Specialist medical equipment known as an autoclave is used in surgeries and hospitals to sterilise re-usable instruments, as well as a number of other products which must be sterilised before use, such as cotton dressings. There are two different types of autoclave, ‘N’ and ‘S’ types. The ‘S’ type is a more modern version, and many dental care professionals suspect that these will succeed the older ‘N’ type, and may soon be a legally required piece of equipment, replacing the ‘N’ type altogether.
Both types of autoclave use heat (134 degrees centigrade) and pressure (2.2 bars) to achieve sterilisation, however there are some differences in how they work.
‘N’ Type Autoclave
- The ‘N’ type autoclave uses steam to move air downwards within the chamber where the instruments are placed on a metal perforated tray; this enables the hot air to contact all of the instruments. It is important for operators to know that the instruments must be laid out on the tray in a single layer – no instruments must overlap one another.
- Sterilisation pouches that are available to hospitals and dental practices must not be used when sterilising instruments in the ‘N’ type autoclave – this would result in sterile bags and unsterilized instruments.
- The operator can choose a cycle which dries the instruments after sterilising them; this is advisable where possible as rust is less likely to occur on metal instruments if they are dried properly after being sterilised.
- The sterilising cycle lasts approximately 15 minutes and the machine is programmed to prevent the door being opened before a cycle is complete.
- Most autoclaves can hold a number of perforated metal trays containing instruments at once – this enables users to sterilise more instruments in any one cycle.
- For operators to be sure that the autoclave has sterilised its contents, they must place a sterilisation indicator strip on to a tray before each cycle. These strips change colour when sterilised and must be kept as a record that sterilisation has taken place.
‘S’ type Autoclave
- The ‘S’ type autoclave sucks out hot air from the chamber where the instruments are placed on a metal perforated tray; this creates a vacuum so that the steam contacts the instruments. It is important for operators to know that instruments must be laid out in a single layer on the tray – no instruments must overlap.
- Sterilisation pouches are used when using the ‘S’ type autoclave, (except for handpieces) these pouches contain individual instruments and are sealed prior to sterilising. The operator must ensure that the pouches are sealed correctly along the line indicated on the pouch, and that no air gaps are present.
- The use of sterilisation pouches means that there is less risk of instruments becoming contaminated after sterilising as the instrument itself is not handled at all.
- The operator can select a cycle which dries the instruments after sterilisation; this is advisable as rust is less likely to affect the metal instruments.
- The sterilising cycle lasts approximately 15 minutes and the door cannot be opened until the cycle is complete.
- Most autoclaves can hold a number of metal perforated trays containing instruments at once, this means that more instruments are sterilised in each cycle.
- ‘S’ type autoclaves usually give a print out of details such as pressure, temperature etc after each cycle.
Operators should lay out treatment and examination trays correctly before placing into the autoclave – this means that there is less handling of instruments after sterilisation and therefore less risk of contamination.
All sterilised instrument trays must be covered with a lid once dried after sterilisation and stored in a cupboard.