Electric handpiece motors can impel burs at up to 40,000 rpm, a fraction of the 400,000 rpm or more that air-driven units can deliver. Electric motors, though, have gear multipliers (usually identified by a red ring) that increase the rotation by a factor of 5 to 200,000 rpm. (There are also reducer gears that decrease bur rotation to 0.0625 times of the nominal speed for endodontic canal preparation and deep dentin removal.) Many electric handpieces have full-range rheostat controls, allowing bur rotation at 100 rpm or less.
Torque (cutting power) is independent of rotational speed, however. Electric handpieces can produce up to 60W of cutting power compared to less than 20W for most air-driven units (although some recent air motors can deliver 30W). This means that the electric handpiece does not slow or stop as the bur cuts various tooth and restorative materials. It simply continues cutting with a constant torque through the entire speed range, regardless of the load. Electric tooth preparation is smoother, faster, and more consistent than air-driven preparation.
The consistent torque of the electric motor maintains cutting concentricity of the rotating bur. Less wobble generates less chatter of the bur blades against the tooth structure, and, thus, a more defined, cleaner cut. The smooth cutting of the electric handpiece mills the tooth structure rather than chopping it (as commonly seen with air turbines). Precise, continuous margins are easier to prepare, and the faster preparation creates less thermal buildup at the tooth surface.
Electric handpieces are significantly quieter than their air-driven counterparts, generating less auditory stress and damage for patient, staff, and dentist. Dentists and staff work many decades in a loud environment, and the noise and pitch damage can accumulate. The full-torque, smoother operation of electric cutting also decreases the high-pitched whine often noted with air driven units.
Electric motors and handpieces are often heavier than similar air-driven units (more internal components). Ergonomic design and painstakingly developed balancing often make this additional weight virtually unnoticeable. Electric motor cutting is faster and more effective, resulting in less operator fatigue at the end of the day and greater comfort for both the patient and the dentist. Conveniently, smaller electric handpieces for smaller hands are now available.
The handpiece is a significant contributor to practice activity and practice overhead. Handpieces should facilitate procedures and have the adequate torque to rotate the operative burs quickly enough such that they can be useful in removing enamel, dentin, filling materials, crowns, bridges, and polishing. While electric motor handpieces command a higher price, they pay many dividends in short- and long-term return-on-investment calculations, including greater efficiency, speed, and endurance.
Head Size
The smaller the handpiece head, the better the clinical visibility. Posterior and pediatric use, particularly with short shank burs, is facilitated. Large and small handpiece heads have similar bearing specs, but smaller heads use more turbine impellers to maintain torque.
Motor RPM Range
The bur revolutions per minute (rpm) indicate the cutting efficiency. Electric handpieces have constant and consistent torque at any bur rotational speed while air-driven handpieces’ cutting torque is related to rotational speed.
Lubrication
The maintenance protocol must be simple and straightforward. Regular lubrication, where required by the manufacturer, greatly improves the handpiece performance and service life.
Chucking
A self-contained chucking process is most efficient. Bur-changing mechanisms are highly user-specific. The more complicated the chucking mechanisms, the more prone they are to break down.
Retrofitting Electric Handpieces Onto Air Lines
Most North American practices use compressed, air-driven handpieces. Electric handpiece systems are easily retrofitted onto existing operatory air tubing. The dentist’s pedal rheostat regulates the handpiece cutting speed, as before.
Air/Water Ports
The handpiece air and water sprays cool the teeth and oral surfaces during cutting and displace debris to permit continuous unobstructed operation. A single water and air outlet may be adequate, but multiple ports offer greater efficiency, better visibility, and less risk of blockage.
Fiber-Optic Illumination
The overhead dental light is often blocked by the dental team’s heads, hands, and instruments, reducing illumination of the treatment area. Fiber-optic handpieces directly lighting the operative site are always preferable. Illumination facilitates diagnosis, tooth preparation, and restoration, decreasing stress and strain for both dentist and staff.
Handpiece 360° swivel
Nonswivel handpieces can cause significant operator hand and arm fatigue. The cumulative damage over months and years may actually shorten the practitioner’s career. A 360° swivel attachment between the handpiece and the hose absorbs and dissipates rotational stresses, decreasing the risk of repetitive dental practice strains, and injuries.
Quick Disconnect
Sterilization of high-speed handpieces between patients is mandatory. A quick disconnect feature saves valuable chairside and assistant time by allowing handpieces to be repositioned quickly between patients.
Sterilization
Many handpieces are cycled through the sterilizer 1,000 times per year or more. High-quality instruments will continue to function without decreased power or efficiency. Some handpieces specify preferred sterilization modes: steam autoclaving, dry heat, or chemical vapors. Note the maximal recommended autoclave temperature that the handpiece components are designed to tolerate.
Cartridge Replacement
All handpieces eventually wear and break down over time. Bearings often go first, but all moving parts tend to deteriorate. The most common and most durable repair is the cartridge replacement, where the old turbine assembly is replaced with a brand new one.