Preparing Instruments for Sterilization

Dentistry Today


Many local home centers offer short courses on a variety of repair and remodeling topics. One popular offering is interior painting of walls, floors, and ceilings. Attendees are surprised when instead of paint and a brush they are handed a bucket of soapy water and a sponge. In order to have a favorable result in the end, proper preparation in the beginning is required. Surfaces need to be repaired, sanded smooth, cleaned well, and then rinsed completely. The paint must contact the surfaces directly. The presence of oils, dirt, adhesives, or stains could negatively affect the quality of the painting. Surface preparation is the key to successful painting.
Correct cleaning is an essential step in preparing instruments for sterilization. Clean-ing removes adherent materials that could interfere with sterilization. Instrument preparation involves 5 sequential activity sets: chairside and transport, holding (presoaking), cleaning, corrosion control/drying/lubrication, and packaging.1-3


Table 1. Categories of Patient Care Items.*


(1) Critical

(2) Semicritical

(3) Noncritical


Penetrates soft tissue, contacts bone, enters into or contacts the bloodstream or other normally sterile tissue.

Contacts mucous membrane or
nonintact skin; will not penetrate soft tissue, contact bone, enter into or touch other normally sterile tissue

Contacts intact skin


Surgical instruments, periodontal scalers, scalpel blades, surgical dental burs

Dental mouth mirror, amalgam condenser, reusable dental impression trays, dental

Radiograph head/cone, blood
pressure cuff, facebow, pulse oximeter

*Modified From References 1 to 4.
**Although dental handpieces are considered a semicritical item, they should always be heat sterilized between uses and not high-level disinfected.

The Centers for Disease Control and Prevention (CDC) has categorized patient care items as critical, semicritical, or noncritical based on the potential risk of infection to the patient during use. The system is based on the classification first proposed by Spaulding in 1968 (Table 1). The CDC recommends that critical and semicritical items be first cleaned and then sterilized by heat.1,4
Semicritical items that are heat sensitive must, at a minimum, be cleaned and treated with a high-level disinfectant. Noncritical items are cleaned and treated with a low-level disinfectant when no blood is visible. Intermediate-level disinfectants are to be used when blood can be seen.1,2


Operatory preparation for the next patient cannot begin until all contaminated items are safely removed, discarded, or processed. The removal of contaminated patient care items from the operatory should be performed in a careful manner to prevent exposure to microorganisms. Contact with nonintact skin on the hands, mucous membranes of the eyes, nose, or mouth, and percutaneous injuries from sharp instruments provide the risk of disease transmission. Instruments being transported to the instrument-processing area must be contained to prevent injury. Containment can be defined as instrument cassettes or cages in which dental care items are cleaned, sterilized, and stored until point of use. Sharp instruments should not be carried openly to the instrument-processing area. Percutaneous injuries may occur to other dental healthcare personnel (DHCP) or patients in hallways leading to the instrument-processing area.


If the DHCP are unable to begin the instrument-processing procedure immediately after transporting the dental care items to the instrument-processing area, the items should be placed into a holding solution in a puncture-resistant container for a precleaning process. This facilitates the cleaning process by preventing patient material from drying on the instruments. Cleaning becomes easier and less time consuming. The holding solution can be a disinfectant/detergent or an enzymatic cleaner. The use of a sterilant/high-level disinfectant (eg, glutaraldehyde) is not considered appropriate and therefore not recommended. Some plastic/resin cassettes should not be placed into a holding solution. Always consult and follow the recommendations made by the cassette manufacturer. Also, be aware that some instruments may corrode if left in the holding solution for more than a few hours. Precleaning is not required when using an instrument washer. Contaminated instruments may be placed directly into the instrument washer and held there until the washer cycle is started.


Cleaning soiled dental instruments is essential for any sterilization procedures. Cleaning reduces the bioburden (microorganisms, blood, saliva, oral hard tissues, and dental materials). Bioburden could isolate or protect microorganisms from sterilizing agents. There are 2 ways to clean dental instruments: mechanically (ultrasonic cleaning, instrument wash-ers/washer-disinfectors) and manually.1-3

Ultrasonic Cleaning

Ultrasonic cleaning, when com-pared to manual scrubbing, reduces direct contact with contaminated instruments and thus decreases the chances of cuts and puncture wounds. Ultrasound, because of its cavitation action (billions of imploding bubbles are generated, which produce a cleaning turbulence that removes and disrupts debris), is usually more effective and efficient than manual scrubbing. For example, office staff can properly clean more instruments within a given period of time. Almost all instruments can be ultrasonically cleaned. One major exception is the majority of dental handpieces, which usually must be hand-cleaned. Both loose instruments and those held in cassettes can be cleaned with ultrasound. Always check the manufacturer’s clean-ing instructions.2,3,5

Table 2. Selecting an Ultrasonic Cleaner.*

•Purchase a unit that meets the practice’s needs (eg, sufficiently large to hold 15 to 20 loose instruments at a time or is configured to clean several stacked cassettes at the same time).
•Purchase the necessary accessories (eg, unit lids, several holding/transport baskets, glass beakers with lids, and general purpose and special cleaning solutions).
•Do not purchase a unit with a solution-heating element.
•Select a unit that has a side spigot that allows for easy drainage directly into an adjacent sink.
•Choose a unit with a timer that terminates cleaning.

*Modified From References 2, 3, 5, and 6.

Ultrasonic cleaners come in a variety of sizes, from pint-sized round units to multiple-gallon, rectangular-shaped types that can be used on a countertop or built into the counter cabinet (Table 2).

Table 3. Recommendations for Using an Ultrasonic Cleaner.*

•Wear appropriate personal protective equipment—heavy duty gloves, masks, protective eyewear, and a clinical gown.
•Presoak or at least rinse off soiled instruments before placing them in the cleaner.
•Place a maximum of 20 instruments in the cleaner.
•Limit the number of instrument cassettes added so that all are completely submerged.
•Use a cleaning detergent specifically designed for use in an ultrasonic cleaner.
•Change the cleaning solution each half working day (assuming regular activity).
•Operate the unit with the lid in place.
•Do not use the unit’s heating element, if present.
•Process loose instruments for 5 to 15 minutes (adjust time if needed).
•Process instrument cassettes for 10 to 20 minutes (consult manufacturer’s recommendations and the actual performance of the unit).
•Rinse cleaned instruments well after processing.
•Drain the cleaner’s tank at least at the end of each workday, dry it completely, and disinfect the inside, lid, and other accessories.
•Perform the aluminum foil efficiency test every week.

*Modified From References 2 and 6.

Loose instruments and those held within cassettes must be suspended within the solution but off the bottom of the unit’s chamber (Table 3). Placement of instruments directly on the floor of the unit will result in poor cleaning, and excessive bouncing could damage the unit and the instruments. The use of a suspending basket or rack will position the instruments or cassettes for optimal cleaning. A cover should be in place whenever the unit is being operated.
The unit’s chamber should be filled (usually within 0.5 to 1 inch of the top) with a detergent solution designed for use in an ultrasonic cleaner. Although these detergents are more expensive than those used in household situations, they are more economical in the long run. Ultrasonic detergents have operational pH levels that will not harm instrument metals and are capable of producing cavitation for extended periods.
One can readily test the function of an ultrasonic cleaner using a process called the aluminum foil test. First, cut a piece of lightweight foil about an inch shorter than the length of the chamber. The foil should be about an inch longer than the depth of the chamber. Place the foil sheet as vertically as possible into a filled chamber without touching any sides. The bottom of the foil should be at least an inch above the floor of the unit. Operate the unit for 30 seconds. Remove the foil and observe for small indentations (pebbling) or even holes in or on the foil. The pebbling should be distributed fairly evenly over the surface of the foil. If there are areas greater than a half-inch without pebbling, the unit may need repair. The manufacturer of specific units may have aluminum foil tests similar to the one just described. In such cases, users should follow those directions.2,5,6

Instrument Washers

Another method of mechanical instrument cleaning is an in-strument washer (sometimes called “a washer-disinfector”). These units have been used in hospitals and larger clinics, and have become available to dental offices.
Washers clean instruments with hot water-detergent sprays followed by high-pressure spray rinses. Washers should be manufactured specifically for use on medical/dental instruments. Those designed for household applications should not be used.
Washers tend to be large and usually can accommodate many instrument cassettes (and loose instruments). A normal cleaning cycle contains multiple episodes of washing and rinsing, often taking as much as an hour to complete. Operation of washers, including selection of cleaning
solutions, is usually well-described by the manufacturers.

Manual Scrubbing

Table 4. Recommendations for Manual Scrubbing.*

•Always wear personal protective equipment, such as heavy duty utility gloves, masks, protective eyewear, and a gown.
•Proceed slowly and carefully; scrubbing can lead to cuts and puncture wounds.
•Position a shallow pan (so that the instruments can always be seen) containing a warm detergent solution in the bottom of a sink.
•Use a long-handled brush to help keep the scrubbing hand as far away as possible from sharp instruments.
•Place a maximum of 5 or 6 instruments in the pan and brush thoroughly while the instruments are submerged to avoid spattering.
•Rinse the instruments well, but avoid spattering.
•Rinse the cleaning brushes well after use and make sure they are allowed to dry.

*Modified From References 2 and 5.

Scrubbing instruments by hand is a traditional method of cleaning and is a relatively effective method for removing debris (Table 4). However, scrubbing is dangerous and is not as effective as mechanical methods of cleaning.
In cases of very adherent materials, handscrubbing may be required to clean some instruments properly. Routine manual scrubbing of all instruments prior to sterilization, however, cannot be recommended. Handscrubbing requires direct contact with contaminated instruments, thus increasing the chances of occupational exposures, even while wearing utility gloves. Today, mechanical cleaners are very effective, thus there is no need to scrub instruments manually prior to placement in an ultrasonic cleaner or instrument washer.2,3,5 Also, staff can perform other instrument recycling tasks while ultrasonic or machine cleaning is being performed.
After cleaning, instruments should look clean (free of debris). However, they must be considered as still being microbially contaminated (nonsterile). This means that personal protective equipment must be worn when handling these items. Exposure to nonsterile (albeit clean) instruments either through mucous membrane or percutaneous accident is a serious matter. Dental offices must prepare a formal, written policy concerning postexposure procedures. All office staff members must be knowledgeable as to what constitutes an exposure and what specific steps must be followed in case of an accident.2


After cleaning, instruments and instrument cassettes should be rinsed well. Some cleaning units (eg, instrument washing machines) have automatic rinsing cycles. After rinsing, instruments and cassettes should be allowed to drain and ideally to dry completely. Shaking the instruments and cassettes can accelerate this process. However, care must be taken so the instruments are not damaged. Drying instruments by hand using some type of toweling materials must be done carefully. Some instruments (eg, hinged types) require lubrication in order to function properly.
Even though the instruments have been cleaned, they are not sterile. They must be handled using appropriate personal protective equipment. This would include utility gloves, protective eyewear, and gowns.
The physical integrity of the instruments can now be determined. Damaged items can be removed and replaced. Carbon steel is susceptible to rusting and dulling when processed in a steam autoclave. Carbon steel is common in dental burs, on the cutting/scraping edges of some instruments (eg, orthodontic pliers, scalers, and hatchets), and the grasping surfaces of forceps.
Rust-inhibiting solutions (eg, those containing sodium nitrite) can be sprayed on instruments prior to processing in a steam autoclave. Such solutions can also be used as instrument dips (“milks”). The usual result is a reduction in instrument rusting. An alternative to using a rust inhibitor would be to dry the cleaned instruments carefully and process them either in a dry-heat oven or an unsaturated chemical vapor sterilizer.1-5


The goal of sterilization is more than just sterilizing instruments between patients; it is delivering sterile instruments chairside every time they are to be used. Proper cleaning is important, but so is maintaining sterility of instruments after they have been processed through the sterilizer. Packaging instruments before processing will help keep them from being contaminated while being stored or when they are transported chairside for use. Unpackaged instruments have no practical shelf-life. Instruments processed without protective packaging can be readily contaminated after processing.2
Packaging is not only protective, but also serves as an organizational tool. Packaging places instruments into functional sets or groupings. Chemical monitors can also be incorporated into packaging materials. Also, biological monitors are easily placed and held within pouches, bags, trays, or cassettes.2

Table 5. Packaging Materials Appropriate for Varying Types of Sterilization.*
Type of Sterilizer
Packaging Materials
Biological Testing
• Standard Cycle
Steam Autoclave

• “Flash” Cycle
Steam Autoclave


• Unsaturated
Chemical Vapor




• Static Air Dry Heat




• Rapid Heat Transfer
Dry Heat—Wrapped
• Rapid Heat Transfer
Dry Heat—Unwrapped

20 to 30 minutes
at 250°F/121°C

3 to 10 minutes
at 273°F/134°C


20 minutes
at 270°F/132°C




60 to 120
at 320°F/160°C



12 minutes
at 375°F/191°C

6 minutes
at 375°F/191°C

• time efficient
• good penetration
• sterilizes aqueous solutions#
• ease of use

• time efficient
• no corrosion
• items dry after processing



• can use closed containers&
• low cost
• items dry after cycle
• no corrosion


• short cycle
• items dry after cycle
• no corrosion

• no closed containers
• can damage plastic and rubber
• carbon steel items corrode
• unwrapped items easily
• hard water leaves deposits

• no closed containers
• can damage plastic and rubber
• must use special solution
• predry instruments
• adequate ventilation required
• cannot sterilize liquids
• cloth wraps may absorb chemicals
• unwrapped items quickly
contaminated after processing

• longer cycle
• can damage plastic and rubber
• must use special solution
• predry instruments
• do not open door during cycle
• cannot sterilize liquids
• unwrapped items quickly
contaminated after processing

• damage to some plastic and rubber
• predry instruments
• do not open door during cycle
• cannot sterilize liquids
• unwrapped items quickly
contaminated after processing

• paper wrap
• nylon “plastic” tubing
• paper/plastic pouches
• thin cloth
• wrapped perforated cassettes

• paper wrap
• plastic/paper pouches
• wrapped perforated cassettes




• paper wrap
• appropriate nylon “plastic”
• closed containers&
• aluminum foil@
• wrapped perforated cassettes


• paper wrap
• appropriate nylon “plastic” tubing
• closed containers&
• aluminum foil@
• wrapped perforated cassettes

strips or vials






Bacillus atropaeus
strips or vials




Bacillus atropaeus
strips or vials

* Modified From References 1 to 6.
** Conditions do not include warm-up or cool-down time; use spore testing to ensure sterilization.
# Best to purchase sterile irrigating fluids for clinical use.
& Processing in closed containers should be checked by spore testing.
@ Aluminum foil tears and rips easily.

Only packaging materials that have been designed for use in sterilizers should be used. Packaging is considered to be a medical device and thus is regulated by the Food and Drug Administration for effectiveness and efficiency. Also, packaging must be appropriate for the type of sterilizer used (Table 5). Improper packaging may retard sterilization, be destroyed during processing, or even release toxic chemicals with the application of heat.
One form of packaging that is becoming increasingly popular is the instrument cassette. Cassettes reduce the direct handling of contaminated instruments and keep instruments together during the entire sterilization process (cleaning, rinsing, drying, and wrapping). Cassettes easily fit into instrument washers, which often are large and can accommodate 5 to 10 in a single cycle. Also, after sterilization, cassettes are easy to store by stacking. Cassettes can also be run through ultrasonic cleaners. However, the proper sized units must be used. Cassettes are made of a variety of materials (stainless steel, aluminum, and plastic/resin) and can withstand steam, chemical vapor, and dry heat sterilization.2


The Organization for Safety and Asepsis Procedures (OSAP) is dentistry’s resource for infection control and safety. OSAP has recently published a book on the CDC guidelines—From Policy to Practice: OSAP’s Guide to the Guide-lines. The book is designed to support the efforts of dental practices to understand better the recommendations and to identify effective and efficient methods for compliance, including preparation of instruments for sterilization. Order information is available at or by calling (410) 571-0003.


1. Kohn WG, Collins AS, Cleveland JL, et al; Centers for Disease Control and Prevention. Guidelines for infection control in dental health-care settings, 2003. MMWR. 2003;52(RR-17):1-61.
2. Miller CH, Palenik CJ. Infection Control and Management of Hazardous Materials for the Dental Team. 3rd ed. St Louis, Mo: Elsevier Mosby; 2005:191-250.
3. Organization for Safety and Aseptic Procedures. From Policy to Practice: OSAP’s Guide to the Guidelines. Annapolis, Md: OSAP; 2004:45-62.
4. Spaulding EH. Chemical disinfection of medical and surgical materials. In: Lawrence CA, Block SS. Disinfection, Sterilization and Preservation. Philadelphia, Pa: Lea & Febiger; 1968:517-531.
5. Palenik CJ. Dental instrument sterilization: a six-step process. J Contemp Dent Pract. 2001;2:84-96.
6. Jorgensen G, Palenik CJ. Instrument sterilization. Dent Equip & Materials. 2004;9:69-71.

Ms. Jorgensen has been employed as an orthodontic assistant, a general chairside assistant, and a trainer for a large group practice. Currently, she is a full-time, clinical procedures, dental assisting instructor at Portland Community College in Portland, Ore. She is an approved speaker on bloodborne pathogens for the National Association of Dental Laboratories (NADL) and is a member of The Dental Assisting National Board, Infection Control Exam (ICE) test construction committee. She can be reached at (503) 977-4036 or

Dr. Palenik has held over the last 25 years a number of academic and administrative positions at Indiana University School of Dentistry. These include professor of oral microbiology, director of human health and safety, director of central sterilization services, and chairman of infection control and hazardous materials management committees. Currently he is director of infection control research and services. Dr. Palenik has published 125 articles, more than 290 monographs, 3 books, and 7 book chapters, the majority of which involve infection control and human safety and health. Also, he has provided more than 100 continuing education courses throughout the United States and 8 foreign countries. All questions should be directed to OSAP at