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Practice Tips #63: What's Up With Chucks?

What to look for in your next handpiece purchase:

There are a wide variety of high-speed handpieces on the market today. There are a host of features and benefits to various makes and models, but one of the most basic decisions a practitioner must make when choosing a handpiece is what type of chucking mechanism to use (i.e. how is the bur retained and changed?).

There are two basic types of chucking mechanism from which to choose: autochucks and manual (also referred to as “standard” or “wrench”) chucks.

An autochuck does not require the use of any other tools to open and close the chuck. The turbine is constructed with a spring-loaded cylinder at the center (the chuck), which is usually factory installed into the handpiece spindles (the central “shaft” of a turbine), so they are effectively one piece. A very small button (“actuator”) is at one end of the spindle, allowing one to depress the chuck moving it forward within the spindle and causing it to open. A mechanism of some sort (most commonly a large push button, but Midwest also has their Power Lever™) is, in turn, incorporated into the end cap of the handpiece, which pushes on the actuator causing it to open and release (or allow insertion of) a bur.

A manual chuck is also a hollow cylinder within the spindle, but rather than being spring-loaded, it is simply threaded into place. A manual chuck is tapered at the front and split so that it will open and close as it is moved backward and forward.

Most manual chucks have a square hole in the back end, allowing insertion of a specialized tool (bur wrench) to rotate the chuck clockwise to tighten and counter-clockwise to loosen (like most threads one might encounter in typical fasteners – “lefty loosey, righty tighty”). The spindle, in turn, will have some sort of mechanism (slots, holes or even a square piece that protrudes out the front of the handpiece), which a separate portion of the bur wrench will engage to hold the rest of the turbine stable while one rotates the chuck with the square shaft at the center of the tool.

Now that we know how chucks work, we can determine what other benefits there are to the different designs to best determine what’s best for you.

A wrench chuck is generally less costly than a push button (auto chuck) handpiece. It is also more resilient being a much simpler design from a mechanical standpoint (just a simple hollow threaded shaft rather than using springs and other tension devices). The way that a wrench chuck closes makes it more flexible (you can easily leave the chuck in a given position to accommodate different sized burs as opposed to an auto chuck which will always clamp down as soon as the chuck is released). Wrench chucks are simply changed if they wear or fracture (auto chucks are normally incorporated into the spindle and aren't usually replaced without also replacing the spindle – this requires using a handpiece repair press).

It is very common for all chucks to get clogged with debris. With a wrench chuck it is usually easier to get more leverage to “crack” the chuck open. Some wrenches are even made of 1/4″ hex stock, so you can use an open-end wrench on the bur wrench to free a stuck chuck. With autochucks, it can be very difficult to free once stuck. Sometimes, all you can do is pull on the bur with pliers, which does not always work.

The only real drawback to the wrench chuck is that you need to use an extra tool to change burs. This makes bur changing more time consuming and difficult. You might have an extra item in the operatory that requires cleaning and sterilization, as well as an extra item to purchase and keep track of. If you lose the wrench, you won’t be able to change burs.

Autochucks afford much greater convenience, however, so they are extremely popular. Many handpiece models are only available in push button.

The next time you’re shopping for a new handpiece, think about how you change burs and know that there is more to the equation than convenience or ease of use.

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