Power to the Handpiece

How do you select a handpiece? Which one fits the workflow rhythm of your practice? The two main types—air-turbine and electric—have unique characteristics with associated advantages and disadvantages. Excellent results can be achieved with both, so the choice of one over another resides with the team’s training, experience, practice needs, and style of working.

Traditional high-speed handpieces employ an air-driven turbine to rotate the rotary cutting instrument. With this equipment, high speeds can be attained, between 250,000 and 420,000 rpm. Air-driven handpieces are appreciated in dental practices for their lighter weight and slimmer design, in addition to generally lower repair and startup expenses.

However, the bur can slow under heavy loads, reducing cutting ability. Another disadvantage of traditional air-driven handpieces are the bearings, which may cause the bur to wobble as they age, causing the “chatter” that patients dislike.

Electric handpieces operate at a minimum of 20 rpm and reach up to 200,000 rpm, depending on the type and attachments used. With these variations, a single electric handpiece can be employed for all high-speed (restorative and endodontic) and low-speed procedures (restorative, hygienic, endodontic, surgical, and laboratory).

With electric handpieces, the bur is connected through gears in the head of the handpiece to a central drive shaft that is physically turned by the motor. Because of the absence of air, these options are quieter and the chance of air embolism in a surgical site is eliminated.

Electric handpieces are also typically heavier and bulkier, due to the mechanics to drive the shaft connected to the bur. The weight and design of the typical electric handpiece has been known to be fatiguing, although newer models have been streamlined to reduce weight and drag and to improve ergonomics. In addition, startup costs may be greater and repairs may be more expensive for these types of handpieces.

One of the issues with using an electric handpiece is ensuring that the handpiece head (“back cap area”) does not overheat. The FDA is again alerting dental professionals that serious patient burns can occur when electric dental handpieces overheat during dental procedures. Burns may not be apparent to the operator or the patient until after the tissue damage has occurred, because the anesthetized patient cannot feel the tissue burning and the handpiece housing insulates the operator from the heated attachment. These burns range from first-degree burns to third-degree burns requiring reconstructive surgery.

To reduce the risk of these types of injuries, the FDA is recommending that dental professionals:

• Be vigilant about maintaining electric dental handpieces and electric oral bone cutting handpieces according to the manufacturer’s instructions.

• Verify with the manufacturer the appropriate routine service interval for your dental practice, based on the actual use of your electric dental handpiece or electric intraoral bone cutting handpieces.

• Train personnel to properly clean and maintain the electric dental handpiece or electric intraoral bone cutting handpiece.

• Develop a method for tracking maintenance and routine service for each dental handpiece or electric intraoral bone cutting handpiece.

• Examine the electric dental handpiece attachments and electric intraoral bone cutting handpiece attachments prior to use. Do not use worn drills or burs.

• Discontinue using poorly maintained electric dental handpieces or electric intraoral bone cutting handpieces.

• Report overheating to the manufacturer.

Adaptation to electric handpieces does have a learning curve. Unlike an air-driven handpiece, the electric model has constant torque; therefore, a lighter touch is required so that over-preparation does not occur when cutting tooth structure.

Cutting efficiency is a balance between the speed and torque delivered to the bur. Although air-driven handpieces reach speeds up to 420,000 rpm, the torque (the tool’s cutting power) is relatively low. When a bur in an air-driven handpiece contacts material to be cut, the speed will drop significantly. Depending on the hardness of the material, as resistance builds during cutting, the air pressure cannot maintain the speed of rotation of the turbine. The harder the material being cut, the more resistance is created and the slower the bur spins. The user’s instinctive reaction is to place more pressure upon the bur, which increases resistance even more.

With electric handpieces, the unit senses the resistance and increases the speed to keep the torque in a specified range. Therefore, the output with electric handpieces is greater, offering 33 to 45 watts of cutting power. Because they offer smooth, constant torque, electric units cut more efficiently and faster, even with less power. Removing difficult crowns, bridges, and restorations becomes easier.

Another difference is that in electric handpieces, power output is not dependent on head size. Some manufacturers offer smaller-head handpieces that may be beneficial in pediatric applications or in the posterior.

The gear ratio imprinted on electric handpieces helps identify what procedures are best performed. The ratio is expressed as X:Y, with a high-speed handpiece having a 1:5 ratio, and those intended for slow-speed procedures having a 1:1 ratio. Some companies also offer handpieces for “ultra” slow-speed procedures with a gear ratio of 10:1 or 16:1.

Typical procedures with a high-speed (1:5) handpiece include cavity preparation, crown preparation, and sectioning existing fixed prosthetics. These high-speed handpieces accept standard friction-grip burs or diamonds and push-button bur chucks.

Slow-speed (1:1) handpieces are indicated for caries removal, preparation refinement, and adjustment of ceramics. Depending on the manufacturer, slow-speed heads are available in either a friction-grip or latch-grip. The benefit of a friction-grip slow-speed head is any bur that can be used in a high speed can be alternatively used in a slow speed.

Many of the models on the market today highlight the superiority of their design. Thoughtful, precise variations add up to a higher quality experience for the dental team and the patient.

For example, head sizes have been reduced to provide better visibility and access. These handpieces are becoming significantly smaller and lighter, increasing practice efficiency and patient comfort. Smaller head sizes allow for greater visibility and access. Improved head angles increase posterior access. Newer body shapes reduce hand and wrist fatigue, while enhancing maneuverability and control.

Turbine cartridges have been steadily improved to enhance longevity and reduce noise. Innovative materials have made it possible to repeatedly sterilize the handpiece without degradation in looks or performance (the current state-of-the-art is titanium, which is lighter and stronger). Chucking mechanisms have been improved with push-button releases to facilitate insertion and removal of the rotary instrument. Swivel connectors reduce the resistance from tubing, and quick disconnects facilitate removal of the handpiece.

A technology has been introduced for air-driven handpieces that monitors the bur speed several hundred times per second. A sensor in the coupler detects the frequency of vibrations from the rotating bur, and when the bur encounters a higher load that could decrease speed, a signal from a small chip in the control source increases air pressure to maintain speed, virtually eliminating stalling to produce a smooth, consistent cutting speed regardless of load. Because the system adjusts speed when the bur is not under load, wear on bearings is minimized, which means fewer turbine replacements.

Another technology, Superior Turbine Suspension, allows the handpiece to operate at 330,000 rpm under load, with no noticeable bur deflection or chattering. This provides control and a consistent transference of power from the handpiece to the bur, helping overall cutting efficiency. It is especially beneficial for margin refinements, veneer preparations, and other fine restorative procedures.

Systems with auto-calibration technology do not require adjustment to other equipment, offering a simplified setup and a seamless transition. Once calibrated, this system allows for an air-like “feathering” effect between 30,000 rpm to 200,000 rpm with the foot pedal.

Fiber-optic lighting has dramatically improved the dentist’s ability to see the work area. Cellular optics offer good resistance to degradation but are more fragile. Significant advances are also emerging with light-emitting diodes (LEDs), which will be able to provide better intraoral illumination and a longer bulb life. These bulbs offer energy-efficient options for handpieces to switch to a cool-white LED light source with a neutral daylight color, which often lasts up to 10 times longer than a halogen bulb.

All these details add up to a better experience for the dental team and the patient. How equipment “handles” is a subjective response. You can quantify some aspects of handpiece performance, but you can’t quantify how seamlessly it works in your practice and your hand. Dentistry has never had such a wide range of options in handpieces—improving efficiency, safety, and comfort, and enabling more precise procedures. These benefits are noticeable to your patients, and often set your practice apart as technologically advanced and patient-friendly.

Constant Torque: An electric handpiece can reach a speed of 200,000 rpm (60 W cutting power). While an air-driven handpiece can reach 400,000 rpm, its torque may drop to less than 20 W when the bur meets resistance (even lower with cast metals). The electric handpiece can maintain constant torque regardless of the material being cut, because the motor can increase its power.

Size and Weight: Electric handpieces have the reputation of being heavier. However, with the constant redesign over the years, electric handpieces are now lighter and smaller since they first appeared on the market—and therefore easier for some to handle—and may warrant reconsideration.

Bur Chatter: Electric handpieces are constructed with solid gear-to-gear contact and bearing support. Because there are no bearings, there is nothing to cause the bur to wobble, and chatter is eliminated. And this lack of vibration allows precision cutting of preparation margins in less time.

Sound Level: Hearing loss is an occupational hazard for the dental team. Today’s electric handpieces are much quieter than traditional air-driven handpieces, with some manufacturers lowering the noise level of electric handpieces significantly.

Equipping the Practice: A standard handpiece connector is attached to the back of the electric system’s control unit box, and the unit is mounted under the bracket table. This connection to the air line allows use of the current rheostat to run the electric handpiece. Additionally, “chip air” is required through the water line, to create a mist at the terminal end of the handpiece during cutting.

Lasers are quiet, vibration-free, and allow many dental restorative procedures to be accomplished without anesthesia. In addition, the ability to move between quadrants without anesthesia improves clinical efficiency. Lasers are also considered kinder to teeth because there is no microfracturing and no smear layer resulting in open dentinal tubules.

Erbium-based lasers are effective in caries removal and cavity preparation, while minimizing thermal and collateral damage. However, they do not cut as fast as high-speed handpieces. Erbium lasers cannot be used to remove amalgam, but can be used to very selectively remove recurrent decay around existing crowns or veneers and to remove composite restorations.

In 2013, the FDA approved a CO² laser technology system for ablation of hard tissue for caries removal and cavity preparation (SOLEA, Convergent Dental, www.convergentdental.com). This system, unlike erbium, does not require a drill to complete most procedures.

Laser dentistry gives practitioners the ability to quickly and effectively remove decay, completing unscheduled procedures in one appointment. Other potential advantages include no-anesthesia procedures, a reduction in postoperative sensitivity, and clinically esthetic adhesive restorations.