Disinfection and Sterilization: Sterilization in Dentistry

Sterilization destroys all microorganisms on the surface of stuff or in a fluid to prevent disease transmission when using that item.

Steam sterilization is moist heat in the form of saturated steam under pressure, which is the most widely used and the most dependable method for sterilization. Steam sterilization is nontoxic, inexpensive, rapidly microbicidal, sporicidal, rapidly heats and penetrates fabrics. However, steam sterilization has some deleterious effects on some materials, such as corrosion and combustion of lubricants associated with dental handpieces.

The basic principle of steam sterilization is to expose each item to steam with direct contact at the required temperature and pressure for the specific time. Thus, there are four parameters of steam sterilization: steam, pressure, temperature, and time. The ideal steam for sterilization is dry saturated steam and entrained water. Pressure is the main aid for obtaining the high temperature necessary to quickly kill microorganism. Specific temperature must be obtained to ensure the microbicidal activity. Two common steam-sterilizing temperatures are 121°C and 132°C. These temperatures must be maintained for a minimum period to kill microorganisms. Generally, the sterilization times at constant temperature vary depending on the type of item and the sterilizer type.

There are two basic types of steam sterilizer autoclaves, the gravity displacement autoclave and the high-speed prevacuum sterilizer. The minimum exposure time for sterilization of wrapped healthcare supplies are 30 minutes at 121°C in a gravity displacement sterilizer or 4 minutes at 132°C in a prevacuum sterilizer.

For the gravity displacement, steam comes out at the top or the side of the sterilizing chamber. Since the steam is lighter than air, it forces air out the bottom of the chamber through the drain vent. The gravity displacement autoclaves are primarily used to sterilize laboratory media, water, pharmaceutical products, regulated medical waste, and nonporous articles whose surfaces have direct steam contact.

The high-speed prevacuum sterilizers are similar to the gravity displacement sterilizers, except they has vacuum pump to remove the air from the sterilizing chamber and load before the steam is admitted. The advantage of using prevacuum sterilizer is that it is nearly instantaneous for the steam to penetrate into porous loads.

Moist heat destroys microorganism by irreversible coagulation and denaturation of enzymes and structural proteins. The presence of moisture significantly affects the coagulation temperature of protein and the temperature at which microorganisms are destroyed.

Steam sterilization should be used to sterilize all possible critical and semicritical items those are heat and moisture resistant. Furthermore, steam sterilizers also are used in healthcare facilities to decontaminate microbiological waste and sharps containers but sterilizer these items with gravity displacement sterilizer require additional exposure time.

Flash sterilization is a type of steam sterilization use to sterilize an unwrapped object at 132°C for 3 minutes at 27-28 lbs. of pressure in a gravity displacement sterilizer. Flash sterilization usually uses for cleaning patient-care items that cannot be wrapped, sterilized, and stored before use. It can also uses for sterilizing an item that does not have enough time to sterilize by package method. However, flash sterilization is not recommended for implantable devices because the potential for serious infections.

Ethylene oxide (ETO), as a low-temperature sterilant, has been used process for sterilizing temperature- and moisture-sensitive medical devices and supplies in health care establishment. There are two types of ethylene oxide sterilizers, mixed gas and 100% ethylene oxide. Ethylene oxide sterilizers combined ethylene oxide with a chlorofluorocarbon (CFC) stabilizing agent. However, there are several disadvantages about chlorofluorocarbon. It has scientific evidence linking it to destruction of the earth’s ozone layer. Fortunately, there are alternative technologies to ethylene oxide with chlorofluorocarbon that be cleared by the FDA for medical equipment include 100% ethylene oxide; ethylene oxide with a different stabilizing gas, such as carbon dioxide or hydrochlorofluorocarbons (HCFC) ; submersion in peracetic acid; hydrogen peroxide gas plasma; and ozone.

Hydrogen peroxide (H₂O₂) gas plasma is a new sterilization technology by producing free radicals within a plasma field that are able to interact with essential cell components and thereby disrupt the metabolism of microorganism. Hydrogen peroxide gas is used to sterilize materials and devices that cannot tolerate high temperatures and humidity, such as plastics, electrical devices, and corrosion- susceptible metal alloys. This method has been compatible with most medical devices and material tested.

After these items are cleaned, dried, and inspected, they must be wrapped or placed in rigid containers and should be arranged instrument trays before sterilization.

The guidelines mention that hinged instruments should be opened; items with removable parts should be disassembled unless the device manufacturer provide specific instructions; complex instruments should be prepared and sterilized according to device manufacturer’s instructions; devices with concave surfaces should be positioned to help water drain; heavy items should be positioned not to damage brittle items; and the weight of the instrument set should be based on the design and density of the instruments and the distribution of metal mass. Further, there are several methods to maintain sterility of surgical instruments, including rigid containers, peel-open pouches, roll stock or reels and sterilization wraps. The packaging material must allow penetration of the sterilant, provide protection against contact contamination during handling, provide an effective barrier to microbial penetration, and maintain the sterility of the processed item after sterilization. The key points of ideal sterilizeation wrap are successful barrier, penetrability, aeration, ease of use, drapeability, flexibility, puncture resistance, tear strength, toxicity, odor, waste disposal, linting, cost, and transparency.

The loading procedures must be able for free circulation of steam around each item. Furthermore, there are several important basic principles for loading a sterilizer, such as allow for proper sterilant circulation; perforated trays should be placed so the tray is parallel to the shelf; non perforated containers should be placed on their edge; small items should be loosely placed in wire baskets; and peel packs should be placed on edge in perforated or mesh bottom racks or baskets.

The wrapped surgical trays remained sterile for varying periods depending on the type of material used to wrap the trays. Safe storage time for sterile packs depend on the porosity of the wrapper and storage conditions. For example, heat-sealed, plastic peel-down pouches and wrapped packs sealed in 3-mil polyethylene overwrap can be sterile for as long as 9 months after sterilization. In addition, items wrapped in double-thickness muslin comprising four layers can remain sterile for at least 30 days.

All of the sterilization procedure should be evaluated the sterilizing conditions and indirectly the microbiologic status of the processed items by using a combination of mechanical, chemical, and biological indicators. The mechanical monitors include temperature record chart and pressure gauge for daily assessment. The mechanical monitors for ethylene oxide include computer printouts, gauges that provide time, temperature, and pressure records. Chemical indicators are convenient, inexpensive, and indicate that the item has been exposed to the sterilization process. Chemical indicator should be used in conjunction with biological indicators, but should not replace them because only a biological indicator consisting can measure the microbial killing power of the sterilization process by resistant spores. Chemical indicators are attached to each pack to show that the package has been processed through a sterilization cycle, but these indicators do not prove sterilization has been achieved. Chemical indicators usually are heat-or chemical-sensitive inks, which will change color when one or more sterilization parameters present. Biological indicators measure the sterilization process directly by using the most resistant microorganisms, not checking the physical and chemical conditions. If a sterilizer is used frequently, using biological indicators everyday allow earlier discover equipment malfunctions or procedural errors, which can minimizes the extent of patient surveillance and product recall needed in the event of a positive biological indicator.

After the sterilization process, medical and surgical devices should be stored with aseptic technique in order to prevent contamination. Sterile supplies should be stored far enough from the floor, the ceiling, and the outside walls to allow for adequate air circulation, ease of cleaning, and compliance with local fire codes. Also, medical and surgical supplies should not be stored in location where they can become wet, such as under sinks. Moisture brings microorganisms from the air and surfaces. The ideal storage is closed or covered cabinet but open shelving can also be used for storage.

In dental clinic, not only the disinfection and sterilization of the dental instruments are important but also clinic environment’s hygiene is a great point to make sure of. In order to keep the hygiene of the clinic in a best condition, regular cleaning is very important. No matter what before or after using the clinic we have to clean and do some simple disinfection. We have few but necessary steps to do.

1. Spray some of disinfectant or high concentration alcohol on the paper towel.

2. Wipe the surface of whole dental chair and both handle and control desk. (Changing different napkin paper in different parts of is necessary.)

3. Using a bucket of diluted detergent to clean the tube of the dental chair by step on the foot controller to let the tube suck the detergent in the machine.