Sterilisation in a dental clinic

The process of cleaning and sterilising dental instruments after each procedure is a major element of dental care. Dental instruments that are inserted into patient’s mouths during dental crown procedures, root canals and other surgeries will be exposed to bodily fluids.

These fluids contain microorganisms and other types of bacteria that remain on the instruments until they undergo a procedure known as instrument reprocessing.

Dental instrument reprocessing involves cleaning, bagging, sterilising and storing all critical and semi-critical instruments for reuse at a later stage. Most non-critical instruments don’t require sterilisation as they pose a low infection risk, however, they must still be thoroughly washed and disinfected after each use.

Disinfection of the instruments does kill many of the microorganisms, however, it’s only when the instruments are subjected to heat sterilisation within an autoclave, that all the bacteria are effectively killed off.

In every dental office, staff members must follow an elaborate process to ensure that contaminated instruments are properly reprocessed without sustaining any injuries to themselves or others.

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Compliance with the ADA’s guidelines on infection control

Internationally-recognised dental organisations closely monitor infection control standards within dental healthcare settings in each of their countries.

In Australia, the Australian Dental Association (ADA) has issued the ADA Guidelines on Infection Control; a manual providing very clear instructions on how to sterilise instruments. As well as having a copy of the ADA’s manual, each dental practice in Australia must have their own infection control manual on hand. All the steps involved in reprocessing instruments must be clearly stated in the Infection Control Manual to minimise confusion or uncertainty.

Furthermore, all dental professionals are required to comply with ADA regulations by recording the details of each sterilisation cycle in a staff logbook. Such record-keeping must include the Batch Code Identification number, serial number of the sterilisation machine used (if there are multiple machines in the dental practice), and the date of sterilisation.

Keeping these details allows for easy tracing in the event of any dental hygiene breaches or steriliser malfunctions. Following each routine cleaning session or any other type of dental procedure, the details of the medical instrumentation used is recorded in the corresponding patient’s file.

The three categories of dental instruments

Dental sterilisation is a matter that every dental clinic must take very seriously to prevent the spread of infections. Dental Assistants and Hygienists must follow set procedures for reprocessing every type of contaminated instrument. They should also undertake regular training to keep their infection control knowledge and skills up to date.

Many dental instruments such as mirrors, dental explorers, dental forceps or needle holders are single-use only and can be disposed of in a biohazard bin following each patient procedure. They require no cleaning or sterilisation. However reusable instruments are designed to withstand multiple procedures and must therefore undergo proper cleaning and sterilisation after each use.

These dental instruments are split into three categories according to their level of infection risk. The three categories are critical, semi-critical and non-critical.

1. Critical instruments

Whether you specialise in Restorative Dentistry, Paediatric Dentistry or Cosmetic Dentistry, you’ll no doubt use critical instruments to perform your procedures. These sharp instruments pose the greatest risk for infection control as they are commonly used to pierce through soft tissue and slice into bones during procedures. Examples of critical instruments include scalpels, surgical burs and periodontal scalers.

2. Semi-critical instruments

These instruments are considered a lower risk than critical instruments because they do not puncture any skin or bone. However, they do still press against soft tissue and oral wounds when they are inserted into patients’ mouths. Examples of semi-critical instruments include amalgam condensers and mouth mirrors. Semi-critical instruments must also be sterilised after each use.

3. Non-critical instruments

These instruments attract the least amount of risk as they are only placed on undamaged skin. Examples of non-critical instruments include blood pressure cuffs, pulse oximeters and facebows. These instruments do require thorough cleaning after every use by washing and disinfecting. However, they generally do not need to undergo sterilisation.

Non-critical instruments may also be covered by single-use barrier sheets during patient procedures to minimise the risk of contamination by aerosols or droplets of blood and saliva.

Reprocessing dental instruments

Every dental practice needs to have a structured system in place for the reprocessing of dental instruments. One of the governing rules of dental infection control is to keep contaminated instruments well away from sterilised instruments and equipment at all times.

While it’s ideal to have a separate room dedicated solely to the cleaning and sterilisation of instruments, some smaller dental clinics may not have this option. If the operating room is the only place in the clinic where this process can be carried out, then room dividers or clinical curtains must be installed to shield the sterilising bay from aerosols.

During a patient procedure, it’s best to place any instruments that are no longer required in a sterile solution to prevent bodily fluids from hardening on them. This can make the cleaning process quicker as there should only be a minimal amount of dried blood to remove if any at all.

The container in which the contaminated instruments are placed should be made from a solid material such as rubber or metal and must have a lid. Carrying the instruments unsecured on a tray to the reprocessing area presents too great an occupational risk.
If the Hygienist or Dental Assistant tripped on their way, they or another person could be scratched and infected by an airborne instrument. Therefore, it’s much safer to keep contaminated instruments sealed in a puncture-resistant container when carrying them.

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The four steps of reprocessing instruments

A reprocessing area must be split into four sections allocated to the Cleaning, Bagging, Sterilising and Storage stages of the process. Dental Hygienists must wear a face mask, protective glasses or a face shield and a gown when in the reprocessing area.

After placing the instrument container on the bench, the Hygienist should remove their surgical gloves and wash their hands, before putting on a pair of puncture-resistant gloves to start the cleaning step.

Carefully removing each instrument from the container using a pair of tongs or forceps, the instruments are then to be placed on a special tray where any sharp disposable parts need to be removed and placed into a biohazard bin. Direct hand contact with the instruments should be avoided to reduce the risk of injuries.


Using the tongs, the Hygienist will then run each instrument under running water and remove any debris with a brush. After rinsing, the Hygienist should then inspect each instrument to make sure there is no remaining debris, before placing the instruments in the Ultrasonic Cleaner or Instrument Washer (Washer Disinfector).

Closely follow the manufacturer’s instructions when operating either of these machines. A copy of these documents should be kept on a shelf or in a drawer within the room.

Each dental handpiece will require lubricating and cleaning of all the surface areas, including the internal cavities, before undergoing the sterilisation process.

While the instruments are undergoing the cleaning cycle, thoroughly wash and disinfect the carrying container, before setting it aside to dry. The loading sink should also be scrubbed with water and disinfectant during this time. Remove the puncture resistant gloves and wash hands with soap.

After changing into a clean set of puncture resistant gloves, the Hygienist should then remove each instrument from the Ultrasonic Cleaner or Instrument Washer and once again wash them under running water. This time to remove any disinfectant residue.

The instruments must then be fully dried before the bagging step can begin.


Dental instruments must be placed in sterilisation or heat resistant pouches prior to being sterilised so they will be protected against contamination.

When inserting the instruments into these pouches, the hygienist must be careful to place them in such a way as to avoid causing any perforations. Important details about the sterilisation of an instrument must be clearly written on its assigned pouch. This information should include the date of sterilisation and the serial number of the steriliser that the instrument was placed in.

Methods used to sterilise dental instruments

These are the four methods used to sterilise dental instruments.

1. Autoclaves

Autoclaves are a preferred choice of sterilisation for most dental professionals. They can effectively kill all microorganisms, viruses and hard to kill bacterial spores using a mixture of temperature, steam, and pressure. The sterilisation times for autoclaves can take anywhere from four minutes up to thirty minutes.

2. Dry heat steriliser

This form of heat sterilisation does not rely on water or steam to kill bacteria and microbes. Instead, dental instruments are subject to intense dry heat. This method of sterilisation is not as effective at killing all microorganisms as the steam autoclaves are.

However, it is an ideal choice for certain instruments that may become damaged when exposed to steam pressure within an autoclave. Instruments can take between twelve to one hundred and fifty minutes to be sterilised in dry heat ovens.

3. Cold Sterilisation

In this method of sterilisation, contaminated instruments are placed in a steel tray and sprayed with chemicals. This method of disinfection is best suited to those instruments that cannot tolerate high temperature sterilisation in an autoclave or dry heat oven. Domestic disinfectants are not considered adequate for this task.

Chemicals that are generally used include Sodium Hypochlorite or Glutaraldehyde. Instruments must be left saturated in either of these chemicals for a substantial period before they are fully sterilised.

4. Chemical Vapour Sterilisation

A combination of Alcohol, Water, Acetone, Formaldehyde and Ketone are mixed together to release a chemical vapour that sterilises contaminated instruments. Metal instruments that are sterilised this way are not as likely to rust or be damaged as there is less water used in this method than in a steam autoclave. This process usually takes between twenty to forty minutes.


After being removed from the steriliser, bagged instruments must then be placed in storage cupboards or drawers. These storage spaces must be kept closed and locked to protect the pouches against contamination. The sterilised instruments remain stored until they are required for their next procedure.

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