory, not optional. Today, several methods are used to disinfect impressions and models, including chemical disinfection (immersion/spray), microwave, autoclave, and ultraviolet (UV) radiation, which we will examine in the next section.

Disinfection Methods

Chemical disinfection methods

For most dental labs, chemical disinfection is the primary approach. When the material allows, immersion is generally the most reliable option because all impression surfaces are fully exposed to the disinfectant solution. This works well for addition and condensation silicones, which are dimensionally stable. However, immersion is not suitable for hydrophilic materials such as alginate and polyether, as they can absorb the solution and distort. It is also more time-consuming and most solutions must be discarded after each use.

In these cases, the spray & store technique is preferred. Spraying reduces the risk of dimensional change, especially for alginate and polyether, but may be less effective in deep undercuts because a smaller volume of disinfectant is used and full coverage is harder to guarantee.

This material-dependent choice between immersion and spray & store is summarized in Figure 1. 

Glutaraldehyde (2%)

Disinfection Level: High 

Overview: Glutaraldehyde is highly effective and capable of destroying a broad range of microorganisms, including bacteria, viruses, tuberculosis bacilli, and even sporulated fungi, when used correctly.

Advantages

• Provides high-level disinfection

• Rapid antimicrobial action

• Effective against a wide spectrum of pathogens

Limitations 

• Contraindicated for routine use due to significant health risks

• Strong odor; can irritate eyes, skin, and respiratory tract

• Requires handling in closed containers and well-ventilated areas

• Not biodegradable → banned in several countries

• Must be handled with nitrile gloves and strict PPE

Sodium Hypochlorite

Disinfection level: Intermediate

Overview: Sodium hypochlorite is a widely used disinfectant with a broad spectrum of antimicrobial activity. It acts mainly through oxidation, which makes it highly effective against many viruses, including COVID-19. Studies have shown that 1% sodium hypochlorite spray on alginate impressions (after rinsing and drying) does not cause severe dimensional changes, although prolonged immersion (e.g., 15 minutes in 0.5%) can lead to slight dimensional alterations.

Advantages

• Broad antimicrobial spectrum

• Fast antimicrobial action

• Easy to use and water-soluble

• Relatively stable at recommended concentrations

• Non-toxic at indicated concentration

• Low cost

• Does not stain materials

• Non-flammable and colorless

Limitations

• Irritates mucous membranes

• Less effective in the presence of organic matter

• Corrosive to metals

• Prolonged immersion may cause slight dimensional changes in some impression materials

Iodoform

Disinfection level: Low to intermediate

Overview: Iodoform provides bactericidal, mycobactericidal, and virucidal activity, with some fungicidal effect, although fungi require longer contact time. It is generally better suited as an antiseptic rather than a primary impression disinfectant. One study reported that 30 minutes of exposure to 0.1% povidone-iodine did not cause significant distortion in polysulfide or polyvinyl siloxane impressions.

Advantages

• Broad antimicrobial activity (bacteria, mycobacteria, viruses, fungi)

• Non-flammable

• Can be used on certain elastomeric impression materials without major distortion

Limitations 

• Not sporicidal

• Can cause staining

• May irritate membranes and mucous tissues

• Effectiveness decreases in the presence of organic debris

• Requires prolonged contact time for reliable disinfection

Alcohol

Disinfection level: Intermediate

Overview: Alcohol-based solutions, typically 70% ethyl or isopropyl alcohol, provide intermediate disinfection and are widely used as antiseptics and for surface cleaning. Ethyl alcohol has stronger bactericidal activity, while isopropyl alcohol is commonly used for general antiseptic purposes. Both are effective against tuberculosis bacilli, fungi, and many viruses.

Advantages

• Fast-acting antimicrobial activity

• Widely available and easy to use

• Effective against a broad range of microorganisms

• Suitable for disinfecting office surfaces and non-porous equipment

Limitations

• Not recommended for impression disinfection due to surface alteration

• Can damage or distort impression materials

• Not suitable for disinfecting acrylic prosthesis bases

• Flammable and requires proper handling

Phenols 

Disinfection level: Intermediate
Overview: Phenolic compounds act as protoplasmic poisons, disrupting microbial cell walls and promoting lysis. Even at low concentrations, they are effective against E. coli, Staphylococcus, and Streptococcus, and also possess antifungal and antiviral properties. Phenols are commonly used in mouthwashes, soaps, and for general surface cleaning.

Advantages

• Effective against a wide range of bacteria

• Antifungal and antiviral properties

• Useful for surface cleaning applications

Limitations

• Not suitable for disinfecting impressions

• Incompatible with latex, acrylic, and rubber

• May cause material degradation or distortion

Chlorhexidine

Disinfection level: Intermediate

Overview: Chlorhexidine is a widely used disinfectant and antiseptic with a broad antimicrobial spectrum. It is commonly found in oral rinses and cleansing solutions. Chlorhexidine is bactericidal, virucidal, and mycobacteriostatic, though its effectiveness decreases in the presence of organic material due to its pH-dependent activity. Studies show that 0.2% chlorhexidine can replace water when preparing alginate, and impressions can also be immersed in chlorhexidine to achieve effective disinfection.

Advantages

• Broad antimicrobial spectrum

• Suitable for immersion disinfection of certain impression materials

• Can be used as mixing liquid for alginate

• Ideal for disinfecting prostheses with metal components, where hypochlorite is contraindicated

Limitations

• Reduced activity in the presence of organic debris

• pH-dependent effectiveness

• May be less effective on heavily contaminated impressions without prior cleaning

Levels of Disinfection With Chemical Disinfectants

Chemical disinfectants are generally classified into three levels based on their effectiveness against vegetative bacteria, tubercle bacilli, fungal spores, and viruses:

• High-level disinfection: Inactivates most pathogenic microorganisms.

• Intermediate-level disinfection: Effective against organisms such as Mycobacterium tuberculosis, but does not reliably destroy spores.

• Low-level disinfection: Provides limited antimicrobial activity, targeting only some bacteria and viruses.

The appropriate disinfection level depends on both the disinfecting agent and the impression material being treated. The compatibility between materials and disinfectant types is summarized in Figure 2, showing which agents can be used safely without compromising dimensional accuracy.

Microwave disinfection methods

Disinfection level: Effective physical disinfection method 

Overview: Microwave disinfection is a quick, simple, and inexpensive method suitable for dentists, assistants, and dental technicians. Microwave disinfection disrupts microbial cell membranes and interferes with cell metabolism, resulting in effective disinfection.

Advantages

• Fast and easy to perform

• Cost-effective compared to many chemical agents

• Does not require specialized chemical handling

• Suitable for dental offices and laboratories

Limitations

• Not all impression materials are microwave-compatible

• Risk of deformation or overheating of certain materials

• Requires correct power and exposure settings to avoid damage

Autoclave disinfection methods

Steam autoclave

Overview: Steam autoclave is a device used to sterilize equipment, surgical instruments in medicine and dentistry by subjecting them to high saturated steam pressure at 121°C or more for 15 to 20 minutes. 

Advantages

• Provides true sterilization, including spores

• Rapid cycle at 134°C (as short as ~3 minutes)

• Compatible with certain addition and condensation silicone impression materials

• Widely available in dental clinics and hospitals

Limitations 

• Not suitable for all tray types or impression materials

• Risk of distortion if materials or custom trays are not heat-stable

• Requires correct loading and cycle parameters to avoid deformation

Ethylene oxide gas autoclave 

Overview: Ethylene oxide gas has been investigated as another method for disinfecting or sterilizing impressions. Studies (Holtan et al., 1991; Olin et al., 1994) reported that gas sterilization of vinyl polysiloxane (VPS) impressions can lead to gas inclusion within the material, which may later be released and cause bubbles in stone dies, especially if poured immediately.

Advantages

• Capable of low-temperature sterilization

• Useful in theory for heat-sensitive devices

Limitations 

• Gas inclusion in VPS can produce bubbles in dies if poured too soon (dies should be delayed ~24 hours)

• Reports of significant structural changes (>0.5% dimensional change) in some silicone impressions and trays

• Longer cycle times and more complex handling than steam autoclaves

• Less practical and less commonly used for routine impression disinfection in dental labs

Ultra-Violet Radiation

Disinfection level: Intermediate to high (dependent on intensity, exposure time, and accessibility)
Overview: Ultraviolet (UV) light can serve as an effective disinfectant, but its efficiency depends heavily on exposure time, light intensity, humidity, and the ability of UV rays to reach microbial surfaces. Because dental impressions and prostheses contain complex surface details that can shelter microorganisms, UV light must be delivered from multiple angles to achieve meaningful microbial reduction.

Studies have shown that UV exposure can significantly reduce C. albicans colonies, with higher-wattage UV tubes producing faster and more complete microbial elimination. Maximum killing efficiency has been observed at 24 watts (3750 μw/cm²). Samra et al. (2018) also reported that UV disinfection is suitable for impressions without compromising dimensional stability.

Advantages

• Effective against fungi such as C. albicans

• Higher wattage results in faster microbial reduction

• Does not involve moisture or chemicals → minimal risk of dimensional distortion

• Suitable for impressions where material stability is a concern

Limitations 

• Effectiveness depends on complete light access to all impression surfaces

• Complex surface undercuts may limit full disinfection

• Performance influenced by environmental conditions (humidity, intensity)

• Requires appropriate equipment and safety shielding to prevent UV exposure to personnel

Step-by-Step Cleaning and Disinfection of Dental Impressions

While each disinfection method offers its own advantages and limitations, none of them can be effective without proper pre-cleaning. Residual blood, saliva, and organic debris can significantly reduce the antimicrobial efficacy of chemical, thermal, or UV-based approaches. For this reason, industry best practices emphasize that cleaning is the mandatory first step before any disinfection protocol is applied. To ensure both biosafety and impression accuracy, the following step-by-step cleaning procedure should be consistently followed in every dental laboratory workflow.

Effective disinfection begins with a proper cleaning process. Removing saliva, blood, and organic debris is essential because residual contamination can reduce the efficacy of any chemical, microwave, autoclave, or UV-based disinfection method. The following steps outline the recommended cleaning protocol for dental impressions:

1. Rinse Under Running Water

Immediately after removal from the patient’s mouth, the impression should be thoroughly rinsed under running water to remove visible contaminants such as blood, saliva, and debris.

• Do not use air or steam for drying, as this may create aerosols and increase biological risk.

• Allow water to drain naturally in the same area to reduce splash dispersion.

2. Avoid Aerosol-Generating Techniques

Techniques such as air-blowing may spread microorganisms into the environment. Maintaining a low-aerosol workflow is critical for technician safety.

3. Prepare the Impression for Disinfection

Shake off excess water gently. The surface should remain moist, as drying may interfere with the action of certain disinfectants, especially when using spray methods.

4. Apply the Appropriate Disinfection Method

Based on the impression material (e.g., silicone vs. alginate), choose the correct method:

• Immersion for dimensionally stable materials like addition or condensation silicone

• Spray & store for hydrophilic materials such as alginate or polyether

• Thermal/physical methods (microwave, autoclave, UV) when compatible

5. Final Rinse

After the recommended contact time with the disinfectant, rinse the impression again under running water.

6. Dry and Proceed to Casting

Gently shake off excess water and allow the impression to dry in a clean area before pouring. Avoid using heat or airflow that could distort the material.

Conclusion

Cross-contamination remains a significant concern in dental laboratories, and impressions represent one of its most common, and preventable sources. By understanding material-specific risks and applying validated disinfection methods, labs can protect both technicians and patients while maintaining the dimensional accuracy essential for high-quality prosthetic outcomes. For modern dental laboratories, consistent cleaning, proper disinfection, and well-designed workflows are not just safety measures, they are essential foundations for reliable, efficient, and trustworthy laboratory practice.

References

Disinfection of Impression Materials: A Comprehensive Review of Disinfection 

Biosafety and Disinfection of Impression Materials for Professionals in Prosthetic Dentistry (Lab Technicians and Dental Surgeons)

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