Dental Impressions: Dangerous Routes of Transmission

Through direct contact with the patient’s oral cavity, dental impressions and dental prosthetic tools can disperse pathogenic germs throughout the clinic or dental laboratory. The sooner these medical devices are disinfected and cleaned, the lower the risk of an infection. Due to the sensitivity of some materials, there are particularly high requirements for suitable disinfectants that do not affect the dimensional stability of dental impressions.

It is the responsibility of the dentist to be sure that all objects contaminated with bodily fluids such as blood and saliva do not leave the treatment area before they are disinfected and cleaned; only then may they be brought into the laboratory. Thus, impressions should be cleaned and disinfected immediately after removal them from the patient’s mouth.

The Specialized Tools

Dental impressions and dental prosthetic tools are made of various types of material. Due to practical considerations, it would make sense to be able to use one disinfectant that would not cause damage to any of the substances. Otherwise, deformities or damages to the surfaces would seriously impair the utility, quality, and accuracy or fit of the object.

Disinfectants for impressions and dental prosthetic tools are identified with yellow color-coding and must possess the following characteristics:

• The manufacturer must certify that the disinfectant is compatible with the materials to be treated. This should be especially valid for the sensitive gypsum of the dental models.
• The disinfectant should have the shortest possible exposure time in order not to endanger the stability of the form.
• It is important that the disinfectant possesses additional cleaning properties. As dental impressions are merely rinsed before the disinfection, pieces of blood or saliva often remain on the surface. 
• The disinfectant may not contain any aldehyde. Aldehydes often have protein errors, which can result in a lowered effectiveness. The cleanup is also more difficult due to the protein fixation. Some materials react to aldehydes with a discoloration.
• Alcohol-based disinfectants are also unsuitable as they can damage the surfaces of these sensitive objects.

Surface Active and Disinfected

Disinfectants used for the preparation of dental impressions and prosthetic tools are normally created with quaternary ammonium compounds (QUAT). Due to their chemical structure, they are surface active and can clean as well as disinfect. They are even a powerful disinfectant against blood and saliva contaminations. Their advantages are a low toxicity, absence of odor, and that they are well tolerated by skin and other materials.

When used in combination with other disinfectants such as alkylamine, the antimicrobial spectrum of QUATs can be expanded and the application time can be considerably shortened.

Cleaning and Disinfecting: The Exact Steps

Dental impressions and prosthetic tools are basically prepared in a similar fashion – the preparation processes only differ in the ordering of the various cleaning and disinfection measures.

Dental impressions should be rinsed carefully under cold water immediately after removal from the patient’s mouth. It is important to avoid having the water deflect onto other objects. Disinfection is usually performed by the immersion method, for which one should obtain specific disinfection box. A daily change of the disinfectant bath is recommended after heavy contamination.

Alternately, the objects can be disinfected by using a spraying device and a ready-to-use working solution. The DAHZ recommends doing the spray disinfection inside a closed system, such as a hygienic sluice, even if the aerosol of the quaternary ammonium compounds are not damaging.

Dental prosthetic tools should first be disinfected (immersion or spray disinfection) and then cleaned under cold water with a brush and toothpaste. Cleaning removable dentures in an ultrasonic bath is particularly recommended. This helps remove all tartar and deposits. For especially tough plaque or stains from tea or smoking, using an acid dissolving cleaner might be required (cement remover).

All tools that enter the patient’s oral cavity must be stored in a closed hygienic bag after the disinfection, which helps protect against a later contamination. The packaging is also proof for the laboratory that the disinfection was conducted. Before the tool is reused (after it returns from the laboratory), it must be disinfected again.

Large dental prosthetic appliances (e.g. articulators), which cannot be disinfected using the immersion method, should be prepared with a wipe disinfection in the same manner that other surfaces are disinfected.

Used impression trays are considered to be semi-critical class A medical products and should thus be disinfected and cleaned (see chapter: Preparation of instruments).

Cleaning and Disinfection of Dental Impressions and Dental Prosthetic Tools