Sterilization

By: Mohit Gupta, Roll No.:45 Mohit Verma, Roll No.:46

STERILIZATION: It is the process by which the article, a surface, or medium is freed of all microorganisms including viruses, bacteria, and spores, fungi both pathogenic and nonpathogenic. DISINFECTION: Process of destruction or removal of organism, capable of giving rise to infection. These are capable of killing vegetative bacteria, fungi, viruses and bacterial spores. ANTISEPSIS: Destruction or inhibition of microorganism in living tissues thereby limiting or preventing harmful effects of infection. A disinfectant applied to a living tissue is antiseptic

STEPS IN STERILIZATION       

Presoaking Cleaning Corrosion control Lubrication Packaging Sterilization Sterilization monitoring

PRESOAKING: Keeping the instrument in holding solution i.e. mild detergent or instrument disinfectant or sterilant. IMPORTANT: Not to presoak for more than few hours as the chances for corrosion of non stainless items. Wearing of gloves and protective eyewear is advisable to prevent contamination from splashing of solution. CLEANING: Cleaning is basic step for all decontamination. Patient debris and body fluids must be removed from instrument before sterilization. It is of two types: o Hand scrubbing o Ultrasonic cleaning

Ultrasonic cleaning involves cleaning in a solution so it advisable to be used over hand scrubbing as hand scrubbing can cause any puncture in skin and can contaminate the operator. 

ULTRASONIC CLEANING INSTRUMENT

Corrosion control and lubrication  Always dry cleaned instrument to be processed through a dry heat, chemical vapor or ethylene oxide gas sterilizer. Drying reduces chances of corrosion.  A rust inhibitor can be applied to non stainless items to be processed through steam autoclave Packaging:  Instruments should be prepackaged before processing through a sterilizer so they will protected from contamination after sterilization.  Unwrapping instrument at chair side in front of patient can help build patient confidence about cleanliness of clinic. Sterilization monitoring:  Sterilization can be monitored by chemical indicator i.e. color change but effectiveness cannot or can be biologically monitored by routine spore testing.

AGENTS OF STERILIZATION Physical Agents

Chemical Agents

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Sunlight Drying Heat Filtration Radiation Low temperature Desiccation

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Alcohols Phenols and phenolic compounds Halogens Heavy metals and their salts Dyes Quaternary tertiary compounds Aldehydes Gases

SUNLIGHT  

Ultraviolet rays with heat rays cause germicidal activity. It is employed for sterilization of water in tanks, rivers, lakes.

DRYING 

Drying has deleterious effect on many bacteria. Spores are unaffected by drying.

HEAT 

Reliable, certain, rapid, most important, widely used method of sterilization and leaves no potentially harmful residues. It is of two types:  Dry heat  Wet heat

DRY HEAT  Kill

microorganism by destructive oxidation of essential cell constituents.  Dry heat at 1000C for 60 minutes and 1150C for 60 min kill all vegetative bacteria and spores respectively.  Spores can be killed by dry heat at 1600C for 1 hour or 1800C for 20 minutes.  Dry heat is less efficient

METHODS OF DRY HEAT Red heat: Inoculating loops, wires, points of forceps and spatulas in Bunsen burner flame till red hot Flaming: Scalpel blades, needles, mouths of culture tubes, bottles, glass slides, cover slips, by passing through Bunsen flame without red hot Incineration:  Soiled dressing and pathological materials are burned to ash and are physically destroyed Incineration plant

HOT AIR OVEN: For glassware, metal instruments, sealed materials, swab sticks are sterilized. It is not suitable for fabrics. It is electrically heated and fitted with thermostat that maintains chamber air at chosen temperature and fan than distributes hot air in chamber. It should not be overloaded and space must be left for circulation of air through load. Holding time in hot air oven is 1 hour at 1600C or 20 minutes at 1800C

Hot Air Oven

WET HEAT It causes denaturizing and coagulation of proteins. It works on the principle that steam condenses on cooler surface, release latent heat and raises temperature of surface. If spores present, steam condenses on them and increase their water content leading to hydrolysis and breakdown of proteins.

Method of wet heat At temperature below 1000C 

Heat labile liquids may be disinfected NOT STERLIZED by heating below 1000C

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Pasteurization of milk and butter is done. The temperature employed is 630C for 30 minutes {holder method} or 720C for 20 seconds {flash method} and followed by cooling to 130C or lower. Non sporing organisms are destroyed. However Coxiella burnetii, causative agent of Q fever survives.

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Ultra pasteurization: Milk is bought in contact with steam at 1400C for 1-2 seconds. Milk is flash cooled by application of a slight vacuum, serves dual purpose of removing excess water in milk from condensing steam.

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Heat labile fluids such as serum, is disinfected by heating at 560C for 1 hour. If temperature rises above 590C it will coagulate.

At temperature of 1000C Boiling at 1000C:  It is done for 10-30 minutes. Kill vegetative bacteria and spores but is inactive against viruses. It is not recommended for sterilization of instruments for surgical procedure as it is ineffective against many bacterial and fungal spores. It is useful for reducing viable levels if no better method is available. Steam Sterilizer

Free steam at 100 C: 0

Tyndallization: 

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It is a lengthy process designed to reduce the level of activity of sporulating bacteria that are left by a simple boiling water method. Complete sterilization is ensured after an exposure of 1000C for 20 minutes on three consecutive days. This process is also called as intermittent sterilization. The three incubating periods are to allow heat resistant spores surviving previous boiling periods to germinate to form heat sensitive vegetative stage, which can be killed by next boiling step. This is effective because many spores are stimulated to grow by heat shock. This procedure only works for media that supports bacterial growth.

TYNDALLI ZATION

At temperature above 1000C AUTOCLAVE: 

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Steam above 1000C or saturated steam more efficient and effective, fast and reliable sterilizing agent than hot air. It provides greater lethal action. Quicker in heating up the exposed article. It penetrates easily pores material like cotton wool stoppers, papers, cloth wrapper, surgical linen, and hollow apparatus. It operates on time temperature relationship. Higher temperature ensures more rapid killing. Standard temperature/pressure is 1210C/15psi for 15 minutes. Longer times are needed for longer loads, large volumes and dense materials. Autoclaving is ideal for sterilizing biohazadous waste, surgical dressing, glassware, and micro media. liquid, instruments Plastics and fiber optic endoscopes cannot withstand autoclaving. When proper condition and time are employed, no living organism survives a trip through autoclave.

Parts Of Autoclave

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Autoclave is an effective sterilizer because an autoclave is a large pressure cooker; it operates by using steam under pressure as the sterilizing agent.  High pressures enable steam to reach high temperatures, thus increasing its heat content and killing power. Most of the heating power of steam comes from its latent heat of vaporization. This is the amount of heat required to convert boiling water to steam. This amount of heat is large compared to that required to make water hot.  For example, it takes 80 calories to make 1 liter of water boil, but 540 calories to convert that boiling water to steam. Therefore, steam at 100º C has almost seven times more heat than boiling water. Steam is able to penetrate objects with cooler temperatures because once the steam contacts a cooler surface it immediately condenses to water, producing a concomitant 1,870 fold decrease in steam volume. This creates negative pressure at the point of condensation and draws more steam to the area. A condensation continues so long as the temperature of the condensing surface is less than that of steam.  These properties ensure rapid heating of surfaces, good penetration of dense materials, and coagulation of proteins.

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Autoclave is essentially a double jacketed steam chamber equipped with devices which permit the chamber to be filled with saturated steam and maintained at a designated temperature and pressure for any period of time. In operation of an autoclave it is absolutely essential that the air in the chamber be completely replaced by saturated steam. if air is present , it will reduce the temperature obtained within the chamber substantially below that which would be realized if pure saturated steam were under the same pressure. It is not the pressure that kills the organisms but the temperature of the steam.

FILTRATION 

Clear liquids that would be damaged by heat, irradiation or chemical sterilization can be sterilized by mechanical filtration.  Commonly used for sensitive pharmaceutical and protein solution in biological research.  Filter with pore size 0.2micrometres will remove bacteria.  If viruses must also be removed a much smaller pore size around 20nanometer is needed

This water filter for hikers and backpackers is advertised to "eliminate Giardia, Cryptosporidium and most bacteria." The filter is made from 0.3 micron pleated glass fiber with a carbon core.

A typical set-up in a microbiology laboratory for filtration sterilization of medium components that would be denatured or changed by heat sterilization. The filter is placed (aseptically) on the glass platform, then the funnel is clamped and the fluid is drawn by vacuum into a previously sterilized flask. The recommended size filter that will exclude the smallest bacterial cells is 0.22 micron.

RADIATION Inactivation of microorganisms occurs either through direct ionization of a vital cellular molecule (DNA, key enzyme, etc.) or indirectly through the reaction of the free radicals produced in the cellular fluid. It includes electron beams, X-rays, Gamma Rays, subatomic particles. Gamma Rays: These are commonly used as they are very penetrating. Used for syringes, needles, cannulas. It requires bulky shielding for safety of operator. Require storage of radioisotope (Co-60) which continuously emits gamma rays. Its disadvantage is that it cannot be turned off and always present a hazard in area of facility.

Electron Beam:  These are commonly used. It uses an on-off technology. It provides a much higher dosing rate than gamma or X rays. Due to higher dose, less exposure time is needed and thereby any potential degradation is reduced. Limitation of electron beams is that they are less penetrating than gamma rays or X rays

X Rays:  These are less penetrating and require longer exposure. Require less shielding. It is generated by X ray machine that can be turned off when not in use.

Ultraviolet Lamps: 

It is useful for sterilization of surface and some transparent objects. Many objects that are transparent to visible light absorb UV. UV irradiation is routinely used to sterilize the interior of biological safety cabinets but ineffective in shaded area including areas under dirt.

NOTE: in some parts of Europe, fruits and vegetables are irradiated to increase their shelf life up to 500%. The practice has not been accepted in US. UV light can be used to pasteurize fruit juices by flowing the juice over a high intensity ultraviolet light source.

Ultraviolet radiation chamber

LOW TEMPERATURE  Most

organisms grow very little or not at all at 00C.  Perishable foods are stored at low temperature to slow down the rate of growth and consequent spoilage.  Low temperatures are not bactericidal.

DESICCATION 

Desiccation of microbial cell causes a cessation of metabolic activity, followed by decline in total viable population.  The time of survival of microorganisms after desiccation varies depending on factors like kind of microorganism, material in or on which the organisms are dried, completeness of drying process, and physical conditions etc.  Species of gram negative cocci such as gonococci and meningococcal are very sensitive to desiccation.  Streptococci are much more resistant.

ALCOHOLS Most

commonly used is ethyl alcohol in concentrations between 50-90%, effective against vegetative or non spore forming cells, For practical application 70% concentration is used. Methyl alcohol is not used in practice, only used for fungal spores, and is highly poisonous as fumes may cause injury to eyes. Ethyl alcohol is used for reducing micro flora of skin It is used for disinfection of clinical oral thermometers

ALCOHOLS contd. Concentration above 60% is effective against

viruses The higher alcohols- propyl, butyl, amyl and others are more germicidal than ethyl alcohol Propyl and isopropyl alcohols in concentrations ranging from 40-80% are bactericidal for vegetative cells. Alcohols are protein denaturants and this property accounts for antimicrobial activity. Alcohols also damage lipid complexes in cell membranes, and are also dehydrating agents.

PHENOLS AND PHENOLIC COMPOUNDS 1st used as disinfectant by Sir Joseph Lister in 1880’s in England.     

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Used to reduce infection of surgical wounds and surgical incisions. Phenol and phenolic compounds are very effective disinfectants. A 5% aqueous solution of phenol rapidly kills the vegetative cells of microorganisms. Phenol, o-Cresol, m-Cresol, p-Cresol, o-Phenylphenol, hexylresorcinol, hexacholophene are commonly used as disinfectants Hexylresorcinol is a derivative of phenol having high bactericidal activity and is employed as general antiseptics. Phenolic substances are bactericidal or bacteriostatic depending on concentration Bacterial spores and viruses are more resistant than vegetative cells. 2-5% aqueous solution is used to disinfect materials like sputum, urine, feces, contaminated instruments, utensils Mode of action of these compounds are they act by disruption of cells, precipitation of cell protein, inactivation of enzymes and leakage of amino acids from cells.

HALOGENS      

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Chlorine and iodine are halogens commonly used as disinfectant. These are bactericidal and sporocidal. IODINE is one of the oldest and most effective germicidal agents. Pure iodine is bluish black crystalline element having a metallic luster. It is slightly soluble in water but readily soluble in alcohol Iodophores are mixture of iodine with surface active agents which act as carriers and solubilizer for iodine. Having an additional advantage of non staining and low irritant property. Used for disinfection of skin, water, air and sanitization of food utensils. Iodine is oxidizing agent, accounting for antimicrobial activity

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CHLORINE another widely used disinfectant. The compressed gas in liquid form is universally employed for purification of municipal water supplies. Available as hypochlorite (calcium hypochlorite, sodium hypochlorite) and chloramines Chloramines used as disinfects, sanitizing agent or antiseptics. Chlorine compounds are widely used in water treatment, in food industry, for domestic uses and in medicine. Solution of sodium hypochlorite of a 1% concentration is used for personal hygiene and as a household disinfectant. Formation of hypochlorous acid forms the basis of antimicrobial action.

HEAVY METALS AND THEIR SALTS 

Most effective are mercury, silver, and copper.  Mercuric chloride, mercurous chloride, silver nitrate, silver lactate, silver picrate, copper sulfate are the salts having antimicrobial activity  They combine with cellular proteins and inactivate them.  High concentration of salts of heavy metals like mercury, copper and silver coagulate cytoplasmic proteins, resulting in damage or death of cell.

DYES        

Triphenylmethane and Acridine dyes are used. Interfere with cellular oxidation processes. Both are bacteriostatic in high dilutions but have low bactericidal activity Much active against gram positive than gram negative Acridine dye includes acriflavine, proflavine, euflavine, aminacine. Used in treatment of burns and wounds Used for Ophthalmic application Used in bladder irrigation

QUATERNARY TERTIARY COMPOUNDS 

It includes cationic detergents having high bactericidal activity against gram positive bacteria  Mode of action is by denaturizing of proteins, interfere with glycolysis, and membrane damage  Used as skin disinfectant, as a preservative in ophthalmic solutions and in cosmetic preparations.

ALDEHYDES

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Low molecular weight compounds are anti microbial. Include formaldehyde and gluteraldehyde Highly microbicidal and both have the ability to kill spores. FORMALDEHYDE simplest compound, and is a gas which is stable in high concentrations and elevated temperatures. Fumes of formaldehyde are noxious; they are irritating to tissues and eyes. Used in sterilization of instruments, used for disinfection and sterilization of enclosed areas GLUTERALDEHYDE more effective than formaldehyde Effective against vegetative bacteria, fungi, bacterial and fungal spores and viruses. Used in medical field for sterilizing urological instruments, lensed instruments, respiratory therapy equipments

GASEOUS AGENTS   

Gaseous sterilization is effective and is employed for substances that are destroyed by heat. Ethylene oxide, beta-propiolactone, formaldehyde, ozone are employed as gaseous agents. Ethylene oxide is a colourless gas soluble in water. It is highly lethal to all kinds of microbes including spores and tubercle bacilli. Plastic and rubber articles, blankets, pharmacy products, complex apparatus such as heart lung machine, dental equipments, books, etc. Inhibition produced is irreversible, resulting in enzyme modification and inhibition of enzyme activity.

Ethylene Oxide gas chamber

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Beta-propiolactone is a condensation product of ketane and formaldehyde known as betapropiolactone with boiling point of 1630C. it has low penetrating power but effective for fumigation purposes than formaldehyde. Limitation is that it is carcinogenic therefore 0.2% BPL is used.

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Ozone is used in industrial settings to sterilize water and air as well as disinfectant for surface. It oxidizes most of organic matter. But it is toxic and unstable gas, so it is not practical to use in many settings. It has been recently approved for use in US. It uses oxygen that is subjected to an intense electrical field that separates oxygen molecules into atomic oxygen, which combines with other oxygen molecules to form ozone. Los Angeles has one of the largest municipal ozone treatment plants in world.

OZONE GAS CHAMBER

Low temperature gas plasma (LTGP) used as an alternative to ethylene oxide. It uses a small amount of liquid hydrogen peroxide which is energizes with radio frequency waves into gas plasma, leading to generation of free radicals and other chemical species which destroy organisms

An LTGP sterilizer that pumps vaporized H2O2 into the chamber.

DISINFECTION 

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Disinfection describes a process that eliminates many or all pathogenic microorganisms on inanimate objects, with the exception of bacterial spores. Disinfection can be accomplished by a number of means that include heat and chemicals. Terminology, which has been adopted by the Center for Disease Control (CDC) and is now widely used, describes disinfectants in terms of their activity as set out below:

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High-level disinfectants: These are chemical sterilants, which when used for a shorter exposure period than would be required for sterilization, kill all microorganisms with the exception of high numbers of bacterial spores.

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Intermediate-level disinfectants: These may kill mycobacterium, vegetative bacteria, most viruses, and most fungi but do not necessarily kill bacterial spores.

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Low-level disinfectants: These may kill most vegetative bacteria, some fungi, and some viruses.

SPAULDING'S CLASSIFICATION  

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In 1968 Earle Spaulding devised a rational approach to disinfection and sterilization. This is now referred to as Spaulding's classification and it has been refined and retained over the years because it is so clear and logical. Spaulding believed that instruments and equipment should be cleaned and reprocessed according to the level of risk associated with their intended use. The three categories he described were critical, semicritical and noncritical as in the table below.

FACTORS IMPACTING ON STERILIZATION & DISINFECTION

There are a number of factors that may nullify or limit the efficacy of sterilization and disinfection processes. These will be discussed in the next section and include: prior cleaning of the object the organic load present the type and level of microbial contamination the concentration of, and exposure time to, the biocide the nature of the object (e.g., crevices, hinges, lumens) the temperature and pH of the process

FACTORS     

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Exponential relationship between the number of organisms killed and the time taken to kill them. Microorganisms vary greatly in their resistance to chemical biocides. More concentrated the biocide the greater its efficacy and the shorter the time necessary to kill all the microorganisms Activity of most biocides increases as the temperature increases The production of thick masses of cells and extracellular materials or biofilms can protect microorganisms from the cidal action of biocides. Biofilms are microbial masses attached to surfaces that are bathed with liquids. A biocide must saturate or penetrate the biofilm matrix before it can kill the microorganisms within it.

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An increase in pH improves the antimicrobial activity of some agents as with glutaraldehyde, but decreases the activity of others such as hypochlorite's. Relative humidity influences the activity of gaseous agents such as ethylene oxide. Water hardness reduces the rate of kill of some biocides because divalent cations such as magnesium and calcium interact with soap to form insoluble precipitates. Organic matter such as serum, blood, pus or faecal material may interfere with the activity of biocides in at least two ways. Sterilize or disinfect an item it must be exposed to the appropriate concentration of biocide for a certain minimum contact time. All surfaces of the item must come in contact with the biocide for that period of time.

NEW METHODS OF STERLIZATION Table 1. New methods in disinfection and sterilization

Process

Agent

Regulatory agency action

Disinfection

Ortho-phthalaldehyde (Cidex OPA)

FDA cleared, October 1999

Antimicrobial coating (Surfacine)

Not FDA/EPA cleared

Superoxidized water (Sterilox)

Not FDA/EPA cleared

Liquid sterilization process (Endoclens)

Not FDA cleared

Sterilization

Rapid readout ethylene oxide biological Not FDA cleared indicator (Attest) New plasma sterilizer (Sterrad 50)

FDA cleared, January 1999

Ortho-phthalaldehyde   

It is a clear, pale-blue liquid (pH, 7.5), which typically contains 0.55% OrthoPhthalaldehyde OPA has demonstrated excellent microbiocidal activity in in vitro studies OPA has several potential advantages compared with glutaraldehyde. It requires no activation, is not a known irritant to the eyes and nasal passages, has excellent stability over a wide range of pH (pH 3-9), does not require exposure monitoring, and has a barely perceptible odor. Like glutaraldehyde, OPA has excellent material compatibility.

Surfacine: A New Antimicrobial

Surfacine is a new, persistent antimicrobial agent that may be used on animate or inanimate surfaces.

Ethylene Oxide (EO) Rapid Readout A new method designed for

rapid and reliable monitoring of EO sterilization. Indicates an EO sterilization failure by producing a flourscene change and a visual pH color change

Superoxidized Water The concept of electrolyzing saline to create a disinfectant is appealing because the basic materials, saline and electricity, are cheap and the end product (water) is not damaging to the environment. A commercial adaptation of this process, Sterilox, is available in the United Kingdom. The mode of action is not clear but probably relates to a mixture of oxidizing species. The main products are hypochlorous acid at a concentration of approximately 144 mg/L and free chlorine radicals. The solution has been shown to be nontoxic to biological tissues.

Endoclens: A New Liquid Chemical Sterilization System The system is designed to provide rapid, automated, point-of-use chemical sterilization of flexible endoscopes and consists of a computer-controlled endoscope- reprocessing machine and a new, proprietary liquid sterilant that uses performic acid.

Hydrogen Peroxide Plasma  

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Alternative technologies to sterilize temperature-sensitive equipment are being developed. A new hydrogen peroxide plasma sterilizer, the Sterrad 50, was recently cleared by FDA. It is a smaller version (44-L sterilization chamber) of the Sterrad 100 (73-L sterilization chamber), cleared in 1991. The Sterrad 50 contains a single shelf for placement of instruments to be sterilized within a rectangular chamber, whereas the Sterrad 100 has two shelves and a cylindrical chamber. The operational design of the two sterilizers is similar except that the Sterrad 50 consists of two hydrogen peroxide vapor-diffusion stage-plasma cycles. The sterilization cycles of the Sterrad 50 and Sterrad 100 are 45 minutes and 72 minutes, respectively.

ANTIBACTERIAL SOAP 

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Antibacterial soap is any cleaning product to which active antibacterial ingredients have been added. These chemicals kill bacteria and microbes. They do not kill viruses. Many, or even most, liquid hand and body soaps contain antibacterial chemicals. Triclosan is a common ingredient, as is alcohol. Since there is a great variety of bacteria, effectiveness against any given type of bacterium does not ensure that it is effective against unrelated types. Some soap contains tetra sodium EDTA which is a chelating agent that sequesters metals that the bacteria require in order to grow. Other microbes also require metals and so it is actually an anti-microbial agent that is widely used even as a preservative. It appears to be fairly harmless in the environment.

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Infectious dental patients are often undetected. Sterilization provides a method of instrument recycling that can be monitored and documented to show that conditions for control of disease transmission were indeed established. Because most instruments contact mucosa and or penetrate oral tissues, it is essential that reuses instruments be thoroughly cleaned and sterilized by accepted methods that can be routinely tested and monitored. Heat sterilization takes less time than high level sporicidal disinfection, which is required when heat or gas sterilization cannot be used. The four accepted methods of sterilization are:  Steam pressure sterilization ( autoclave )  Chemical vapor pressure sterilization ( chemiclave )  Dry heat sterilization ( dryclave )  Ethylene oxide sterilization

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Stainless steel instruments and mirrors used for operative, endodontic, periodontics, or dental hygiene procedures can be sterilized by any accepted methods. Both high speed and low speed headpieces are best autoclaved. Burs can be safely sterilized by dry heat or chemical vapour in chemiclave or in gas sterilizer, but they may rust or corrode if not protected from steam in autoclave. Patient load, turnaround time for instrument reuse, size of instrument inventory and instrument variety, and instrument quality must all be balanced against the type and size of sterilizer selected and number of auxiliary personnel employed. Dirty areas which cannot be disinfected easily between patients or which are not practical to disinfect between patients such light handle and switches, dental unit switches, ultrasonic handle, control buttons on the dental chair can be covered with clear plastic wrap (cling film) or impervious plastic sleeves.

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Such covering become contaminated by splatter and direct contact with gloved hands, the covering should be disposed of (wearing gloves) into hazardous waste bags and replaced between patients. If impermeable plastic coverings are not employed then a surface disinfectant should be used to disinfect these items and surfaces between patients. At the end of the clinical session all work surfaces whether within the clean or dirty zones need to be thoroughly cleaned and disinfected. Wearing of heavy duty household gloves offers greater protection to the skin when using chemical disinfectants. Protective eyewear and masks should be worn during environmental cleaning to protect the staff from exposure to hazardous chemicals and infectious material.

Dental chair covered with plastic sheet to prevent

Preventing contamination during X-ray taking

Before and during patient treatment  

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Designate dirty zones (likely to be contaminated during dental treatment) from clean zones Clean zones: Cabinets, surgery drawers, radiographs, patients notes, computer keyboards and pens are clean zones and should not be touched with contaminated gloved hands or instruments During patient treatment impervious clinical sheets or plastic sheaves should cover all work surfaces that cannot be readily disinfected between patients Items can be passed into "dirty zones" but contaminated items should not be passed out into "clean zones" Storage containers of dental materials should not be placed in the "dirty zone" Remove cling film/plastic sheaves and disinfect "dirty zones" between patient At the end of a working session all surfaces should be thoroughly cleaned and disinfected using alcohol spray/wipe or proprietary antimicrobial disinfectant spray/wipe

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Cleaning of spittoons : Clean outer surface first. Inner surface of bowladd (metered) dose of non-foaming disinfectant, wipe evenly around inside of bowl, leave for time interval specified by manufacturer for disinfectant to destroy microorganisms, rinse with bowl flush and then discard disinfection cloth as hazardous waste Suction apparatus, aspirators, drains and spittoons should be flushed daily with a non-foaming disinfectant/ detergent (e.g. Tridaclens, Dekaseptol or Orotol) according to the manufacturer's instructions. Trap filters must be removed and cleaned on a daily basis. Rinse thoroughly before replacing. Bleach or hypochlorite should not be used as they rust metal. Replace with new filters as specified by the manufacturer. Dental unit waterlines should be drained down at the end of the day and purged with a biocide for the time recommended by the manufacturer Work surfaces should be kept clear overnight

DENTAL IMPRESSIONS: Dental impressions become contaminated with saliva, blood and oral bacteria. Less commonly they may become contaminated with respiratory pathogens, which are coughed up into the mouth from the lungs. For example, impressions taken on a patient previously diagnosed with tuberculosis were found to harbor the causative agent Mycobacterium tuberculosis .

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All impression must be cleaned and disinfected before being sent to the laboratory.  Wear gloves, mask, goggles /visor  All impressions should be rinsed thoroughly in running water to remove all visible signs of contamination.  Use a disinfectant that is compatible with impression material. Immerse the impression in the disinfectant for the specified time. Avoid spray disinfectants, which are less effective and may create an inhalation risk. Rinse off the disinfectant with water.

  IMPRESSION TRAYS: 

Commercially manufactured plastic impression trays are for single patient use only. Do not clean or reprocess then for subsequent reuse. After single use they should be disposed of as clinical waste by the practice or the dental laboratory.  Metal impression trays are reusable and should be thoroughly cleaned, immersed in an ultrasonic bath or processed in a thermal washer disinfector and then steam sterilized.

Instrument tray to hold the instruments during sterilization

The following table is adapted from ACCEPTED DENTAL THERAPEUTICS AND DENTIST’S DESK REFERENCE: MATERIALS, INSTRUMENTS AND EQUIPMENT. (++) Effective and preferred method. (+) Effective and acceptable method. (-) Effective method, but risk of damage to materials. (- - -) Ineffective method with risk of damage to materials.

S. No.

Item

Steam sterilizer

Dry

heat Chemical

Ethylene

oven

vapour

oxide

+

+

+

++

Carbon steel

-

++

++

++

Steel

+

++

++

++

Tungsten-carbide

+

++

+

++

3.

Condensers

++

++

++

++

4.

Dappen dishes

++

+

+

++

5.

Endodontic instruments

1.

Angle attachments

2.

Burs

Other methods

Hot salt or glass bead sterilizer for 10-20 seconds at 2180C

6.

7.

Stainless steel handles

+

++

++

++

Stainless with plastic handles

++

++

-

++

Heat resistant plastic

++

---

-

++

Non heat resistant plastic

---

---

-

++

Glass slabs

++

++

++

++

Fluoride gel trays

Discard ++

S. No.

Item

Steam

Dry heat oven

sterilizer 8.

Chemical

Ethylene oxide

Other methods

++

Steam autoclave with

vapour

Hand instruments Carbon steel

-

++

++

chemical protection

Stainless steel 9.

++

++

++

++ Autoclave preferably

Hand pieces Autoclavable

++

-

+

++

Contra angles

-

-

-

++

Nonautoclavable

-

-

-

++

Prophylaxis angles

+

+

+

+

Aluminum metal

++

+

++

++

Chrome plated

++

++

++

++

Custom acrylic resin

---

---

---

++

Plastic

---

---

---

++

Instruments in packs

++

+ small packs

++

++ small packs

Combination synthetic phenolics

10

11

iodophores(-)

Impression trays

Discard ++

or

S. No.

Item

Steam

Dry heat oven

sterilizer 12

Chemical

Ethylene oxide

vapour

Instrument tray setups Restorative or surgical

+ Size limit

+

+ Size limit

++ Size limit

13

Mirrors

-

++

++

++

14.

Needles disposable

---

---

---

---

15.

Nitrous oxide Nose piece

++

---

++

++

Hoses

++

---

++

++

High quality ss

++

++

++

++

Low quality ss

-

++

++

++

With plastic parts

---

---

---

++

17.

Pluggers

++

++

++

++

18.

Polishing wheels and disks Gamet and cuttle

---

-

-

++

Rag

++

-

-

++

Rubber

+

-

-

++

16

Other methods

Orthodontic pliers

Discard++

S. No.

Item

Steam

Dry heat oven

sterilizer 19

Prostheses, removable

20

Rubber dam equipment

Chemical

Ethylene oxide

Other methods

vapour

-

-

-

+

Carbon steel clamps

-

++

++

++

Metal frames

++

++

++

++

Plastic frames

-

-

-

++

Punches

-

++

++

++

21.

Stainless steel clamps

++

++

++

++

22

Rubber items -

-

-

++

Discard ++

Low melting plastic

-

-

-

++

Discard++

High melting plastic

++

+

+

++

Diamond

+

++

++

++

Polishing

++

+

++

++

Sharpening

++

++

++

-

Prophylaxis cups 23

24

Saliva evacuators, ejectors

Stones

S. No.

Item

Steam

Dry heat oven

sterilizer 25

Chemical

Ethylene oxide

vapour

Surgical instruments Stainless steel

++

++

++

++

26

Ultrasonic scaling tips

+

---

---

++

27.

Water air syringe tips

++

++

++

++

28

X-ray equipment Plastic film holder

++

---

+

++

Collimating

-

---

---

++

Other methods

DISINFECTANTS AND ANTISEPTICS IN DENTISTRY S.No 1.

Type of disinfectant/antiseptic

Proprietary name

Use in dental surgery

CHLORHEXIDINES Chlorhexidine gluconate liquid 4%

Hibiscrub surgical scrub

Hand washing

Chlorhexidine 2.5% / 70% alcohol solution in a glycerine base

Hibisol hand rub

Hand rub

Chlorhexidine 0.5% in 70% alcohol

Alcoholic chlorhexidine

Skin disinfection prior to peri-oral biopsy, implant surgery and periodontal

2.

IODOPHORS Povidone iodine 7.5% solution

3.

surgery

Betadine surgical scrub

Hand washing

Alcohol gel/solutions

Purell, Sterillium, Desderman

Hand rub

70% Isopropyl alcohol wipes

Azowipes or Cliniwipes

Surgery hard surface disinfection or

ALCOHOLS

external surface of handpieces Ethanol and 1-propanol alcohol spray

4.

Mikrozoid

Surgery hard surface disinfection

Aquasept

Hand disinfection

TRICLOSAN Triclosan 2%

References: 

Microbiology book by Michael J pelczar, JR; E.C.S.Chan; Noel R. Krieg  Microbiology book by Ananthanarayan  Microbiology book by C.P.Baweja  Sturdevant’s art and science of Operative Dentistry  General surgery book by Bailey and Love  Internet source via pubmed.com and winkipedia.com