Sterilization protocol encompasses the following:
1. Transport of instruments to the sterilization area
2. Cleaning of instruments
3. Instrument examination and care
4. Packaging
5. Sterilization methods
Before going into the details of methods of sterilization, let us first have a quick review as to how to transport the instruments to the sterilization area from treatment area.
Transport of Instruments to the Sterilization Area
Most dental offices have a designated area for instrument reprocessing that is separate from the dental treatment room. This is ideal, since cleaning, sterilizing and storing instruments in the same room where the delivery of patient care is provided increases the risk of cross-contamination.Some instruments and materials are single-use only. Single-use items should be segregated in the operatory, and those that are sharp or otherwise pose a risk of injury must be discarded into a sharps container. Items without risk, such as a saliva ejector, can be thrown into the trash. Finally, the tray or cassette of reusable instruments is taken to the cleaning and sterilization area for processing
The Centres for Disease Control and Prevention (CDC) states that, "Contaminated instruments should be handled carefully to prevent exposure to sharp instruments that can cause percutaneous injury. Instruments should be placed in an appropriate container at the point of use to prevent percutaneous injuries during transport to the instrument processing area." In addition, the Occupational Safety and Health Administration (OSHA) says, "The person handling the instruments through removal, cleaning, packaging and sterilization needs to use heavy-duty gloves to help prevent injury with sharp contaminated instruments." Although heavy-duty gloves (utility gloves) may feel more awkward than examination gloves, they provide extra protection while handling instruments during the cleaning, rinsing,drying, packaging and sorting procedures that take place during instrument reprocessing. Additionally, nitrile utility gloves are available in a variety of sizes, allowing a more secure fit.
1. Transport of instruments to the sterilization area
2. Cleaning of instruments
3. Instrument examination and care
4. Packaging
5. Sterilization methods
Before going into the details of methods of sterilization, let us first have a quick review as to how to transport the instruments to the sterilization area from treatment area.
Transport of Instruments to the Sterilization Area
Most dental offices have a designated area for instrument reprocessing that is separate from the dental treatment room. This is ideal, since cleaning, sterilizing and storing instruments in the same room where the delivery of patient care is provided increases the risk of cross-contamination.Some instruments and materials are single-use only. Single-use items should be segregated in the operatory, and those that are sharp or otherwise pose a risk of injury must be discarded into a sharps container. Items without risk, such as a saliva ejector, can be thrown into the trash. Finally, the tray or cassette of reusable instruments is taken to the cleaning and sterilization area for processing
The Centres for Disease Control and Prevention (CDC) states that, "Contaminated instruments should be handled carefully to prevent exposure to sharp instruments that can cause percutaneous injury. Instruments should be placed in an appropriate container at the point of use to prevent percutaneous injuries during transport to the instrument processing area." In addition, the Occupational Safety and Health Administration (OSHA) says, "The person handling the instruments through removal, cleaning, packaging and sterilization needs to use heavy-duty gloves to help prevent injury with sharp contaminated instruments." Although heavy-duty gloves (utility gloves) may feel more awkward than examination gloves, they provide extra protection while handling instruments during the cleaning, rinsing,drying, packaging and sorting procedures that take place during instrument reprocessing. Additionally, nitrile utility gloves are available in a variety of sizes, allowing a more secure fit.
Using mechanical means of instrument cleaning rather than hand scrubbing should minimize handling of instruments. If procedures are used whereby hand scrubbing is necessary, heavy-duty (utility) gloves, mask, eyewear and gown should always be worn while cleaning.
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| Instrument Washing |
Minimize the risk of puncture injury by scrubbing only one instrument at a time while holding it low in the sink. Use of a system utilizing locked cassettes eliminates the need to sort, handle and hand scrub individual instruments reducing the risk of infection from contaminated instruments and results in saving of, on an average, five minutes during instrument reprocessing, as well as fewer damaged instruments, since the instruments are locked in position during reprocessing. As with any standardized procedure, a standardized instrument reprocessing protocol also results in easy staff training and cross-training.
In general, three classifications of mechanical cleaning devices are available for the dental office.They are:
In general, three classifications of mechanical cleaning devices are available for the dental office.They are:
- ultrasonic cleaner,
- instrument washer and
- instrument washer/disinfector
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| Ultrasonic Cleaner |
Instrument Examination and Care
Cleaning instruments, provides a good opportunity to examine, replace or remove damaged instruments; lubricate items such as handpieces; and otherwise prepare instruments for sterilization. Instruments must be dry before packaging - if drying was not part of the cleaning process, time must be taken to dry the instruments completely. High-quality metal dental cassettes specially designed to withstand high temperatures are preferred for use with steam and chemical vapor sterilizers.Most sterilizers on the market today offer a cassette rack, which helps to prevent over-loading in the sterilizer, thereby reducing the risk of ineffective sterilization and ultimately of infection and cross-infection.
Packaging
Packaging used for instruments and cassettes prior to sterilization includes wrap, paper pouches, plastic pouches, combination paper/plastic pouches and nylon tubing. Sterilization packaging is specifically designed to allow penetration of heat, steam or vapor and then to seal the sterilized instruments inside the package for sterile storage. After sterilization, instruments should remain in packages until use. Different materials are appropriate for different types of sterilizers. Unless otherwise specified, all packaging is single use only. Using tape to reseal previously used packaging material may inhibit its ability to continue to function as intended by the manufacturer.
Modalities Available for Sterilization
The most accepted methods of sterilization can be classified as follows:
Physical Agents: These comprise of:
Cleaning instruments, provides a good opportunity to examine, replace or remove damaged instruments; lubricate items such as handpieces; and otherwise prepare instruments for sterilization. Instruments must be dry before packaging - if drying was not part of the cleaning process, time must be taken to dry the instruments completely. High-quality metal dental cassettes specially designed to withstand high temperatures are preferred for use with steam and chemical vapor sterilizers.Most sterilizers on the market today offer a cassette rack, which helps to prevent over-loading in the sterilizer, thereby reducing the risk of ineffective sterilization and ultimately of infection and cross-infection.
Packaging
Packaging used for instruments and cassettes prior to sterilization includes wrap, paper pouches, plastic pouches, combination paper/plastic pouches and nylon tubing. Sterilization packaging is specifically designed to allow penetration of heat, steam or vapor and then to seal the sterilized instruments inside the package for sterile storage. After sterilization, instruments should remain in packages until use. Different materials are appropriate for different types of sterilizers. Unless otherwise specified, all packaging is single use only. Using tape to reseal previously used packaging material may inhibit its ability to continue to function as intended by the manufacturer.
Modalities Available for Sterilization
The most accepted methods of sterilization can be classified as follows:
Physical Agents: These comprise of:
- Sunlight
- Drying
- Dry heat: flaming, incineration, hot air
- Moist heat: pasteurization, boiling, steam under pressure
- Filtration: candles, asbestos, pads, membranes
- Radiation
- Ultrasonic and sonic vibration
Chemical Agents: these include the following:
- Alcohols: ethyl alcohol, isopropyl alcohol, trichlorobutanolz Aldehydes: formaldehyde, glutaraldehyde
- Dyes
- Halogens
- Phenols
- Surface active agents
- Metallic salts
- Gases: ethylene oxide, formaldehyde, betapropiolactone
Now let us discuss the methods of sterilization one by one:
Sunlight
It possesses appreciable bactericidal activity under natural condition. The action is primarily due to content of the ultraviolet rays; however most of the u/v rays are screened by glass and the presence of ozone
Drying
Moisture is essential for bacteria, drying therefore has a deleterious effect on most bacteria. Spontaneous drying can often kill bacteria while viruses are more resistant. However, the method is highly unreliable, spores are unaffected by drying and can remain viable for long periods.
Heat
Some other methods using heat are:
Boiling
Though highly unreliable as a sterilization technique and more effective for disinfection, it is used very often. Boiling water in hot water sterilizer reaches 100 o C and a time period of 10-30 minutes promotes sterilization. Sterilization may be promoted with addition of 2% sodium bicarbonate.Steam at atmospheric pressure (100 o C): Koch or Arnold steamer or lab autoclaves are used. A 90 minute exposure is recommended.
Tyndallisation
John Tyndall devised a process of sterilisation by steaming for a few minutes at 100 o C on 3-4 successive operations separated by 24 hour intervals at room temperatures. The principle is that the first exposure kills all vegetative bacteria; spores will germinate and be killed on subsequent occasions.
Flaming
Inoculating loops or wires, points of forceps and searing spatulas are held in a Bunsen flame till they become red hot. Scalpels, needles, mouth of culture tubes,glass slides, and cover slips can be flame sterilized.
Incineration
This is an excellent method for rapidly destroying materials such as soiled dressings, animal carcasses, bedding and pathological materials. Plastics like PVC and polythene can also be incinerated. Incinerated material should be carefully disposed off.
Autoclave sterilization
Word "autoclave" means self locking and is used to denote an apparatus that sterilizes by use of steam under pressure. It operates on same principle as pressure cookers. Because the steam is formed in a closed system, the steam completely fills (saturates) the sterilizer chamber, pushing the cooler air out of an escape valve, which then closes and allows the build up of pressure.Because air pockets in the chamber cannot reach sterilizing temperatures, some steam sterilizer manufacturers have added a pre sterilization vacuum cycle.At 100 O C there is at least 7 times as much available heat from saturated steam as from boiling water.
Sunlight
It possesses appreciable bactericidal activity under natural condition. The action is primarily due to content of the ultraviolet rays; however most of the u/v rays are screened by glass and the presence of ozone
Drying
Moisture is essential for bacteria, drying therefore has a deleterious effect on most bacteria. Spontaneous drying can often kill bacteria while viruses are more resistant. However, the method is highly unreliable, spores are unaffected by drying and can remain viable for long periods.
Heat
Some other methods using heat are:
Boiling
Though highly unreliable as a sterilization technique and more effective for disinfection, it is used very often. Boiling water in hot water sterilizer reaches 100 o C and a time period of 10-30 minutes promotes sterilization. Sterilization may be promoted with addition of 2% sodium bicarbonate.Steam at atmospheric pressure (100 o C): Koch or Arnold steamer or lab autoclaves are used. A 90 minute exposure is recommended.
Tyndallisation
John Tyndall devised a process of sterilisation by steaming for a few minutes at 100 o C on 3-4 successive operations separated by 24 hour intervals at room temperatures. The principle is that the first exposure kills all vegetative bacteria; spores will germinate and be killed on subsequent occasions.
Flaming
Inoculating loops or wires, points of forceps and searing spatulas are held in a Bunsen flame till they become red hot. Scalpels, needles, mouth of culture tubes,glass slides, and cover slips can be flame sterilized.
Incineration
This is an excellent method for rapidly destroying materials such as soiled dressings, animal carcasses, bedding and pathological materials. Plastics like PVC and polythene can also be incinerated. Incinerated material should be carefully disposed off.
Autoclave sterilization
Word "autoclave" means self locking and is used to denote an apparatus that sterilizes by use of steam under pressure. It operates on same principle as pressure cookers. Because the steam is formed in a closed system, the steam completely fills (saturates) the sterilizer chamber, pushing the cooler air out of an escape valve, which then closes and allows the build up of pressure.Because air pockets in the chamber cannot reach sterilizing temperatures, some steam sterilizer manufacturers have added a pre sterilization vacuum cycle.At 100 O C there is at least 7 times as much available heat from saturated steam as from boiling water.
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| Autoclave |
The several types of steam sterilizers that are in use.
1. Lab Autoclave
2. Hospital dressing sterilizer
3. Bowl & instrument sterilizer
4. Rapid cooling sterilizer Parameter:
121 O C (250 O F) for 15 minutes at 15 psi or 132 O C (270 O F) for 3-7 mins at 30 psi (flash sterilization) for unwrapped instruments.Add 5 minutes for moderately wrapped packs.
The typical dental office steam sterilizer usually operates through 4 cycles:
After adding the water one loads the chamber, closes the door & turns on the unit & the heat up cycle begins to generate steam.The steam pushes out the air in the chamber (in a gravity steam sterilizer ) or a vacuum is drawn (in a vacuum steam sterilizer ) & when the set temperature is reached, the sterilization cycle begins. The sterilizer maintains the temperature for the set time, usually ranging from 3-30 minutes.At the end of the sterilizing cycle, the depressurization cycle begins & steam is slowly released, with decrease in temperature & pressure. At the end of this cycle, all the items inside are wet & the drying cycle is initiated. Most steam sterilizer manufacturers provide drying instructions & some even may have a programmed closed door or open during cycle.
Some sterilizers have a post sterilizer vacuum cycle to facilitate drying. Other steam sterilizers pull in fresh air through a microbial filter. Others have an automatic open door drying cycle that maintains the heat inside chamber to evaporate the remaining water but the chamber is opened to the air so that water vapour can escape and items can dry.The cooling of the warm pack should be done slowly to avoid the formation of condensation on the instruments. One should not place warm packs under air conditioning or cool air vents.Recommended packaging: either "loose" or wrapped in muslin cloth, paper, nylon aluminium foil, steam permeable plastics.
Advantage: most efficient and reliable sterilization method available. Its quite simple to operate and relatively inexpensive. There is flexibility of packaging loading and cycles
Disadvantage: non stainless steel instruments may oxidize (rust) unless protectedn by reducing agent or "emulsion" dip prior to packaging and autoclaving.Low melting plastics and rubber cups may melt or distort. Items that retain moisture take time to dry.
Dry heat sterilization
It is used to sterilize glass ware, forceps, scissors, scalpels, all glass syringes,swabs, some pharmaceuticals products such as liquid paraffin, dusting powder,fats & grease.This method requires more time to sterilize (10-90 mins /cycle) owing to warm up time. Efficiency of dry heat oven depends mainly on power available per cubic foot of chamber. The minimum for 30 minutes warm up time is 550 watts per cubic foot.An accurate pyrometer, thermocouple or thermometer in needed to verify actual temperature for determining cycle time.
Radiation: can be
Ionizing radiation are high energy electromagnetic waves including X-rays, gamma rays, particulate radiation, cosmic rays which are highly lethal with high penetrating power. This is a cold sterilization with no heat involved.Non ionising radiation include infrared and UV rays. Lethal effect is through generation of heat and DNA damage. Penetration is low but efficacy is high. Infra red is used for sterilization of syringes while UV rays are used for disinfection of enclosed areas such as entry ways, hospital wards, and operation theatres.Lasers like CO 2 , Argon, Nd-YAG etc. are used. Hoob and colleagues found that exposure of instruments for 35 secs to laser beam is sufficient to sterilize.
Ultrasonic and sonic vibrations
Cells of all types can be destructed by intense sonic and ultrasonic vibrations generated by magnetostrictive oscillations or peizo electric crystals. It has limited practical significance for sterilization but valuable in instrument cleaning.
Filtration
It is a method of choice for heat labile liquids and solution. The various types of filters are candle filters, asbestos filters, sintered glass filter, membrane filters,nucleopore filters.
Chemical agents
Ethylene oxide:
This is considered as the only chemical sterilant while the others are considered merely as disinfectants. It is a gas at temperature above 10.8 degree Celsius, a highly toxic compound that destroys by alkylation. Commercial mixtures contain 12% ETO and 88% CFC. Advantages include high penetration, no damage to heat sensitive and complex devices, evaporation with no residue.
Disadvantage are its slowness, toxicity, dry instrument to be used, flammability of material and degassing required.
Aldehydes:
Formaldehyde: widely employed for the fumigation of operation theatres.
Glutaraldehyde: commercial preparations are active at different pH and have percentage of 2-3.2. They can destroy microbes in 10 hours. They have a surprising resistance to activation by organic matter and do not harm rubber and plastic hence are indicated for impression materials. However they may corrode or discolour metal.
Beta Propiolactone: this is a condensation product of ketone and formaldehyde with a boiling point of 163 o C. 0.2 % BPL is used for sterilization. It is more efficient than formaldehyde for fumigation but is carcinogenic. It is also used for sterilizing vaccines, graft tissue and other delicate biological materials.
1. Lab Autoclave
2. Hospital dressing sterilizer
3. Bowl & instrument sterilizer
4. Rapid cooling sterilizer Parameter:
121 O C (250 O F) for 15 minutes at 15 psi or 132 O C (270 O F) for 3-7 mins at 30 psi (flash sterilization) for unwrapped instruments.Add 5 minutes for moderately wrapped packs.
The typical dental office steam sterilizer usually operates through 4 cycles:
- The heat up cycle
- The sterilizing cycle
- The depressurization cycle
- The Drying cycle
After adding the water one loads the chamber, closes the door & turns on the unit & the heat up cycle begins to generate steam.The steam pushes out the air in the chamber (in a gravity steam sterilizer ) or a vacuum is drawn (in a vacuum steam sterilizer ) & when the set temperature is reached, the sterilization cycle begins. The sterilizer maintains the temperature for the set time, usually ranging from 3-30 minutes.At the end of the sterilizing cycle, the depressurization cycle begins & steam is slowly released, with decrease in temperature & pressure. At the end of this cycle, all the items inside are wet & the drying cycle is initiated. Most steam sterilizer manufacturers provide drying instructions & some even may have a programmed closed door or open during cycle.
Some sterilizers have a post sterilizer vacuum cycle to facilitate drying. Other steam sterilizers pull in fresh air through a microbial filter. Others have an automatic open door drying cycle that maintains the heat inside chamber to evaporate the remaining water but the chamber is opened to the air so that water vapour can escape and items can dry.The cooling of the warm pack should be done slowly to avoid the formation of condensation on the instruments. One should not place warm packs under air conditioning or cool air vents.Recommended packaging: either "loose" or wrapped in muslin cloth, paper, nylon aluminium foil, steam permeable plastics.
Advantage: most efficient and reliable sterilization method available. Its quite simple to operate and relatively inexpensive. There is flexibility of packaging loading and cycles
Disadvantage: non stainless steel instruments may oxidize (rust) unless protectedn by reducing agent or "emulsion" dip prior to packaging and autoclaving.Low melting plastics and rubber cups may melt or distort. Items that retain moisture take time to dry.
Dry heat sterilization
It is used to sterilize glass ware, forceps, scissors, scalpels, all glass syringes,swabs, some pharmaceuticals products such as liquid paraffin, dusting powder,fats & grease.This method requires more time to sterilize (10-90 mins /cycle) owing to warm up time. Efficiency of dry heat oven depends mainly on power available per cubic foot of chamber. The minimum for 30 minutes warm up time is 550 watts per cubic foot.An accurate pyrometer, thermocouple or thermometer in needed to verify actual temperature for determining cycle time.
Radiation: can be
- Ionizing
- Non-ionizing
- Lasers
Ionizing radiation are high energy electromagnetic waves including X-rays, gamma rays, particulate radiation, cosmic rays which are highly lethal with high penetrating power. This is a cold sterilization with no heat involved.Non ionising radiation include infrared and UV rays. Lethal effect is through generation of heat and DNA damage. Penetration is low but efficacy is high. Infra red is used for sterilization of syringes while UV rays are used for disinfection of enclosed areas such as entry ways, hospital wards, and operation theatres.Lasers like CO 2 , Argon, Nd-YAG etc. are used. Hoob and colleagues found that exposure of instruments for 35 secs to laser beam is sufficient to sterilize.
Ultrasonic and sonic vibrations
Cells of all types can be destructed by intense sonic and ultrasonic vibrations generated by magnetostrictive oscillations or peizo electric crystals. It has limited practical significance for sterilization but valuable in instrument cleaning.
Filtration
It is a method of choice for heat labile liquids and solution. The various types of filters are candle filters, asbestos filters, sintered glass filter, membrane filters,nucleopore filters.
Chemical agents
Ethylene oxide:
This is considered as the only chemical sterilant while the others are considered merely as disinfectants. It is a gas at temperature above 10.8 degree Celsius, a highly toxic compound that destroys by alkylation. Commercial mixtures contain 12% ETO and 88% CFC. Advantages include high penetration, no damage to heat sensitive and complex devices, evaporation with no residue.
Disadvantage are its slowness, toxicity, dry instrument to be used, flammability of material and degassing required.
Aldehydes:
Formaldehyde: widely employed for the fumigation of operation theatres.
Glutaraldehyde: commercial preparations are active at different pH and have percentage of 2-3.2. They can destroy microbes in 10 hours. They have a surprising resistance to activation by organic matter and do not harm rubber and plastic hence are indicated for impression materials. However they may corrode or discolour metal.
Beta Propiolactone: this is a condensation product of ketone and formaldehyde with a boiling point of 163 o C. 0.2 % BPL is used for sterilization. It is more efficient than formaldehyde for fumigation but is carcinogenic. It is also used for sterilizing vaccines, graft tissue and other delicate biological materials.
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