Electric Dental Handpiece are rapidly replacing traditional air-driven, high-speed handpieces in the US market. Industry estimates indicate that only 20% of practices employ an electric handpiece for restorative treatment, whereas in the European market over 80% of restorative practices are employing electric handpieces to prepare teeth for restorations. Practitioners who have tried electric handpieces become quick converts to the benefits of preparing a tooth for a crown with an electric handpiece.
Speed and Torque
Two factors to understand when comparing air-driven vs electric handpieces are speed and torque. Speed is expressed in revolutions per minute (rpm), whereas torque is expressed in watts and is an indication of the tool’s cutting power. Air-driven high-speed handpieces typically will have speeds between 250,000 and 420,000 rpm but the torque is relatively low, whereas an electric handpiece may have speeds around 200,000 rpm but relatively high torque. This implies that air-driven handpieces are faster than electric handpieces. However, when a bur in an air-driven handpiece contacts material to be cut, the speed will drop by as much as 40% or more (depending on the hardness of the material) because as resistance builds during cutting, the air pressure is insufficient to 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. Our instinctive reaction is to place more pressure upon the bur to get it to cut the material, which increases resistance even further, creating a vicious circle.
An electric handpiece offers smooth, constant torque that does not vary as the bur meets resistance. 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 handpieces are quieter and the chance of air embolism in a surgical site is eliminated. Thus, the power output with electric handpieces is greater than with air-driven handpieces, offering 33 to 45 watts of cutting power. Because the speed and torque are constant, removing difficult crowns, bridges, and restorations becomes easier. Electric motors also offer accuracy by enabling the end user to set precise speeds for procedures, rather than the conventional “feathering” of the rheostat. Another difference between air and electric handpieces to consider is that in electric handpieces, power output is not dependent on head size. Some manufacturers offer smaller-head handpieces that may be beneficial in pedodontic applications or when operating in the posterior in confined spaces (Figure 1).
Cutting efficiency is actually a balance between the speed and torque delivered to the bur. A good way to demonstrate this is the “penny test.” Take a penny and grasp one end with a pair of locking hemostats to stabilize the penny. Next, using a carbide bur in the handpiece, cut a slot in the penny. Typically, the air-driven handpiece will bog down as it attempts to cut the slot and may stall as increasing pressure is placed on the bur. The electric handpiece will demonstrate smooth, even cutting without bogging down. This test is a good demonstration of how the handpiece may act clinically when preparing a tooth with an amalgam core or cutting a slot in a nonprecious crown to aid in its removal.
Understanding Gear Ratios
Electric handpieces will have a gear ratio imprinted on the handpiece which helps identify what procedures are best performed with that particular gear ratio. 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 ratio expressed as 1:1. Some companies also offer handpieces for “ultra” slow-speed procedures such as pin placement or endodontics with a gear ratio of 10:1 or 16:1.
Typical procedures done with a high-speed (1:5) handpiece would be 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 would be 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. Additionally, friction-grip burs typically retail for less than half the cost of latch-grip burs and diamonds are only offered in friction-grip applications.
Couplings and Connectors
Currently, all electric handpieces offer the standardized ISO coupling between motor and attachment (also called electric or universal coupling). The abbreviation for this universal electric connector is termed an “E” connector. The benefit of this is that most electric handpieces will fit any manufacturer’s motor. The exception is the Star Dental (Lancaster, PA) connector, which has a variation on the aligning tab used to line up the fiber optics that differs from the standard alignment tab. This variation presents as a round tab on the motor end and a corresponding round dimple on the handpiece. The standardized E connector that is used by other manufacturers presents with a rectangular depression on the motor with a corresponding tab on the handpiece. But before switching to a different brand of handpiece than the motor’s manufacturer, make sure that if the handpiece is lighted that the optics connection in the coupling will work with your current motor cable (Figure 2).
Sirona also offers a propriety connector in addition to its standard E connector. This connector places the motor deeper within the handpiece. Practitioners with smaller hands may find the balance more efficient (china dental supplier).
Warranties
Warranties can be confusing in terms of understanding what exactly is covered and for what period of time. Most handpiece companies will warrant the handpiece for at least 1 year. Warranties may be extended and the manufacturer should be contacted for further information on the details. Extended warranties often require use of that company’s lubricant and some require use of their particular lubricating unit.
One aspect to understand is the warranty on the handpieces optics. Current glass-rod technology (fused bundle) is very durable. Most manufacturers provide a 5-year warranty on the optics. Glass rods basically do not deteriorate under repeated sterilization cycles. However, if you drop the handpiece and the rod breaks, typically manufacturers will consider this a void in the warranty and the owner of the handpiece will need to cover any repair costs. Therefore, extended warranties on the glass rods is more or less a marketing tool.
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