Methods of Sterilization in a Dental Office

Steps followed in dental offices for achievement of sterilization are:

1. Cleaning

Manual Cleaning: Scrubbing with a brush and a surfactant or detergent with water removes debris and contaminants. If critical and noncritical items cannot be cleaned immediately after use, they should be placed in a puncture-proof, covered container and soaked in a detergent, disinfectant/detergent or an enzymatic cleaner (holding solution) until the soil is dissolved and removed. High-level disinfectants/ sterilants are not appropriate for presoaking instruments.

Automated Cleaning: Ultrasonic cleaners or washer-disinfecting units are safer and are recommended because they do not require presoaking or the manual scrubbing of instruments and therefore, minimize the exposure to blood and body fluids.

 Ultrasonic cleaners Sterilization

2. Corrosion Control

Always dry the cleaned instruments as it reduces the chances of corrosion. A rust inhibitor can be applied to the instruments before autoclaving.

3. Packaging

Instruments should be pre-packaged before sterilization to protect against contamination after sterilization. Use proper packaging material according to the method of sterilization. Too thin a wrap may cause sharp instruments to tear the wrap.

4. Sterilization

Heat: Heat sterilization is most commonly used in dental settings; however, steam and chemical vapor sterilization units are also used. High temperature methods include steam, dry heat and unsaturated chemical vapor while low temperature automated sterilization involves ethylene oxide (ETO) and plasma sterilization. Of these methods the autoclaves is the most preferred method in a dental setup. Autoclave is a self locking setup based on the efficacy of steam under pressure of 121 degree Celsius for 15 minutes and 15 pounds pressure. Another method is that of "Flash Sterilization" for unwrapped instruments using 270 degrees Fahrenheit at 30 pounds pressure for 4 -7 minutes.

Hot air ovens are electrical devices used in sterilization. The oven uses dry heat to sterilize articles. They do not require water and there is not much pressure build up within the oven, unlike an autoclave, making them safer to work with. They can be more rapid than an autoclave and higher temperatures can be reached compared to other means. As they use dry heat instead of moist heat, some organisms like prions, may not be killed by them every time. The standard settings for a hot air oven are:

 Hot air ovens

  1. 1.5 to 2 hours at 160°C (320 OF)
  2. 6to 12 minutes at 190°C (374 OF)

These are widely used to sterilize articles that can withstand high temperatures and not get burnt, like glassware and powders. Linen gets burnt and surgical sharps lose their sharpness.

Liquid Sterilants used for "cold sterilization" are intended only for the reprocessing of heat-sensitive instruments and devices. If the critical or semi critical item is heat sensitive, it should be immersed in a liquid sterilants.

Glutaraldehyde is a dialdehyde that is slightly acidic in its natural state. In a buffered (PH balanced) alkaline solution, it is a highly effective microbicidal agent. Glutaraldehyde is corrosive to metal instruments and is not to be used as a holding solution prior to instrument cleaning and sterilization. It is widely used in the cold sterilization of dental items, such as suction hoses. Glutaraldehyde is usually a clear liquid that turns green when activated. It has a strong odor and is an irritant to the skin, eyes, and respiratory system. It can cause allergic reactions in some individuals. The chemical should be used in separate areas where there is control over ventilation and occupational exposure.

Ortho-phthalaldehyde (OPA) is a chemical sterilizing agent used in a 0.55% solution, OPA shows better myco¬bactericidal activity than Glutaraldehyde. It also is effective against Glutaraldehyde-resistant spores. OPA has superior stability, is less volatile, and does not irritate skin or eyes, and it acts more quickly than Glutaraldehyde. On the other hand, it is more expensive, and will stain proteins (including skin) gray in color.

Ethylene oxide is a colorless gas used at room temperature to kill micro-organisms by chemical reaction. As it is toxic & irritating to skin & mucous membrane so it can only be used in an aerated & well ventilated room. The two most important ethylene oxide sterilization methods are: (1) the gas chamber method and (2) the micro-dose method.

Ozone is used in industrial settings to sterilize water and air, as well as a disinfectant for surfaces. It has the benefit of being able to oxidize most organic matter. On the other hand, it is a toxic and unstable gas that must be produced on-site, so it is not practical to use in many settings.

Ultraviolet Light (UV, from a germicidal lamp) is useful only for sterilization of surfaces and some transparent objects.


Ultraviolet Light Sterilization

Many objects that are transparent to visible light absorb UV. UV irradiation is routinely used to sterilize the interiors of biological safety cabinets between uses, but is ineffective in shaded areas, including areas under dirt (which may become polymerized after prolonged irradiation, so that it is very difficult to remove). It also damages some plastics, such as polystyrene foam if exposed for prolonged periods of time.

5. Storage & Shelf Life

All sterile items should be stored in an area and manner whereby the packs or containers will be protected from dust, dirt, moisture, animals and insects. Packs and containers with sterile (or high-level disinfected) items should be stored 20-25 cm (8-10 inches) off the floor, 45-50 cm (18-20 inches) from the ceiling and 15-20 cm (6-8 inches) from an outside wall. The shelf life of an item after sterilization is event ¬related. The item remains sterile until something causes the shelf life of sterilization depends on the following factors:

  1. Quality of the wrapper or container
  2. Number of times a package is handled before use
  3. Number of people who have handled the package
  4. Whether the package is stored on open or closed shelves
  5. Condition of storage area (e.g., humidity and cleanliness)
  6. Use of plastic dust covers and method of sealing

6. Monitoring Sterilization Procedures

Sterilization procedures can be monitored routinely using a combination of biological, chemical and mechanical. indicators as parameters. The biological indicator types.

Steam Sterilizers: Bacillus stearothermophilus, weekly and as needed.

Steam Sterilizers

Dry Heat Sterilizers: Bacillus subtilis, weekly and as needed. Chemical indicators include indicator tape or labels, which monitor time, temperature and pressure for steam sterilization, and time, temperature for dry-heat sterilization.

Steam Sterilizers

These indicators should be used on the inside and outside of each package or container. Mechanical indicators for sterilizers provide a visible record of the time, temperature and pressure for that sterilization cycle. This is usually a printout or graph from the sterilizer, or it can be a log of time, temperature and pressure kept by the person responsible for the sterilization process that day.

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