Robert DeFrancesco's childhood trips to the dentist were terror-filled ordeals. Still haunted by memories of the high-pitched whine of the drill, he vowed that when he started his own practice he would make the experience more serene for his patients.
Luckily for him, he doesn't seem like the kind of guy who would want to hurt you. And as an Assistant Clinical Professor at Tufts University School of Dental Medicine, he has a jump on some of the latest dental gadgetry designed with patient comfort in mind.
The most recent addition to DeFrancesco's operatory is an electric handpiece (aka drill), manufactured by KaVo, a Germany-based company that also developed the motor technology inside. It is used to perform simple restorative procedures such as cavity preparation, as well as more advanced procedures including crown preparation and root canals. And just think!, if the statistics hold up, most of us stand an extremely good chance of getting to experience this new technology first-hand!
Integrating the electric KaVo 700L motor
directly into the handpiece system was a challenge for engineers, who
wanted to maintain the compact size of a pneumatic drill. Along with a
3.75-inch-long brushless motor, engineers had to locate air and water
coolant lines, as well as a bright light bulb inside the housing. A
patented winding design for the stator provided the necessary clearances.
A primary advantage of the brushless motor is that torque remains constant
over a wide speed range and does not stall out under load, unlike
air-driven drills -- allowing dentists to cut through tooth structure more
quickly and easily.
Air to electric. The innovation from air to electric-powered dental drills actually took place here in the U.S. nearly a decade ago. What's changed today is that KaVo's electric handpiece is one of several new designs to incorporate a dc brushless motor. The technology has several inherent advantages that developers hope will increase electric's share of the U.S. dental drill market, which is estimated to be at only around 15%.
Targeted for non-dental applications as well, KaVo's KL700 motor features a two-pole permanent magnet on the rotor and a patented, 3-phase stator winding. A microcontroller-based unit provides speed control. A significant benefit is its ability to deliver constant, high torque (up to 3.68 oz-in) over a wide speed range (10,000 to 40,000 rpm, extendable to 74,000 to 200,000 rpm with attachments). The dentist selects the desired motor speed via a foot pedal and digital tachometer display. The attachment gears are made of stainless steel or nickel silver, durable enough, says Product Manager Frank Berlinghoff, to hold up under the highest rotational speeds.
He also points out that at 45W, the power output of the motor is substantially higher than the 18W produced by an air-driven turbine. Though perhaps he could have put it a bit more delicately, Berlinghoff says that the increased power gives the dentist more "excavating power," which results in less time to perform a particular procedure.
KaVo isn't the only motor maker that is targeting the market. Danaher Motion's Specialty Motors Group (Amherst, NY) is jumping into dental applications with its own version of a miniature brushless dc motor. Called the "B" series, it employs a 4-pole, permanent magnet rotor design with a 3-phase stator winding. Top speed is 100,000 rpm, and torque can be boosted up to 40 oz-inch through a series of precision planetary gearheads that are available in single and dual stage versions. The unit is also designed to withstand repeated autoclaving.
Torque it up. In most dental procedures, high torque is required to cut through the enamel, or outer layer of the tooth, which has a hardness of 300-400 Vickers. While the amount of material removed depends on the specific procedure, the typical reduction is in the neighborhood of 1 to 2 mm. To achieve the necessary torque with an air-driven turbine requires extremely high speeds (see chart), which can overheat the tooth surface and inflict damage.
"Using the electric handpiece, I am able to cut through tooth structure more quickly, with no stalling of the bur, resulting in less trauma to the tooth," says DeFrancesco, who also noted that it takes less time to perform a complex procedure like preparing a crown. Though he couldn't quantify the exact savings in minutes, DeFrancesco says that it could be substantial once a dentist is fully up to speed (no pun intended) using the new technology.
Not to be underestimated is the potentially enormous benefit of the electric drill's low noise output, especially with regard to the patient's psychological health. In fact, the sound of the drill is what people fear most about going to the dentist, says DeFrancesco. Anyone who has actually had a root canal might debate that, but at 56 dbA (in the range of normal conversation) the KL700 is significantly quieter than an air-driven turbine at around 75 dbA. The reduction is all the more impressive when you consider that decibels are logarithms of noise levels. When DeFrancesco de-monstrated the two drills side-by-side, bystanders agreed that the electric drill was quieter and less harsh-sounding.
Cost a limitation? While dentists may be intrigued with the new drill, the higher cost of electric tools is likely to continue to be a deterrent for some of them—at least in the short term. Costs are expected to fall as volumes increase.
"Cost has been the primary reason that the electric handpiece has been slow to catch on in the U.S. market," says DeFrancesco. "The total price tag including attachments can run anywhere from $2,000 and $3,000 for one unit. Contrast that with an air-driven handpiece, which only costs $500 to $800." He is planning to purchase one electric handpiece for his practice, which he will use only for longer, more complicated procedures.
However, he acknowledges that if maintenance costs are factored into the equation, the electric unit may wind up costing him less in the long run. Several features, including a lube-free motor and faster cutting, could give it the edge. Also, pneumatic drills require air-turbine replacement every 1-2 years.
Summing things up, DeFrancesco says that the electric handpiece "makes dentis-try easier and more enjoyable." Hey wait, dentists aren't actually supposed to take pleasure in drilling teeth, are they?