Impression disinfection

Dental impressions invariably are contaminated with patient saliva or blood. Such fluids can contain viral and bacterial pathogens, including HIV and hepatitis A, B, and C viruses. Although most infectious agents do not survive for extended periods outside the body, many pathogens, if present in high enough numbers, can survive several days in protein-containing body fluids. Microorganisms can be transferred from contaminated impressions to dental casts, and oral bacteria can remain viable in se

Dental impressions are among the items that are considered potentially infectious.

Dental impressions invariably are contaminated with patient saliva or blood. Such fluids can contain viral and bacterial pathogens, including HIV and hepatitis A, B, and C viruses. Although most infectious agents do not survive for extended periods outside the body, many pathogens, if present in high enough numbers, can survive several days in protein-containing body fluids. Microorganisms can be transferred from contaminated impressions to dental casts, and oral bacteria can remain viable in set gypsum materials for up to seven days.

Under OSHA`s 1991 Bloodborne Pathogens Standard, items contaminated with saliva in dental procedures are considered potentially infectious. Dental impressions are included in this category.

Disinfection method

Optimally, impressions should be decontaminated through chairside disinfection immediately after removal from the patient`s mouth. Personal protective equipment must be utilized and adequate ventilation in place when hazardous materials, such as disinfectants, are used.

Tuberculocidal hospital disinfectants with both hydrophilic and lipophilic virus kill are recommended. It should be noted that no single disinfectant is compatible with all impression materials. In selecting an impression disinfectant, material compatibility is a requirement (see Table 1).

Impressions should be rinsed thoroughly under running tap water before disinfection to remove as much bioburden as possible.

Both immersion and spraying have been recommended for disinfection of impressions. Spraying uses less solution, and often the same disinfectant can be used for general disinfection of operatory surfaces. Spraying does increase the chances for staff exposure to hazardous chemicals. Using stream spray can minimize aerosolization.

When using impression materials that are predisposed to distortion from immersion, spraying may provide an acceptable alternative to immersion. Impressions can be sprayed thoroughly and placed in airtight plastic bags. After the appropriate contact time the impression can be removed, rinsed thoroughly with tap water, shaken gently to remove adherent water, and poured.

For adequate inactivation of microbial contaminants, the contact time between impression and disinfectant should be at least equal to the time for tuberculocidal activity as recommended by the manufacturer of the germicide. Rinsing after impression disinfection also is essential to remove residual stone, soap, or disinfectant from the impression surface.

Alginate impressions

A number of studies have evaluated the effects of disinfection on irreversible hydrocolloid (alginate) impressions. Results have varied greatly depending on the techniques and materials evaluated. Generally, however, distortion has been found to be minimal and not clinically significant. Based on these findings, disinfection via immersion in dilute hypochlorite or iodophor is recommended. However, studies have reported significant adverse effects on specific materials with disinfectants that do not react with other alginates. Consequently, caution (coupled with in-house tests for material/disinfectant compatibility) should be exercised.

Elastomeric impressions

Rubber-base silicone impressions can be disinfected adequately by immersion in an iodophor, diluted hypochlorite solution, chlorine dioxide, glutaraldehyde, or complex phenol for the time required for tuberculocidal activity. However, the method of disinfection should be verified with the material manufacturer to prevent distortion of the impression or loosening of the adhesive bond between the impression tray and the impression material. Phenols with a high alcohol content, for example, can desiccate some impression materials.

ZOE and compound impressions

Limited data are available on disinfection of zinc oxide eugenol (ZOE) and compound impressions. Current ADA recommendations for ZOE suggest disinfection via immersion in a 1:213 iodophor or 2 percent glutaraldehyde solution prepared according to the manufacturer`s instructions.

Compound impressions reportedly can be disinfected via immersion in a 1:10 sodium hypochlorite solution or with an iodophor.

Wax bites, wax rims ...

Because the delicate nature of wax prevents wax bites from being safely immersed in disinfectant without distortion, wax rims and wax bites are disinfected using an iodophor, chlorine dioxide, or sodium hypochlorite spray and a "spray-wipe-spray" technique. Following the second spray, the wax bites can be enclosed in a sealed plastic bag for the proper contact time.

The bites should remain wet with disinfectant for the time recommended for tuberculocidal activity.

Impression trays

Impression trays should be rinsed thoroughly under running water to remove residual blood and saliva. Precleaning removes additional bioburden and any adherent impression materials.

Consistent with dental infection-control guidelines for semicritical instruments, chrome-plated and aluminum impression trays can be cleaned, packaged, and heat-sterilized. Single-use, plastic impression trays provide a disposable alternative to heat sterilization.

Office/lab communication

Communication between the dental practice and the laboratory is essential to ensure that appropriate disinfection protocols are implemented without overlap. Repeated exposure to disinfectants could compromise the quality of the impression and the restoration or appliance.

This resource was reprinted with the permission of OSAP. OSAP is a nonprofit organization providing information and education on dental infection control and office safety. For more information, please call (800) 298-6727.

More in Macro/Op-Ed