The most important part in
your dental equipment!
There exists a tiny device without which
we wouldn't easily have air planes, cars, trucks, tractors, air conditioners, or dental units – in fact just
about anything with motion. You use one every time you step on the brake in your car. Its costs only a small
amount and it has made headlines only once. It is the tiny, ubiquitous but mighty O-ring.
You've likely heard about O-rings during the Space Shuttle Challenger disaster of 1986, and I'm sure you've seen one, the name is
self-descriptive - they are usually just a thin tube of rubber like material shaped into a ring. It seems so
simple and obvious that it couldn't have been really invented - yet it isn't that obvious, there is a trick to
making an O-ring work. Usually we think of such a world changing invention as coming from some inspired young thinker,
but the O-ring came from a senior citizen, Niels Christensen.
Danish immigrant to North America, was an expert on brakes. He'd travelled to America 1891 at age 26 to be
the leading draftsman at a Chicago engineering firm, but after a year or two the company reorganized and he
lost his job. While unemployed he read of a major streetcar crash where the breaks failed. How, he wondered,
could he improve the breaking system? At that time the break shoes were pressed against the wheels by the
strength of the conductor, amplified by the electricity that ran the train. The problem: A sudden loss of
electrical power and the breaks were out. Christensen realized there needed to be a way to store the energy
and release it later - to do this the ingenious inventor used air.
Before the car
started out, Christensen used an electric motor to force air into a cylinder, which when released drove the
break drums. Because the air was stored and released mechanically it didn't matter if the electricity shut
off. How does this relate to the tiny O-ring?
to seal the compressed air cylinder, the seal he used was a cumbersome and tricky triple value; the O-ring
had not even been thought of, but it put the problem of sealing foremost in his mind. Some forty years later
in 1933 Christensen, now 68, was still working on sealing the fluid in breaks - this time though for
He tried this time
a simple rubber ring. He cut a groove into his piston, slipped the O-ring over it and pressurized the
container; he found, as others before him did, that it failed. If he had been a younger man he wouldn't have
had the insight and intuition to continue. Patiently Christensen changed the size of the groove, cutting new
ones with slightly different dimensions. In time he found the magic to an O-ring: Make the groove one and
half times the O-ring radius. The result was remarkable: "This packing ring", he wrote in his notebook, "has
been tested" nearly three millions times and "has never leaked and is still tight."
It was so simple
that no one believed it would work until finally two World War Two army Air Crops engineers used it to fix
some leaking breaks on the landing gear of Northrop bomber. It worked like magic and was, from that time on
used in all military aircraft - and soon this simple, but ingenious O-ring seal appeared everywhere: fountain
pens, soap dispensers, plumbing systems, hydraulic presses, car breaks, washing machines, infact hundreds of
places, including of course dental units.
The O-ring is the most widely adapted seal in history because of its simplicity, low cost, ease of
installation, and small space requirements without supporting structures. It is suitable for dynamic or static
seals within the temperature limits of elastomeric materials. Successful use depends upon proper groove
dimensions and selection of the right compound for the O-ring, but most importantly it needs to be kept
clean and well lubricated!
CAUTION - Use
only silicone lubricant only when lubricating dental instrumentation O-rings. (Petroleum products like Vaseline will cause permanent damage to the O-rings in your dental
unit unless they are made of special material for that specific purpose.)