The Difference Is Air Not Temperature
Both classes reach the same sterilization temperature. What separates them is what happens to the air in the chamber before the steam arrives.
Steam sterilizes by condensing on a surface and giving up its latent heat. Anywhere a pocket of air remains, steam cannot condense, and that spot is not sterilized however long the cycle runs. Air is the enemy, not time.
What A Class N Cycle Can And Cannot Do
A Class N cycle pushes air out by displacing it with incoming steam. That works for solid unwrapped instruments laid out on a tray, where every surface is exposed and gravity can carry the air out.
It fails wherever air can hide. Inside a wrapped pouch, inside the lumen of a handpiece, inside a hollow tube, air stays put and steam never reaches the surface. A Class N sterilizer is therefore limited to unwrapped solid loads that are used immediately.
- Suitable for solid unwrapped instruments used straight away
- Not suitable for pouched instruments that go into storage
- Not suitable for hollow instruments such as handpieces and tubes
- Not suitable for textiles or any porous load
What A Class B Cycle Adds
A Class B cycle uses fractionated vacuum. Before the sterilization phase it runs repeated vacuum and steam pulses, each one pulling more air out and replacing it with steam. By the time the hold phase starts, the pouch and the lumen are full of steam rather than trapped air.
This is the class defined for small steam sterilizers in EN 13060, and it is the class every Novo Pro model runs. It is what makes it possible to wrap an instrument, sterilize it, and store it sterile until it is opened at the chairside.
How To Tell Which One You Need
The question is not the size of your practice. It is what you put in the chamber.
If any instrument is wrapped before it goes in, or if any instrument is hollow, you need Class B. In practice that includes almost every dental practice, because handpieces are hollow and surgical kits are wrapped.
- Do you pouch instruments so they stay sterile until use - Class B
- Do you reprocess handpieces or any hollow instrument - Class B
- Do you sterilize gauze, bandages or any textile - Class B
- Only unwrapped solid instruments used immediately - Class N may be enough
What Else Changes With The Class
A Class B machine has more to prove, so it comes with more to check. Expect on board test programmes to run before the first load of the day, and expect cycle data to be recorded rather than written down.
It also has a stricter appetite for feed water. Fractionated vacuum cycles put the boiler through more work, and EN 13060 Annex C sets the feed water requirement at a conductivity below 5 microsiemens per centimetre. Tap water will scale the machine and the damage is not a warranty fault.
