Hydrogen Peroxide Gas Plasma - A Low-temperature Sterilization Technology

    Low-temperature sterilization technologies are used for heat-sensitive or moisture-intolerant medical equipment and supplies. Ethylene oxide (ETO) has been used as a low-temperature sterilization technology since the 1950s. Until 1995, ethylene oxide was most commonly combined with chlorofluorocarbon (CFC) stabilizing agent. For many reasons, such as ETO exposure represent a health hazard, and the CFCs were discovered to pollute the earth’s ozone layer by Clean Air Act in 1995, many new technologies are developed as an alternative to the use of ethylene oxide with chlorofluorocarbon, including 100% ethylene oxide, ethylene oxide with other stabilizing gas, immersion in peracetic acid, hydrogen peroxide gas plasma and ozone. However, the ideal technologies does not exist, understanding the limitation imposed by restrictive device designs is important for proper application of new low-temperature sterilization technologies.

Plasma globe [1]

    Before getting through hydrogen peroxide plasma, we have to know what are plasmas? Plasma is a fourth state of matter which is distinguishable from solid, liquid and gas. Plasma is a gas-like substance consisting of positively and negatively charged particles. They aren't things that happen regularly on Earth. In nature, plasma is widespread in outer space.

    Hydrogen peroxide gas plasma uses hydrogen peroxide vapor and low-temperature gas plasma to sterilize items with no toxic residues. Usually, the process operates in the range of 34-44^oC and takes about 75 minutes for wrapped and dry instruments. According to the manufacturer, a deep vacuum is drawn and hydrogen peroxide solution is vaporized into the sterilization chamber. All surfaces of the loads are then exposed to the hydrogen peroxide vapor. Gas plasma are generated under vacuum using radio frequency to excite the gas molecules and produce free radicals, which are capable to disrupt the metabolism of microorganisms. Once the free radicals have reacted, they recombine to form water vapor, oxygen, and other nontoxic by-products, so there is no need for aeration. In the final stage, the chamber is vented to the atmospheric pressure in order to let the chamber door open. Sterilized materials are ready for immediate use.

Hydrogen peroxide gas plasma [2]

    
It’s not difficult to find out that hydrogen peroxide gas plasma has many advantages, such as short sterilization cycle, low temperature, low moisture, no aeration requirement and no toxic by-products. But it still has its limitation, including the inability to process liquids, powders, or strong absorbers, and some lumen restrictions. Therefore, gas plasma sterilization is not recommended for paper, cellulose or linen products.

Low-temperature plasma sterilization process

See more information on these links:
1. Centers for Disease Control and Prevention
2. Infection Control Today

Picture resources:
1. http://www.instructables.com/id/Amazing-plasma-globe-tricks-that-you-never-knew-be/
2. http://www.hpnonline.com/inside/2010-01/1001-CS2.html

Basic Cleaning of the Dental Clinic

Before we getting into the concept, it is important to have a general idea of the dental office.

1. Dental chair cleaning steps

1) Wash our hands.

2) Wear on gloves and masks.

3) Take a piece of paper and spray some detergents on it.

4) Wipe everywhere on the dental chair, especially the chair arm, light switch and control unit.

5) Take out the detergents for tubes and press hard on it one time to make the cup full of detergents.

6) Let the tube inhales all the detergents inside the cup.

Watch more details on video

2. Instruments cleaning before sterilization

1) Wash our hands.

2) Wear on gloves and masks.

3) Rinse all the instruments. Instruments with multiple pieces must be disassembled.

4) Brush the instruments while rinsing.

5) After brushing, immerse the instruments into detergents.

6) Dry them with paper towel.

7) Put them into self-sealing sterilization bag.

Cleaning and sterilization process of dental instruments

See more information on these links:
1. Blog recommend 
2. Dental treatment room maintenance

Steam sterilization

    Sterilization completely eliminates or destroys all living microorganisms and their spores in order to prevent disease transmission with the use of instruments. Comparing to many different methods available for sterilization, the techniques using saturated steam under pressure is the most reliable and should be used whenever possible on all critical and semi-critical items that are heat and moisture resistant. Saturated steam under pressure in an autoclave achieves their destruction by the irreversible coagulation and denaturation of enzymes and structural proteins. The two common types of steam sterilizers (autoclaves) are the gravity displacement autoclave and the high-speed prevacuum sterilizer.

Dental Autoclave [1]

    The basic principle of steam sterilization is to expose each instrument to steam directly at the specific temperature and pressure for an adequate time. According to the basic principle, there are four parameters of steam sterilization: steam, pressure, temperature and time.

    The ideal steam for sterilization is dry saturated steam. Pressure can help quickly obtain the requiring high temperature to kill microorganisms. Specific temperatures must be achieved to ensure the microbicidal activity. The two common steam-sterilizing temperatures are 121^oC and 132^oC. These temperatures must be maintained for a minimal time to kill microorganisms. The sterilization periods varies with the temperatures, the lower the temperature the longer the exposure time. In general, the minimal time for wrapped items are 30 minutes at 121^oC in a gravity displacement sterilizer or 4 minutes at 132^oC in a prevacuum sterilizer.

Steam Sterilization Phases [2]

Understanding steam sterilization

See more information on these links:
1. Centers for Disease Control and Prevention
2. Gravity v.s Vacuum System
3. UNC environment. Health and Safety

Picture resources:
1.http://www.medicalexpo.com/prod/sirona-dental-systems/dental-autoclave-bench-top-vacuum-cycle-70662-470828.html
2.http://www.gdnash.com/sterilization/

Factors Affecting the Efficacy of Disinfection and Sterilization

    If we want to achieve the desired sterilization or disinfection results, we have to first know what factors will affect these processes. Some of which are related with bacteria themselves, others of which are related with chemical and external physical conditions, and even might be operator error. After we clearly know these factors, we can avoid many risks of incomplete sterilization.

1. Quantity and Location of Microorganisms

    The lager the quantity of microorganisms, the more time or the more amount of disinfectant needs to damage all of them. The location of the microorganisms is equally important, because instruments that have crevices, joints, and channels are more difficult to disinfect than instruments that have flat-surfaces. If the instruments are consist of multiple pieces, then it must be disassembled.

Bacterial spore

2. Resistance of Microorganisms

    Many organisms have innate resistance to certain germicides, so choosing a proper germicide or sterilization process is important. For example, spores are resistant to disinfectants, ultraviolet radiation, high temperature, dryness and freezing, therefore, they required a longer exposure time or higher concentration of germicide than less resistant microorganisms.

3. Concentration and Potency of Disinfectants

    If everything else is constant then the higher concentration of the disinfectant, the greater its efficacy and the shorter the time to kill all the microorganisms. The potency of a disinfectants affects the exposure time required to achieve the same level of germicidal activity.

4. Physical and Chemical Factors

    There are several physical and chemical factors influence the efficacy of disinfectants, including temperature, pH, relative humidity and water hardness.
    Generally, as the temperature increases, the activity of most disinfectants increases. But if the temperature is too high then it might cause the disinfectants to degrade and the germicidal activity will decline. As the pH increases, the antimicrobial activity might increase in some disinfectants, such as glutaraldehyde, but decreases in others such as phenols. This effect is caused by altering the germicidal molecule or the cell surface. Relative humidity influences the activity of gaseous disinfectants/sterilants, such as chlorine dioxide and formaldehyde. Water hardness reduces the rate of killing microbes of some disinfectants, because divalent cations such as magnesium and calcium in hard water will interact with disinfectant forming insoluble precipitates.

5. Organic Matter

    Organic matter such as serum, blood, pus, fecal or saliva can influence the antimicrobial activity of disinfectants in at least two ways.

    First, disinfectant and organic matter can occur chemical reaction and forming a complex which is less germicidal or non-germicidal. Second, organic matter may protect microbes from attack by acting as a physical barrier.

    Therefore, it is very important to clean the instruments with water and brushes before any sterilization or disinfection process.

6. Duration of Exposure

    Instruments must be exposed to the biocide for an appropriate minimum contact time. In general, the longer exposure time the more effective on microbes kill. For endoscopic equipment the biocide must contact with all lumens and channels. Presence of air pockets or incomplete immersion into biocide will cause failure of the disinfection.

7. Biofilms

    Biofilm is a group of microorganisms which are tightly stuck together onto a surface and cannot be easily removed. Microorganisms may protect themselves by producing biofilms.





See more information on these links:
1. Centers for Disease Control and Prevention
2. Queensland Health

Guidelines for infection control in dentistry

    There are many different equipments that we use in the dental clinic. Base on their application and composition, we can divide them into three categories: critical, semi-critical and non-critical. According to their classification, we can choose the optimal way to sterilize and disinfect them. In this way, we can prevent transmission of infections among patients and dental health care personnel.

Critical Items [1]

1. Critical items: Items that will enter tissue or vascular system or blood will flow through them. They should be sterilized after each use.
Ø   Examples: Extraction forceps, scalpel blades, bone chisels, periodontal scalers, and surgical burs.

Amalgam condensers [2]

2. Semi-critical items: Items that will come in contact with mucous membrane or non-intact skin. If they are heat-tolerant, sterilization after each use is recommended. If they are heat-sensitive, high-level disinfection should be done.

Ø   Examples: Dental mouth mirrors, amalgam condensers and impression trays.

3. Non-critical items: Items that will come in contact with intact skin. They can be further divided into clinical contact and housekeeping surface.

1) Clinical contact surfaces:

    Surfaces that are touched frequently with gloved hands during patient care, or may become contaminated with blood, saliva, or other potentially infectious material and then come in contact with instruments, devices, hands, or gloves. Proper treatment of clinical contact surfaces is a combination of barriers and cleaning and disinfection. Using barriers to protect surfaces that are likely to become contaminated with blood or difficult to clean. Remove and discard barriers between patients. If barriers are not used, surfaces must be cleaned and disinfected between patients by using intermediate-disinfectant or low-level disinfectant. 

Ø   Examples: Light handles, switches, dental X-ray equipment, chair-side computers and air/water syringe buttons.

Clinical Contact Surfaces [3]

2) Housekeeping surfaces:

    Surfaces that are not contact directly with patients or devices used in dental procedures. Proper Treatment of housekeeping surfaces can occur at the end of the day with a detergent and water or an EPA-registered hospital disinfectant.

Ø   Examples: Floors, walls and tabletops.

Housekeeping Surfaces [4]

Introduction of different kinds of dental instruments

See more information on these links:
1. Critical/ Semi-critical/ Non-critical items
2. Clinical contact/ housekeeping surface

Picture resources:
1. http://www.amerdental.com/blog/practice-tips-76/
2. http://www.amerdental.com/amalgam-instruments/amalgam-condenser-1-2-round.html
3. http://www.slideshare.net/DanaSinzianaBreharCi/dental-healthcare-associated-infections-an-overview-of-pathogens-risks-and-control-measures
4. http://www.slideshare.net/DanaSinzianaBreharCi/dental-healthcare-associated-infections-an-overview-of-pathogens-risks-and-control-measures