Helix tests for autoclaves
What is it and why is it important?
The Helix Test measures the strength of steam penetration into the chamber. This is an essential test because, in dental practices, there are instruments with fairly long cavities that, if not properly sterilized, can harbour bacteria and viruses that may infect patients and operators. With the Helix Test, the device is run and sterilisation of hollow loads is evaluated, particularly:
- the effectiveness of the initial vacuum phase and, therefore, how well steam penetrates cavities
- the temperature and pressure of saturated steam during the sterilisation phase
This test can only be carried out with class-B autoclaves (with fractionated vacuum process).
In dentistry, this test is particularly important because the use of hollow instruments is widespread and we must protect operators who come into contact with a patient’s mucous membranes and blood, as well as the patients themselves. Instruments defined as hollow and used in dentistry are divided into two types:
- Type A, including small devices such as handpieces and turbines;
- Type B, including cannulas and tubes.
These instruments can only be sterilized in a type-B autoclave that penetrates hollow tools with steam—the sterilizing agent—even if they are bagged. For all types of loads and cycles, the EN 13060 standard requires users to verify that their autoclave is functioning properly by carrying out tests:
- To check that the autoclave is functioning properly, the Vacuum Test, Bowie-Dick Test and Helix Test are carried out before the autoclave is used;
- Biological and chemical checks (sterilisation indicators) are performed during the sterilisation cycle to ascertain whether or not sterilization parameters are met.
Standard EN 13060 recommends the Helix Test as a way of checking and ascertaining that cycles used to sterilise type-A hollow instruments (turbines and contrangles) are effective.
The Helix Test is performed after an initial empty cycle is carried out. The Helix Test is then placed in the sterilization chamber alone (no other instruments) by the steam outlet (lowest tray), or as per the manufacturer’s instructions.
The test involves placing a chemical test strip inside a cap connected to a 1.5 metre-long tube that acts as the dental instrument cavity. In order for the test to be successful, all the air must first be removed from the whole tube to create a vacuum, and then steam must go through it to ensure that the autoclave is able to sterilise properly. When the sterilising agent comes into contact with the indicator strip, it will change colour, indicating how effective the sterilisation process is. If the Helix Test fails, it means that steam did not penetrated properly and sterilization was not successful. If this is the case, the test must be repeated, and if the subsequent result is a failure, the autoclave must be repaired or replaced.
Carrying out a Helix Test on a daily basis provides the practise with timely and accurate information regarding autoclave performance and how effectively instruments are sterilised. This can be useful if a patient develops an infection. Therefore, it is recommended that you keep a register where the indicator strip and cycle printout are stored, so that you are always able to demonstrate that your autoclave is functioning properly.