The sterilization section of the processing area should include the sterilizers and related supplies, with adequate space for loading, unloading and cool down. The area can also include incubators for analyzing spore tests and enclosed storage for sterile items and disposable (single-use) items. Manufacturer and local building code specifications will determine placement and room ventilation requirements.
Heat-tolerant dental instruments usually are sterilized by 1) steam under pressure (autoclaving), 2) dry heat, or 3) unsaturated chemical vapor. All sterilization should be performed by using medical sterilization equipment cleared by FDA. The instructions specified by the manufacturer should be followed.
Items to be sterilized should be arranged to permit free circulation of the sterilizing agent (eg, steam, chemical vapor or dry heat); manufacturer’s instructions for loading the sterilizer should be followed. Instrument packs should be allowed to dry inside the sterilizer chamber before removing and handling. Packs should not be touched until they are cool and dry because hot packs act as wicks, absorbing moisture, and hence, bacteria from hands.
Steam sterilization or autoclaving is the most efficient and dependable way to sterilize critical and semi-critical items. It requires that each item be exposed to direct steam contact following the instructions of the sterilizing unit.
The steam sterilizers used in the dental offices are gravity displacement sterilizers. In gravity displacement sterilizers, steam is admitted through steam lines, a steam generator or selfgeneration of steam within the chamber. Unsaturated air is forced out of the chamber through a vent in the chamber wall. When packing of items is not done properly or the chamber is overloaded, cool air pockets may result in failure of sterilization.
Prevacuum sterilizers are fitted with a pump to create a vacuum in the chamber and ensure air removal from the sterilizing chamber before the chamber is pressurized with steam.
UNSATURATED CHEMICAL-VAPOR STERILIZATION
Unsaturated chemical-vapor sterilization involves heating a chemical solution of primarily alcohol with 0.23% formaldehyde in a closed pressurized chamber. Unsaturated chemical vapor sterilization of carbon steel instruments (eg, dental burs) causes less corrosion than steam sterilization because of the low level of water present during the cycle. Instruments should be dry before sterilizing. State and local authorities should be consulted for hazardous waste disposal requirements for the sterilizing solution.
Dry heat is used to sterilize materials that might be damaged by moist heat (eg, burs and certain orthodontic instruments). Although dry heat has the advantages of low operating cost and being noncorrosive, it is a prolonged process and the high temperatures required are not suitable for certain patient-care items and devices.
Dry-heat sterilizers used in dentistry include static-air and forced-air types.
• The static-air type is commonly called an oven-type sterilizer. Heating coils in the bottom
or sides of the unit cause hot air to rise inside the chamber through natural convection.
• The forced-air type is also known as a rapid heat-transfer sterilizer. Heated air is circulated throughout the chamber at a high velocity, permitting more rapid transfer of energy from the air to the instruments, thereby reducing the time needed for sterilization.
STERILIZATION OF UNWRAPPED INSTRUMENTS
An unwrapped cycle (sometimes called flash sterilization) is a method for sterilizing unwrapped patient-care items for immediate use. The time required for unwrapped sterilization cycles depends on the type of sterilizer and the type of item (ie, porous or nonporous) to be sterilized. The unwrapped cycle in tabletop sterilizers is preprogrammed by the manufacturer to a specific time and temperature setting and can include a drying phase at the end to produce a dry instrument with much of the heat dissipated. If the drying phase requirements are unclear, the operation manual or manufacturer of the sterilizer should be consulted. If the unwrapped sterilization cycle in a steam sterilizer does not include a drying phase, or has only a minimal drying phase, items retrieved from the sterilizer will be hot and wet, making aseptic transport to the point of use more difficult. For dry-heat and chemical vapor sterilizers, a drying phase is not required.
Unwrapped sterilization should be used only under certain conditions:
• Thorough cleaning and drying of instruments precedes the unwrapped sterilization cycle
• Mechanical monitors are checked and chemical indicators used for each cycle
• Care is taken to avoid thermal injury to DHCP or patients
• Items are transported aseptically to the point of use to maintain sterility
Because all implantable devices should be quarantined after sterilization until the results of biological monitoring are known, unwrapped or flash sterilization of implantable items is not recommended.
Critical instruments sterilized unwrapped should be transferred immediately by using aseptic technique, from the sterilizer to the actual point of use.
Semi-critical instruments that are sterilized unwrapped on a tray or in a container system should be used immediately or within a short time. When sterile items are open to the air, they will eventually become contaminated. Storage, even temporary, of unwrapped semicritical instruments permits exposure to dust, airborne organisms and other unnecessary contamination before use on a patient. A carefully written protocol for minimizing the risk of contaminating unwrapped instruments should be prepared and followed.
Sterilization of Unwrapped Instruments
1. Clean and dry instruments before the unwrapped sterilization cycle.
2. Use mechanical and chemical indicators for each unwrapped sterilization cycle (ie, place an internal chemical indicator among the instruments or items to be sterilized).
3. Allow unwrapped instruments to dry and cool in the sterilizer before they are handled to avoid contamination and thermal injury.
4. Semi-critical instruments that will be used immediately or within a short time can be sterilized unwrapped on a tray or in a container system, provided that the instruments are handled aseptically during removal from the sterilizer and transport to the point of use.
5. Critical instruments intended for immediate reuse can be sterilized unwrapped if the instruments are maintained sterile during removal from the sterilizer and transport to the point of use (eg, transported in a sterile covered container).
6. Do not sterilize implantable devices unwrapped.
7. Do not store critical instruments unwrapped.
8. Storage of unwrapped semi-critical items is discouraged
OTHER STERILIZATION METHODS
Chemical germicides must be approved by the FDA. Examples of these are gluteraldehyde, peracetic acid and hydrogen peroxide. While some of these chemicals have the capacity to destroy even resistant organisms they do have several limitations:
• They items should completely be immersed for approximately 10 to12 hours
• They are highly corrosive
• They are highly toxic
• They are also very costly
• Medical gloves lack chemical resistance to gluteraldehyde
For this reason certain post-sterilization becomes important. Items need to be:
• Rinsed with sterile water after removal to remove toxic or irritating residues
• Handled using sterile gloves and dried with sterile towels
• Delivered to the point of use in an aseptic manner.
For all these reasons, the use of liquid chemical germicides is discouraged. Heat tolerant or disposable alternatives are instead suggested. These chemicals may have a better use as high level disinfectants. While these agents may be used for high-level disinfection, they must be used only for purposes indicated on their label.
Gas sterilization using ethylene oxide (ETO) has been used in large healthcare facilities. They are however impractical for dental clinic settings. ETO cannot effectively sterilize handpieces because of their decreased ability to penetrate the small lumen of the instrument. Bead sterilizers have been used in dentistry to sterilize small metallic instruments (eg, endodontic files). FDA has determined that a risk of infection exists with these devices because of their potential failure to sterilize dental instruments and has required their commercial distribution to cease unless the manufacturer files a premarket approval application. If a bead sterilizer is employed, the DHCP assumes the risk of employing a dental device FDA has deemed neither safe nor effective.
Monitoring of sterilization procedures should include a combination of process parameters, including mechanical, chemical and biological. These parameters evaluate both the sterilizing conditions and the procedure’s effectiveness.
Mechanical techniques for monitoring sterilization include assessing cycle time, temperature
and pressure by observing the gauges or displays on the sterilizer and noting these parameters
for each load.
Chemical indicators—internal and external—use sensitive chemicals to assess physical conditions (eg, time and temperature) during the sterilization process. These indicators do not necessarily prove sterility of the items. External chemical indicators only determine that the sterilization process has reached the package. Internal indicators ensure that the sterilizing medium has penetrated the package and actually reached the instrument. These indicators may allow detection of equipment malfunction of procedural errors such as packaging. Because chemical indicator test results are received when the sterilization cycle is complete, they can provide an early indication of a problem and where in the process the problem might exist. If either mechanical indicators or internal or external chemical indicators indicate inadequate processing, items in the load should not be used until reprocessed.
Biological indicators (BIs) commonly use spores (spore test). Since they are more resistant and are usually present in greater numbers, destruction of these organisms will indicate destruction of other potential pathogens. This is the most accepted method for monitoring sterilizations process. Correct functioning of sterilization cycles should be verified for each sterilizer by the periodic use (at least weekly) of BIs.
Every load containing implantable devices should be monitored with such indicators, and the items quarantined until BI results are known. However, in an emergency, placing implantable items in quarantine until spore tests are known to be negative might be impossible. BI placement is determined by manufacturer’s instructions.
Overloading, failure to provide adequate package separation and incorrect or excessive packaging material are all common reasons for a positive BI in the absence of mechanical failure of the sterilizer unit.
1. Use mechanical, chemical, and biological monitors according to the manufacturer’s instructions to ensure the effectiveness of the sterilization process.
2. Monitor each load with mechanical (eg, time, temperature and pressure) and chemical indicators.
3. Place a chemical indicator on the inside of each package. If the internal indicator is not visible from the outside, also place an exterior chemical indicator on the package.
4. Place items/packages correctly and loosely into the sterilizer so as not to impede penetration of the sterilant.
5. Do not use instrument packs if mechanical or chemical indicators indicate inadequate processing.
6. Monitor sterilizers at least weekly by using a biological indicator with a matching control (ie, biological indicator and control from same lot number).
7. Use a biological indicator for every sterilizer load that contains an implantable device.
8. Verify results before using the implantable device, whenever possible.
. The following are recommended in the case of a positive spore test:
a. Remove the sterilizer from service and review sterilization procedures (eg, work practices and use of mechanical and chemical indicators) to determine whether operator error could be responsible;
b. Retest the sterilizer by using biological, mechanical and chemical indicators after correcting any identified procedural problems;
c. If the repeat spore test is negative, and mechanical and chemical indicators are within normal limits, put the sterilizer back in service.
9. The following are recommended if the repeat spore test is positive:
a. Do not use the sterilizer until it has been inspected or repaired or the exact reason for the positive test has been determined;
b. Recall, to the extent possible, and reprocess all items processed since the last negative spore test;
c. Before placing the sterilizer back in service, rechallenge the sterilizer with biological indicator tests in three consecutive empty chamber sterilization cycles after the cause of the sterilizer failure has been determined and corrected.
10. Maintain sterilization records (ie, mechanical, chemical and biological) in compliance with state and local regulations.