Practice Tips #100: O-rings 101

American Dental Accessories is proud to present our 100th Practice Tips newsletter! Since 2008, we have been appearing in your inbox with useful maintenance and equipment repair tips to empower your independence and reduce overhead costs.

This month, we discuss a common thread throughout all of your dental supply, repair, and maintenance needs: O-RINGS! They are used in many types of equipment throughout the dental office. O-rings are in handpieces, delivery system blocks, air/water syringes, and autoclaves—even in the hydraulics of your dental chair. They can serve vital functions sealing various valves or even holding components together.

An o-ring consists of a circular material that is used to form a circular seal. Not only is the o-ring round, but the cross section of the material is a perfect circle as well. A gasket that has a different shape is not an o-ring. While o-rings can be used as gaskets, not all gaskets are o-rings. The circular shape and cross section defines an o-ring.

What is a cross section? Simply stated, it’s the shape and thickness of the material. If one were to cut an o-ring and look at the end, the cross section is the shape you’d see (in the case of an o-ring, a circle). Obviously, you don’t need to actually cut the material to determine the shape—simply feeling it will allow you to make such a conclusion. For example, the cross section of your forearm is a rough oval, but you don’t need to cut your arm off to make this determination (NOTE: please don't try this).

O-ring Cross SectionAs o-rings are perfect circles formed from perfect circles, they are also measured in only two dimensions – inside diameter (i.d.) and cross section (c.s.). Mathematically, this makes sense. With the i.d. and c.s., you can easily extrapolate the outside diameter (o.d.). See our Practice Tip #95 for more common dental terms and abbreviations.

However, o-rings are made to exacting tolerances, so it really isn’t practical to measure them. For instance, the standard syringe tip o-ring (#01-04) has an i.d. of 0.114” (+/-.005”) and a c.s. of 0.070”. Taking into account the elasticity, even if you have precise calipers, it’s still extremely difficult to avoid compressing the o-ring when attempting to measure. The best way to measure them is to compare a sample to a sizing chart, we offer a handy o-ring sizing page in our catalog or you may print off the sizing chart by clicking here.

There is an entire industry dedicated to the manufacturing of o-rings with a variety of standard sizes and an industry numbering system created just for them. Even more interestingly, many dental manufacturers incorporate the o-ring industry part number into their part numbers.

For example, our #18-OR-002 is the same as the o-ring industry #002 (sometimes referred to as a 1-002). The A-dec part number for this same size is 030-002-02 (or 030.002.02). Note the “002” in the part number; this can help you cross-reference some o-rings very easily.

As these o-rings are so common as to be given their own numbering system by the industry, they are often used in equipment because manufacturers can procure them easily. Many of the “standard” o-rings throughout your equipment (and in both our deluxe and standard kits) are these easily numbered sizes.

O-rings are made from a wide range of materials. In view of their role in the dental office, they are usually made out of some sort of flexible material, typically a synthetic rubber. These materials are made in a whole rainbow of colors, so any individual o-ring could exist in any color. Many manufacturers will color-code theirs for specific applications, but one should not make any assumptions of suitability or size based on color alone, as such color-coding is highly individualized and ultimately arbitrary. That is, just because your original o-ring was green, it does NOT mean you can only replace it with a green one. In fact, a green o-ring might not even be correct. You simply need to find the correct size, regardless of color. The numbering system referenced above can also help in determining the correct one for your application.

For simplification, the vast majority of o-rings we stock are black, but that doesn’t mean they can’t be used when the original equipment manufacturer uses blue, red, green, or any other color.

While color doesn't matter, the ability of the material an o-ring is made from to withstand the rigors of sterilization is important. It’s important to be sure your o-ring can be sterilized if it’s used in a device that needs to be sterilized. Since they may be used in many different applications, American Dental Accessories only stocks o-rings that can be autoclaved. That way, no matter what you’re using one of our o-rings for, you can be assured it’s safe to sterilize if necessary. You don’t need to worry about keeping them separated based on application, keep them stored by size for all of your equipment in an organized bin or buy a kit with multiple o-ring sizes for any of your needs.

Our deluxe o-ring kit repairs vacuum valves, syringes, and more (item #18-OR-85).

Like light bulbs, sterilizer door gaskets, and other frequently replaced equipment parts, the added benefit of having common dental o-rings on hand keeps operatories up and running and reduces expensive service calls.