Practice Tips #93: Sterilizer Door Gaskets (The Seal of Sterility)

The steam (autoclave) and chemical vapor (chemiclave) sterilizer are the workhorses of the dental office. All sterilizers use a "seal" or "door gasket" of some sort. In this month's Practice Tip, we’re going to look a little further into door gaskets. How they work and why they wear out as frequently as they do.

In an earlier post (Practice Tip #14), we gave you a routine maintenance checklist for your sterilizer. One component of that list consists of checking and maintaining the door gaskets, as well as how often to change these simple, but important components.

Door Gasket Material

Almost all sterilizer door gaskets contain fluorosilicone. This material is great, because of its oil and fluid resistance and its toleranance to high temperatures with a melting point in excess of 400° F. It is soft enough to seal well, but resilient enough to withstand the punishment of repetitive cycles.

While fluorosilicone has a high melting point, it constricts (shrinks) at about 200° F. Most sterilizer cycles run at 250° F - 275° F, which is above this point. This means every time you run your sterilizer, your door gasket shrinks slightly. To allow for this shrinkage, door gaskets come slightly larger than the surface area they are sealing.

Gaskets “shrink to fit” (just like your Levi’s). Unlike blue jeans, your door gasket will expand after the cycle completes and it returns to room temperature. This means that every time you use your sterilizer, the door gasket stretches and then shrinks. Considering that, it’s pretty amazing they hold their shape and integrity for hundreds of cycles or more.

Switching Out the Gasket

As gaskets contract and expand hundreds of times, they will typically end their usefulness smaller than when they were first installed. This is one of the reasons you need to be careful about comparing a new, fresh gasket, to an old, worn-out one to gauge specifications. More often than not, a worn gasket appears undersized and often gets pinched in the door. This causes large pieces to come off of the gasket.

Since it’s expected for a new gasket to be oversized, how will it fit your sterilizer?

You need to plan for the contraction of the gasket when you install it. It’s important that the gasket allows to shrink evenly throughout its circumference, so it seals when it reaches the temperature of a cycle.


When installing a door gasket, seat the gasket at the “corners” first. This allows the excess to be evenly spaced around the circumference, leaving you with several very small gaps. These small gaps close as the gasket shrinks once the cycle begins.

If you seat one section of the gasket at a time and then run your finger around the circumference to seat the remainder, you will be left with one large gap in a corner. The resulting gap will be far too large for the inevitable shrinkage to correct. This is not what you want.

Gasket Fitting

As you can see above, it is normal to have gaps around the circumference after installing a new gasket. The small gaps will correct once the sterilization cycle begins and the gasket shrinks. Having many small gaps is much better than only one or two very large gaps.

You can download our door gasket instructions to remind your staff on how to install them, every gasket we sell comes with them. See below for a more detailed version:

Gasket Instructions

By following the above instructions, you can be assured of a proper fit and will maximize the longevity of your sterilizer door gaskets.


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