Magnetostrictive vs. Piezoelectric: Survey compares merits of ultrasonic scalers

By Karissa Sebero, CRDH, CDA, and Rachel Kelly, CRDH, BS

The use of power scalers benefits the gingiva and also produces less operator wrist fatigue than hand scaling. Powered scaling devices can be grouped into two categories, sonic and ultrasonic, based on the frequencies at which they operate. Sonic scalers (e.g., the Titan scaler) operate at a frequency of 3,000 to 8,000 hertz (i.e., cycles per second; Hz). They attach to the dental unit's high-speed handpiece tubing and are driven by compressed air. Ultrasonic scalers operate at a higher frequency of about 20 to 50 kilohertz (kHz) and may be either magnetostrictive or piezoelectric. They are typically portable units. A significant benefit of ultrasonic scalers over sonic scalers is the water lavage that deplaques and washes away debris in the periodontal pocket. Additionally, cavitation occurs when bubbles form in the water stream. When these bubbles collapse, they disrupt the cell walls of harmful bacteria. Sonic scalers do not cause cavitation.

Magnetostrictive (available from Dentsply and Parkell) and piezoelectric (available from EMS and Hu-Friedy) power scalers are the two types of ultrasonic devices seen in dental hygiene practice. Both have been clearly proven to be effective for calculus and stain removal. They also both have a variety of inserts for various needs such as removing heavy deposits, root planing, etc. The differences lie in how the two devices function. Magnetostrictive power scalers operate at an optimal frequency of 20 kHz to 40 kHz, whereas piezoelectric power scalers operate at a slightly higher optimal frequency of 29 kHz to 50 kHz. In magnetostrictive scalers, energy is converted to vibrations from the elliptical stroke patterns of the unit's metal rod or stack of metal sheets. All surfaces of the tip are active in the removal of debris. For the piezoelectric scaler, strokes occur in a linear pattern via crystals activated by the ceramic handpiece. Only the lateral sides are effective in the removal of debris.

Energy dispersion

The energy dispersion for the magnetostrictive power scaler makes all its sides effective. The energy output at the tip produces the greatest amount of vibrations. This can cause damage and discomfort to the patient. Therefore, the tip should never be applied directly on the tooth surface. The face of the tip produces the second greatest amount of vibrations. The back of the tip produces less energy than the point or face. The lateral surfaces of the tip produce less energy than the point or the face and are most often used during power scaling.

The energy dispersion for the piezoelectric scaler differs from that of the magnetostrictive scaler, as only the lateral sides are effective. The most effective portion of the tip is the last 2.4 mm and can be compared to a Gracey curette.

Magnetostrictive advantages-All magnetostrictive inserts are universal regardless of the manufacturer, whereas piezo tips are not. Small piezo tips need to be inserted into the handpiece with a special tool and can easily be misplaced. The magnetostrictive handpiece maintains greater infection control than the piezo handpiece as less of it is in direct contact with the patient's mouth. As previously mentioned, another advantage is that all sides of the magnetostrictive tip may be used for removing deposits, unlike the piezo.

Piezoelectric advantages-The piezo requires less water to control heat. It may be more comfortable for patients with breathing conditions such as asthma and chronic obstructive pulmonary disease. The piezo can also be used on all patients with pacemakers, whereas magnetostrictive scalers may not. Older-style pacemakers do not include a shield, so the magnetism from the scaler could interfere with their operation. A thorough medical review to determine if the patient has an older pacemaker is critical. It may require a call to the physician if the patient is unsure.

Metal stacks on magnetostrictive inserts can be easily bent, which could impair vibration and overall function. This is not an issue for the piezo. The piezoelectric handpiece is also wider and therefore more ergonomically designed than the thinner magnetostrictive one. Since the entire handpiece does not vibrate, there may be greater tactile sensitivity with the piezo.

Clinic patients' preferences

With 20 patients included in our patient requirements at Eastern Florida State College, we did a study of our own. We wanted to test the theory that the patients would prefer the piezoelectric scaler over the magnetostrictive because of the decreased water output and vibrations. Before the study, we ensured that all inserts and equipment were adequate and passed manufacturers' guidelines. During the study we used the same clinician, equal power settings, and comparable inserts at the same appointment. This was all performed on the same arch but different quadrants, assuming uniform dentition throughout the arch. Our results from this experiment showed that eight patients preferred the piezoelectric, eight preferred the magnetostrictive, and four were indifferent.

Some patients in favor of the piezo did prefer the decreased water output and vibrations. Patients in favor of the magnetostrictive were indifferent to the water output but believed the vibrations were actually more comfortable than those of the piezoelectric scaler.

We next did a simulation on a typodont with imitation calculus to compare effectiveness and efficiency of calculus removal. For the calculus we used equal parts of plaster of Paris, paint thickener, water based paint, and shellac. We placed it uniformly on the facials of the twelve anterior teeth and let it dry overnight. We then used the same clinician, 66% of each machine's maximum power, and the 100 tip insert for each. Our results revealed that the piezoelectric scaler took nine minutes and 25 seconds to remove the imitation calculus from the six left side anteriors, while the magnetostrictive scaler only took 3 minutes and 37 seconds for the right side!

Although piezoelectric ultrasonic power scalers tend to have the reputation of being superior with respect to patient comfort, our study has presented that this is often not the case. Through our research, the magnetostrictive power scaler has proven its ability to be more effective with time management. We understand, however, that the piezo will prove itself to be the preferred choice in certain situations. For example, if a dental practice has a large patient base from the geriatric population, conditions such as COPD and pacemakers are commonplace. In this scenario, if given the choice of power scalers, the piezoelectric would be preferred. In your typical general practice, however, it appears that magnetostrictive scalers are superior overall. Based on our results, we conclude that what is trending is not necessarily superior; what is most important is effectiveness, patient comfort, and clinician efficiency.

Hygienists' preferences for scalers

We conducted a survey through Survey Monkey via e-mail and social media. The majority of the 40 hygienists who responded to the survey are currently practicing in or near Brevard County, Florida.

81% surveyed said they use only magnetostrictive scalers in their dental office. 4% said they use only piezoelectric, and 15% reported using both. Of these same hygienists surveyed, 65% stated their employer is not open to purchasing their preferred scaler. Some employers believe there is an extra cost for the piezo. Sometimes this is true, but in our research, we were able to find many comparably priced piezoelectric scalers. While there are many models to choose from for each type, we have shown a typical piezo and magnetostrictive scaler one might find in any standard general practice. Prices vary greatly, but we found the average to be approximately $2,700 for each. Some employers may want what they believe to be the "best" product on the market. Patients who are uneducated about the differences between the two may believe that the piezoelectric power scaler is superior, as they may tend to look more glamorous (e.g., the Acteon model with color coding for power settings). One can understand that employers are not willing to change devices with each hygienist that comes to the practice. Most hygienists will need to adapt to the equipment that is available. This can lead to confusion and improper use of the devices if the principles of operation are not clearly understood.

In the survey, we also asked hygienists which power scaler they believe removes calculus more effectively:

• 33% believed the magnetostrictive did
• 4% believed the piezoelectric did
• 37% believed that both were approximately equal
• 26% were unsure
• 89% reported having a preference to magnetostricitive over piezoelectric
• 11% reported having a preference to piezoelectric over magnetostricitive

There was a wide variety of explanations for each preference. Some hygienists surveyed have never had the opportunity to use the piezo. Some hygienists like that all sides of the magnetostrictive inserts can be used. Others say there are more tip choices for the magnetostrictive, but we have found that many are actually made for use with the piezo; they are perhaps just not as widely available for purchase with all manufacturers. Lastly, many hygienists believe that magnetostrictive tips adapt better to the tooth.

Those in favor of the piezo believe that patients are more comfortable with the piezo due to the mild vibrations and decreased water output. Some believe piezos are becoming "the way of the future," as they are already very popular in areas such as Europe and South America, and are becoming increasingly so in the United States. In our survey, we inquired about the opinion on patient preference. 75% of our community hygienists believed that if given the choice, patients would prefer the piezoelectric power scaler over the magnetostrictive power scaler.

Rachel Kelly, CRDH, BS, obtained her bachelor of science in biology from the University of Central Florida in Orlando and is a recent graduate from the dental hygiene program from Eastern Florida State College in Cocoa. Rachel currently resides in Palm Bay, Fla., and works for a wonderful growing private practice in Melbourne, Fla. Karissa Sebero, CRDH, CDA, is a recent graduate of Eastern Florida State College. As a dental assistant, she worked in the public health setting before continuing her education in dental hygiene. She was elected president of her class, and she has enjoyed participating in many extracurricular events. Karissa is currently employed at a corporate dental office in Palm Bay, Fla.

References

1. Matsuda SA. Achieve Success with Ultrasonic Therapy. Dimensions of Dental Hygiene website. http://www.dimensionsofdentalhygiene.com/2013/09_September/in_Brief/Achieve_Success_with_ULTRASONIC_THERAPY.aspx. Published September 2013. Accessed August 29, 2016.
2. Miller KR. Good, good, good...Good vibrations! RDH magazine website. http://www.rdhmag.com/articles/print/volume-29/issue-9/feature/good-good-good-good-vibrations.html. Accessed August 29, 2016.
3. Nield-Gehrig JS. Fundamentals of Periodontal Instrumentation and Advanced Root Instrumentation. 7th ed. Baltimore: Lippincott Williams & Wilkins; 2013.
4. Prater SL. Ultrasonic techniques. RDH magazine website. http://www.rdhmag.com/articles/print/volume-31/issue-5/features/ultrasonic-techniques.html. Accessed August 29, 2016.