Dirt and dental instruments

Treating instruments in the dental practice

Dirt, infectious microorganisms and surgical instruments

During the normal activity of a dental practice, the use on patients of reusable surgical instruments requires a proper disinfection procedure before the instruments are placed in the autoclave and decontaminated.

The effective treatment of the dirt that adheres to the instruments used for each operation is essential, because:

  •        it reduces the potentially infectious bioburden
  •        it removes organic and inorganic dirt
  •        It prevents dirt from getting fixed to the surface (which would render the subsequent sterilisation phases ineffective)

Adequate cleaning and disinfection therefore make it possible to remove dirt and residue, which stick to the instruments and thus carry and protect potentially infectious microorganisms. This boosts the efficacy of the subsequent sterilisation process.

In this article, we’ll be looking at the various types of dirt that can settle on the surface of reusable instruments, and the importance of implementing adequate cleaning procedures to allow for an effective sterilisation process.

“Dirt”: deposits on the surface of instruments

During any operation on the patient, dirt settles on and sticks to the instruments used.

Excess dirt can harbour disease-carrying microorganisms or spores.  This phenomenon regards the surfaces of all reusable medical devices, such as surgical instruments, tongs, spatulas, burs, tips, turbines and wands, and presents an even greater risk in the case of complex and hollow instruments, where dirt can settle more easily and is more difficult to reach.

The dirt that settles on instruments can be of two kinds:

Inorganic dirt

  •        This dirt is not of organic origin, and is usually caused by the action of water, such as mineral deposits (or substances used by dentists, such as plaster, resin or cement).
  •        It is normally alkaline, with a pH of 8–14
  •        It can be removed most effectively using acid detergents

Organic dirt

  •        This dirt comes from humans, and normally has an acid pH (pH 0-6)
  •        It can come from the skin (pH 5.5), saliva (pH 6) or blood (pH 7.4)
  •        It is composed of long molecules (carbohydrates, fat, protein), which of course are difficult or impossible to dissolve in water
  •        With the cleaning process, these molecules must be solubilised and removed with the washing water

Removing dirt (and part of the microorganisms) with washing is essential in preparation for the subsequent sterilisation phases, in particular the use of the autoclave. The solution for tackling this type of dirt (especially in the case of ingrained dirt and hollow equipment) is ultrasonic tanks .

Ultrasonic cavitation allows these machines to go to work even on the surfaces of the instruments that cannot be reached, allowing for in-depth cleaning and the removal of particularly difficult to handle residue such as cement or plaster.

Medical dirt: carrying and protection of infections

Treating medical dirt effectively is essential before autoclave sterilisation. Dirt transports and protects the microorganisms responsible for infection. Specifically, it can originate from three different sources:


Present even in routine operations, such as tartar removal, blood:

  •        coagulates rapidly on surfaces such as stainless steel
  •        contains particles of fibrin, which become fixed and compact and create microscopic irregularities on the surface of medical devices
  •        contains salts that can corrode the surfaces of the instruments


A dense cluster of microorganisms that adheres to the surface of a device, and:

  •        develops when humidity/water is present
  •        adheres to the surface of the device thanks to the protein coating of the microorganisms
  •        secretes substances that bind together and protect the microbial cells.
  •        The structure of this biofilm protects the interior of the microbial community, boosting its resistance to detergents and disinfectants


The contamination found on reusable medical devices is entirely or mostly due to proteins (UNI EN ISO 15883-1, Annex C).

  •        The protein (solvent) component accessible to water is usually equivalent to 10-15% of the total mass
  •        This component keeps the protein soluble
  •        A change in pH or temperature, or the presence of oxidants, alters the nature of the protein, making it difficult to solubilise

Dental instruments and hygiene protocols

Together with the use of barrier systems, disposable PPE (gowns, gloves, masks and safety glasses, drapes and covers for the dentist chair and trays), decontamination and disinfection of the surgical environment, the sterilisation of reusable instruments is a primary element in the safety protocol.

The instruments that come into direct contact with the patient’s mouth, and therefore with saliva and blood, must be treated in such a way as to prevent the survival of any pathogens.

This is why the phases preceding the use of the autoclave are of fundamental importance, in particular the treatment of any dirt remaining on the instruments.

Cleaning removes the microorganisms and the organic material protecting them from the surfaces of the instruments, thus boosting the efficacy of the subsequent contact between the disinfecting/sterilising agent and the microorganisms still present.

If you’d like to find out more, here are two articles dedicated to the technologies for treating dirt on non-disposable dental instruments: