Abstract
The use of ultrasound in dentistry was first proposed by Catuna in 1953 as a method of cutting enamel and dentin for cavity preparations, but soon thereafter work by other researchers indicated that ultrasound could effectively be used to remove deposits from teeth. From the initial acceptance as a method of supragingival calculus removal to the current application for removal of supra- and subgingival calculus, plaque biofilms, and bacterial by-products, research has shown power scaling to be at least as effective as hand instrumentation and, in some cases, to be superior. Rapidly changing technology has revolutionized periodontal therapy by providing a wide variety of power scaling devices and instrument tips to meet the needs of almost all clinicians and treatment settings. Integration of effective power scaling techniques into periodontal debridement can improve clinical outcomes and patient comfort and reduce time and physical demands on clinicians.

A Historical Perspective
When the development of the high-speed handpiece made the use of ultrasonics impractical for the original purpose of cavity preparation, a new era of calculus removal arrived.¹ By the late 1950s, the first power scalers were being used to remove heavy supragingival calculus deposits (Figure 1), and by the 1960s they were declared acceptable, effective alternatives to hand instrumentation. Throughout the 1960s and 1970s, both patients and operators found the process of calculus removal less tiring; however, the bulky tip design severely limited access to subgingival areas. The Gracey curet continued to be the instrument of choice for use in periodontal pockets.²

During this time, evidence was mounting that bacterial plaque was the primary causative agent in periodontal diseases, and the removal of all calculus and a glassy, smooth root surface were not necessarily requirements for periodontal health. Studies showed that although hand instrumentation produced a significantly smoother root surface compared with ultrasonics, there was no corresponding relationship in the reduction in inflammation between the 2 techniques. In 1983, Khatiblou and Ghodossi reported that surface roughness actually promoted reattachment of connective tissue to the instrumented root surfaces, indicating that hard, glassy root surfaces, previously considered clinical endpoints of treatment, were not necessary for healing.³

By the late 1980s, the need for improved access to subgingival areas led to the development of slim-diameter ultrasonic instrument tips that were significantly smaller than the working end of a standard Gracey curet. This improved technology allowed disruption of plaque biofilms and calculus deposits in deep periodontal pockets and furcation areas that was equal to or superior in some cases to hand instrumentation.^1-19

By the 1990s, it had been established that lipopolysaccharides or endotoxins contained in the cell walls of gram-negative periodontal pathogens were extremely cytotoxic, and that they could easily be removed from diseased root surfaces by both hand instrumentation and power scalers.^1,2,4-8,10 The removal of "necrotic cementum" was no longer the endpoint of treatment, and a new era of cementum conservation was ushered in.

The new terms nonsurgical periodontal therapy and periodontal debridement more accurately reflect the new treatment goals of dental hygiene than the traditional term scaling and root planing. Periodontal debridement includes supra- and subgingival scaling, but the primary focus is to disrupt the plaque biofilms while minimizing the removal of tooth structure.²⁰ The primary goal is to control bacterial plaque to a level that is compatible with gingival health, not necessarily the hard, glassy root surface that had been the ideal during the 1970s and 1980s.² Periodic removal of subgingival microbial biofilms is imperative to arrest periodontal infection and destruction because the pathogenic bacteria can repopulate pockets within weeks of active therapy.⁵ 

• Manufacturers of Power-driven Scalers and Instrument Tips

Although modern power scalers play a crucial role in successful periodontal debridement, many clinicians are still hesitant to use ultrasonic and sonic scalers for deplaquing or for patients without heavy calculus deposits. Frustration and the perception of poor performance are often based on lack of understanding about and training on the proper use of either the devices or the instrument tips.^2,3,11-16

Mechanisms of Action of Power-driven Scalers
Today's electronically powered devices include ultrasonic and sonic scalers (Figures 2 through 4). Ultrasonic scalers have an electric generator and do not need to be connected to the dental unit. The 2 main types are magnetostrictive and piezoelectric. Sonic scalers are connected to the dental unit's compressed air valve. Research indicates that all types of powered scalers are as effective as hand instrumentation, and each type has its advantages and disadvantages.^1-19 Table 1 provides a comparison of powered and hand instrumentation. Selection of specific devices should be based on operator preference and patient needs. Table 2 details the different types of power-driven devices. To obtain the maximum benefit from the use of these devices, it is important to understand how they work.

Frequency is the number of times an instrument tip vibrates per second. A hertz (kHz) is a unit of energy that measures the cycles per second. Frequency varies from 2500 Hz to 8000 Hz for sonic scalers and from 18,000 Hz to 50,000 Hz for ultrasonic scalers. Although frequencies can vary among available power-driven scalers, all instrument tips vibrate fewer times per second at low power settings than at high power settings.

Amplitude or stroke refers to the distance the instrument tip moves during one cycle. Stroke length, which ranges from 10 µm to 100 µm, is controlled by the power setting. High power settings produce longer, more forceful strokes; lower power settings produce shorter, less forceful strokes. As a general rule, the strokes produced by high power settings are more uncomfortable for the patient, more likely to cause tooth surface damage, and are no more effective than medium power settings. Therefore, use of high power settings is not recommended by most clinical experts.^1,2,5,10

Cavitation is the action created by the formation and collapse of bubbles in the water or fluid exiting the tip, creating shock waves that lyse or tear the bacterial cell walls.

Acoustic streaming or turbulence is the agitation of this discharged fluid in the confined space of the periodontal pocket produced by the continuously vibrating tip. This intense swirling effect will disrupt bacterial biofilms.

Lavage or irrigation is the therapeutic washing of the periodontal pocket and cemental surface from the constant stream of water exiting the point of the instrument tip. The irrigation washes away toxic bacterial by-products and provides a cleaner working area by removing blood from the treatment area.

Stroke motion is the motion in which the operator moves the instrument tip. Multidirectional, light, overlapping strokes are recommended by many clinical experts.^{2,4,8,12-15,19,20,22}

Effectiveness of electronically powered instruments is determined by the instrument tip's frequency, stroke length, stroke motion, and the tip surfaces in contact with the tooth. Electrical currents are used to produce rapid vibrations of the instrument tip. The high vibrational energy crushes and removes calculus with a cooling water lavage. The main action of the power-driven scalers is mechanical vibration; however, cavitation, acoustic turbulence, and lavage all have positive roles in periodontal debridement.^{1-18, 20}

Advantages of Power-driven Scalers
Most periodontal experts today report that the best results for nonsurgical periodontal therapy are achieved by a blended approach: the combined use of power-driven devices and hand instrumentation.^1-8,11-18,20 Research indicates that electronically powered devices are not only as effective as hand instrumentation, but also have some significant advantages over hand instrumentation when used by a skilled clinician.

• Calculus removal—Power-driven instrumentation is as effective as hand instrumentation in shallow pockets, and significantly more effective in pockets > 4 mm.^1,2,4-8,20

• Removal of oral biofilm— Power-driven instrumentation is extremely effective in disrupting and removing subgingival plaque biofilm from root surfaces and pocket areas, making these devices especially helpful for patients on frequent recare appointments whose primary need is deplaquing for maintenance of periodontal health.^2,17-19

• Furcation access—Power-driven instrument tips with slim diameters are more effective in treating class II and III furcations in the hands of experienced clinicians.^{1,2,7,13,17-20}

• Conservation of tooth structure—Used properly, power-driven instrument tips on low or medium power settings remove less root surface than hand instrumentation, although the amount of root surface removed depends on the specific power scaler type used. Ritz and colleagues found that ultrasonics removed 11.6 µm, sonics removed 93.5 µm, hand instruments removed 108.0 µm, and diamond burs removed 118.7 µm.^{1,2,13,15,20,21}

• Penetration into deep periodontal pockets—Power-driven instruments with slim-diameter tips penetrate more deeply into periodontal pockets than hand instruments.^{1,2,4-8,17-20}

• Lavage—Irrigation improves vision and helps speed healing by removing toxic bacterial by-products.^2,17-19

• Bacteriocidal effect—Cavitation and acoustic turbulence allow power-driven tips to disrupt plaque biofilms even slightly beyond the tip of the activated instrument.^2,17-19

• Shorter instrumentation time compared with hand instrumentation.^1-8,10-20

• Increased patient comfort— Tissue distention is a primary factor in patient discomfort. Power-driven devices require very little lateral pressure and a slim-diameter tip allows less tissue distention, resulting in increased patient comfort.^12-14

• Improved operator ergonomics—Dental hygienists are estimated to apply over 32 tons of scaling force per year by using over 25,000 scaling strokes for calculus removal. Use of power-driven scalers reduces the need for lateral force to remove calculus deposits, thereby reducing the risk of carpal tunnel syndrome and other musculoskeletal disorders.^{2,7,8,15,17,18,20}

• Increased tactile sensitivity during longer appointments—Research from Ryan and colleagues found that dental hygiene students lost tactile sensitivity after hand scaling for 45 minutes. Students using ultrasonic instrumentation reported no decline in tactile sensitivity.^15,16

Limitations and Concerns with Power-driven Scalers
• Aerosol production—Powered instruments may generate high levels of contaminated aerosols, although adjusting water flow so that a drip rather than a mist is produced will greatly decrease aerosol production.  Adjusting the frequency and power setting is another method of decreasing aerosol production. Having a patient use a preprocedural mouthrinse can reduce bacterial counts in aerosols by more than 90%. Patients with communicable diseases or at high risk for infection should not be treated with power-driven scalers because of the high production of potentially infective aerosols.^2,13,14 Proper use of personal protective equipment, effective surface disinfection and barriers, high-velocity evacuation systems, and air-filtration systems are additional safety measures.^1,2,15,17

• Effect on cardiac pacemakers—Although all modern pacemakers are shielded, care must be taken if magnetostrictive ultrasonics or ultrasonic instrument cleaning devices are used that generate a magnetic field that might interfere with certain types of cardiac pacemakers.^1,2,18,19

• Infection control—Not all components of electronically powered devices can be sterilized. When purchasing a new unit consider whether the handpiece and fluid reservoir bottles may be sterilized.²

• Water production and visibility— Operators must learn to manage water production and visibility. Position the patient in a supine position with the head turned to the side and chin pointed down. This position allows the water to pool in the corner of the mouth, where it can easily be suctioned. Cup the patient's lips and cheeks to form barriers to deflect the water spray. Use of a power-driven scaler is contraindicated with patients who are at risk of aspiration into the respiratory tract because of breathing or swallowing difficulties or patients with a strong gag reflex.^2,13,14

• Primary or newly erupted teeth with large pulp chambers— In the past, power-driven scaling was contraindicated for these patients because of the possibility of damage to the large pulp chambers from vibrations and the heat produced by ultrasonic instrumentation. These concerns are no longer valid if the recommended low to medium power settings and adequate water flow are used because the amount of heat generated will not be sufficient to harm the pulp.

• Oral conditions—Ultrasonic or sonic use is contraindicated for patients with hypersensitivity, demineralized areas, porcelain or composite resin restorations, and titanium implants (unless a specially designed tip for this purpose is used).

Tip Selection
Use of early power-driven tips was limited to supragingival and gross debridement because the tips' bulky design lacked the complex shanks needed to adapt to deep periodontal pockets. Drs. Thomas Holbrook and Sam Low are credited with adapting Dentsply International's (York, Pa, www.dentsply.com) original Cavitron tips to work in subgingival spaces by filing down the tips and modifying the fluid supply mechanism.¹⁴

By the early 1990s, manufacturers began to produce slim-tipped inserts that were approximately 30% to 40% thinner than standard inserts. The slimmer profile greatly increased access to pocket depths > 4 mm, improved patient comfort by reducing tissue distention, and decreased tooth surface lost.^{1,2,5,11,12,20}

An array of tips for both ultrasonic and sonic scalers is available, varying in tip shape, diameter, length, curvature, and tip material composition. Specialty tips are available to use on implants and to remove amalgam overhangs. Diamond-coated tips for tenacious calculus can increase clinician effectiveness; however, they are only indicated for use with an endoscope or during open-flap surgery. Plastic-covered tips can safely debride implants. Power-driven tips also have a multitude of features to increase operator comfort, such as cushioned grips, swivel mechanisms, and fiber-optic lights.

The primary factor in selection of an instrument tip is the type of deposits to be removed (biofilm; light, medium, or heavy calculus) and the location of these deposits²²:

• Standard-diameter tips should be used for heavy or medium calculus deposits and orthodontic cement removal.

• Slim-diameter tips should be used for light calculus deposits and biofilm disruption in pockets > 4 mm. Using a slim-diameter tip to remove medium to heavy calculus is ineffective, causes excessive tip wear, and may result in tip breakage and burnishing of calculus.

• Straight or universal tips are designed to be used in pockets < 4 mm.

• Curved tips with right and left access are designed for deeper pockets, using the back of the instrument against the curved root surface in the same manner as using a periodontal probe.

Technique
Research validates that a skilled clinician can adequately remove calculus with both hand and power-driven instruments; however, power scaling instruments have additional benefits, such as reduced operator fatigue and scaling time.^{1,4,5,7,8,12-15,17-20,22} The techniques used with power-driven scalers are different from those used during hand instrumentation, requiring significant training for clinicians just starting to use power scalers. To be effective, hand instrumentation depends on strong lateral pressure and adaptation of the instrument below the calculus deposit (bottom-up). Power scaling requires very light pressure to allow the vibrations to break up the deposit, and adaptation at the most coronal portion of the deposit (top-down). Just as multiple working strokes are required to remove heavy deposits with hand instruments, multiple working strokes and adequate instrumentation must be used with power scaling instruments. Power scalers are not magic wands that can simply be tapped on deposits to make them disappear. The correct portion of the tip (follow manufacturers' directions) must be in contact with the deposit, and a series of gentle taps on the deposit will gradually fracture it and allow it to be removed. Subgingival deplaquing is effectively accomplished with a series of gentle sweeping movements and short, multidirectional, overlapping strokes that cover every millimeter of root surface. It is critical with both calculus removal and deplaquing that the tip be constantly moving in combination with light, gentle strokes.²² If using curved tips, complete debriding with the right tip before switching to debride with the left tip (Figure 5). Table 3 lists tips for effective power-driven scaling.

Clinicians new to power scaling are often frustrated with the units' water production and the lack of visibility. Adjust the patient's position with the head tilted to one side so that the water pools in the corner of the mouth where it can be easily evacuated. This will greatly improve the clinician's access and visibility. Some units have a fiber-optic light within the tip, providing excellent illumination. With a little practice, clinicians will quickly feel comfortable using power-driven scalers along with hand instruments to provide the most effective patient care with the least amount of effort and discomfort to both patients and the operators. Clinicians who are skilled with hand instruments can become skilled with power instruments within a few practice sessions as long as well-maintained tips (Figure 6) and the principles of power scaling are used.

Conclusion
A new understanding of the cause and progression of periodontal disease has led to dramatic changes in treatment. The gram-negative periodontal pathogens in oral biofilms are necessary to initiate and continue disease progression, and disruption and control of these biofilms are essential to periodontal health. Nonsurgical periodontal therapy can effectively accomplish this goal as well as provide the best possible treatment results for our patients by combining hand instrumentation and power-driven scaling. Understanding the debridement options can maximize operator and patient comfort and provide more efficient and timely treatment.

References
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19. O'Neill-Smith K. The use of ultrasonics for the disruption of subgingival plaque biofilm. J Prac Hyg. 2006;15:14-15.

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22. Nield-Gehrig JS. How to get the most out of ultrasonic instrumentation. Special Report. Available from: Parkell, Inc, Edgewood, NY: http://parkell.com/gehrigarticle.html Accessed May 14, 2007.

Barbara L. Bennett, CDA, RDH, MS
Barbara has been actively involved in dentistry for more than 30 years, and involved with presenting and developing dental hygiene and dental assisting national board review workshops for the past 15 years. She is the department chair for Texas State Technical College dental hygiene and dental assisting programs, and the division codirector for Allied Health Programs. She has been a contributing author for several dental hygiene textbooks, and has reviewed and written articles of interest to dental personnel in several professional publications.