The classification is about load type, not quality tier
It’s easy to assume “Class B” means “the best autoclave” and “Class N” means “the cheap one.” That’s not what the letters encode. EN 13060 classifies small steam sterilizers by which load types they’ve been type-tested to sterilize, based entirely on how the cycle removes air from the chamber before steam is admitted. A Class N unit can be a perfectly reliable machine — it’s just built and tested for a narrower job.
This matters for a purchasing decision because the class isn’t optional or negotiable once you know what you sterilize. A practice running wrapped instruments or anything with a lumen (a handpiece, an endodontic file, a cannula) needs Class B. There’s no “manual workaround” that lets a Class N machine do that job safely.
Class N — gravity displacement, solid unwrapped instruments only
Class N cycles push steam in and let gravity displace the air downward and out through a drain. There’s no active vacuum pulse. This works fine for solid, unwrapped instruments with no internal channels — a plain mirror or a solid probe, for instance — because air has nowhere to hide. It does not reliably reach wrapped packs or anything with a hollow bore, since trapped air pockets simply aren’t removed by displacement alone.
Class S — whatever the manufacturer specifically defines and tests for
Class S sits between N and B and is the least standardized of the three: EN 13060 lets the manufacturer define exactly which load types (solid, specific wrapped items, specific hollow loads) the unit has been tested against, rather than requiring the full load range B covers. In practice this means two Class S machines from different manufacturers can validly handle different things — the only way to know is to check that specific machine’s declared load types, not assume from the class letter alone.
Class B — fractionated pre-vacuum, all load types
Class B cycles run repeated vacuum pulses (fractionated pre-vacuum) before the steam phase, actively drawing air out of the chamber and out of hollow and porous items, not just letting it settle out under gravity. That’s the mechanical difference that lets a Class B cycle claim solid, hollow, and porous loads, wrapped or unwrapped — the full range a dental or clinical setting typically needs. It’s also why a Bowie-Dick test — which specifically checks that those vacuum pulses cleared air evenly — is a Class B-only test; a machine without a fractionated vacuum phase has nothing equivalent to check.
A quick way to check what you actually need
Ask what leaves the sterilizer wrapped, and what has an internal channel. If the honest answer is “sometimes” or “yes” to either, Class N is off the table and Class S needs its declared load types checked line by line against your actual instrument mix. For most dental and general clinical reprocessing — where wrapped storage and hollow instruments are routine — Class B is the default starting point, which is also why it’s the class every product in this catalog’s tabletop-autoclave category is built to.