Asepsis in Endodontics
INSTRUMENT PROCESSING PROCEDURES Instrument processing is the collection of procedures which
prepare the contaminated instruments for reuse. For complete sterilization process, prevention of the disease transmission and instruments should be processed correctly and carefully (Flow Chart 9.2).
Steps of Instrument Processing 1. Presoaking (Holding)
2. Cleaning
3. Corrosion control
4. Packaging 5. Sterilization
6. Monitoring of sterilization
7. Handling the processed instrument.
Presoaking (Holding)
It facilitates the cleaning process by preventing the debris from drying.
Procedure
• Wear puncture resistant heavy utility gloves and personnel protective equipments
• Place loose instruments in a perforated cleaning basket and then place the basket into the holding solution. Holding solution can be:
a. Neutral pH detergents b. Water
c. Enzyme solution.
• Perforated cleaning basket reduces the direct handling of instruments. So, chances of contamination are decreased
• Holding solution should be discarded atleast once a day or earlier if seems to be soiled
• Avoid instrument soaking for long time as it increases the chances of corrosion of instruments.
Cleaning
It aids in the subsequent cleaning process by removing gross debris. It is considered to be one of the important steps before any sterilization or disinfection procedure. The advantage of this procedure is that it reduces the bioburden, i.e. micro-organisms, blood, saliva and other materials.
Methods used for cleaning:
1. Manual scrubbing 2. Ultrasonic cleaning
3. Mechanical – instrument washer
1. Manual scrubbing: It is one of the most effective method for removing debris, if performed properly. Now-a-days, this method is not recommended because of the risk-factors involved.
Procedure
a. Brush delicately all surfaces of instruments while submerged in cleaning solution.
b. Use long-handled stiff nylon brush to keep the scrubbing hand away from sharp instrument surfaces.
c. Always wear heavy utility gloves and personnel protective equipments.
d. Use neutral pH detergents while cleaning.
e. Instruments’ surfaces should be visibly clean and free from stains and tissues.
Disadvantages: This procedure is not recommended as there are maximum chances of direct contact with instrument surfaces and also of cuts and punctures.
2. Ultrasonic cleaning (Fig. 9.3): It is excellent cleaning method as it reduces direct handling of instruments. So, it is considered safer and more effective than manual scrubbing.
Flow Chart 9.2: Instrument processing procedure
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Procedure
a. Mechanism of action: Ultrasonic energy generated in the ultrasonic cleaner produces billions of tiny bubbles which, in further, collapse and create high turbulence at the surface of instrument. This turbulence dislodges the debris.
b. Maintain the proper solution level.
c. Use recommended cleaning solution.
d. Time may vary due to i. Nature of instrument ii. Amount of debris
iii. Efficiency of ultrasonic unit.
Usually the time ranges vary from 4-16 minutes.
e. After cleaning, remove the basket/cassette rack and wash under tap water. Use gloves while washing under tap water as the cleaning solution is also contaminated.
f. Discard the solution atleast daily.
3. Mechanical–instrument washer: These are designed to clean instruments in hospital setup. Instrument washer has also the advantage that it reduces the direct handling of the instrument.
Control of Corrosion by Lubrication
It prevents damage of instruments because of drying. Some instruments or portions of instruments and burs (made up of carbon steel) will rust during steam sterilization, for example, grasping surfaces of forceps, cutting surfaces of orthodontic pliers, burs, scalers, hoes and hatchets.
For rust-prone instruments, use dry hot air oven/chemical vapor sterilization instead of autoclave. Use spray rust inhibitor (sodium nitrite) on the instruments.
Packaging
It maintains the sterility of instruments after the sterilization.
Unpacked instruments are exposed to environment when sterilization chamber is opened and can be contaminated by dust, aerosols or by improper handling or contact with contaminated surfaces.
Packaging is the procedure in which cleaned instruments are organized in functional sets, thereafter with wrapping, these are placed in sterilization pouches or bags. One may also add chemical and biological indicators of sterilization in the pouches or bags.
Varieties of packaging materials are available in the market such as self-sealing, paper-plastic and peel-pouches. Peel-pouches are the most common and convenient to use (Fig. 9.4).
Packs should be stored with the following considerations:
• Instruments are kept wrapped until ready for use
• To reduce the risk of contamination, sterile packs must be handled as little as possible
• Sterilized packs should be allowed to cool before storage;
otherwise condensation will occur inside the packs
• Sterile packs must be stored and issued in correct date order.
The packs, preferably, are stored in UV chamber (Fig. 9.5) or drums which can be locked.
Methods of Sterilization
Sterilization is process by which an object, surface or medium is freed of all microorganisms either in the vegetative or spore state (Table 9.1).
Fig. 9.3: Ultrasonic cleaner
Fig. 9.4: Peel-pouches for packing instruments Table 9.1: Sterilization method and type of
packaging material Sterilization method Packaging material
Autoclave • Paper or plastic peel-pouches Wrapped cassettes
• Plastic tubing (made up of nylon)
• Thin clothes (Thick clothes are not advised as they absorb too much heat)
• Sterilization paper (paper wrap) Chemical vapor • Paper or plastic pouches
• Sterilization paper
Dry heat • Sterilization paper (paper wrap)
• Nylon plastic tubing (indicated for dry heat)
• Wrapped cassettes
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Classification of Sterilizing Agents Physical agents:
1. Sunlight 2. Drying 3. Cold 4. Dry heat
a. Flaming b. Incineration c. Hot air oven 5. Moist heat
a. Boiling
b. Steam under pressure c. Pasteurization 6. Filtration
a. Candles b. Membranes c. Asbestos pads 7. Radiation
Chemical agents:
1. Alcohols a. Ethanol
b. Isopropyl alcohol 2. Aldehydes
a. Formaldehyde b. Gluteraldehyde 3. Halogens
a. Iodine b. Chlorine 4. Dyes
a. Acridine b. Aniline 5. Phenols
a. Cresol b. Carbolic acid 6. Metallic salts gases
a. Ethylene oxide
b. Formaldehyde c. Betapropiolactone 7. Surface active agents
The accepted methods of sterilization in our dental practice are:
1. Moist/steam heat sterilization.
2. Dry heat sterilization.
3. Chemical vapor pressure sterilization.
4. Ethylene oxide sterilization.
Moist/Steam Heat Sterilization
Autoclave: Autoclave provides the most efficient and reliable method of sterilization for all dental instruments. It involves heating water to generate steam in a closed chamber resulting in moist heat that rapidly kills microorganisms (Fig. 9.6).
Use of saturated steam under pressure is the most efficient, quickest, safest, effective method of sterilization because:
1. It has high penetrating power.
2. It gives up a large amount of heat (latent heat) to the surface with which it comes into contact and on which it condenses as water.
Types of autoclaves: Two types of autoclaves are available:
1. Downward (gravitation) displacement sterilizer: This is non-vacuum type autoclave.
2. Steam sterilizers (autoclave) with pre and post vacuum processes.
Steam sterilizers (Autoclave) with pre and post vacuum processes: In this, the sterilization process is composed of three main phases:
1. Pre-treatment phase/heat-up cycle: All air is virtually expelled by a number of pulses of vacuum and the introduction of steam, so that the saturated steam can affect the instruments during second phase.
2. Sterilizing phase/sterilization cycle: The temperature increases adequately upto the degree at which sterilization
Fig. 9.5: UV chamber for storage of sterile instruments Fig. 9.6: Autoclave for moist heat sterilization
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is to take place. Actual sterilizing period (also called “Holding Time”) starts when the temperature in all parts of the autoclave chamber and its contents has reached the sterilizing temperature. This should remain constant within specified temperature throughout the whole sterilization phase.
3. Post-treatment phase/depressurization cycle: In this phase either the steam or the revaporized condensed water is removed by vacuum to ensure that the goods are dried rapidly.
Three main factors required for effective autoclaving:
1. Pressure: It is expressed in terms of psi or kPa.
2. Temperature: For effective sterilization the temperature should be reached and maintained at 121°C. As the temperature and pressure increases, superheated steam is formed. This steam is lighter than air, thus rises to the upper portion of the autoclave. As more steam is formed, it eliminates air from autoclave. The reason of complete elimination of air is to help superheated steam to penetrate the entire load in the autoclave and remain in contact for the appropriate length of time.
3. Time: A minimum of 20 to 30 minutes of time is required after achieving full temperature and pressure.
Significance: Higher the temperature and pressure, shorter is the time required for sterilization.
• At 15 psi pressure, the temperature of 121°C, the time required is 15 minutes
• At 126°C, time is 10 minutes
• At 134°C, time is 3 minutes.
Wrapping instruments for autoclaving: Packing instruments before sterilizing prevents them from becoming contaminated after sterilization till it is opened and used. For wrapping, closed containers such as closed metal trays, glass vials and aluminium foils should not be used, since they stop the steam from reaching the inner part of the packs.
For packaging of autoclaving instruments, one should use porous covering so as to permit steam to penetrate through and reach the instruments. The materials used for packaging can be fabric or sealed paper or cloth pouches (Fig. 9.7) and paper-wrapped cassettes. Finally the wrap is heat-sealed or sealed with tape.
If instruments are to be stored and not used shortly after sterilization, the autoclave cycle should end with a drying phase to avoid tarnish or corrosion of the instruments.
Advantages of Autoclaving 1. Time efficient.
2. Good penetration.
3. The results are consistently good and reliable.
4. The instruments can be wrapped prior to sterilization.
Disadvantages of Autoclaves
1. Blunting and corrosion of sharp instruments.
2. Damage to rubber goods.
Dry Heat Sterilization
It is alternative method for sterilization of instruments. This type of sterilization involves heating air which on further transfers energy from air to the instruments. In this type of sterilization, higher temperature is required than steam or chemical vapor sterilization.
Conventional hot air oven: The hot air oven utilizes radiating dry heat for sterilization as this type of energy does not penetrate materials easily. So, long periods of exposure to high temperature are usually required.
Packaging of instruments for dry heat: Dry heat ovens usually achieve temperature above 320°F (160°C). The packs of instrument must be placed atleast 1 cm apart to air to circulate in the chamber. In conventional type of hot air oven, air circulates by gravity flow, thus it is also known as Gravity convection. The type of packaging or wrapping material used should be able to withstand high temperature otherwise it may get char.
Packaging Material Requirements for Dry Heat
• Should not be destroyed by temperature used
• Should not insulate items from heat.
Acceptable Materials
• Paper and plastic bags
• Wrapped cassettes
• Paper wrap
• Aluminum foil
• Nylon plastic tubing.
Unacceptable Materials
Plastic and paper bags which are unable to withstand dry heat temperatures.
Recommended temperature and duration of hot oven
Hot air oven
Temp °C T i m e Temp °C T i m e
141°C 3 hours 170°C 1 hour
149°C 2.5 hours 180°C 30 minutes
160°C 2 hours
Fig. 9.7: Cloth pouches for instrument wrapping
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Mechanism of action: The dry heat kills microorganisms by protein denaturation, coagulation and oxidation It is very important that organic matter such as oil or grease film must be removed from the instruments as this may insulate against dry heat.
Instruments which can be sterilized in dry hot oven are glassware such as pipettes, flasks, scissors, glass syringes, carbon steel instruments and burs. Dry heat does not corrode sharp instrument surfaces. Also it does not erode glassware surfaces.
Before placing in the oven, the glassware must be dried. The oven must be allowed to cool slowly for about 2 hours as glassware may crack due to sudden or uneven cooling.
Rapid heat transfer (forced air type): In this type of sterilizer, a fan or blower circulates the heated air throughout the chamber at a high velocity which, in turn, permits a more rapid transfer of heat energy from the air to instruments, thereby reducing the time.
Temperature/Cycle Recommended
370-375°F - 12 minutes for wrapped instruments 370-375°F - 16 minutes for unwrapped instruments Advantages of Dry Heat Sterilization
1. No corrosion is seen in carbon-steel instruments and burs.
2. Maintains the sharpness of cutting instruments.
3. Effective and safe for sterilization of metal instrument and mirrors.
4. Low cost of equipment.
5. Instruments are dry after cycle.
6. Industrial forced draft types usually provide a larger capacity at reasonable price.
7. Rapid cycles are possible at higher temperatures.
Disadvantages
1. Poor penetrating capacity of dry heat.
2. Long cycle is required because of poor heat conduction and poor penetrating capacity.
3. High temperature may damage heat sensitive items such as rubber or plastic goods.
4. Instruments must be thoroughly dried before placing them in sterilization.
5. Inaccurate calibration and lack of attention to proper settings often lead to errors in sterilization.
6. Heavy loads of instruments, crowding of packs and heavy wrapping easily defeat sterilization.
7. Generally not suitable for handpieces.
8. Cannot sterilize liquids.
9. May discolor and char fabric.
Chemical Vapor Sterilization
Sterilization by chemical vapor under pressure is known as chemical vapor sterilization. In this, special chemical solution is heated in a closed chamber, producing hot chemical vapors that kill microorganisms.
The various modes of action are:
1. Coagulation of protein.
2. Cell membrane disruption.
3. Removal of free sulphydryl groups.
4. Substrate competition.
Contents of chemical solution: The solution contains various ingredients which are as follows:
1. Active ingredient – 0.23% Formaldehyde 2. Other ingredient – 72.38% Ethanol + Acetone
+ Water and other alcohols Temperature, pressure and time required for completion of one cycle is – 270°F (132°C) at 20 lb for 30 minutes. Chemical vapor sterilizer is also known as chemiclave. Usually four cycles are required for this sterilizer which is as follows:
1. Vaporization cycle.
2. Sterilization cycle.
3. Depressurization cycle.
4. Purge cycle (which collects chemicals from vapors in the chamber at the end of cycle).
Advantage
Eliminates corrosion of carbon steel instruments, burs and pliers.
Disadvantages
1. The instruments or items which are sensitive to elevated temperature are damaged.
2. Sterilization of liner, textiles, fabric or paper towels is not recommended.
3 Dry instruments should be loaded in the chamber.
Precautions to be Taken
• Use gloves and protective eyewear while handling the chemical solution
• Use paper/plastic peel-pouches or bags recommended for use in chemiclave
• Use system in ventilated room
• Space should be given between the instruments that are to be sterilized in the chamber for better conduction and penetration
• Water should not be left on the instruments.
Ethylene Oxide Sterilization (ETOX)
This sterilization method is best used for sterilizing complex instruments and delicate materials.
Ethylene oxide is highly penetrative, noncorrosive gas above 10.8°C with a cidal action against bacteria, spores and viruses.
It destroys microorganisms by alkylation and causes denaturation of nucleic acids of microorganisms.
Since it is highly toxic, irritant, mutagenic and carcinogenic, thus should not be used on routine bases. It is suited for electric equipment, flexible-fiber endoscopes and photographic equipment.
The duration that the gas should be in contact with the material to be sterilized is dependent on temperature, humidity, pressure and the amount of material.
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Advantages
1. It leaves no residue.
2. It is a deodorizer.
3. Good penetration power.
4. Can be used at a low temperature.
5. Suited for heat sensitive articles, e.g. plastic, rubber, etc.
Disadvantages
1. High cost of the equipment.
2. Toxicity of the gas.
3. Explosive and inflammable.
Irradiation
Radiations used for sterilization are of two types:
1. Ionizing radiation, e.g. X-rays, gamma rays and high-speed electrons.
2. Non-ionizing radiation, e.g. ultraviolet light and infrared light.
Ionizing Radiation
Ionizing radiations are effective for heat labile items. They are commonly used by the industry to sterilize disposable materials such as needles, syringes, culture plates, suture material, cannulas and pharmaceuticals sensitive to heat. High energy gamma rays from cobalt-60 are used to sterilize such articles.
Non-ionizing Radiation
Two types of non-ionizing radiations are used for sterilization, i.e. ultraviolet and infrared.
1. Ultraviolet rays: UV rays are absorbed by proteins and nucleic acids and kill microorganisms by the chemical reactions. Their main application is purification of air in operating rooms to reduce the bacteria in air, water and on the contaminated surfaces. Care must be taken to protect the eyes while using U-V radiation for sterilization.
2. Infrared: It is used for sterilizing a large number of syringes sealed in metal container, in a short period of time. It is used to purify air in the operating room. Infrared is effective, however, it has no penetrating ability.
Glass Bead Sterilizer
It is rapid method of sterilization which is used for sterilization of instruments (Fig. 9.8). It usually uses table salt which consists approximately of 1 percent sodium silico-aluminate, sodium carbonate or magnesium carbonate. So it can be poured more readily and does not fuse under heat. Salt can be replaced by glass beads provided the beads are smaller than 1 mm in diameter because larger beads are not efficient in transferring the heat to endodontic instruments due to presence of large air spaces between the beads.
The instruments can be sterilized in 5 to 15 seconds at a temperature of 437-465°F (260°C) even when inoculated with spores.
The specific disadvantage of these sterilizers is that the handle portion is not sterilized and therefore these articles are not entirely “sterile”. These are not recommended unless absolutely required (Fig. 9.9).
Advantages
• Commonly used salt is table salt which is easily available and cheap
• Salt does not clog the root canal. If it is carried into the canal, it can be readily removed by irrigation.
DISINFECTION
It is the term used for destruction of all pathogenic organisms, such as, vegetative forms of bacteria, mycobacteria, fungi and viruses, but not bacterial endospores.
Methods of Disinfection Disinfection by Cleaning
Cleaning with a detergent and clean hot water removes almost all pathogens including bacterial spores.
Fig. 9.8: Glass bead sterilizer
Fig. 9.9: Files placed in glass bead sterilizer
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Disinfection by Heat
Heat is a simple and reliable disinfectant for almost anything except living tissues. Mechanical cleaning with hot water provides an excellent quality of disinfection for a wide variety of purposes.
Low Temperature Steam
Most vegetative microorganisms and viruses are killed when exposed to steam at a temperature of 73°C for 20 minutes below atmospheric pressure. This makes it a useful procedure to leave spoiled instruments safe to handle prior to sterilization.
Disinfection by Chemical Agents
They are used to disinfect the skin of a patient prior to surgery and to disinfect the hands of the operator.
Disadvantages of using chemicals
• No chemical solution sterilizes the instruments immersed in it
• There is a risk of producing tissue damage if residual solution is carried into the wound.
Levels of Disinfectant
Alcohols Low Level Disinfectant
• Ethanol and isopropyl alcohols are commonly used as antiseptics
• Possess some antibacterial activity, but they are not effective against spores and viruses
• Act by denaturing proteins
• To have maximum effectiveness, alcohol must have a 10 minutes contact with the organisms
• Instruments made of carbon steel should not be soaked in alcoholic solutions, as they are corrosive to carbon steel
• Rubber instruments absorb alcohol thus their prolonged soaking can cause a reaction when material comes in contact with living tissue.
Phenolic Compounds—Intermediate Level, Broad-spectrum Disinfectant
Phenol itself is toxic to skin and bone marrow. The pheno-lic compounds were developed to reduce their side effects but are still toxic to living tissues. These compounds, in high concentration, are protoplasmic poison and act by precipitating the proteins and destroy the cell wall.
Phenol itself is toxic to skin and bone marrow. The pheno-lic compounds were developed to reduce their side effects but are still toxic to living tissues. These compounds, in high concentration, are protoplasmic poison and act by precipitating the proteins and destroy the cell wall.