Sterilization in Dentistry

Sterilization destroys all microorganisms on the surface of stuff or in a fluid to prevent disease transmission when using that item. 

Steam sterilization is moist heat in the form of saturated steam under pressure, which is the most widely used and the most dependable method for sterilization. Steam sterilization is nontoxic, inexpensive, rapidly microbicidal, sporicidal, rapidly heats and penetrates fabrics. However, steam sterilization has some deleterious effects on some materials, such as corrosion and combustion of lubricants associated with dental handpieces.

The basic principle of steam sterilization is to expose each item to steam with direct contact at the required temperature and pressure for the specific time. Thus, there are four parameters of steam sterilization: steam, pressure, temperature, and time. The ideal steam for sterilization is dry saturated steam and entrained water. Pressure is the main aid for obtaining the high temperature necessary to quickly kill microorganism. Specific temperature must be obtained to ensure the microbicidal activity. Two common steam-sterilizing temperatures are 121°C and 132°C. These temperatures must be maintained for a minimum period to kill microorganisms. Generally, the sterilization times at constant temperature vary depending on the type of item and the sterilizer type.

There are two basic types of steam sterilizer autoclaves, the gravity displacement autoclave and the high-speed prevacuum sterilizer. The minimum exposure time for sterilization of wrapped healthcare supplies are 30 minutes at 121°C in a gravity displacement sterilizer or 4 minutes at 132°C in a prevacuum sterilizer.

 For the gravity displacement, steam comes out at the top or the side of the sterilizing chamber. Since the steam is lighter than air, it forces air out the bottom of the chamber through the drain vent. The gravity displacement autoclaves are primarily used to sterilize laboratory media, water, pharmaceutical products, regulated medical waste, and nonporous articles whose surfaces have direct steam contact. 

The high-speed prevacuum sterilizers are similar to the gravity displacement sterilizers, except they has vacuum pump to remove the air from the sterilizing chamber and load before the steam is admitted. The advantage of using prevacuum sterilizer is that it is nearly instantaneous for the steam to penetrate into porous loads.

Moist heat destroys microorganism by irreversible coagulation and denaturation of enzymes and structural proteins. The presence of moisture significantly affects the coagulation temperature of protein and the temperature at which microorganisms are destroyed.

Steam sterilization should be used to sterilize all possible critical and semicritical items those are heat and moisture resistant. Furthermore, steam sterilizers also are used in healthcare facilities to decontaminate microbiological waste and sharps containers but sterilizer these items with gravity displacement sterilizer require additional exposure time.

Flash sterilization is a type of steam sterilization use to sterilize an unwrapped object at 132°C for 3 minutes at 27-28 lbs. of pressure in a gravity displacement sterilizer. Flash sterilization usually uses for cleaning patient-care items that cannot be wrapped, sterilized, and stored before use. It can also uses for sterilizing an item that does not have enough time to sterilize by package method. However, flash sterilization is not recommended for implantable devices because the potential for serious infections.

Ethylene oxide (ETO), as a low-temperature sterilant, has been used process for sterilizing temperature- and moisture-sensitive medical devices and supplies in health care establishment. There are two types of ethylene oxide sterilizers, mixed gas and 100% ethylene oxide. Ethylene oxide sterilizers combined ethylene oxide with a chlorofluorocarbon (CFC) stabilizing agent. However, there are several disadvantages about chlorofluorocarbon. It has scientific evidence linking it to destruction of the earth’s ozone layer. Fortunately, there are alternative technologies to ethylene oxide with chlorofluorocarbon that be cleared by the FDA for medical equipment include 100% ethylene oxide; ethylene oxide with a different stabilizing gas, such as carbon dioxide or hydrochlorofluorocarbons (HCFC) ; submersion in peracetic acid; hydrogen peroxide gas plasma; and ozone.

Hydrogen peroxide (H₂O₂) gas plasma is a new sterilization technology by producing free radicals within a plasma field that are able to interact with essential cell components and thereby disrupt the metabolism of microorganism. Hydrogen peroxide gas is used to sterilize materials and devices that cannot tolerate high temperatures and humidity, such as plastics, electrical devices, and corrosion- susceptible metal alloys. This method has been compatible with most medical devices and material tested.

After these items are cleaned, dried, and inspected, they must be wrapped or placed in rigid containers and should be arranged instrument trays before sterilization. 

The guidelines mention that hinged instruments should be opened; items with removable parts should be disassembled unless the device manufacturer provide specific instructions; complex instruments should be prepared and sterilized according to device manufacturer’s instructions; devices with concave surfaces should be positioned to help water drain; heavy items should be positioned not to damage brittle items; and the weight of the instrument set should be based on the design and density of the instruments and the distribution of metal mass. Further, there are several methods to maintain sterility of surgical instruments, including rigid containers, peel-open pouches, roll stock or reels and sterilization wraps. The packaging material must allow penetration of the sterilant, provide protection against contact contamination during handling, provide an effective barrier to microbial penetration, and maintain the sterility of the processed item after sterilization. The key points of ideal sterilizeation wrap are successful barrier, penetrability, aeration, ease of use, drapeability, flexibility, puncture resistance, tear strength, toxicity, odor, waste disposal, linting, cost, and transparency.

The loading procedures must be able for free circulation of steam around each item. Furthermore, there are several important basic principles for loading a sterilizer, such as allow for proper sterilant circulation; perforated trays should be placed so the tray is parallel to the shelf; non perforated containers should be placed on their edge; small items should be loosely placed in wire baskets; and peel packs should be placed on edge in perforated or mesh bottom racks or baskets.

The wrapped surgical trays remained sterile for varying periods depending on the type of material used to wrap the trays. Safe storage time for sterile packs depend on the porosity of the wrapper and storage conditions. For example, heat-sealed, plastic peel-down pouches and wrapped packs sealed in 3-mil polyethylene overwrap can be sterile for as long as 9 months after sterilization. In addition, items wrapped in double-thickness muslin comprising four layers can remain sterile for at least 30 days.

All of the sterilization procedure should be evaluated the sterilizing conditions and indirectly the microbiologic status of the processed items by using a combination of mechanical, chemical, and biological indicators. The mechanical monitors include temperature record chart and pressure gauge for daily assessment. The mechanical monitors for ethylene oxide include computer printouts, gauges that provide time, temperature, and pressure records. Chemical indicators are convenient, inexpensive, and indicate that the item has been exposed to the sterilization process. Chemical indicator should be used in conjunction with biological indicators, but should not replace them because only a biological indicator consisting can measure the microbial killing power of the sterilization process by resistant spores. Chemical indicators are attached to each pack to show that the package has been processed through a sterilization cycle, but these indicators do not prove sterilization has been achieved. Chemical indicators usually are heat-or chemical-sensitive inks, which will change color when one or more sterilization parameters present. Biological indicators measure the sterilization process directly by using the most resistant microorganisms, not checking the physical and chemical conditions. If a sterilizer is used frequently, using biological indicators everyday allow earlier discover equipment malfunctions or procedural errors, which can minimizes the extent of patient surveillance and product recall needed in the event of a positive biological indicator.

After the sterilization process, medical and surgical devices should be stored with aseptic technique in order to prevent contamination. Sterile supplies should be stored far enough from the floor, the ceiling, and the outside walls to allow for adequate air circulation, ease of cleaning, and compliance with local fire codes. Also, medical and surgical supplies should not be stored in location where they can become wet, such as under sinks. Moisture brings microorganisms from the air and surfaces. The ideal storage is closed or covered cabinet but open shelving can also be used for storage.

In dental clinic, not only the disinfection and sterilization of the dental instruments are important but also clinic environment’s hygiene is a great point to make sure of. In order to keep the hygiene of the clinic in a best condition, regular cleaning is very important. No matter what before or after using the clinic we have to clean and do some simple disinfection. We have few but necessary steps to do.

1.     Spray some of disinfectant or high concentration alcohol on the paper towel.

2.     Wipe the surface of whole dental chair and both handle and control desk. (Changing different napkin paper in different parts of is necessary.)

3.     Using a bucket of diluted detergent to clean the tube of the dental chair by step on the foot controller to let the tube suck the detergent in the machine.

 

Remember, wearing the gloves in the entire process is essential.

Factors Affecting the Efficacy of Disinfection and Sterilization

The efficacy of germicides against microorganisms depends on several factors, such as intrinsic qualities of the organism and the chemical and external physical environment. By knowing of these factors will lead to better use of disinfection and sterilization.

        When all other conditions remaining constant, the larger number of microbes, a germicide needs more time to destroy all of them. This emphasizes the importance of cleaning medical instruments before disinfection and sterilization. The location of microorganisms also must be considered. Since penetration of the disinfectant is difficult, medical instruments with multiple pieces must be disassembled before disinfection. In addition, only surface that directly contact the germicide will be disinfected, so the equipment must be completely immersed for the entire exposure period.

        Each microorganism has greatly different in their resistance to chemical germicides and sterilization process. The most resistant microbial subpopulation controls the sterilization or disinfection time.

        When all other variables remaining constant, the more concentrated the disinfectant has the greater efficacy and the shorter the time necessary to kill microbial. So, the potency of the germicide will decide the length of the disinfection time.

Several physical and chemical factors, such as temperature, pH, relative humidity, and water hardness, also influence disinfectant procedures. In most of the cases, as the temperature increases, the activity of most disinfectants increases. However, too much increase in temperature will causes the disinfectant to degrade and weakens its germicidal activity. The pH influences the antimicrobial activity by altering the disinfectant molecule or the cell surface. The water hardness reduces the rate of kill of certain disinfectants because divalent cations in the hard water interact with the disinfectant to form insoluble precipitates.

This further emphasizes the importance of cleaning of medical devices before any sterilization of disinfection procedure because both organic and inorganic soils are easily removed by washing. In general, longer contact times are more effective than shorter contact times.

Biofilms, thick masses of cells and extracellular materials, can protect microorganism from disinfectants. Biofilms are microbial communities that are tightly attached to surfaces and cannot be easily removed. Once these masses form, microbes within them can be resistant to disinfectants by multiple mechanisms. Some enzymes and detergents can degrade biofilms or reduce numbers of viable bacteria within a biofilm, however, no products are EPA-registered or Food and Drug Administration (FDA)-cleared for this purpose.

Hypochlorites are the most widely used of chlorine disinfectants. The most prevalent products are aqueous solution of 5.25-6.15% sodium hypochlorite, usually called household bleach. The exact mechanism is by free chlorine destroys microorganism has not been elucidated. There are a number of mechanisms bring about inactivation by chlorine, such as oxidation of sulfhydryl enzymes amino acids; ring chlorination of amino acids; loss of intracellular contents; decreased uptake of nutrients; inhibition of protein synthesis; decrease oxygen uptake; oxidation of respiratory components; decreased adenosine triphosphate production; breaks in DNA; and depressed DNA synthesis. Low concentrations of free available chlorine have a biocidal effect on mycoplasma and vegetative bacteria in seconds in the absence of an organic load. Higher concentrations of chlorine are required to kill M. tuberculosis. Hypochlorites are widely used in healthcare facilities in a variety of settings. Inorganic chlorine solution is used for disinfecting tonometer heads and for spot-disinfection of countertops and floor. For decontaminating blood spills, a 1:10-1:100 dilution of 5.25-6.15% household bleach or an EPA-registered tuberculocidal disinfectant has been recommended. For small blood spills on noncritical surfaces, the area can be disinfected with a 1:100 dilution of 5.25-6.15% sodium hypochlorite or an EPA-registered tuberculocidal disinfectant. Furthermore, since hypochlorites and other germicides are substantially inactivated in the presence of blood, the surface with large spills of blood require cleaning before an EPA-registered disinfectant or a 1:10 solution of household bleach is applied. Clinicians should not alter their use of chlorine on environmental surface on basis of testing methodologies that do not simulate actual disinfection practices. Other uses in health care include as an irrigating agent in endodontic treatment and as a disinfectant for manikins, laundry, dental appliances, hydrotherapy tanks, regulated medical waste before disposal, and the water distribution system in hemodialysis centers and hemodialysis.

Glutaraldehyde is a saturated dialdehyde, which as a wide acceptance high-level disinfectant and chemical sterilant. When the alkalinating agents activate the aqueous solutions of glutaraldehyde, these become sporicidal. However, after activated, these solutions have a shelf-life of minimally 14 days because the polymerization blocks the active sites of the glutaraldehyde molecules that are responsible for its biocidal activity. The use of glutaraldehyde-based solutions in health-care facilities is widespread because of their advantages including excellent biocidal properties; activity in the presence of organic matter; and noncorrosive action to endoscopic equipment, thermometers, rubber, or plastic equipment. The biocidal activity of glutaraldehyde results from its alkylation of sulfhydryl, hydroxyl, and amino groups of microorganisms, which alters RNA, DNA, and protein synthesis. 2% or less aqueous solutions of glutaraldehyde buffered to pH 7.5-8.5 with sodium bicarbonate effectively killed vegetative bacteria in 2 minutes or less; M. tuberculosis, fungi, and viruses less than 10 minutes; and spores of Bacillus and Clostridium species in 3 hours. FDA has cleared a glutaraldehyde-phenol/phenate concentrate as a high-level disinfectant that contains 1.2% glutaraldehyde with 1.93% phenol/phenate at its use concentration. Glutaraldehyde is used most commonly as a high-level disinfectant for medical equipment. Glutaraldehyde is noncorrosive to metal and does not damage lensed instruments, rubber, and plastics. However, glutaraldehyde is too toxic and expensive for cleaning noncritical surfaces. Area using glutaraldehyde should be monitored to ensure a safe environment. Healthcare staff members can be exposed to elevated levels of glutaraldehyde vapor when equipment is processed in poor fresh air rooms. Acute or chronic exposure can result in dermatitis, skin or mucous membrane irritation, and pulmonary symptoms.

Approach to Disinfection and Sterilization

Disinfection and sterilization are important of the guaranteeing that medical and surgical instruments do not transmit infectious pathogens between patients. “Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008”, written by William A. Rutala, David J. Weber and the Healthcare Infection Control Practices Advisory Committee (HICPAC), has presents a proper use of disinfection and sterilization process. The approach is based on well-designed studies assessing the efficacy and effectiveness of disinfection and sterilization procedures.

There are different terms use in disinfection and sterilization, and each stands for different purpose.

Cleaning is removing the visible soil from objects and surfaces and normally is accomplished manually or mechanically using water with detergents or enzymatic products. Careful cleaning is necessary before high-level disinfection and sterilization because inorganic and organic materials that remain on the surfaces of instruments intervene with the effectiveness of these processes.

Disinfection is a process that eliminates most or all-pathogenic microorganisms, except bacterial spores, on non-living objects. In health-care settings, instruments usually are disinfected by liquid chemicals or wet pasteurization. There are several factors that affect the efficacy of both disinfection and sterilization include prior cleaning of the object; amount of organic and inorganic present; type and level of microbial contamination; concentration of and exposure time to the germicide; physical nature of the object; presence of biofilms; temperature and pH of the disinfection process; and in some case, relative humidity of the sterilization process.Although disinfection is not sporicidal, chemical sterilants will kill spores with prolonged exposure times (3 - 12 hours).

Sterilization is a process that destroys or eliminates all forms of microbial life. In health-care installations usually perform by physical or chemical methods. The principal sterilizing agents used in health-care facilities are steam under pressure, dry heat, ETO gas, hydrogen peroxide gas plasma, and liquid chemicals.

Germicide is an agent that can kill microorganisms, particularly pathogenic organisms. The term germicide includes both antiseptics and disinfectants. 

Antiseptics are germicides applied on living tissue and skin. 

Disinfectants are antimicrobials applied only to non-living object. Normally, disinfectants cannot be used for skin antisepsis because they can injure skin and other tissues.

Spaulding categorized the instruments and items for patient care into critical, semicritical, and noncritical according to the degree of risk for infection involved in use of the items. Critical items have high potential for infection if they are contaminated with any microorganism. Critical items must be sterile because these items enter sterile tissue or the vascular system that microbial contamination could transmit disease. Critical items should be purchased in sterile or be sterilize with steam. Semicritical items contact mucous membranes or non intact skin. These medical devices should be free from all microorganisms. Since intact mucous membranes, such as lungs and the gastrointestinal tract, generally are resistant to infection by common bacterial spores, small numbers of bacterial spores are permissible. Semicritical items minimally require high-level disinfection using chemical disinfectants. Noncritical items get into contact with nonintact skin for a brief period of time. Thee items should be disinfected with intermediate-level disinfectants, such as phenolic, iodophor, alcohol, or chlorine.

Dental instruments as possible agents for pathogen transmission, the American Dental Association recommends that surgical and other instruments that normally get across soft tissue or bone be classified as critical device that should be sterilized after each use or discarded. Handpieces can be contaminated with patient material and should be heat sterilized after each patient. For heat-stable crtitical or semicritical dental instruments and materials can sterilize by steam under pressure (autoclave), chemical vapor (formaldehyde), or dry heat (320 °F for 2 hours).

 

Centers for Disease Control (CDC) has divided noncritical surfaces in dental offices into clinical contact and housekeeping surfaces. Clinical contact surfaces are surfaces that be touched with gloved hands during clinic or that become contaminated with blood or other infectious material and subsequently contact items, such as light handle, switches, dental X-ray equipment, and chair-side computers.  For these surfaces especially surfaces that are difficult to clean, barrier protective coverings can be used. The coverings should be changed when damaged and routinely. If the surface is not barrier-protected, these surfaces should be disinfected between patients with an intermediate-disinfectant. On the other hand, housekeeping surfaces need to be cleaned only with a detergent and water or an Environmental Protection Agency (EPA)-registered hospital disinfectant.

Similar with antibiotics, reduced susceptibility of bacteria to disinfectants can arise by with chromosomal gene mutation or acquisition of genetic material. Nevertheless, reduced susceptibility to disinfectants does not associate with failure of the disinfectant since concentrations used in disinfection still greatly exceed the cidal level. Nowadays, evidence and reviews indicated enhanced tolerance to disinfectants could be developed in response to disinfectant exposure. However, the level of tolerance is low and unable to compromise the effectiveness of high concentration disinfectants. In addition, the rotational use of disinfectants in pharmacy production units has been recommended and practiced in an attempt to prevent development of resistant microbes.

The effective use of disinfectants is part of a multibarrier strategy to prevent health-care-associated infections. Although use of noncritical items or contact with noncritical surfaces carries little risk of causing an infection in patients or staff, medical equipment surfaces can become contaminated with infectious agents and contribute to the spread of health-care-associated infections. For this reason, noncritical medical equipment surfaces should be disinfected with an EPA-registered low- or intermediate-level disinfectant.

Even more, there are five reasons to use a disinfectant on noncritical surfaces, which particularly support the use of a germicidal detergent.

1.     Hospital floors become contaminated with microorganism from settling airborne bacteria. The removal of microbes is a factor of controlling health-care-associated infections. The use of phenolic disinfectant has higher effective in reducing the numbers of bacteria than the use of soap and water.

2.     Soap and water detergents without disinfectants become contaminated and result in spread bacteria to patient’s environment.

3.     CDC Isolation Guideline recommends that noncritical equipment contaminated with blood, body fluid, secretions, or excretions be cleaned and disinfected after use. It also recommends that to cleaning, disinfection of the bedside equipment and environmental surface for certain pathogens, which can survive in the non-living environment for prolonged periods.

4.     Occupational Safety and Health Administration (OSHA) requires that surfaces contaminated with blood and other potentially infections materials be disinfected.

5.     Using a single product throughout the installation can simplify both training and appropriate practice.

Testing

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