Console

The console contains all of the electrical circuitry; the controls for speed, torque, irrigation pumps, and handpiece selection; the power source; and a light-emitting diode (LED) readout for revolutions per minute (rpm). Even the foot-controlled rheostat plugs into the unit and is powered by the console (Fig. 6-3).

FIGURE 6-3. The console, an electrical housing for low-speed, high-torque drilling equipment, should show the speed in an LED readout. It also should have adjustments for controlling the equipment, the capability to pump irrigant to the drills and to signal reverse direction, and when available, the capacity for two motors.

Power is supplied to the console directly from any standard 110-V electrical wall outlet. Consoles are produced as solid-state electronic devices. They are explosion and spark proof and lightweight (weighing 7 to 11 pounds). If implant surgery is planned in a hospital operating room, a special shockproof attachment is required for the console, and its electrical safety must be verified for the institution’s biomedical engineers. Either the manufacturer’s or the hospital’s engineering department can provide these services.

Electric Motors

The motor housing cord plugs into the front of the console and uses its voltage supply, much the same way a cassette or CD player uses a stereo amplifier (Fig. 6-4). The tiny motors inside the housing are commonly referred to as micromotors, and they are designed to run at different speeds.

FIGURE 6-4. Electric motors are handheld and should be capable of a variety of speeds and torques. Backup equipment is recommended in case of motor failure during the procedure.

The motors most commonly used for root form implants turn at 20,000, 30,000, and 40,000 rpm. However, some motors from the same manufacturer and even the same lot can run 2000 to 3000 rpm faster or slower than others. For simplicity, these motors can be grouped into any of the three rpm ratings categories (20,000, 30,000, and 40,000). It is critical that surgeons know the motor rating, for two reasons: (1) generally, a 20,000-rpm motor has more torque (power) for bone tapping at lower speeds, and even at equal speeds, than does a motor rated at 30,000 or 40,000 rpm; and (2) because all motors loose some speed when drilling bone, a 20,000-rpm motor may not be capable of delivering the speed required to maintain the power that a high-rated motor may have.

An example can clarify the second point: Implant company A recommends using no less than 1200 rpm to perform a certain procedure. Different handpieces are available that can motors of 20,000, 30,000, or 40,000 rpm to 1200 rpm. In dense bone, electric motors often lose as much as 50 to 300 rpm per 1200 rpm (up to 25%) while cutting. The actual top speed for a 20,000-rpm motor with a reduction handpiece might drop to as low as 900 rpm at full power, which might result in burnishing of the bone. However, if the same handpiece is used with a 30,000-rpm motor, the speed could be increased another 600 rpm (to as high as 1500 rpm), which would compensate for the loss caused by the dense bone.

As a simple rule of thumb, when speeds higher than 1000 rpm are needed, a 30,000- to 40,000-rpm motor should be selected. If most of a practitioner’s procedures require less than 1000 rpm and many ultraslow procedures are expected (i.e., below 300 rpm), both a 20,000-rpm motor and a 40,000-rpm motor cut adequately at speeds well under 300 rpm; however, as may be seen in the following section, the practitioner should have many more speed-reduction handpieces.

The significance of the LED speed readout found on electrical consoles requires explanation. If a motor is rated at 20,000 rpm and a 10:1 reduction angle is chosen, the practitioner presses the 10:1 selector button on the console. The readout then shows a velocity of 2000 rpm. It is important to understand that the selector switch neither increases nor decreases actual speed; it simply calculates the change mathematically on the LED display. The only way to increase or reduce speed on any electrical or air- or nitrogen-powered system is to change the posture of a hand or foot rheostat.

Most practitioners who purchase an electrical delivery system buy the console and motor together, because one manufacturer’s motor may not couple with the console of another manufacturer. To ensure greater accuracy in readings, one brand should be chosen for all components.

The practitioner also must choose between single-motor and double-motor systems. A single-motor system can accommodate one motor. A dual arrangement allows two independent motors to be attached to a single console. The main differences between the two systems are price and versatility. With a double-motor console, the surgeon may set the motor and the handpiece for different speeds independently of each other. Motor 1, for example, can be programmed to cut at a maximum of 1200 rpm for development of an osteotomy, and motor 2 can be set to cut at 15 rpm for bone tapping. Because they cannot work simultaneously, such features as LED readout, irrigant pumps, and rheostats work only with the motor in use. If the budget permits and more than one speed range is required for certain implant surgical procedures, a double-motor system is recommended. In addition, double units eliminate the wasted time spent changing handpieces and water spray cannulas. Because most system failures occur in the motor and not the console, an additional benefit of a dual drive is the assurance of a backup device if one motor fails.

Piezoelectrical Ultrasonic Surgical Unit

The piezoelectrical ultrasonic surgical unit is not new, but it currently is not as extensively used as perhaps it should be. The ultrasonic micro-oscillation motion of the root form diamond insert, which has a rounded end cutting tip and parallel side-cutting edges, immediately creates an osteotomy by virtue of a simple vertical sweeping motion. Also, the osteotomy can be expanded sequentially to the approximate desired diameter through use of insert tips of incrementally increasing diameter.

Troubleshooting

If any of the following are noted while the motor is in use, action must be taken:

In such instances, the rheostat should be used to increase motor speed, because this may help reduce the difficulties. To prevent these problems, the practitioner should:

Table 6-1 20,000 rpm Electric and 90 psi 20 k Air or Nitrogen Motors

* Minimum speed at which the bur will cut without stalling.

Table 6-2 30,000 rpm Electric and 90 psi 20 k Air or Nitrogen Motors

* Minimum speed at which the bur will cut without stalling.

The sterility of electric motors is an issue involving cost and versatility. Most autoclavable motors cost three times as much as motors that cannot be autoclaved. Autoclavable motors usually are rated at no more than 20,000 rpm, and they run hotter than motors that cannot be autoclaved because they have no cooling vents. However, motors that cannot be autoclaved can be used with sterile, transparent drapes (e.g., Steri-Drapes, which are supplied with adhesive). These wraps are inexpensive and disposable and fit any standard electric motor (Fig. 6-5). They cover the connections at the console and allow the controls to be used through them.

FIGURE 6-5. A disposable plastic sleeve, which is inexpensive and simple to place, permits motor and cord use without the need to autoclave them.

Handpieces

The term handpiece is one of the most misused words in dentistry. Simply defined, a handpiece is any apparatus attached to an electrical or an air- or nitrogen-powered motor that accepts a bur. There are two types of handpieces: contra-angle and straight (Fig. 6-6); these enable the practitioner to increase or maintain a motor’s speed reliably.

FIGURE 6-6. Dental surgeons need both straight and contra-angle handpieces.

Handpieces that reduce a motor’s top speed are referred to as speed-reduction handpieces. These are rated by the ratio of speed decrease they can achieve (e.g., a 16:1 reduction handpiece reduces a motor’s top speed by 16 times). As speed is decreased, torque is increased by the same ratio. Conversely, reduction handpieces have more power at higher speeds than at lower speeds. This phenomenon is called the handpiece power zone. With a 16:1 reduction on a 20,000-rpm motor, power is greater at 1250 rpm than at 500 rpm. Table 6-1 shows that a 16:1 reduction handpiece has near-maximum power between 950 and 1250 rpm. Below 950 rpm, both speed and power are lost rapidly. If the same 16:1 reduction handpiece is used on a 30,000-rpm motor, the top speed increases to 1875 rpm, and the power zone is found at the 1200-rpm level. It is critical that the surgeon know the motor’s top-rated speed and the handpiece power zone.

Universally, green stripes on a handpiece denote reduction capabilities. If a handpiece is not marked, the reduction ratio should be marked on its surface with a bur.

Instruments that increase a motor’s highest velocity are referred to as speed-increasing handpieces and universally are marked with a red stripe. As speed is increased by a certain ratio, power is decreased by the same ratio. For this reason, speed increases are contraindicated for root form surgery; they should be used primarily for placing blade implants.

Both speed-increasing and speed-reduction handpieces require high maintenance and are up to three times more expensive than ordinary handpieces. Generally, the higher the reduction ratio, the higher the price.

Handpieces that do not increase or reduce speed are commonly known as 1:1 handpieces. They are universally marked with blue stripes.

Power Ranges of Handpieces

Every handpiece has more power at higher speeds than at lower speeds. It is important for the practitioner to know the speed at which the torque of each system is highest. Most of the problems that occur during root form surgery happen because changes in drill diameter are not made in sufficiently small increments and because dull drills are not changed often enough. If the practitioner observes the following six simple rules, as well as the power ranges in Tables 6-1 and 6-2, the chances for problem-free surgery are greatly enhanced:

Table 6-3 presents a list of currently available systems and some of their specifications.

Table 6-3 Handpiece Selection