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The Ultimate Guide to Autoclaves

The Ultimate Guide to Autoclaves

The Ultimate Guide to Autoclaves

Whether fitting out a new practice, replacing a broken-down machine or simply upgrading, deciding on the best autoclave to buy should not be a rushed decision.

As an expensive piece of equipment that plays a pivotal role in infection control, your autoclave should tick as many boxes as possible.

Our Ultimate Guide to Autoclaves will arm you with everything you need to make an informed purchase.

What is an autoclave?


Sterilization is critical within dentistry. From direct patient care to laboratory work, large numbers of instruments and handpieces are used each day.

Each of these items come with the risk of contamination by spores, bacteria, viruses and other dangerous microorganisms that cannot always be removed by other forms of cleaning.

Autoclaves, also known as steam sterilizers, are self-sealing steel machines that use a combination of heat and time to kill these microorganisms and make the instruments safe to use again.

Typically, an autoclave chamber is cylindrical as this shape more easily withstands high pressures than a box or cube.

Tabletop autoclaves commonly used in dental practices are roughly the size of a microwave and compact enough to not take up too much space.

The autoclave machine was invented by Charles Chamberland in 1879 and the meaning of the name autoclave can be translated from Greek and Latin as a ‘self-locking’ device.

Autoclaves are also used by other professions such as tattooists.

How do autoclaves work?

Autoclaves use steam to create a high-pressure environment at a temperature too high for microbial survival. This eliminates pathogens that may be resistant to soaps and detergents.

The steam created in the autoclave allows for thorough sterilization within dental instruments and tiny holes and crevices that could be missed during cleaning with detergent.

The first stage of the autoclave sterilization process is sometimes referred to as the “purge” phase. This is when steam created from heating water displaces the air within the autoclave chamber. Both temperature and pressure then begin to increase.

The second stage is the sterilization phase. During this phase, the exhaust remains closed causing the temperature and pressure to rapidly rise to the desired levels required to destroy bacteria, spores and other pathogens.

The third phase is the exhaust phase. This is when pressure is released from the chamber, but temperatures remain high.

The fourth and final stage is the cooling down phase. Once temperatures are low enough, the load can be removed from the chamber ready to be reused.


Autoclave sterilization temperature and time

The recommended temperature for optimal autoclave sterilization is between 120 and 135ºC.

The duration of the sterilization phase is usually between 5 and 20 minutes but will depend on factors such as load quantity.

What are the different types of autoclaves?

The three main classifications of autoclaves are S class autoclaves, B class autoclaves and N class autoclaves.

The key differences between these three steam sterilizers can be summarised as follows:

N class autoclaves (generally not used in dental practices)

  • Air removal happens by gravity displacement where the steam pushes the air out of the autoclave.
  • Used for sterilizing only simple materials, such as scalpels, and therefore not recommended for dental practices.
  • Cannot be used to sterilize textiles, porous loads, hollow items or items in pouches as the cycles do not have the right characteristics to pass specific physical tests.

S class autoclaves

  • Remove the air inside the chamber using a steam wall which is denser than air. During the sterilisation cycle they perform this process three times to ensure that all the air inside the chamber is removed.
  • Selective models of S class autoclaves come with a vacuum pump, but this is not a common feature.
  • Essentially an intermediate class between N class and B class autoclaves and the characteristics are not defined by specific standards.
  • Can be used to sterilise porous bagged products but not textiles, unless upgraded to B class.
  • Usually has options for cycle programming, temperature selection and a drying mechanism to get the instruments dry.

B class autoclaves (Vacuum Sterilizers)

  • The most suitable machine for a dental practices in accordance with European Standard 13060.
  • Offer great flexibility and are suitable for a wide range of settings.
  • Remove air from inside the chamber by means of a vacuum pump, creating a negative pressure that forces steam in.
  • Can be used to sterilize all loads including solids, type A hollow instruments, type B hollow instruments, textiles, porous loads and wrapped instruments, both bagged and loose.
  • Generally capable of much faster sterilization and drying cycles, enabling dental staff to work much more efficiently.

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Autoclave testing

helix test

The effectiveness of sterilisation of any one cycle can be checked with the use of indicators or tape placed within the load.

Colour changing sterilisation tape can be used in autoclaves to indicate necessary temperatures have been achieved and sterilisation has taken place.

Class B autoclaves require a steam penetration test once a day using either a Helix test device or Bowie and Dick.

The Helix test is aimed more at testing the effectiveness of air removal and steam penetration of hollow instruments and the Bowie Dick pack test is aimed more for testing the effectiveness of steam penetration on large porous loads.

A printable data logger automatically records and prints out this test. It provides written confirmation of sterilisation times, temperature, and whether the autoclave passed the test successfully.

For autoclaves not fitted with a data logger or printer, an ACT (automatic control test) using Class 6 indicator strips is carried out to measure time, steam and temperature within the autoclave.

The other important test is the vacuum test. This is used is used to determine the air-tight integrity of a vacuum autoclave’s chamber and plumbing system.

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Autoclave validation

Sterilisation process validation is a procedure for obtaining, recording and interpreting the results required to establish that the process yields reliable, repeatable load sterilisation complying with predetermined specifications for sterility.

Under healthcare standards and guidelines such as BS-ENISO:13060:2014, BS-ENISO:15883:1 and HTM 01-05, revalidation should be completed annually or in accordance with the manufacturer’s recommendations.

What to consider when purchasing an autoclave


Autoclave capacity, or chamber size, indicates how many instruments or pieces of equipment can be placed inside the chamber at any one time.

B class autoclave capacity ranges between 8-22 litre. The larger the capacity the more expensive the autoclave and greater the energy consumption.

The autoclave capacity required will depend on the requirements of an individual practice.

Some practices choose to use two smaller capacity autoclaves for faster cycle times and to allow two cycles to be carried out at once. Having two autoclaves is also practical should one break down.

w&h autoclave


Not all B class autoclaves can deliver sterilization cycles at the same speed. Some autoclaves offer shorter cycle time than others, but this generally will come at a greater initial cost.

Some autoclaves offer gentle cycles ideal for sterilizing sensitive items and porous loads.

It is important to ensure the autoclave has the appropriate choice of cycles to meet your sterilising requirements.

Autoclave price

As one of the more expensive pieces of smaller equipment your practice will need, it is always worth looking around for deals from trusted brands and manufacturers.

W&H, one of the world’s leading manufacturers of autoclaves often has special offers on its Lyla and Lara sterilizers. See here for any currently available offers.


One of the more recent advances in autoclave technology is the introduction of built-in USB functionality to record sterilization cycles.

Most B class and S class autoclaves now have label printers that can be connected to the sterilizer for printing barcodes

This is designed for legal protection and as a way of improving your practice’s overall traceability system.

Autoclave repair, servicing and maintenance

The components and technology in autoclaves do fail from time to time, so it is beneficial to purchase from manufacturers who have a technical servicing department based in your country.

W&H for example has a team of factory trained field-based engineers supporting dental autoclave repairs across the UK.

To ensure the autoclave is working to maximum efficiency and reduce your chances of needing a repair, autoclave cleaners can be purchased for fast, effective and easy use.

Kent Express Recommends

Vacuklav 31 B+ Autoclave


These flexible B class steam sterilizers are not only distinguished by the effective air-cooling of the vacuum pump, but also by their reliability and ease of use.

The innovative design of the Vacuklav 31 B+ simultaneously features fast operating times, along with versatility in recording and safety. The integrated monitoring of the feed water and the electronic control of the Vacuklav 31 B+ avoid operating faults and secure high quality sterilization and maximum gentleness for your instruments.

Instruments of up to 5 kg in weight may be sterilized on 5 trays in the compact sterilization chamber (depth 35 cm, volume 17 litres). Two special, ergonomic water containers (for feed and waste water) are already integrated in the steam sterilizer as well as the important monitoring of the water quality.

  • Reliable all-round steam sterilizer with short operating times.
  • Simple operation and versatile documentation.
  • Stand-alone with effective air-cooling system.

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