DENTAL HANDPIECES

A dental handpiece is a precision-built mechanical device designed for use with rotary instruments, such as burs, stones, wheels, and discs, used in dental treatment. Handpieces may be air driven, electric, or compressed gas (for surgical handpieces). Surgical handpieces are discussed in Dental Technician, Volume 2, Chapter 5, "Oral Surgery Assistance."

Handpieces can be classified according to the revolutions per minute (rpm) or speed at which they operate. One type is the low- or slow-speed, and the other is referred to as the high-speed contra-angle.

Both the low- and high-speed handpieces use an air system to operate several parts of the handpiece. The main function of the air is to rotate the air turbine or vane drive. Basically, this means the air system is the main power source for these handpieces.

Fiber optic accessories attached to dental handpieces allow the provider to operate handpieces with a light source and is discussed in this section.

CONTRA-ANGLE HANDPIECES

This type of handpiece is used in cavity preparations to remove the bulk of enamel, dentin, and old metal restorations. It is also used to prepare retention grooves and bevels with a cavity preparation and to develop the cavity outline. The high-speed contra-angle handpieces (fig. 11-8) turn at a higher rate of speed than the slow-speed handpieces. Its speed ranges from 380,000 to 400,000 rpm depending on the model. High-speed handpieces are operated by air pressure. The term contra-angle describes the angle at the head of the handpiece. The contra-angle allows for easy access to treatment sites. Straight designed high-speed handpieces are available, but the contra-angle is the most commonly used in restorative procedures. Before you use one, consult the appropriate manufacturer's instructions.

The high-speed handpieces are designed to use smooth shank burs that are 1/2-inch in length. All models work on the same basic principle: Burs are inserted into a plastic or metal friction chuck and held tight in the handpiece by either manual tightening or a power lever lock. The bur is rotated when air is forced through the airports into the head of the handpiece and to the air turbine.

The high-speed handpiece uses a water system to keep the handpiece cool. The water system also produces a fine spray mist, which aids in flushing debris from the treatment site. Constant preventive maintenance is essential in caring for handpieces. If they are not properly cleaned and lubricated, abrasives, such as finely ground tooth, metal, and other particles, will cause excessive wear and undue vibration. The proper lubrication of handpieces is of such importance that it cannot be overstressed. Read and follow the manufacturer's instructions to make sure that you understand the lubrication, cleaning,

Figure 11-8.\High-speed contra-angle handpiece.

and sterilization requirements. Perform the necessary maintenance as recommended. It takes only a few seconds to ruin a handpiece that has been improperly or insufficiently lubricated, cleaned, or sterilized. Always ensure your handpieces meet the required infection control standards as outlined in BUMEDINST 6600.10,

Dental Infection Control Program.

LOW- OR SLOW-SPEED HANDPIECES

This type of handpiece is used for removing caries, refining a cavity preparation, and performing a prophylaxis.

The low-speed handpiece consists of a motor or power driven unit (fig. 11-9) and various attachments (fig. 11-10). The speed of the motor ranges from 0 to 5,000, or 80,000 rpm depending on the model.

The head of the handpiece attachment contains a chuck into which a dental bur or other rotary instrument is fitted. Most heads contain a latch-type chuck. Some heads contain a friction-grip chuck. On the slow-speed motor is a speed control ring. By turning this ring, you can control the speed with which a bur rotates and its direction of rotation.

Many units and models have some method of quickly connecting and disconnecting the motor and attachments. Some models have a quick ring disconnect, while others have a button to depress or an indicator to press. As with the high-speed handpiece, read and follow the manufacturer's instructions for operation, lubrication, cleaning, and sterilization requirements for the slow-speed motor and attachments.

Figure 11-9.\Slow-speed motor.

Figure 11-10.\Selection of attachments for the slow-speed handpiece, including (from left) straight, latch-type contra-angle, and prophylaxis attachment.