CHAPTER 10

STERILIZATION AND DISINFECTION

Concerns about transmitting infectious agents, suchas hepatitis virus (HBV) and human immunodeficiencyvirus (HIV), have caused the dental community tobecome more aware of the need to sterilize and disinfectinstruments, materials, and other equipment to protectproviders and patients. In this chapter, we will explainthe sterilization and disinfection process with whichyou, as a dental assistant, will be involved. We will alsogive you an overview of the procedures so you caneffectively carry out your duties.

The highest level of contamination control issterilization because it results in the total destruction ofall forms of microbial life. A variety of sterilizationmethods and many types of liquid chemicaldisinfecting agents are available. Heat sterilization ispreferable for all equipment and materials that canwithstand high temperatures. Heat sterilization iseffective, relatively easy to use, comparativelyinexpensive, and readily monitored for effectiveness.Sterilization and the availability of sterile products foruse in dental healthcare delivery depend on manyfactors. The most critical factors are as follows:

Proper and efficient sterilization facility design

Sound infection control practices before, during,and after sterilization

The effectiveness of the actual sterilizationprocess

PHYSICAL DESIGN

Dental Treatment Facilities (DTFs) must have acentral sterilization room (CSR) or a centralsterilization area. Centralization of sterilizationactivity is safer, provides more efficient use ofmaterials and personnel, and standardizes executionand monitoring procedures. We will explain thecritical design elements that make up a CSR area next.

Dedicated Work Areas

The design and outfitting of a sterilization areamust include work areas for receiving, cleaning,processing, sterilizing, storing, and issuing ofinstruments and equipment.

Functional Flow of the SterilizationProcess

Most large dental clinics will have a permanentCSR technician assigned to the sterilization area. Aspart of your indoctrination, you may be temporarilyassigned in the CSR so you can learn your command’ssterilization processes. All CSRs should have afunctional flow system where equipment, instruments,and materials are first introduced into the receivingarea, and work their way through to the issue area in aspecific order. Figure 10-1 illustrates a CSRfunctional flow chart that all personnel should adhereto while working in the CSR.

Once you are physically in an area of the CSR, youmust not go backwards or skip an area. This willcompromise the entire sterilization process. Do notprocess contaminated instruments, materials, orequipment in an area that may contaminate thesterilized items.

Figure 10-1.—CSR functional flow chart.

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Traffic Control

Controlled access to the sterilization areasminimizes the potential for transfer of micro-organisms between contaminated items, patients, andstaff. These areas must be off limits to anyone notinvolved in the sterilization process.

Receiving and Cleaning

Ideally, these areas will be physically separatefrom the remainder of the sterilization area. If physicalseparation is not obtainable, proper outfitting andequipment selection are critical. Commands shouldpurchase equipment that minimizes the handling ofcontaminated materials and instruments. There mayalso be an area equipped with the utilities necessary foroperating dental handpieces as shown in figure 10-2.Some commands require that the disinfection,cleaning, lubrication, and sterilization of dentalhandpieces take place in the CSR instead of the dentaltreatment room (DTR). Check to see what yourcommand’s policies are on where handpiecemaintenance should take place.

Processing

A processing space should have ample worksurface for the volume of materials processed. Allinspecting, sorting, wrapping, and packaging ofcontaminated materials occur here.

Sterilization

The space requirements for the sterilizationprocess should be determined by the available size, thedegree of sufficient access for the loading andunloading, and the ability to service the sterilizer.

Sterile Storage and Issue

To protect and maintain all sterile items, thestorage and issue areas should not be in the immediatevicinity of the contaminated processing areas.

THE STERILIZATION PROCESS

The sterilization process takes place in a CSR.There are many benefits to the centralized approach.Centralized instrument decontamination andsterilization are usually safer and more cost effectivethan instrument processing in the DTR. The

Figure 10-2.—Operating a dental handpiece in CSR.

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elimination of large numbers of small capacityultrasonic baths and tabletop sterilizers in each DTRcan be replaced by the central sterilization approachthat has larger capacity centralized equipment.

Whether a centralized or individual sterilizationarea is used, contaminated instruments and equipmentmust be processed as described next.

Management of Contaminated Instruments

Following the completion of a patient’s treatment,the dental assistant will take the contaminatedinstruments and equipment directly to the CSRtechnician in the receiving area of the CSR. Figure10-3 illustrates a contaminated instrument pack thathas been placed in the designated drop-off location inthe receiving area. The CSR technician should take thecontaminated instruments and equipment and set themin the receiving area that has been designated as atemporary hold area until they can be processed.

Do not rinse, scrub, or unnecessarily handlecontaminated instruments or materials in DTRs orother patient treatment areas. In the most extenuatingcircumstances, only the CO (designee) or the infectioncontrol officer (ICO) under written direction maymake exceptions to this requirement. This does notinclude handpiece maintenance that will be performedin the CSR or DTR depending on your clinic’s policy.

Instrument Cleaning

You should take contaminated instruments fromthe receiving area wearing heavy duty puncture-resistant gloves while handling all potentiallycontaminated items. Break down all packs and placedisposable items and contaminated linens inappropriate containers. All contaminated, reusableitems must be decontaminated by immersion in anEnviormental Protection Agency (EPA) registereddisinfectant before further handling. This step can beeliminated if these items are cleaned in an ultrasoniccleaner (bath) with an EPA-registered disinfectant thatalso is approved as an ultrasonic cleaning solution.Process instruments using one of the followingmethods. They are discussed in order of preference.

AUTOMATED WASHER PROCESSOR.—The automated washer processor is the safest methodand provides an effective cleaning process. It iscommonly used in hospitals or very large dentalclinics. Contaminated instruments are placed incassettes or baskets. Then they are run through theunit’s cycle of cleaning, rinsing, and disinfection attemperatures high enough to provide at least a highlevel of disinfection. This results in a “not touch”system in which the potential for injury duringinstrument processing is greatly reduced.

Figure 10-3.—Contaminated instrument pack placed at the entrance of the receiving area in the CSR.

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ULTRASONIC CLEANING.—This process issafer and more effective than manual scrubbing. Theultrasonic cleaner eliminates the possibility ofaccidental puncture wounds on the hands thatfrequently occur with manual scrubbing. It alsoeliminates the splatter of organism-laden debrisgenerated by scrubbing with a brush. The ultrasoniccleaner uses electrical energy to generate sound waves.When the sound waves travel through the liquid,millions of tiny bubbles form and burst continuously.This process is called a “cavitation” effect. Thebursting bubbles scrub everywhere the liquid canpenetrate. Intricate surfaces and difficult access areas,such as burs, endodontic files, serrated instrumenthandles, and hinged instruments, are cleaned morethoroughly and rapidly. The usage life of cuttinginstruments, such as burs and endodontic files, isextended by thoroughly removing debris thatinterferes with the cutting surfaces.

There are several sizes of ultrasonic cleaning units.Figure 10-4 illustrates small and large size ultrasoniccleaners. The ultrasonic cleaner should be located inthe processing area of the CSR. The manufacturer’sinstructions must be followed when using ultrasoniccleaners. These instructions should be posted orreadily available in locations where the units are used.

The following general guidelines are common tothe proper use of all ultrasonic cleaners:

Always keep the ultrasonic cleaner reservoir 1/2to 3/4’s full with ultrasonic solution at all times.

The solution must completely cover the items forthe ultrasonic action to occur.

Avoid the use of disinfectants, plain water, andnonultrasonic soaps or detergents.

Cleaning solutions must be changed at leastdaily or sooner, if visibly contaminated.

guidelinesWhen using the ultrasonic cleaner follow these

Place instruments into a perforated or wire meshbasket and rinse under water first.

Place basket holding the instruments into theultrasonic cleaner unit filled with solution.

Never place items directly on the bottom oftanks. This would reduce the amount ofultrasonic waves produced and could damagethe unit.

Always close the lid or cover on the unit when inuse to decrease aerosols and avoid splattering ofthe solution onto adjacent surfaces.

Limit ultrasonic cleaning time to 5 minutes toavoid damage to instruments. Followmanufacturer’s instructions for exact cleaningtimes for different models.

Longer cleaning times may be required for somenonmetallic instrument cassettes.

Never use your hand to remove instruments fromthe unit. Instead, use the basket to lift the instrumentsfrom the solution, drain, and rinse them under runningwater. Be sure to rinse the instruments thoroughly toremove all the remaining solution. Inspect theinstruments for remaining blood or debris, then drythoroughly.

MANUAL SCRUBBING.—Although manualscrubbing is time consuming and presents an increasedpotential for contamination injury, this method iseffective for cleaning instruments when automatedwasher processors or ultrasonic cleaning units are notavailable. Triple-sink modules allow personnel toperform in an orderly sequence multiple functionssuch as prerinsing, soaking, washing, and final rinsing.While wearing heavy-duty utility gloves, face mask,plastic apron, and eye protection, place instruments in

Figure 10-4.—Small and large size ultrasonic cleaners.

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a disinfecting solution, allow them to soak, and thenscrub them under water to avoid generating splatter.

PRESTERILIZATION PROCESSING

You are still in the processing area of the CSR andhave just finished cleaning your instruments using oneof the three methods of cleaning discussed previouslyand letting them dry as shown in figure 10-5. Performthe following procedures in the sterilization processnext.

Inspection and Sorting ofInstruments

After drying, you must inspect items closely forwear, breakage, and cleanliness. Sort instrumentsaccording to sets or packs. This is the prestaging areawhere your instruments are sorted before wrappingand packaging.

Wrapping and Packaging

Wrapping and packaging is the last step just beforethe sterilization process. Many different types ofsterilizers, packaging, and wrapping materials are usedin the CSR.

Before terminal (final) sterilization, wrap orpackage all critical and semicritical items individuallyor in sets. Ensure you place consumable supplies (fig.

10-6) that are required by your command in eachparticular pack before wrapping such items as needles,cotton rolls and pellets, gauze, aluminum foil fordental light handles, internal indicators, and towels.

Dental instruments are usually placed in packs, ontrays or cassettes, before placing them into thesterilizer. The most common wrapping materials andcontainers are paper, paper/plastic, nylon tubing, andcloth. Aluminum foil, closed metal trays, andperforated cassettes may also be used. The packagingor wrapping materials that you select depends on thecompatibility of what type of sterilization method youare using. Table 10-1 shows various sterilizationpackaging materials and their suitability to withstandsteam or dry heat sterilization. Always refer to thesterilizer manufacturer’s instructions for suitability.

Paper materials are available in the form of bags orflat disposable wraps. Both types are sealed withadhesive indicator tape. The combination paper/plastic peel packs (fig. 10-7) are available in variedsizes of preformed bags or rolls of varied widths thatcan be cut to the desired length. Either type can besealed with the adhesive indicator tape or self-sealed.

Heat sealed plastic or nylon tubing should only beused as an overwrap after the pack has been sterilized.Heat sealed overwrapping will extend a 30 day shelflife to 180 days.

Figure 10-5.—Instruments drying in the processing area.

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Figure 10-6.—Consumable supplies.

Table 10-1.—Sterilization Packaging Materials and Suitability for Steam or Dry Heat Sterilization

THICKNESS SUITABLE FOR

MATERIAL NATURE OR GRADE STEAM DRY HEAT

MuslinJean clothBroadclothKraft brownKraft whiteGlassineParchmentCrepeCellophanePolyethylenePolypropylenePolyvinylNylonPolyamideAluminumPeel packs

Test tubes

TextileTextileTextilePaperPaperCoated paperPaperPaperCellulose filmPlasticPlasticPlasticPlasticPlasticFoilPaper withplasticGlass with heatresistant caps

140 count160 count200 count30-40 lb.30-40 lb.30 lb.Patapar 27-2TDennison wrapWeek sterilizable1-3 mils1-3 mils1-3 mils1-2 mils1-2 mils1-2 mils

YesYesYesYesYesYesYesYesYesNoNo*NoNo*No*No

Yes

No

YesNoNoNoNoNoNoNoNoNoNoNoNoNoYes

No

Yes

*Specifically not recommended due to difficulty in eliminating air from packs.DTB1t1001

The practical use of some semicritical items may Wrapping loosely to allow steam to circulatepreclude wrapping or packing. Basic guidance inproper wrapping techniques includes the following:

freely throughout the pack. Arrange items sothat all surfaces receive direct exposure to the

Using trays or cassettes to reduce the possibilityof puncturing the wrapping material and risk ofinjury during post-treatment handling.

sterilization agent.

Opening all hinged instruments during packagingto allow steam to penetrate these areas.

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Using proper wrapping material for instrumentsets. The use of muslin wraps are discouraged.

Cloth and nonwoven wraps are sealed withexternal indicator tape as illustrated in figure10-8. The indicator tape will change color ifexposed to the sterilization elements.

When wrapping instrument packs with indicatortape, always turn the tabs down on the tape. Thisprovides a folded edge to aid in opening thepackage and removing the tape.

Launder muslin towels after each use and inspectfor tears or pinholes.

Follow the manufacturer’s time and temperaturesettings on sterilizers for the types of wrappingmaterial used.

Figure 10-7.—Paper/plastic peel packs.

event-related. Your command ICO will determinewhat method your sterilization program will use.

TIME-RELATED.—Time-related shelf life isidentified with an exact expiration date. After thisdate, the item is considered to be outdated and shouldnot be used. Table 10-2 lists the different wrappingmethods and their time-related shelf life in accordancewith BUMEDINST 6600.10.

EVENT-RELATED SHELF LIFE.—The use ofthe event-related method presumes continued sterilityuntil the package is damaged, wet, or torn. It is awell-recognized standard for items in good quality,self-sealed or hermetically (airtight) sealed, packagedin paper or plastic, or sequentially-wrapped and sealed

Table 10-2.—Time-Related Shelf Life of Sterilized Items

Using internal and external chemical indicatorsor multi-parameter integrators (measurestemperature, steam and time).

Expiration Dates

After the packs, instruments, and supplies arewrapped or placed into containers and sealed, theymust be labeled with the identification number of thesterilizer, the preparer’s initials, and the dates ofsterilization and expiration before they are placed inthe sterilizer. To label, use an ink marker, preprintedindicator tape, or a marking device that won’t run orfade when exposed to sterilization.

The shelf life or expiration date of sterilized itemsis the period during which an item is considered safefor use. Shelf life can be time-related or

WRAPPING TIME-RELATEDMETHOD SHELF LIFE

Paper envelope (sealed 365 dayswith sterilization tape)

Nonwoven blue wrap 30 days

Nonwoven blue wrap,plastic covered, heat- 365 days

sealed

Peel plastic packs, heat-sealed or self-sealed

365 days

Parchment paper orDennison wrap

Glass test tubes with screwcaps

30 days

indefinite

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Figure 10-8.—Cloth and nonwoven wraps with external indicator tape.

in dust covers within a few hours after sterilization. Ifthis method is used, the command policy must beclearly defined and consistently used throughout theDTF. When using the event-related method, allsterilizers must be biologically monitored at leastweekly.

Sterile Storage

Sterility of dental materials, instruments, andsupplies is much harder to maintain than it is toachieve. There is little value in precise sterilizationprocedures if instruments are contaminated uponcompletion of the process. Items must be dry beforethey are handled or stored. The time required fordrying depends on the type of packs in the load and thesterilizing agent used. Freshly sterilized items arenever placed on metal or cold surfaces. Packagesbecome damp from the condensation that occurs andbecome contaminated.

All sterile supplies, including sterile reusabledental items, must be stored in a manner that willpreserve their sterility until used. The followingfactors affect this process:

Environmental conditions including cleanliness?proper ventilation, and control of excess heat andhumidity are important.

The location where sterile supplies are storedshould not be in a manner that may contribute to theincreased possibility of contamination. Figure 10-9

shows an acceptable sterile storage cabinet containingsterilized packs and instruments.

Sterile items should not be stored in patienttreatment or decontamination areas unless they areprotected by enclosures, such as drawers or cabinets.

Sterile and clean patient treatment items may bestored in the same drawers or cabinets, as long as there isno possibility of nonsterile items being usedinadvertently when sterility is required.

Sterile items should not be stored with items notintended for clinical use (e.g., office and cleaningsupplies).

Items must not be stored on the deck, undersinks, in window sills, adjacent to heating and airconditioning vents, or in any area where undetectedcontamination may occur.

When storing sterilized items, arrange themaccording to expiration date, placing items with laterdates toward the rear. Check supplies periodically todetermine any need for resterilizing. Items must beresterilized if the wrapper becomes wet, if the packtouches the deck, if there is any question ofcontamination, or if the safe storage period hasexpired.

STERILIZATION METHODS

Because of the composition of many of the itemsused in dentistry, no single sterilization method is

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Figure 10-9.—Sterile storage cabinet.

suitable for all dental items. As a basic dental assistant,you will need to know several approved methods ofsterilization.

Steam Heat Sterilization

Steam under pressure (saturated steam) is the mosteffective means of sterilization for almost all itemsused in dentistry. To achieve sterility, moist heat underpressure must come in contact with all surfaces of allitems for the appropriate length of time. To effectivelysterilize items using saturated steam, the temperatureof the steam throughout the load must be high enough

to destroy the most resistant micro-organisms in thetime allotted for sterilization. For example, somespores can withstand temperatures above the normalboiling point of water (212°F or 100°C); so therelationship of temperature to spore killing power iscritical. Steam temperature and exposure time, notpressure, are crucial components of this process.Pressure is used only to raise the temperature of thesteam and, in itself, has nothing to do with microbialkilling action. At 15 pounds per square inch (psi), theboiling point increases to 121°C (250°F), atemperature at which all known organisms are killed.

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In addition to the high temperature, steam must besaturated so that it will quickly release heat throughcondensation when it comes into contact with a coolobject. Sterilization will not occur unless all air iseliminated from the chamber at the beginning of theprocess and periodically throughout sterilization. Thepackaging of supplies and loading of the sterilizer mustbe done so that steam comes in contact with all areas orsurfaces of the items being sterilized.

Flash sterilization is defined as the sterilization ofunwrapped items in a gravity displacement orprevacuum sterilizer with recommended minimumexposure times and temperatures. Steam sterilizationby this unwrapped method is not recommended. Itshould be used only for emergency sterilization.

Types of Steam Sterilizers

A steam sterilizer, also know as an “autoclave,” isa pressure-type vessel with a door or cover, valves tocontrol the entry and exit of steam and air, andmonitoring devices to allow the operator to observeconditions inside. It is designed to hold items andallow steam under pressure to penetrate these items.Steam sterilizers are available in many sizes, rangingfrom portable countertop to the fixed room-sizesterilizer. Two of the most common types of steamsterilizers used in the Navy are the gravitydisplacement and prevacuum sterilizers.

GRAVITY DISPLACEMENT.—Once thissterilizer is loaded and the door is closed as shown infigure 10-10, steam is admitted through an inlet and thesterilization process begins. A typical standard forsteam sterilization is achieved at 250°F or 121°C after20 to 30 minutes at 15 psi. It is important to refer to themanufacturer’s instructions for operation, sinceexposure times can vary according to the design of theparticular sterilizer.

You should observe the following precautionswhen loading the sterilizer chamber:

Do not overload. The passage of steam from thetop of the chamber to the bottom should not beblocked.

Place all packages on edges, with large packs atthe bottom of the chamber, and small packagesin an upper layer crosswise to the lower layer.This allows free passage of steam.

If mixed loads of metal items and linen aresterilized together, the linen is placed on theupper shelf and the metal items on the lower.

Articles that require the same amount of timeand the same final steps should be sterilizedtogether.

Enclosed fluids are sterilized separately becausethe pressure must be slowly released.

Load all packages at the same time when you areready to sterilize.

A standard operation chart for the correct exposureperiod of all supplies should be prepared and posted foreasy daily reference. It is important to note thatsterilizing conditions are based on temperature ratherthan on pressure. Effective steam sterilization andexposure time are measured from the moment thethermometer in the discharge line indicates the desiredpreset temperature. The pressure inside the sterilizer isnot an indication of positive sterilization because otherfactors determine the pressure inside the sterilizer.Pressure merely maintains temperature.

PREVACUUM STEAM STERILIZER.—Theprevacuum steam sterilizer (fig. 10-11) was designedto help overcome the trapping of air in the chamber.Trapping of air is one of the greatest dangersencountered when using saturated steam under gravitycycles. When errors are made by improperlypackaging items or overloading the sterilizer chamber,cool air pockets may form resulting in items not beingsterilized. The speed and efficiency of the steamsterilizer may be improved by removing air from thechamber with a powerful pump, creating a nearlyperfect vacuum before steam is introduced into thechamber. This procedure allows fast and more positiveheat to penetrate the entire sterilizer load. Theimproved sterilizer is referred to as the prevacuumsteam sterilizer.

Full heating of the loads is faster in the prevacuumsterilizer than in the gravity displacement sterilizer.For example, wrapped instruments can be sterilized at270°F (131°C) after 4 minutes exposure in aprevacuum steam sterilizer. Consult the manu-facturer’s instructions for specific details on operationand user maintenance information.

The Bowie-Dick type test was developed forprevacuum sterilizers to determine if the air has beenremoved from the chamber during the prevacuumstage. Air must be removed so that steam can penetratethe load instantaneously. It must be understood thatthis is not a test for adequate exposure to heat in termsof time-at-temperature. A commercially preparedBowie-Dick type test can be used by carefully readingand following the manufacturer’s instructions. All

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Figure 10-10.—Gravity displacement steam sterilizer.

Navy prevacuum sterilizers will be tested daily usingthe Bowie-Dick type test.

Level One Maintenance

The interior of the steam sterilizer should becleaned each day before being heated. This simpleprocedure can easily be accomplished by using a milddetergent to wash the surfaces. Follow the wash with athorough rinse of plain water. Unless this is done, thechamber walls will collect mineral deposits and maybecome greasy. Do not use wire brushes, steel wool, orany type of abrasive cleaning compounds on thesterilizer. The manufacturer’s directions must be

followed to maintain a properly functioning sterilizer.If the sterilizer does not appear to function properly,dental equipment repair personnel should check it atonce. Sterilizers should be spot checked frequently forleaks in lines and improperly functioning gauges,dials, thermometers, doors, drain strainers, and valves.

Dry Heat Sterilization

The least expensive form of heat sterilization ofinstruments is dry heat. Destruction of micro-organisms by dry heat in a DTF is accomplished byusing a unit that has been tested and approved by theFDA as a commercial sterilizer.

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Figure 10-11.—Prevacuum steam sterilizer.

Dry heat is suitable for sterilizing metalinstruments that rust or dull in the presence of watervapor. A disadvantage is that the high temperaturesdestroy many rubber and plastic based materials, meltthe solder of most metal impression trays, and weakensome fabrics, as well as discolor other fabrics andpaper materials.

A complete cycle involves heating the dry heatoven (fig. 10-12) to the appropriate temperature andmaintaining that temperature for the proper timeinterval. Depending on the location, dry heat ovenscan use one of the following heating elements toachieve sterilization:

Conduction (direct contact with a heat source)

Radiation (long electromagnetic waves)

Convection (heated air)

Because dry air is not as efficient a heat conductoras moist heat at the same temperature, a much highertemperature is required for sterilization. One of themost common problems with the use of dry heatsterilization is the failure to properly time theexposure. A typical dry heat cycle is 90 minutes at320-345°F, plus the time required to preheat the

chamber before beginning the sterilization cycle. Acommon misuse of the dry heat method occurs whenthe oven door is opened, and an instrument is quicklyremoved during the timed cycle. This interrupts thecycle and timing must begin all over again.

Advances in the design of the dry heat ovenresulted in the development of the dry heat convectionunit, which uses forced air at higher temperatures.This method of rapid heat transfer achievessterilization in 12 minutes at 375°F (190°C) forwrapped items and in 6 minutes for unwrapped items.Biological monitoring will be performed weekly.Consult the manufacturer’s instructions of each type ofdry heat sterilizer for specific details on its operationand user maintenance.

Chemical Vapor Sterilization

This process uses a mixture of chemicals,including alcohol, formaldehyde, ketone, acetone, andwater, that are heated under pressure to form asterilizing gas. Sterilization requires 20 minutes at270°F with 20 psi when instruments are eitherunwrapped or bagged following the manufacturer’sinstructions.

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Figure 10-12.—Dry heat sterilizer.

Advantages to chemical vapor sterilization are asfollows:

No corrosion, rusting, and dulling of instrumentssince water content is only 15 percent (ifinstruments are dry when placed in chamber).

Prevents destruction of dental items, such asendodontic files, orthodontic pliers, wires andbands, burs, and carbon steel instruments.

Instruments are dry at the end of the cycle.

The major disadvantage of this sterilizationmethod is the requirement for adequate ventilation.Chemical vapors, particularly formaldehyde, can bereleased when the chamber door is opened, leaving atemporary but unpleasant odor in the area.

Chemical vapor sterilization is not routinely usedin Navy dentistry. Consult the manufacturer’sinstructions for specific details on operation andrequired user maintenance.

Ethylene Oxide Sterilization

Ethylene oxide (ETO) gas uses relatively lowtemperatures for sterilization. Using a heated unit,sterilization can be achieved in 2-3 hours at 120°F.However, a lengthy aeration time must follow eachcycle.

Materials such as suction tubing, handpieces,radiographic film holders, and prosthetic appliancesmay be sterilized without adverse effects. Follow themanufacturer’s instructions for safety precautions,operation, and maintenance. Because of the seriousOccupation Safety Health Agency (OSHA) problemswith ETO gas, COs of Naval Dental Clinics (NDCs)should not purchase new ETO equipment. Large navalhospitals with ETO capabilities in their CSR may usethem to sterilize nonheat stable dental instruments andequipment.

Liquid Chemical Sterilization

The Food and Drug Administration (FDA)classifies chemical disinfectants that are sporicidal asdisinfectants, the FDA classifies all sterilants. Sincemonitoring the liquid sterilization process is virtuallyimpossible, treat these products as high-leveldisinfectants rather than sterilants. Be sure to followthe manufacturer’s directions exactly.

Bead and Salt Sterilizers

Use bead and salt sterilizers only during theendodontic procedure for sterilization of cleanmetallic instruments. Do not use them to sterilizeinstruments between patients. Clean contaminatedinstruments with an alcohol saturated gauze to removeblood and debris before inserting into the bead and salt

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sterilizers. Monitor and record at least weekly thetemperature in the sterilizer well. If using salt in placeof beads in the sterilizer, line the well with aluminumfoil to prevent corrosion.

CRITICAL CATEGORY ITEMSREQUIRING STERILIZATION

All critical category items require sterilization.Table 10-3 lists a variety of different dentalinstruments and materials and shows what type ofsterilization or disinfection is effective and preferredfor each particular item. It also lists methods that areeffective and acceptable, effective but risk damage,and ineffective with risk of damage to materials.Sterilize critical category items before turning them infor service or repair.

Following BUMEDINST 6600.10, sterilizecritical category items as follows:

Surgical instruments—Effective and preferredmethods of sterilization are the steam autoclave, dryheat oven, chemical vapor, or ethylene oxide.

Handpieces—Handpieces include: low-speedmotor attachments, sonic scaler, and tips. Followmanufacturer’s instructions. See table 10-3, forrecommended method of sterilization. Followmanufacturer’s instructions for the cleaning of the fiberoptic bundle.

Burs and diamonds—Clean burs and diamondsand dry before sterilizing. Many burs and diamondsare used only for single patient use. One acceptedmethod of sterilization for burs and diamonds are toplace them in a screw cap glass test tube (fig. 10-13) oran aluminum foil wrapped bur block and dry heatsterilize for 90 minutes at 320-345°F. Place a chemicalindicator in each tube or wrapped bur block. At leastweekly, place a biological monitor in one tube or foilwrapped block during the first load of the day,. retrieveand send for culture testing following themanufacturer’s recommendations.

Endodontic files and Gates-Glidden burs—Arrange sets in file blocks and seal in peel packs beforeautoclaving. When additional files or burs arenecessary, take them from a new package or from a filestorage box and sterilize them in a bead or salt sterilizerbefore use. Use endodontic broaches once and discardinto a sharps container. Dental Technician, Volume 2,NAVEDTRA 12573, chapter 7, illustrates andexplains endodontic broaches.

STERILIZATION MONITORING

Any number of factors can reduce theeffectiveness of sterilizers. Overloading and improperwrapping can prevent adequate penetration into theinstrument surface. Improper timing, temperaturevariations, worn gaskets and seals, and sterilizermalfunctions can prevent sterilization. Heatsterilization methods are generally reliable andeffective. Nevertheless, regular monitoring ofsterilization cycles is necessary to detect inadequateprocess conditions caused by human error orequipment malfunction.

Types of Sterilization Monitors

Commands should base selection of sterilizationmonitors on reliability, appropriateness to the process,safety, and cost effectiveness. Many types of monitorsare available. The three most commonly usedsterilization monitors in the Navy DTFs are biologicalmonitors, internal indicators, and external indicators.

BIOLOGICAL MONITORS.—Biologicalmonitors are designed to assess whether sterilizationactually occurred. These systems consist of bacterialendospores impregnated in paper strips or sealed inglass ampules or plastic vials.

INTERNAL INDICATORS.—Internalindicators are chemical dyes that change color whenexposed to steam, dry heat, or chemical vapor for aspecified period of time. When placed inside aninstrument pack, they determine whether theconditions necessary for sterilization have been met.

EXTERNAL INDICATORS.—Externalindicators are chemical dyes that change color uponshort exposure to sterilizing conditions. They aregenerally printed on packaging materials or supplied intape form and are necessary to distinguish processedpackages from those that have not been cycled.External indicators are not sensitive enough to beprocessed as an internal indicator and should not beused.

Biological Monitoring

After endospore tests are processed through asterilization cycle, they must be incubated according tothe manufacturer’s instructions. A pH indicator in themedium changes color when the ampule of endosporesgerminate and produce acids. This visually identifies afailure in the sterilization process. As a minimum,

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Table 10-3.—Sterilization and Disinfection of Dental Instruments and Materials

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Figure 10-13.—Burs in glass test tubes.

perform biological monitoring weekly. Figure 10-14shows a biological incubator with endospore tests.

TEST PROCEDURE.—Since biologicalmonitoring systems are designed for specificsterilization methods, you must be sure to use a systemcompatible with the sterilization method used. Thefollowing test procedures should be used to ensureeffectiveness of the sterilization process:

The use of a “test pack” is most practical whileprocessing an instrument pack.

Biological spore strips or ampules should beplaced between several layers of foldedwrapping material, and then the test pack isdouble-wrapped in the normal manner.

Always follow the biological monitormanufacturer’s directions for the placement ofthe test pack within the sterilizer.

As a general rule, the biological spore strips orampules should be placed within an area of thesterilizer that is least accessible to the sterilizingagent that is being used.

If using steam under pressure sterilizers, placethe test pack in the lower front of the sterilizationchamber.

If using tabletop units, place the test pack in thecenter of the load.

For each test, use an unprocessed monitor for acontrol.

Figure 10-14.—Biological incubator.

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EVALUATION CRITERIA.—After thecompletion of the sterilization cycle, open the test packand evaluate the dosage indicator to see if it passes orfails the cycle. If it passes, you can distribute the sterilegoods and continue the biological test procedure. If itfails, follow the procedures under guidelines forinternal and external indicators.

POSITIVE RESULTS.—When positivebiological monitoring occurs, you must follow theseguidelines:

Notify the ICO and record the test results in thesterilization log.

If another sterilizer is available, perform thefollowing actions:

— Retrieve and resterilize all items sterilizedsince the last negative test of that sterilizertested positive.

— Process a test pack with both a chemical andbiological monitor and secure the sterilizerfrom further use until the results of thebiological and chemical tests are read.

— If the results of the biological and chemicaltests indicate negative growth or pass thesterilization test, the sterilizer can be placedinto service.

— If the results from the test still indicatepositive growth or failure of sterilization,the sterilizer must be secured and dentalrepair personnel notified.

If another sterilizer is not available, perform thefollowing actions:

— Notify dental repair personnel.

— Retrieve and resterilize all items processedsince the last negative test. Use a test packwith a biological and chemical monitor ineach load when resterilizing all items thatcame up positive from the last test.

— If a chemical monitor in the test packindicates a pass of the sterilization test, theseloads can be distributed if necessary. Theideal situation is to have adequateinstruments and equipment to be able to holdthese items for 48 hours after a negativebiological test and then distribute.

— If the biological test again fails, secure thesterilizer and notify dental repair personnel,and the ICO.

Make a narrative entry in the log of each actiontaken and the results as they occur.

Retest the sterilizer using biological monitors.

Confirm exposure of the biological monitor tosterilization process.

Review the sterilization log for recent repairs ormaintenance.

GUIDELINES FOR INTERNAL ANDEXTERNAL INDICATORS.—Use internalindicators inside and external indicators on theoutside of each instrument pack. When using glasstest tubes during dry heat sterilization, ensure aninternal indicator is in each test tube before the screwtop is secured. When any indicator of a load test packfails, resterilize it with a new test pack containingboth chemical and biological monitors. Be sure toclosely monitor the temperature, pressure, andsterilizing time of the load. Watch the timer to be sureit does not start before the correct temperature isreached. Watch for steam leaks from the sterilizerduring the sterilization cycle. If the indicator againfails, notify the ICO and dental repair personnel. Login the results from the failure, and secure the sterilizerfrom use until the results of the biological monitor canbe evaluated.

Follow the manufacturer’s instructions whenreading the indicators. Please be aware that internaland external indicators are not replacements forbiological monitoring. Only biological monitoringcan tell you whether or not sterilization has actuallyoccurred.

LIQUID STERILANTS.—Since liquidsterilants cannot be biologically monitored, their useis discouraged. In using these agents, the key is thetime that instruments and equipment are in contactwith the sterilizing agents. Test strips forconcentration levels must be used according tomanufacturer’s instructions.

DISINFECTION

Disinfection is a less lethal process thansterilization, which kills disease causing micro-organisms. This does not include the destruction ofresistant bacterial spores. Disinfection is achieved byeither chemical or heat means. Selecting anappropriate chemical germicide or heat disinfectionmethod depends on what requirements need to be met

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Table 10-4.—Micro-organisms and Levels of Disinfectionfor that particular product. The following are some ofthe criteria for effective chemical disinfection:

The degree of microbial kill or deactivationrequired

The composition and texture of the item beingtreated

The technical requirement and ease of use of theavailable agents

Regardless of the product selected, there is nosingle chemical or heat agent available today that willmeet all these criteria. As always, follow labeldirections precisely. Give strict attention to theproper use of the product regarding mixing, dilution,method and duration of the application, temperaturerequirements, shelf-life, and if applicable, reuse life.

Organic Debris Present

Blood, saliva, and other organic material maycontribute to the failure of a germicidal process byeither direct inactivation of the disinfectant or theactual layering of the micro-organisms on theinstruments or equipment, thereby preventingpenetration of the germicide.

LEVELS OF DISINFECTION Type and Concentration of the Germicide

The EPA classifies disinfectants as high,intermediate, or low level, based on the effectivenessand contact time of the solution and the biocidalactivity of an agent against bacterial spores,mycobacterium tuberculosis, lipid and nonlipidviruses, and vegetative bacteria. Table 10-4 describesthe level of disinfection required to kill themicro-organism named.

Generally, when all other variables are constant,the higher concentrations of a chemical agent are moreeffective and require a shorter time to disinfect. Useof dilutions other than those specified by themanufacturer adversely affect some intermediate-level disinfectants, specifically iodophors. In allinstances, follow the manufacturer’s recommendations.

GENERAL CATEGORIES OF LIQUIDCHEMICAL AGENTS

FACTORS INFLUENCING GERMICIDALPROCEDURES A large variety of liquid disinfectants are available

today, and it is probable that many new ones willbecome available in the future. When selecting aproduct, make sure that the label has an EPAregistration number on it. Table 10-15, is a guide tochemical agents for disinfection and sterilization.Since they may be subject to change, be sure to read themanufacturer’s instructions before using. Next, wewill discuss the four most commonly used chemicalagents, glutaraldehyde and chlorine dioxide basedsolutions, iodophors, and phenolics.

The factors associated with the micro-organisms,as well as those associated with the surroundingphysical and chemical environment, influence theantimicrobial efficiency of the germicides. They aredescribed next.

Bioburden

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Nature of the Material

The easiest surface to disinfect is a smooth,nonporous, and cleanable one. If the materials areincompatible with disinfectant, damage and corrosioncan occur.

Glutaraldehyde-Based Solutions

These agents are available in several formulationsdiffering in pH, concentration, use in dilution, andexposure time. They are classified as high-leveldisinfectants or sterilants.

Always wear impermeable gloves and protectiveeyewear when handling these solutions. Irritation ofthe hands is common and personnel are always at riskof splashes occurring whenever liquids are being

Under a given set of circumstances, the higher thelevel of microbial contamination, the longer therequired exposure to the disinfectant is needed.Additionally, resistant micro-organisms requirelonger exposure times.

Level ofBacterial Bacterial Tubercle Nonlipid Lipid VegetativeActivity Spores Bacillus Viruses Viruses Bacteria

High Maybe Yes Yes Yes YesIntermediate No Yes Yes Yes Yes

Low No No No Yes Yes

In the absence of gross organic contamination.

Table 10-5.—Guide to chemical agents for disinfection and sterilization.

handled, so direct physical contact betweenglutaraldehyde solutions and human tissues should beavoided. When using these agents, they require properventilation because their vapors are extremely toxic.

Immersed items must be rinsed with sterile waterbefore using. Glutaraldehydes of 2 to 3.2 percent areFDA-registered. These solutions are not recognized asacceptable surface disinfectants because of the

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excessive amounts of exposure time required,corrosiveness, skin sensitization, and odor.

Phenolics

Chlorine Dioxide-Based Solutions

Chlorine dioxide is an effective surfacedisinfectant or sterilant. These solutions may be usedfor high-level disinfection of semicritical items thatare not subject to corrosion. It has a rapid action of 3minutes for disinfection or 6 hours for sterilization. Aswith sodium hypochlorite (bleach), there are severaldisadvantages: chlorine dioxide must be discardeddaily; has a 24-hour use life as a sterilant; and does notreadily penetrate organic debris.

It must be used with protective eyewear and glovesbecause it is extremely irritating to the eyes and skin. Itshould always be placed in closed containers, and youmust ensure adequate ventilation when using forsurface disinfection. In addition, it corrodes aluminumcontainers.

Iodophors

Iodophors are classified as intermediate-leveldisinfectants or can be used as antiseptics if the productlabel claims tuberculocidal (lethal to mycobacteriumtuberculosis) activity. They are compounds consistingof iodine and usually detergents to which the iodinequickly binds. Iodophor preparations are less irritatingto tissues, cause less allergies, and do not normallystain skin or clothing. They should not be used onwhite or pastel vinyls that are subject to staining fromrepeated exposure to iodine. Their biocidal activity isaccomplished within 10 to 25 minutes of exposure. Toensure tuberculocidal activity, fresh solutions must beprepared daily. As iodophors lose effectiveness, thecolor changes from amber to clear. Iodophors becomesomewhat unstable at high temperatures and can havea rapid loss of antimicrobial activity when inactivatedby hard water and alcohol. Distilled or at least softenedwater is recommended to dilute the iodophors beforeusing. Iodophors are EPA-registered andADA-accepted as surface disinfectants. They may notbe used as sterilants.

Iodophor antiseptics are useful in the preparationof oral mucosa for local anesthesia, surgicalprocedures, and handwashing. Not only does theiodophor remove the microbial populations from theskin, but also a residual antimicrobial effect remainson the scrubbed areas. Although iodophors are used asboth antiseptics and disinfectants, the same product isnever used for both.

Note: All semicritical category items shouldreceive high-level disinfection as shown in table 10-3.

NONCRITICAL CATEGORY ITEMSREQUIRING CHEMICAL DISINFECTION

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Examples of noncritical category items requiringchemical disinfection are the following: dental

Phenolics are also classified as an intermediate-level disinfectant, provided the product label indicatesa claim to tuberculocidal activity. They act as goodsurface spray cleaners and are effective in the presenceof detergents. Phenolics are useful on metal, glass,rubber, and plastic, and are less toxic and corrosivethan glutaraldehyde solutions. However, they create afilm accumulation, can degrade certain plastics, andetch glass with prolonged exposure. They are veryirritating and contact with skin and mucousmembranes should be avoided. To prevent skin andeye irritation, protective gloves and eyewear must beworn during their use.

SEMICRITICAL CATEGORY ITEMSREQUIRING CHEMICAL DISINFECTION

Examples of semicritical items requiring chemicaldisinfection are three-way syringe tips, high-volumeevacuator (HVE) and saliva ejector tips, radiographicpositioning devices. For the chemical disinfection ofsemicritical items, use the following procedures:

Follow the manufacturer’s instructions.

Thoroughly wipe the item with absorbentmaterial saturateddisinfectant.

with an EPA-registered

Allow the disinfecting solution to remain incontact with the item for the length of timespecified by the manufacturer.

Whenever possible, all semicritical items thatcan withstand sterilization should be sterilized.

Although nitrous oxide masks and breathing tubesfall into the semicritical category, if they areautoclavable, clean and sterilize them using steamheat. If not autoclavable, wipe after each use with twoseparate gauze pads saturated with a high-leveldisinfectant. If breathing tubes are not autoclavable,after each use, rinse inside and outside with runningwater, wipe and flush with a high-level disinfectant,and rerinse with water.

delivery systems (DDSs), consisting of a chair, unit,and light; portable dental units; surgical table andchair; and X-ray apparatus. For the chemicaldisinfection of noncritical category items, use the\following procedures:

Disinfect the DDS at least daily.

Use disposable barriers since they reduce thenumber of surfaces requiring disinfection.

Change paper or plastic headrest and brackettray covers after each patient. If headrest coversare not available, disinfect the headrest aftereach patient.

Disinfect hand-operated controls, switches, andhandles after each patient.

Follow the manufacturer’s instructions whendisinfecting the lamp head and protective shield.

Flush HVE and saliva ejector tubing andcuspidor weekly with a central evacuationsystem cleaner. Use more often as needed.Follow the manufacturer’s instructions.

Anesthetic cartridges for nonsurgical use shouldbe dispensed under unit dose guidelines to preventcontamination of bulk supplies. Use only individualdose dental carpules and discard them after use.Always follow the manufacturer’s instructions. Sincedisinfectants can diffuse through the diaphragm andcontaminate the anesthetic solution, do not storecartridges in these agents.

Note: All noncritical category items require atleast intermediate-level disinfection as shown in table10-4.

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