How Dental Handpieces Become Contaminated

Dental Handpieces are a critical tool used in routine and complex dental treatments. Inside the head of a high-speed handpiece, a turbine the size of a fingernail spins at speeds that would cause most mechanical components to fail within seconds — yet these instruments are expected to perform with clinical precision dozens of times a day, every day, for years. That reliability is the product of extraordinary engineering, and it makes them one of the most technically sophisticated tools used in routine healthcare.

This complexity, however, creates one of the most difficult infection control challenges in dentistry. Contamination that has entered its internal components during use is invisible, inaccessible and, without the right protocol, will remain there through the autoclave cycle.

How dental handpieces become contaminated

The internal channels of the dental handpieces can become contaminated from suckback, also known as retro-contamination.

While the handpiece is in operation, positive air pressure keeps the internal channels flowing outward. Air and water move through the instrument and exit at the bur tip. This outward pressure prevents anything from the patient’s oral environment from travelling back into the instrument. As soon as the air supply cuts, pressure inside the handpiece drops.

This brief negative pressure pulls back blood, saliva, tissue debris, and oral micro-organisms through the bur orifice into the internal channels of the instrument. Handpieces are fitted with anti-retraction valves to prevent sucback, however these valves are known to fail.

Interactive diagram — step through each stage of the suckback event

What evidence is there to illustrate the risk?

The risk of internal handpiece contamination is not theoretical. Several peer-reviewed studies have directly measured what is present inside used dental handpieces taken from active clinical practice — and the findings are consistent.

Study 1 — Protein contamination

Dental handpiece contamination: a proteomics and surface analysis approach

Smith A et al., Biofouling, 2014 · University of Glasgow

Three handpiece types were dismantled and their internal components tested using orthophthalaldehyde assay, SDS-PAGE, mass spectroscopy, Western blotting and ELISA. Mass spectroscopy confirmed the surgical gear contamination was predominantly serum-derived — patient blood.

Surgical handpiece gears403µg

Low-speed spray channels17.7µg

High-speed turbine<5µg

For reference, the MediCheck residual protein test flags a fail at just 5 µg. The surgical gear reading is 80× that threshold — and every handpiece type tested would fail.

Close-up of contaminated dental handpiece turbine heads

Contamination inside handpiece

Study 2 — Microbial contamination

Microbial contamination of used dental handpieces

Smith A et al., American Journal of Infection Control, 2014 · University of Glasgow

Used, unprocessed handpieces were dismantled aseptically, immersed in phosphate-buffered saline, ultrasonicated and cultured for live bacteria.

High-speed turbine200CFUn=40

Spray channels400CFUn=40

Surgical gear1,000CFUn=20

Isolates included oral streptococci, Pseudomonas spp., and Staphylococcus aureus.

The authors concluded that recovery of S. aureus — a recognised healthcare pathogen, not a routine oral commensal — confirms the need for appropriate cleaning and sterilisation after every patient to prevent cross-infection.

Dismantled NSK SG20 surgical handpiece showing internal contamination

Surgical handpiece dismantled

Study 3 — Real-world clinical conditions

High-speed dental instruments: protein-contaminated handpieces investigated with the bicinchoninic acid assay

Schalli M et al., Int. J. Environmental Research & Public Health, 2023 · Medical University of Graz

Spray-water samples were collected from handpieces in seven real dental offices — both before and after patient treatment — measuring protein concentration across 398 samples using the BCA assay.

Samples with measurable protein91.2%

Contaminated before treatment79.8%

Protein increased after treatment68.4%

Protein decreased (expelled)27.9%

The 27.9% decrease is direct evidence of cross-contamination — the handpiece expelling retained material from a previous patient into the current patient's mouth. The only office with clean pre-treatment water was the one performing internal disinfection after every patient.

Dismantled handpiece components showing accumulated contamination

Internal components showing accumulated contamination

Why does sterilisation not fix the issue?

This is the question most professionals ask when first seeing this evidence. If the handpiece goes through a sterilisation cycle, has the contamination inside has been dealt with?

The answer is no due to one of the fundamental pillars of infection prevention and control, what is not clean cannot be sterilised. Sterilisation eliminates microbial life. It does not remove the physical material, such as the blood, protein and tissue debris that suckback has deposited inside the handpiece.

Steam sterilisation works through direct contact: the steam has to physically reach a surface to sterilise it. Where contamination forms a layer over a surface, it acts as a barrier that the steam cannot penetrate.

Additionally, when blood protein is exposed to autoclave temperatures without being cleaned off first, it doesn’t disappear — it bonds to the surface it’s sitting on. In effect it becomes baked on. This is why water temperature should not exceed 45 degrees when manually cleaning or using an ultrasonic bath. The contamination that was removable before the cycle is now fixed to the internal surfaces of the instrument, and harder to remove than it was to begin with. Over time this burnt on material can damage the delicate internal components of the handpiece.

The type of autoclave used also has a baring on the handpiece decontamination process.

Type N — Non-vacuum

How it works

Displaces air with steam under pressure, surrounding the instrument and sterilising its external surfaces.

The limitation

No mechanism to remove air from inside hollow instruments. Steam entering a handpiece channel meets a trapped air pocket it cannot displace — blocking it from reaching the internal surfaces entirely.

Internal lumens not sterilised

Type B — Vacuum

How it works

Uses a vacuum phase to actively pull air out of the chamber and the lumens of hollow instruments before steam is introduced.

The capability

With trapped air removed, steam flows into the internal channels and reaches surfaces a Type N never could — but only the surfaces it can physically contact.

Internal lumens sterilised

A Type B is not a substitute for cleaning

A Type N cannot reach the internal surfaces. A Type B can reach them — but cannot clean them. If those surfaces are coated in baked-on protein, the steam sterilises the outside of the contamination without removing it. In both cases, internal cleaning must come first. The autoclave confirms the cycle conditions were met — it never confirms the inside of the instrument is clean.

How to effectively decontaminate a handpiece internally

Several effective methods exist for internal cleaning and disinfection before sterilisation.

Washer Disinfectors

Washer-disinfectors have excellent supporting evidence for internal handpiece cleaning and disinfection. A 2022 study showed “an approximate 5 log or greater reduction in microbial cfu and a >93% reduction in protein from DHP heads and channels was consistently recorded following washer-disinfection for all DHPs under all conditions tested.”

For effective cleaning and disinfection of handpieces in washer disinfectors a few key rules must be followed.

Always follow manufacturers guidelines, not all handpieces are suitable for use in a washer disinfector.
Handpieces must be placed on the handpiece stand.
Check the pH level of your detergent. Any value over 10.5 will be too harsh and can invalidate your warranty.
Oil the handpiece after processing in the washer disinfector, not before.
Remember disinfection is NOT sterilisation. Handpieces must still be sterilised after washer-disinfection.

Manual system

In lieu of a washer-disinfector, a manual handpiece cleaning and disinfection system can be implemented.

The WL system is our state of the art handpiece cleaning and disinfection system. WL will completely remove any blood or debris in the handpiece. WL-Clean cleans the internal surfaces, WL-Cid disinfects with broad-spectrum antimicrobial activity (including any enveloped viruses such as coronavirus), finally WL-Dry blows out any leftover solution or tissue ready for lubrication with an oiling solution.

The WL-System has been tested to EN ISO/TS 15883-5 and has been proven to be as effective as a washer-disinfector for internal handpiece cleaning/disinfection.

Internal contamination of handpieces is now a known and evidenced issue. Handpieces are a potential transmission risk for several diseases. Adopting a handpiece internal cleaning and disinfection protocol will future-proof your practice and protect your staff and patients.

References

Smith A, Smith G, Lappin DF, et al. Dental handpiece contamination: a proteomics and surface analysis approach. Biofouling. 2014;30(1):29–39. PMID: 24138163
Smith G, Smith A. Microbial contamination of used dental handpieces. Am J Infect Control. 2014;42(9):1019–1021. PMID: 25179340
Schalli M, Platzer S, Schmut R, et al. High-speed dental instruments: an investigation of protein-contaminated dental handpieces with the bicinchoninic acid assay in dental offices in Styria, Austria. Int J Environ Res Public Health. 2023;20(3):2224. PMC9914004
Sterilization of dental handpieces. Am J Infect Control. 2017. Confirms non-vacuum autoclaves cannot sterilise handpiece internal components. View article
Smith GWG, Smith AJ, Creanor S, et al. Survey of the decontamination and maintenance of dental handpieces in general dental practice. Br Dent J. 2009;207(4):E7. View article

Free Service

Free Decontamination Review

Need help with transportation or any part of the decontamination cycle? Get a free review of your decontamination procedures from our expert team — fully tailored to your practice.

Book Your Free Review →

Completely free

How Dental Handpieces Become Contaminated