Your handpiece operates at high-speeds, but do you know about its torque? Simply stated, torque is a unit of force causing its rotation. As rotary instruments, dental handpieces generate tremendous amounts of torque to perform the work needed. As such, torque can have a great impact on how effective your handpiece is. But what affects torque?
Handpiece Design
First of all, the construction of the dental handpiece influences its performance. Check out Practice Tips issue #22 on High-speed Handpiece Design for the fundamentals. Illustration below shows the basic construction of a Midwest Quiet Air™ standard chuck turbine. Most turbines are similar in design and use the same types of components.
Turbine Impeller
The impeller catches the drive air, which causes the turbine to spin. Naturally, the more air the impeller catches, the more energy from the drive air transfers into torque. As they can catch more air, usually larger impellers = more torque. Of course, engineers spend countless hours designing the impellers of dental handpieces to capture as much air as possible while keeping size to a minimum.
Its size doesn't mean more handpiece torque. The number of vanes, the shape of the impeller, using twin impellers, or a number of other engineering tweaks and tricks can all result in more efficient impeller designs without increasing size.
Turbine Bearing
Next, we have the bearings. The bearings reduce friction and allow the turbine to spin. Without bearings, turbines do NOT spin at all. Given their role, the bearings also have a tremendous influence on torque. Cage types, materials, shielding, (just to mention a few factors) all have an effect on bearing performance and thus, torque.
Larger bearings often go hand-in-hand with large impellers, but again, don’t put too much confidence in size. This is only one method of potentially increasing torque.
Keep your bearings in good shape, so they can do their job. Most practitioners will notice a degradation of performance as bearings wear. Worn bearings increase friction, requiring more energy to spin the turbine. With extreme wear, concentricity can also be affected further. Reducing torque as energy diffuses with lateral movement (i.e. bur wobble) in addition to further increased friction.
- To get maximum torque, it’s important to keep your bearings in good shape through good routine maintenance (as discussed in Practice Tips #9).
Bearings simplify rotation of the turbine as the impeller catches the drive air. The drive air itself provides the motive force, so drive air has a tremendous impact on handpiece torque.
Handpiece Cleaning
You need clean dry air to run your handpieces. Debris in the air can clog the lines, which impedes air flow and reduces pressure. It also wreaks havoc on the delicate components of your dental handpieces (particularly the bearings).
While having a lesser impact, the same can be said of water in the air lines. Make certain your air properly filters and the filters are well maintained. Make sure to check your compressor regularly (see issue #34 On Routine Office Maintenance) and be attentive to the quality of air coming out of your unit. Small problems can turn into big ones if ignored for too long; just as a small cavity can lead to a root canal if ignored for too long.
Incorrect Air Pressure?
Air pressure also influences torque, but more doesn't mean better. Once again, dental handpieces are precision-engineered instruments designed to operate under very specific conditions. While turning up your air pressure may give you more torque, this also stresses the components, giving you shorter turbine life.
In addition, under extreme pressure turbines can stall out (analogous to flooding the engine of your car). Just as many cars are designed to get their best mileage at a certain speed, many dental handpieces are designed to yield the best performance at a certain air pressure. Check with the manufacturer of your dental handpiece for their recommendations.
Drive air pressure (and thus, torque) can also be affected by exhaust. If your handpiece isn’t properly exhausting, this causes back-pressure, reducing the net pressure on the impeller (or even counter pressure). This has a significant effect on torque.
- Most dental units ("bracket tables") and dental handpieces in the United States use a standard ISO-B (or ISO-C) coupler. See Practice Tips #36 “ABC’s of ISO” for more information on couplers.
Couplers allow the exhaust to flow back into the unit. Keep this line clear, open, kink-free, and free of obstructions. Properly exhausted air flows over the impeller better, also yielding more torque.
Turbine Spindle
While the impeller and bearings impact torque, the other components of the turbine should not have much impact. The spindle (central shaft) of the turbine provides a location to mount the bearings and impeller. It holds the chuck, which in turn holds the bur.
A worn spindle affects the balance of the turbine, which would result in a loss of torque (and wear to the bearings). A spindle in good condition should have almost no impact. As the chuck resides in the center of the spindle, it has just as much effect on torque as the spindle. The main impact on performance from the chuck would be poor bur retention. While this wouldn’t directly affect torque generated, this does impact the transference of torque to the bur (as the bur slips), so you would have a net reduction of applied torque.
Handpiece Chuck
Test for good bur retention every time you use your handpiece (just tug on the bur a little). Clean the chuck (if a push button or lever handpiece) as part of routine maintenance. If using a chuck with a wrench (aka standard chuck), unscrew the chuck from the back of the turbine to inspect it. A properly functioning chuck should have no jagged or irregular edges and should be split evenly at the end. With wear, the chuck will often lose a piece at the end (which affects bur retention).
As you can see, a number of factors can impact the torque of your dental handpiece. Keep an eye on your air. Make certain to perform routine maintenance. And always test for good bur retention. By doing these things, you should get great performance from your dental handpieces.
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