The evidence for ultrasonic cavitation

...We have conflicting laboratory findings, and no reliable way to evaluate the clinical effects of ultrasonic cavitation ...

...We have conflicting laboratory findings, and no reliable way to evaluate the clinical effects of ultrasonic cavitation ...

Trisha E. O`Hehir, RDH, BS

You hear a lot these days about evidence-based dental hygiene. The big question is: What evidence should you believe? Ideally, there are double-blind, placebo-controlled clinical trials.Unfortunately, not much of what we do is supported by studies of that magnitude. Many times we have only a few laboratory studies and some case reports on the subject. What do you do then? Here`s an interesting example of an assumption with little or no scientific evidence to support it.

We often read about and hear speakers discuss the value of acoustic streaming and the cavitational effect of ultrasonic scalers. I know - I`m one of them! But what kind of evidence do we have to support that claim? It`s pretty weak, I`m afraid.

It is assumed that the cavitational effect of the fluid lavage - especially with ultrasonic instruments - is an advantage. You`ve probably heard that the cavitational effect associated with ultrasonic instruments is more effective against subgingival bacteria than that of sonic instruments. It is assumed that bacterial cell walls are ruptured by vibrations within the fluid lavage. These assumptions, based on laboratory findings, have not been clinically proven. Now, we have new laboratory research that questions the earlier findings. Besides the conflicting laboratory findings, we really don`t have clinical research to support the idea.

The cavitational effect in the fluid lavage is caused by rapid movement of air bubbles creating shock waves. These waves appear to be responsible for the reported bacterial cell death. A few studies have shown gram-negative bacteria to be more susceptible to these shock waves than gram-positive bacteria. Differences in cell-wall structure may be a reason for this. These conclusions are reached by testing power scalers in the laboratory.

Our assumptions are based in part on research reported in 1992. Researchers in Geneva measured the effects of sonic and ultrasonic scaling on bacteria. This was done in the laboratory, using bacteria in test tubes. It also was done in clinical evaluations by measuring the remaining bacteria after instrumentation. Plaque samples were collected from 27 pockets and placed in individual test tubes. Half were subjected to a piezoelectric scaler and half were treated with a sonic scaler. The peizoelectric scaler destroyed more spirochetes than the sonic scaler. The researchers concluded that this result was probably due to higher frequency of the piezoelectric scaler and the resulting cavitational effect of the vibrations.

They then looked at the clinical effects. Power scaling was done with the piezoelectric scaler in 46 pockets, and the sonic scaler was used in 20 pockets. Bacterial samples were taken with paper points before and after instrumentation. Both scalers were equally effective in reducing bacterial counts. No differences between the two instruments were observed. In fact, both scalers were very effective in reducing subgingival bacteria through mechanical action and flushing.

Researchers speculated that the irrigational effect of both instruments was responsible for the differences between the laboratory and clinical findings. The cavitational effect may not be as important as the lavage. As long as the bacteria are removed from the pocket, healing can occur.

That was in 1992. Earlier this year, researchers in Germany hypothesized that excessive heat buildup during ultrasonic scaling in a test tube may actually account for the reported cell death. To control for heat buildup, they immersed the tubes in ice water during testing. They used an ultrasonic and a sonic scaler to test the cavitational effects on four periodontal bacteria. Bacterial counts did not change after use of either the sonic or ultrasonic scaler when the bacterial samples were kept at a constant temperature. It actually may be the heat buildup that caused cell death in the earlier study.

On a clinical level, as long as the bacteria are removed from the pocket - either alive or dead - they are no longer creating problems for the surrounding tissue.

As you can see, we have conflicting laboratory findings, and no reliable way to evaluate the clinical effects of ultrasonic cavitation, since the fluid lavage overshadows the cavitational effect. Continue to look for scientific evidence for your treatments, but always look for the clinical results.

References

Y Schenk, G., Flemmig, T., Lob, S., Ruckdeschel, G., Hickel, R.: "Lack of Antimicrobial Effect on Periodontopathic Bacteria by Ultrasonic and Sonic Scalers in Vitro." J of Clinical Periodontology 27: 116-119, 2000.

Y Baehni, P., Thilo B., Chapuis, B., Pernet, D.: "Effects of Ultrasonic and Sonic Scalers on Dental Plaque Microflora in Vitro and in Vivo." J of Clinical Periodontology 19: 455, 1992.

Trisha E. O`Hehir, RDH, BS, is a senior consulting editor of RDH. She also is editor of Perio Reports, a newsletter for dental professionals that addresses periodontics. The Web site for Perio Reports is www.perioreports.com. She can be reached by phone at (800) 374-4290 and by e-mail at trisha@

perioreports.com.

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