Reports & Studies

Sterilization in modern dentistry: Get it right!

Reprocessing instruments involves complex hygiene procedures and protocols which need to be permanently questioned, optimized and updated according to the latest developments of science and technology. Every step of the hygiene circle is important especially cleaning.

Sterilization, the last but not least is defined as:
"Validated process used to render a product free from viable microorganisms" European Norm 13060.

Being in permanent contact with practitioners and nurses, I recognize increased awareness surrounding sterilization, motivating me to improve hygiene in the profession.

Increasingly targeted questions come up such as:

  • Is my current sterilization method outdated and inappropriate?
  • Is the reprocessing cycle still valid for all my instruments?
  • If not, what could be the consequences?
  • Sterilizers typically offer many cycles, why?
  • Do I need so many and all of them?
  • I get confused, which cycle is the safest?
  • I need to rely on my staff, is specific training required and how often?
  • Which are the "typical" mistakes made by my staff which results in non-sterile instruments?
  • Most of my pouches are wet after cycle completion, are the contents sterile?

All these points are crucial and need to be clearly addressed to guarantee the safety of practitioners, staff, patients and their respective families.The scope of this article is to create awareness about the risks of using inappropriate sterilizers and cycles which will increase the risk of infection.

Healthcare Associated Infections (HCAI) also called "Nosocomial infections" refer to infections occurring during treatment in health care facilities, including staff injuries. The WHO reports that worldwide 2 million patients get infected each year which lead to prolonged hospital stays, massive costs for healthcare systems (and patients) and significant mortality as approximately 100,000 of them would die. More concerning is that despite the implementation of enhanced hygiene procedures, constantly improved equipment, more dedicated and better trained staff; no institution or country has yet solved the problem. I see the need for both healthcare professionals and the industry to focus more on implementing any measure which could contribute to improve this situation!

Which is the ideal sterilization method?

It is heat that kills micro-organisms. Moist heat in the form of saturated steam is the most efficient, economical and environmental friendly means for sterilization. It is also the safest provided that the sterilization cycle is designed and adequate for the processed instruments. Obviously the processing of a wrapped implantology cassette calls for a much higher performance level than a non-pouched (solid) handpiece bur or probe. Water steam sterilizers commonly offer several cycles featuring contrasting levels of performance and efficiency.

The "power" of steam to your benefit

Steam has the capacity of gathering energy and thus distributing high "killing" power. Compared to dry heat sterilizers, which are still widely used, steam releases 300 times more energy onto the load resulting in drastic reductions of the sterilization plateau (3' vs 60') and overall cycle times, though at a much lower and gentle temperature (134°C vs 180°C). In addition to time saving, the much appreciated benefit for the user is that all instruments, including high and low speed handpieces, can be repeatedly processed without affecting their characteristics.

Is there any valuable reference for sterilizers?

EN 13060 is the European reference norm for small steam sterilizers which are widely used in healthcare facilities, dental practices and increasingly by tattooists, body piercers and veterinary surgeons. This norm, published in June 2004, raised the performance level of bench top sterilizers up to hospital grade which indeed improved prevention of cross infection. It obviously defines how sterilizers must be technically constructed. Though, what is more relevant for the user is the description and classification of load types or families as well as the cycle categories B, S and N. It has to be noted that most of the manufacturers of sterilizer, even from outside Europe, make reference to EN13060.

The new generation

In what way can cycles be inappropriate?

Every instrument from every manufacturer is built differently. Each has its own design and technology. The internal parts are constantly miniaturized and complex, resulting in rising challenges for the sterilization processes. The complexity of each item corresponds to a particular resistance to steam penetration. The Australian/New Zealand standard explicitly points out: "The choice of sterilizer and selected sterilization cycles may be inappropriate for particular items or types of loads." AS/NZ 4815:2006.

As mentioned before, steam is the ideal means for sterilization provided that it comes into contact with all internal and external surfaces of the instrument. What could prevent steam from accessing all internal cavities? Simply air. Thus, the initial air removal phase of a cycle, also called pre-vacuum is crucial. The level of residual air inside the chamber and the load must be lowered to almost 0% to ensure proper steam penetration of the most challenging items such as high and low speed instruments or porous products. Air trapped inside a lumen impedes steam from reaching and thus sterilizing the concerned internal surfaces. The difficulty further rises when objects are pouched or wrapped. This is why many guidelines stress that "Wrong cycle selection may lead to non-sterile instruments".

To verify this point, the following test was run:
A 30cm double-ended open glass pipette was filled with a liquid and then processed with a B and N type cycles to compare and illustrate their respective air removal thus steam penetration capacities.

Steam penetration capacities

The bottom picture (N type) demonstrates steam could not remove the liquid from the centre of the tube lumen. Thus part of the internal surface would not have been sterilized.

Comprehensive load classification

The table below shows the load classification according to the EN13060. There are actually 6 load "families" which are considered to be processed unwrapped and kept sterile until the point of use single or double pouched or wrapped (storage and transportation). In total there are 18 load types relating to 18 different challenges. The norm therefore describes corresponding test methods which allow the manufacturer to prove the cycles are capable of processing the load(s) they were designed for. The tests are to be run and documented in the so called "type test", prior to launching production of any new sterilizer or cycle.

Load classification
Description of the18 load types.
Assortment of instruments with narrow lumen.

B, S, N cycle description


N Cycle
Appropriate exclusively for unwrapped (Naked) solid products (N°1 in the table).
No transportation, no storage, for immediate use only.

S Cycle
Designed for processing Specific products as specified by the manufacturer in the cycle table. It is essential that this cycle is used only for the loads it was designed for.

B Cycle
Provides medical grade sterilization as per a Big sterilizer. It will process all 18 load types specified in the Standard and shown in the table above.

How can users know sterilization cycles match with loads?

The manufacturer must provide a detailed cycle table indicating for all available cycles their types (B-S-N) and which load(s) they are suitable for. It is then the user’s, hence the Doctor's responsibility to ensure that the selected cycle is appropriate for the sterilized instruments. A wrong cycle selection may lead to non-sterile items and increase the risk of cross infection. Opting for the B-type cycle is certainly the best choice. Peace of mind for the Doctor as no mistake can occur during cycle selection. There is no need for specific training on load and cycle types for staff.

How many cycles do we need?

Sterilizers usually offer up to 10 or more cycles which at first glance could be seen as an advantage. However, only one or two can be of B-type at 134°C and/or at 121°C. There might be a third one called "134-PRION" (or "Extended") that features a longer plateau time of 18 minutes complying with the WHO recommendations on the inactivation of the prion protein (CJD: mad cow disease).

All others are of S or N type and left to the operator's appreciation, expertise and responsibility. Some, usually called "quick" or "flash", are wonder fast which is appreciated but…once more at risk because they are designed for a restricted number of load types. From a legal point of view, the B-cycle prevents the need to prove the load vs cycle compatibility. It is definitely safer!

What Cycle?

How fast is a sterilizer?

To get a factual comparison between brands and technologies, I would exclusively comment on B-type cycles. Well-designed sterilizers and B processes feature maximum cycle times around 45 minutes including drying. Some fast B-cycles (not flash) designed for smaller (lighter) loads are within 20-30 minutes including drying. It is recommended to test any sterilizer prior to purchase to verify claimed features. Take into account that the overall time duration also fluctuates in relation to the weight and number of processed instruments.

Why is drying so important?

After cycle completion and door opening, non-dried items and pouches cannot be considered sterile and released for storage and use. Many guidelines make reference to this essential point. Wet pouches are permeable which allows microorganism to penetrate and multiply. Moisture left inside transmission instruments will significantly reduce their lifespan. Obviously the drying phase is a crucial phase of any cycle.

How much should I spend?

As a conclusion, I may say that an efficient hygiene protocol including clearly defined procedures, well trained staff and up to date equipment stands for significant cost. However, decisions should not always come down to price. Priority should be given to personnel and patient safety. One single mistake could lead to dramatic consequences, much higher expenses and the practitioner being held to account if cross infection occurs.

Christian Stempf

Christian Stempf
Hygiene adviser of the W&H Group.

About the author

Christian Stempf comes from the European dental industry. He has been involved in infection prevention and sterilization for over 20 years. He is a member of both French and European hygiene committees and working groups which formulated the first European Norm on small steam sterilizers.

Christian has gathered valuable rational knowledge through his daily activities and contacts with hygiene professionals throughout the world. He shares this experience offering vendor independent lectures in all objectivity on the topic of sterilization and infection prevention to expert audiences.