Disinfecting and sterilising dental handpieces

Both in clinical and dental practice, handling handpieces correctly has always been a sensitive and highly debated topic given the special nature of these instruments.

In fact, regardless of whether they run using turbines or micromotors, dental handpieces have specific features that make cleaning, disinfecting and sterilising them a complicated and skilful process.

Key aspects of caring for dental handpieces

The main challenge is structural, as handpieces are essentially hollow bodies consisting of an external and an internal surface with a cavity that houses a bur or any other kind of rotating tool. (1,2)

Turbines and the ‘suck back’ phenomenon

Moreover, turbines have their own specific challenges. Compressed air is used to turn a rotor to make the turbine work. When compressed air is no longer applied, the rotor continues to rotate for a short time afterwards due to the inertia of the rotor.

This inertia-powered rotation creates a negative pressure inside the system, which can cause the aspiration of contaminants into the turbine.

This is known as the ‘suck back’ phenomenon and is extremely dangerous as the next time the turbine is used, the contaminated material can leave the system once again. (3,4)

In micromotors, (straight or contra-angle handpieces), the compressed air normally means that negative pressure will not be generated inside the handpiece. The issue arises when, in certain surgical procedures, the flow of the compressed air is obstructed when the movement of the gears creates a pump effect, with the potential aspiration of contaminants into the handpiece. (5,6)

A particularly useful technique to try to reduce these issues is to run the turbines and handpieces in idle for a few seconds at the end of the procedure in order to ‘clean’ the inner systems of any contaminants.

Disinfection and sterilisation methods for dental handpieces

There are numerous studies on different handpiece sterilisation methods, including:

1. the application of moist heat (steam) or dry heat;
2. boiling;
3. the use of ethylene oxide gas;
4. sterilisation with ultraviolet rays;
5. the use of bactericidal compounds (7-10).

To date, autoclave sterilisation is the most commonly used method in medical and dental settings. (1)

Autoclave sterilisation: benefits and types (N and B)

Autoclave sterilisation has various benefits, including its minimal equipment footprint, low cost, short run times, minimal damage to handpieces and its high reliability in terms of sterilisation. (11-13)

There are also various different types of autoclave, classified based on their removal method of air from the chamber.

N-type autoclaves are effective in the sterilisation of solid, non-packaged instruments, while B-type autoclaves are effective in the sterilisation of packaged instruments, thereby offering a major advantage as they limit cross-contamination, meaning that the sterility of the final product is protected thanks to its packaging.

Indeed, B-type autoclaves are more suitable in the sterilisation of handpieces. (1)

Want to know more? Discover Zetaclave B, the Zhermack autoclave for sterilising solid instruments, hollow instruments (types A and B), packages and porous loads.

Based on the Spaulding classification, handpieces are defined as semi-critical articles (14) and are used inside the mouth without penetrating hard and soft tissues. Sterilisation is the treatment of choice for semi-critical articles, whereas for heat-sensitive instruments, high-level disinfection is required. (14)

Due to the challenges already explained, handpieces are considered critical items for all intents and purposes (1). For these instruments, high-level disinfection is not sufficient, and sterilisation is therefore required.

CDC guidelines on cleaning handpieces

The CDC (Centers for Disease Control and Prevention) is extremely clear and strict when it comes to handpieces and their sterilisation. The CDC guidelines state that handpieces and all devices and instruments connected to the dental unit’s air/water system should be cleaned and heat sterilised by properly trained staff between two patients. (15,16) This is particularly important given the demonstrated cases of contamination inside handpieces (5).

The CDC is clear: if a handpiece cannot be heat sterilised according to its instructions for use, it should be prohibited. (17)

Regarding the cleaning, lubrication, disinfection and sterilisation of handpieces, the CDC encourages professionals to follow the directions in the medical device instruction manual. (18)

Lubrication of handpieces

Handpiece lubrication is a delicate matter.

Correct lubrication is thought to reduce friction and the formation of blockages, increasing the device’s lifespan. (19) However, an excess of lubricant could prevent steam from reaching all components inside the handpiece during sterilisation, undermining the efficacy of the sterilisation process. (20,21)

For this reason, it is absolutely essential to follow only the manufacturer’s instructions, which are comprehensive and validated.

Thus, if a handpiece cannot be heat sterilised and valid manufacturer’s instructions are not provided for the correct reprocessing of the device, its use should be prohibited. (18)

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Bibliography

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14. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/rational-approach.html
15. https://www.cdc.gov/oralhealth/infectioncontrol/statement-on-reprocessing-dental-handpieces.htm
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18. https://www.cdc.gov/oralhealth/infectioncontrol/faqs/dental-handpieces.html
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