STERILIZATION OF INSTRUMENTS Sterilization - the complete elimination or destruction of all forms of microorganisms → bacteria, viruses, fungi and spores. High-level disinfection - destroys all microorganisms, except high levels of bacterial spores. The difference between HLD and sterilization is that only sterilization can kill high numbers of bacterial spores. Intermediate-level disinfection – kills Mycobacterium tuberculosis, vegetative bacteria, most viruses, and most fungi, but it does not necessarily kill bacterial spores. Low-level disinfection - kills most bacteria, some viruses and some fungi, but it cannot be relied on to kill resistant microorganisms such as tubercle bacilli or bacterial spores. It is impossible to sterilize all instruments, items, and surfaces etc that become contaminated during dental procedures. The choice of decontamination regimes may be based on how an item or instrument will be used. Instruments are defined as critical, semi-critical and non-critical. (CDC) Critical instruments: scissors, forceps, elevator and scaler. If an instrument will be used to penetrate tissue or to touch bone it must be sterilized. Semi-critical instruments: mirror, probe, amalgam carrier and tweezers. If an instrument will touch mucous membranes, but will not be used to penetrate tissue or to touch bone, it should be sterilized if al all possible or, if the instrument is susceptible to heat damage, it should be subjected to high-level disinfection. Non-critical instruments: These are defined as equipments and surfaces which contact only intact skin, such as mixing slabs and spatulas. Work surfaces are decontaminated by using intermediate-level disinfection. Summary: - Heat sterilizes all critical instruments and semi-critical instruments which are not damaged by heat. - Semi-critical instruments damaged by heat may be treated after use by high-level disinfection - Non-critical environmental surfaces are decontaminated using intermediate-level disinfection. CATEGORIES OF TASKS, WORK AREAS AND PERSONNEL The following guidelines evaluate and classify tasks undertaken in a dental practice into one of three categories. Category I: tasks that involve exposure to blood, body fluids or tissues. - All procedures or other job-related tasks that involve an inherent potential for contact of mucous membrane or skin with blood, body fluids, or tissues, or a potential spills or splashes of these. - Every employee engaged in category I tasks should be required to use appropriate protective measures. - Most (but not all!) tasks performed by the dentist, oral hygienist, chairside assistant and laboratory technician would fall into this category. Category II: tasks that involve no exposure to blood, body fluids or tissues, but personnel carrying out these tasks may be required to perform unplanned Category I tasks. - The normal work routine of these personnel involves no exposure to blood, body fluids or tissues, but the understanding that exposure or potential exposure may be required is a condition of employment. - Every employee engaged in category II tasks should have appropriate protective measures readily available. - Tasks performed by clerical or non-profesional workers who may, as part of their duties, help to clean up the office, handle instruments or impression materials, or send out dental materials to laboratories, would be classified as Category II. Category III: tasks that involve no exposure to blood, body fluids or tissues. - The normal work routine of these personnel involves no exposure to blood, body fluids or tissues. They are not called upon , as part of their employment, to perform or assist in emergency medical care or first aid, or to be potentially exposed in some other way. - A front-office receptionist, book-keeper, or insurance clerk who does not handle dental instruments or materials would be a Category III worker. These classifications are not rigid and there may be crossover, depending on the job performed. Critical and semi-critical items and instruments are sterilized by heat. There are four distinct stages which achieve safe instrument sterilization: Pre-cleaning disinfection, using “holding” solutions. Pre-sterilization cleaning Sterilization Aseptic storage. The sterilization area The layout of the sterilization area Dirty Sink Cleaning Ultrasonic area area bath Area of high contamination Packaging Sterilizer Clean area area Area of Area of low medium contamination contamination The area for cleaning and sterilization needs careful planning with a generous amount of room allowed for wide worktops, a sink, an ultrasonic cleaner and sterilizer(s). Some offices have a separate central sterilization area. This should be easily accessible to all the separate surgeries in the practice. Instruments must be carried safely to surgery areas; closed trays, baskets, or trolleys are recommended. Many offices locate the sterilization area within the surgery. If this is the case, it should be situated away from the operating area. Dirty area Trays containing contaminated instruments and disposables are taken to this area after use. Disposables are placed carefully in a waste receiver. Sink A deep-sink with elbow or foot operated tap controls and an efficient splash back is essential. A deep sink is necessary to minimize splashing when washing or rinsing instruments. The sink is for cleaning only. A separate sink, located nearby, should be reserved for hand washing. Decontamination of rubber utility gloves may be carried out in the cleaning sink. Instruments in holding baths are rinsed and then taken to the cleaning area. Cleaning area After removal of contaminated disposable items, instruments and trays are taken to the cleaning area, where they are organized into baskets prior to ultrasonic cleaning. If trays cannot be ultrasonically cleaned, they are wiped clean in this area, which should be sufficiently large for several trays. Ultrasonic bath It should be a good quality product which cleans large number of widely spaced instruments. Packaging area After cleaning, instruments are thoroughly rinsed and taken to the packaging area where they are dried and then either loaded into trays, placed in pouches, or wrapped. Trays are wrapped in this area. Sterilization pouches, paper wraps, chemical indicator strips are stored in cupboards above the packaging area. Sterilizer - A good quality autoclave - A second sterilizer (a chemiclave) for use both as back-up and to sterilize instruments which would be damaged by autoclaving. Clean area Hot trays and packaged instruments are taken from the sterilizer to this area before being stored in adjacent closed cabinets. Precautions Adequate lighting is essential to facilitate careful inspection and handling of instruments. Heavy rubber utility gloves, protective eyewear, a mask and a plastic apron should be worn when performing the decontamination stages of sterilization. PRE-STERILISATION DISINFECTION After use, place the instruments into a disinfectant detergent solution in a container located within the operating zone near to the dentist. At the end of the dental procedure, take the container to the sterilization area. Thoroughly rinse the instruments with water. The solution is reused but should be discarded daily. Place heavily contaminated endodontic files and rotary instruments into a small volume of holding solution contained in a beaker located on the bracket table tray. Discard holding solutions, rinse the instruments and add ultrasonic solution to the beaker, then suspended this in an ultrasonic bath. PRE-STERILIZATION CLEANING Proteinaceous material protects microorganisms on the surface of instruments from heat and other sterilization conditions. Pre-sterilization cleaning may be achieved in one of three ways: 1. Hand scrubbing of instruments 2. Ultrasonic cleaning 3. Dishwasher instrument cleaning Heavy rubber utility gloves, protective eyewear, a mask and a plastic apron should be worn when decontaminating instruments in the sterilization area. 1. Hand scrubbing of instruments Hand scrubbing increases the chance of injury from contaminated instruments and from contact with contaminated fluids. This method of cleaning should be avoided if at all possible. If an item must be manually scrubbed, splatter should be kept to a minimum. This is achieved by scrubbing under water in a deep sink, not under fast-running water from a tap. A long-handled brush is always used. 2. Ultrasonic cleaning → more efficient than manual cleaning. When correctly performed, ultrasonic cleaning will remove dried serum, whole blood, plaque, zinc phosphate cement and polycarboxylate cement from instruments, metal surfaces and dentures. Ultrasonic cleaning minimizes the handling of contaminated instruments and reduces the chance of injuries from sharp, contaminated instruments. Instruments are loaded into a metal basket which is then placed into the ultrasonic bath. The unit is activated for the time recommended by manufacturer (≈ 6 minutes). Instruments which are contained in the cassettes are cleaned for 12 minutes. After the cleaning cycle is complete, the basket is taken to the sink and the instruments are carefully and thoroughly rinsed under tap water. The instruments are checked for residual debris which may be safely removed manually. Instruments are taken to the packaging area, where they are unloaded from the baskets onto a thick disposable paper towel. The instruments are thoroughly dried using strong paper towels. Drying is important! Small rotary and endodontic instruments should be held in beakers of ultrasonic cleaning solution which are suspended in the cleaning bath. 4. Dishwasher instrument cleaners These machines are popular in Germany and Scandinavia. Dishwasher cleaners are capable of holding either instrument sets in cassettes or single instruments in containers. These machines first pre-rinse the instruments at a low temperature, to prevent the coagulation of proteins. Washing then takes place at 900C for 10 minutes using recommended disinfectant/detergent and instruments are dry after the cycle is completed. STERILISATION Instruments must be clean and dry before sterilization. There are four types of sterilizers used routinely in dentistry: - The steam autoclave - The chemical vapor pressure sterilizer - The dry heat oven - The glass bead/salt sterilizer The steam autoclave A steam autoclave sterilizes by the use of steam under pressure. Non-vacuum autoclaves are used in dental practice → the use of incoming steam pressure to evacuate air. Many good quality, modern non-vacuum autoclaves are very efficient in air removal if the autoclave is not overloaded. DENTAL AUTOCLAVES A prescribed temperature, pressure and time are necessary to destroy bacterial spores. The temperature-time combinations for autoclaves are shown in the following tables: In UK: Temperature Pressure Minimum holding (0C) (kPa) time 134 – 138 207 3 min 121 – 124 103 15 min In USA: Temperature Pressure Minimum (0C) (kPa) holding time 132 270 3 min 121 103.5 15 min Lightly wrapped 132 270 8 min items 121 103.5 20 min Heavily wrapped 132 270 10 min items 121 103.5 20 min Unwrapped items Items suitable for autoclaving The steam autoclave is suitable for the sterilization of: High-quality stainless steel instruments Hand pieces which can be autoclaved Cloth goods Glass slabs, dishes, stones. Stones should be dry, wet stones may rupture under steam sterilization. Large plastic suction tips Packaged and wrapped instruments Heat resistant, plastic instruments. Limitations for use Carbon-steel instruments will rust after a limited number of autoclave cycles → prior to autoclaving, instruments susceptible to rust should be treated with a non-toxic, non-silicone, oil emulsion. This tends to reduce rust and lubricates instruments without leaving a noticeable oily or sticky film. These emulsions do not impair sterilization. Sodium nitrite 2% is used to reduce rusting and corrosion. Needles should NOT be autoclaved, nor oil, wax and dry powder! Practical aspects Steam autoclave sterilizers are required to: - Have an instruction manual; - Have been evaluated for the ability to sterilize, i.e. destroy bacterial spores; - Have a drying cycle → dry instruments in trays and packages may be stored safely for long periods without corrosion. - The chamber size of the autoclave to be large enough to allow the sterilization of standard trays. Directions for use - Do not overload the trays - Load the trays carefully to allow free circulation of steam round the instruments - Use trays with perforated basis to allow air displacement and free steam circulation - Separate wrapped items, do not stack together - Do not overload the autoclave with trays and pouches - Sterilization failure in a steam autoclave can usually be avoided if proper cleansing, packaging and loading precautions are taken - Remove all particles of amalgam, cements, which adhere to instruments, after ultrasonic cleaning. This will avoid clogging up the chamber and prevent impaired operation of the air-valve. - Rinse disinfectants and cleansers from instruments to avoid the failure of air-valve and the likelihood of instrument corrosion. - Sometimes distilled \ deionized water is recommended. In “hard water” areas, tap water will form scales deposits in the water chamber. Autoclave maintenance - Clean the autoclave chamber weekly with a weak detergent and rinse well. - Clean the gasket weekly, applying a recommended silicone compound to it. - Check the level of the reservoir twice daily. Do not overfill the reservoir or fill during the cycle, since this may cause flooding at the end of the cycle. - Empty the water reservoir weekly and remove particles on the chamber floor using high-velocity aspiration. CHEMICAL VAPOUR STERILISERS Chemical vapor sterilizers operate by heating a deodorized alcohol, formaldehyde and ethyl methyl ketone solutions to 132 0C at 138-276 kPa for 20 minutes in a closed chamber. Three main advantages: - A fairly short cycle → 30 minutes. Short “flash cycles” of 7 minutes a re now available on new models when sterilizing unwrapped items. - Instruments do not dull, rust or corrode → a longer useful life. - Instruments are dried at the end of the cycle. Disadvantages: - A good ventilation is required to eliminate residual formaldehyde from the chamber - An extra cost of purchasing the sterilizing solutions. A CHEMICLAVE MODEL Instrument suitable for sterilization with chemical vapor The chemical vapor sterilizer is suitable for: - All dental hand instruments - Hand pieces - Carbon-steel and diamond burs - Endodontic instruments - Orthodontic wires and bands - Orthodontic pliers, where rusting of the joints may cause problems. DRY-HEAT STERILISERS Dry heat is an effective means of sterilization, when it is used properly. Unwrapped, moderate loads of instruments placed in an oven can be sterilized at 160-1700C in 1 hour. Wrapped loads require a longer time of exposure. The standard dry-heat oven which is manufactured for dental use (see picture below) is NOT recommended for a busy dental practice for the following reasons: - Low temperature pockets in the chamber during sterilization cycle may prevent sterilization of the load. - The complete cycle is very long (≈ 90 minutes) → unsuitable for a busy dental practice. - Most ovens do not have a door-locking system, which allows interruption of the sterilization cycle. If cycle is interrupted, loads are not sterile. - Turbine hand pieces are damaged if heated to a temperature of 1600C THE DRY-HEAT OVEN Rapid dry-heat sterilization The Cox rapid dry-heat oven operates by circulating air at a steady temperature of 1900C. At this temperature, most metal instruments are not damaged. Sterilization time: 6 minutes for unwrapped instruments 12 minutes for wrapped instruments The load size of this sterilizer is comparatively small. HOT BEAD / SALT STERILIZERS Glass bead/salt sterilizers are useful for sterilizing small instruments: - Endodontic files - Rotary instruments The sterilizer is a metal cup in which the medium is maintained at 218 - 246 0C. It is useful for sterilizing endodontic files during endodontic treatment of multirooted teeth, to prevent transfer of infection between canals. A minimum of 15 seconds immersion is recommended for effective sterilization. The instruments to be sterilized should be thoroughly clean. Hot salt sterilizers are preferably to glass bead sterilizers for endodontic therapy. Residual salt or glass beads on the surface of the sterile endodontic instruments can cause blockage of the root canals. If salt granules are the cause of the blockage, they can be dissolved with irrigation. A suitable thermometer should be routinely used to ensure that the temperature reaches 2180C, as the temperature of the medium at the centre of the sterilizer may be lower than that at the sides of the container. MONITORING STERILIZATION A high sterilization failure in dental sterilizers (≈ 51%) Positive results may be caused when: - Packs are improperly wrapped - The sterilizer is improperly loaded - The sterilizer does not work properly - The process time is too short 1. Tests using chemical indicators Test strips and tubes are available for autoclaves, chemiclaves and dry-heat ovens → very useful for early detection of problems. Chemical indicators show that sterilizing conditions have been reached, not that sterilization has occurred. Color-change strips or tapes → indicate temperature change Superiors color-change indicators → sensitive to both temperature and time Indicator strip before use After successful sterilization → color change 2. Biological monitors Self-contained biological indicators: bacterial spores on a paper carrier packaged within a small, thermoplastic culture tube. Inside the thermoplastic culture tube is a sealed glass ampoule of specially formulated soybean casein digest culture medium containing a color indicator that turns a dramatic yellow when spores grow. Advantages: Easy-to-use; produces visual results within 48 hours without laboratory transfers.
