Reports & Studies

Cleaning of transmission instruments: What do you expect?

The dental profession, treatments and related techniques have evolved over the years, as have hygiene procedures. Today, reprocessing instruments involves complex hygiene procedures and protocols which need to be regularly questioned, optimized and updated according to the latest developments of science and technology. Some products are more challenging to decontaminate than others such as transmission instruments i.e. turbines, straight and angled handpieces also called high- and low-speeds. They are complex to clean and to sterilize without adequate equipment and specific processes, with greater requirement on validation to prove the process is correct.

Proper cleaning is the foundation of the whole reprocessing cycle and is fundamental for safe sterilization. During sterilization, residues, debris, blood proteins and lipids, etc. present an obstacle to steam. As most guidelines specify: "only clean instruments can be sterilized".

Instruments must be clean and visually free from organic residues (blood proteins and lipids, biofilm), mineral deposits, debris and stains prior to steam sterilization. Appropriate cleaning contributes to reducing the microbial population.

As illustrated by the Sinner Circle, cleaning combines four factors interacting in variable proportions:

Sinner Circle

Sinner Circle

  • Chemical action
  • Mechanical action
  • Temperature
  • Contact time

If one factor is reduced, the loss must be compensated by increasing one or more of the other factors.

Chemicals represent the action of an acidic or alkaline detergent solution. Detergents contain surfactants with cleaning properties acting as wetting, foaming, emulsifier and dispersant agents. The efficiency is increased or decreased by its concentration. However, higher concentrations of the detergent may lead to greater usage costs, additional rinsing and cause damage to instruments. The choice of detergent depends on the type of contamination (organic, mineral, microbial, etc.), the type of surface, the surface finish (smooth, rough, scratched) and the shape of the instrument.

The mechanical factor generates friction and pressure i.e. the force needed to remove dirt as well as renewing the cleaning solution in contact with the instrument. Additionally, it helps disperse the dirt.
If no equipment is used, the person doing the manual cleaning provides the mechanical action by scrubbing and brushing the instruments.

The temperature reduces surface tensions of liquids, speeds-up chemical reactions (wetting, foaming), softens soil and debris and improves surfactant penetration. Temperature improves detergency but importantly the temperature shall not exceed 45°C to prevent the fixing of blood proteins onto the surfaces.

The contact time strictly linked to the duration of the cleaning process is the result of the other three factors.

The challenge of manually processing transmission instruments

The internal parts of transmission instruments are constantly miniaturized and complex, resulting in rising challenges for cleaning processes. They mount components made of different materials (composite, rubber, steel alloys) as well as electronics.


transmission instrument

Unless the instruments can be disassembled, it is challenging to manually clean all internal parts such as gears, chucking system, ball bearings, tiny spray channels and nozzles, etc. The transmission instruments cannot be soaked or cleaned in an ultrasonic bath which doesn't help either! It is normally recommended to clean the external surfaces with soft brushes under running water whilst avoiding too much tap water inside the instruments. After cleaning and drying, the instruments must be lubricated prior to packaging and sterilization. Completing this step manually with propellant lubricant may lead to over lubrication if not done correctly; this increases the cost of handpiece maintenance whilst not being environmentally friendly.

With this in mind, anyone would agree that maintaining and reprocessing transmission instruments is really challenging! If these operations are not performed properly, it will likely reduce the lifespan of the instruments by up to 50%. Importantly, it may lead to non-sterilized instruments with direct implications towards the safety of the team and patients.Transmission instruments go from one patient's mouth into another increasing the risk of transmitting blood borne diseases such as Hepatitis B, C, D and HIV.

What about automated maintenance?

The hygiene protocol for reprocessing transmission instruments starts with pre-disinfection immediately after use. Usually the Dental Assistant will wipe the instruments with a disinfectant cloth whilst disconnecting them from the coupling or motor-drive.

The following 4 essential steps can be performed by specific processes/ machines. However, it must be underlined that not every machine fulfills all 4 steps! Some machines exclusively clean inside and lubricate, others simply lubricate. Thermal washer disinfectors clean inside and outside but do not lubricate. In these cases, one or more extra manual operations are still required. Prior to purchase, it is vital to understand the manufacturer's claim i.e. which pre-treatment steps does the machine fulfill?

Automated Maintenance
4 pre-treatment steps

How can machines correctly process transmission instruments?

Obviously we are talking about "all in one" devices that clean inside, clean outside, rinse, dry and lubricate i.e. fulfilling the 4 essential steps.

Thorough internal cleaning of the instruments is crucial for asepsis and the challenge for an automated process is to ensure the spray channels, gear parts and ball bearings are thoroughly cleaned. Usually internal cleaning is done via pressurized diluted detergent flushed through the internal components of the instrument. This satisfies the previously described cleaning principles (sinner circle) combining chemicals (detergent), mechanical forces (air pressure) and temperature for a defined time. Some devices flush the instruments with steam.

Efficient cleaning requires the four factors seen in the Sinner circle be correctly balanced. There is no issue for applying chemicals at defined temperature for a certain time to the outer parts of the instruments. However, the challenge regards the missing main factor i.e. how to generate the mechanical action. As mentioned before, if one factor is reduced, the loss must be compensated by increasing one or more factors. Therefore if no or little mechanical action (nebulization) is applied, the concentration and/or harshness of the chemical must be intensified. The working temperature and/or the contact time must also be augmented. Too high concentration of chemicals may damage instruments and certainly requires additional rinsing. The over-application of chemicals on transmission instruments could lead to drastic reduction of their lifespan and increased repair costs.

High-end devices offer perfect lubrication. A tiny oil droplet is blown thought the mechanical parts by pressurized air. The extra oil is removed in a second phase by a flow of compressed air only that leaves a thin layer of lubricant on the mechanical components. This system of lubrication is very efficient and more economical when compared to propellant cans.

Processing with Assistina 3x3

For over 125 years, the family owned company W&H Dentalwerk is one of the leading providers of dental instruments and devices in the world. The main core business is the manufacturing of transmission instruments, maintenance and cleaning devices as well as steam sterilizers. W&H has gathered significant know-how and experience by being active in these fields for decades.

When designing the new Assistina 3x3, the goal was to fulfill the 4 essential steps of the pre-treatment process by combining the relevant parameters, to provide the highest level of safety for users and patients and to preserve the long-term integrity of the instruments. The engineers succeeded in designing an innovative reprocessing device that offers thorough cleaning of internal components and optimal external cleaning thanks to the cleaning ring that travels along the instruments, spraying a cleaning solution at very high pressure through 6 spray nozzles.

Following the Sinner Circle principles, the chemical action i.e. the amount of detergent, could be drastically reduced to a very mild concentration thanks to the high mechanical action. This patented system avoided heating both the cleaning solution and the instruments. It also shortened the overall cycle time to 6:30 min and reduced the preparation cost per instrument to few € cents. This type of external cleaning cannot be reproduced manually. By eliminating brushing and scrubbing, we also avoid micro-scratches on the instruments which can harbor future debris.

Assistina 3x3
Christian Stempf
Christian Stempf
Hygiene adviser of the W&H Group

About the author

Christian Stempf has worked extensively within the European dental industry. He has been involved in infection prevention and sterilization for over 20 years. He is a member of the European normalization committee which formulated the first norm on small steam sterilizers. He has gathered valuable practical knowledge and experience through his daily activities and contacts with healthcare professionals and experts in the field of infection prevention throughout the world. Christian Stempf shares this experience offering vendor independent lectures in all objectivity on the topic of sterilization and infection prevention to expert audiences.