What Infection Preventionists Need to Know About Ultrasonic Cleaning

Cleaning systems for medical instruments. Ultrasonic cleaner

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Cleaning and sterilization are fundamental concepts in medicine. We have come a long way in methods of sterilization since Ignaz Semmelweis introduced handwashing in the maternity ward of Vienna.¹ Although he was met with resistance during his time and ultimately died in a mental asylum due to his ideas, his research paved the way for modern sterilization and hygiene.

Ionizing radiation, dry heat sterilizers, microwaves, and liquid chemicals are all methods of sterilization in the medical industry.² Ultrasonic cleaning is a revolutionary method that has been used in multiple industries due to its ability to reach smaller areas.

What is ultrasonic cleaning?

Ultrasound cleaning utilizes sound waves in a conducting liquid to clean surfaces, including those that are difficult to reach with traditional methods.³ Other cleaning technologies, such as turbulence, spray washing, and agitation, require direct contact with the contaminated surface to be effective. Cleaning in these methods is achieved by the impact of a high-velocity stream on the contaminated surface.

Mechanism of ultrasonic cleaning

The first step in ultrasound cleaning is the removal of any physical debris. The object must be visually clean before it is put in the cleaner. The ultrasound cleaner is a metal tank made of stainless steel that has piezoceramic transducers (PZT) bonded to the bottom or side of the tank. PZT, which contains lead zirconium titanate, provides an alternative to chlorofluorocarbon-based cleaners.⁴

The object to be cleaned is placed in the tank containing water, where an ultrasonic wave is generated to produce bubbles. The bubbles expand and collapse rapidly, leading to mechanical disturbance and agitation of the fluid. This enhances its cleaning and degreasing effectiveness. Sound waves generated in the tank function in 2 ways, 1 of which is the production of ‘cavities’ due to compression and expansion cycles. This cycle of compression and expansion produces liquid jets that travel at extremely high speeds. The combination of temperature, pressure, velocity, and liquid jets frees contaminants from their bond with the object. Due to the tiny size of liquid jets and relatively large energy, ultrasonic cleaning can reach small crevices.

Ultrasonic Cleaning in Medicine

Ultrasonic cleaning in cleaning and sterilization

Endoscopic submucosal dissection used in the treatment of early-stage gastrointestinal cancer leads to the sticking of carbonized clots and tissues to the knife.⁵ In multiple hospitals, the debris is cleaned by scrubbing the tip of the knife with gauze soaked in pronase or saline. However, it is difficult to remove the debris quickly and properly using this method. There is also a risk of damaging the tip by applying too much pressure. A study found that a combined cleaning method, involving cleaning the knife for 10 seconds in an ultrasonic cleaner and then cleaning it with a saline-soaked gauge for 20 seconds, proved more effective.

Ultrasonic cleaning is widely used for cleaning dental instruments due to its effectiveness and efficiency.⁶ Dental instruments that regularly come into contact with saliva, blood, and oral tissues need to be cleaned thoroughly. A study found that cleaning products performed more effectively when combined with ultrasonic agitation compared to static conditions during the cleaning of dental instruments. Another randomized crossover clinical trial found that a combination of ultrasonic cleaning followed by immersion in a denture cleansing solution achieved better denture cleanliness.⁷

Ultrasonic cleaning was also favored by older people for cleaning dentures due to its lower manual labor requirement and greater cost efficiency. Traditional methods for cleaning dentures often require manual scrubbing, which may be challenging for older adults due to their limited strength and mobility. The cost of an ultrasound cleaner was also less in the long run.

Ultrasonic Cleaning in Treatment

Infection is the most common cause of root canal failure, with Enterococcus faecalis being the most commonly isolated bacterium. Root canal disinfection control is typically performed using mechanical instruments and chemical irrigants. However, traditional methods still have limitations due to the narrow space and complex anatomy of the root canal. E. faecalis especially poses a risk due to its ability to survive in harsh environments, invade dentin tubules, and its resistance to common disinfectants.

The combination of plasma-loaded microbubbles and ultrasonic cleaning has been shown to be an innovative approach to endodontic cleaning. This method exhibits a strong biofilm removal effect, in addition to a significant antibacterial effect against E. faecalis. It has also been shown to be safe on tooth-hard tissue.

Factors Affecting Ultrasonic Cleaning

Temperature: The temperature of the solvent appears to be a strong indicator of cleanliness. A study on dentures found that the group subjected to ultrasonic cleaning with cold water (16 °C) had the lowest decrease in bacterial count, whereas cleaning in warm water (40 °C) had the highest decrease.⁹ higher temperatures enhance the cavitation effect and improve the solubility and reactivity of cleaning agents.⁶

Cleaning products: The cleaning products used in ultrasonic cleaners can be either enzymatic or nonenzymatic.⁶ Enzymatic products consistently performed better than nonenzymatic products for the removal of organic contaminants. Products used at their highest recommended concentrations performed better than in diluted concentrations.

Time: The time required for effective cleaning forms an integral part of the overall sterilization sequence.⁶ Some enzymatic products perform better with longer cycles (30 minutes), whereas other products perform similarly in shorter (10 minutes) as well as longer cycles. However, longer cycles can affect health care facilities as they would need to maintain a larger inventory of instruments.

Complexity of instruments: Simple and rigid instruments made of stainless steel are relatively easy to clean using ultrasound cleaners. However, more complex instruments and those made from porous materials may not be suitable candidates for ultrasound cleaning.⁶

Ultrasonic cleaning has proven to be highly beneficial in today’s medical system. Small and complex medical equipment, such as endoscopes and dental instruments, cannot be cleaned efficiently using traditional methods. Ultrasonic cleaning, due to its use of small but powerful jets, can reach small crevices that are usually inaccessible by other methods. Despite its effectiveness, certain factors, such as temperature, cleaning agent, time, complexity, type of material, and type of contaminant, may reduce the effectiveness of ultrasonic cleaning.

References

1. Pittet D, Allegranzi B. Preventing sepsis in healthcare – 200 years after the birth of Ignaz Semmelweis. Euro Surveill. 2018;23(18). doi:10.2807/1560-7917.ES.2018.23.18.18-00222
2. Other Sterilization Methods. Infection Control. CDC. June 12, 2024. Accessed May 14, 2025. https://www.cdc.gov/infection-control/hcp/disinfection-sterilization/other-sterilization-methods.html
3. Fuchs FJ. Ultrasonic cleaning and washing of surfaces. In: Power Ultrasonics. Elsevier; 2015:577–609. doi:10.1016/B978-1-78242-028-6.00019-3
4. Muthurajan H, Kumar HH, Kharat DK. Piezoceramic-based chlorofluorocarbon-free tunable ultrasonic cleaning system. J Sci Ind Res. 2005;64(12):960–964.
5. Murakami K, Hirata D, Haraguchi K, et al. Ultrasonic cleaning is effective in removing carbonized clots and tissue from the insulation‐tipped diathermic knife‐2. DEN Open. 2022;2(1). doi:10.1002/deo2.101
6. Seneviratne CJ, Khan SA, Zachar J, et al. Efficacy of ultrasonic cleaning products with various disinfection chemistries on dental instruments contaminated with bioburden. Int Dent J. 2025;75(3):1632–1639. doi:10.1016/j.identj.2025.02.009
7. Lim TW, Burrow MF, McGrath C. Efficacy of ultrasonic home-care denture cleaning versus conventional denture cleaning: a randomised crossover clinical trial. J Dent. 2024;148:105215. doi:10.1016/j.jdent.2024.105215
8. Zhu M, Dang J, Dong F, et al. Antimicrobial and cleaning effects of ultrasonic-mediated plasma-loaded microbubbles on Enterococcus faecalis biofilm: an in vitro study. BMC Oral Health. 2023;23(1). doi:10.1186/s12903-023-02813-6
9. Iwawaki Y, Matsuda T, Kurahashi K, et al. Effect of water temperature during ultrasonic denture cleaning. J Oral Sci. 2019;61(1):140–145. doi:10.2334/josnusd.17-0387