Sterilization, Disinfection, and Asepsis in Dentistry

Sterilization, Disinfection, and Asepsis in Dentistry

Chris H. Miller

Charles John Palenik


The practice of dentistry spans a wide variety of oral treatments, ranging from the simple polishing of a restoration (filling) to complex and extensive surgery of the osseous and soft orofacial tissues. Standard procedures of sterilization, disinfection, and asepsis must be applied to all types of dental care to reduce the chances of cross-contamination that may lead to serious infectious diseases. The main source of potential pathogenic microbes in dental facilities is the patients’ mouths. Cross-contamination is the spread of microorganisms from one person to another, and there are three main pathways by which this may occur in dentistry: (1) patient to dental personnel, (2) dental personnel to patient, and (3) patient to patient.1 These pathways involve one or more of the four major modes by which microorganisms may be shared between individuals: (1) direct contact (touching oral surfaces and fluids), (2) droplet infection (airborne contamination with larger droplets of aerosols or spatter of oral and respiratory fluids), (3) indirect contact (contact with contaminated instruments, needles, environmental surfaces or hands), (4) airborne (spread of smaller particles of respiratory fluids such as droplet nuclei through the air). In the dental setting, microbes can enter the body through (1) needlesticks and instrument punctures and cuts; (2) invisible breaks or cuts in the skin; (3) mucous membranes of the mouth, nose, eyes; (4) through open lesions; (5) inhalation; and (6) ingestion. Thus, the pathways for cross-contamination in dentistry involve numerous possible combinations of modes of microbe spread and entrance into the body, all of which must be addressed in a dental infection prevention program.

Cross-contamination from patient to the dental team mainly involves microorganisms present in the patient’s mouth in saliva, blood, gingival crevice fluid, plaque, subgingival debris, or open lesions. The dental team may be exposed to these microbes through all three routes of spread by directly touching any oral surface; through dental aerosols and body fluid spatter; and by contact with previously contaminated instruments, surfaces, and supplies. In the absence of adequate protective measures, the dental team is exposed to the risk of infection by oral microorganisms and blood-borne pathogens present in the patients’ mouths. For example, the incidence of hepatitis B among dentists (before the hepatitis B vaccine became available) was approximately two to six times greater than that of the general population.2 Similar increases were noted among other health care professionals who also had frequent exposures to human blood and body fluids that may harbor the hepatitis B virus (HBV).

The risk of exposure to blood-borne and other pathogens for all health care workers (HCWs) and patients and the need for prevention have been recognized by the Centers for Disease Control and Prevention (CDC)3 and by professional health care organizations, including the American Dental Association (ADA)4 and the Organization for Safety and Asepsis Procedures (OSAP).5 In 1991, the Occupational Safety and Health Administration (OSHA) of the US Department of Labor promulgated the blood-borne pathogens standard that requires employers to protect employees from exposure to human body fluids such as blood and saliva. Similar best practices and regulations are applicable internationally. Guidelines and specific local, state, and federal regulations now exist requiring all health care facilities to practice specific sterilization, disinfection, cleaning, and aseptic techniques.

Cross-contamination from a member of the dental team to the patient is a relatively rare event in dentistry that might involve the hands or respiratory fluids of dental personnel. This pathway of disease spread has been documented with case reports of dentist-to-patient transmission of hepatitis B.2 Because these carrier dentists did
not routinely wear gloves during care of the patient, it is assumed that the blood-borne virus periodically contaminated their hands as a result of blood or serum leaking through small cuts or abrasions. The virus was then apparently transferred to patients through a break in their oral mucosa during intraoral care. Instances of apparent occupational spread of the human immunodeficiency virus (HIV) from an infected dentist6 and physician7 to patients have been reported.

Cross-contamination from one patient to another patient may occur by indirect routes through contaminated instruments, surfaces, equipment, or the hands of dental personnel. This pathway, involving improperly washed hands of a dental hygienist, has been documented in the spread of herpes simplex virus from a herpes labialis lesion of one patient to the mouths of several other patients, resulting in herpes gingivostomatitis.8 In another incident, the CDC confirmed that hepatitis B was spread from one patient to another on the same day in 2001 in an oral surgery practice.9 The source patient was an asymptomatic carrier of the HBV and did not tell anyone in the office she was a carrier. After, she has some teeth extracted the same oral surgeon, and staff extracted seven teeth from another patient (a 61-year-old female) who later developed hepatitis B. Molecular epidemiology techniques determined that the same virus caused hepatitis B in both women. Fourteen of 15 employees in the practice showed evidence of hepatitis B vaccination, and none had a history of the disease. Several of the patients seen after the source patient that week tested positive for hepatitis B immunity. Although the transmission was clearly documented, no clear-cut mode of viral spread was identified. The spread was likely limited to one patient due to the high incidence of hepatitis B immunity in the staff and several patients.

Two other routes of microbe spread involving dentistry are (1) dental office to community (eg, improper containment of contaminated medical waste during transport or sending a contaminated dental impression to a dental laboratory) and (2) community to dental office (eg, contaminated municipal water being used in patient care). A report from England in 1987 describes how two cancer patients acquired oral infections with Pseudomonas aeruginosa from dental unit water.10 In 2015, 20 children ages 3 to 11 who received pulpotomies (removal of tooth pulps) in a pediatric dental practice in Georgia, developed oral infections with Mycobacterium abscessus.11 All required hospitalization with granulomatous swellings of the face or neck. M abscessus (an opportunistic microbe commonly present in domestic water supplies) was isolated from the water exiting all seven dental units in the practice and the isolates were indistinguishable from those isolated from the children. The water samples from the dental units had a total microbial count averaging 93,333 colony-forming units (CFUs) per milliliter well above the CDC-recommended maximum of 500 CFUs/mL (the drinking water standard indicated by the US Environmental Protection Agency [EPA]). One CFU is considered as one or a small number of bacterial cells.

The two main approaches to control cross-contamination involve reducing the dose of microorganisms that might be shared between patients and the dental team and increasing the resistance of the dental team through immunization against specific diseases. The infection control procedures in these approaches can be categorized into the eight major areas discussed in this chapter. These are (1) personal protective equipment (PPE), (2) reusable instrument processing, (3) surface and equipment asepsis, (4) aseptic techniques, (5) laboratory asepsis, (6) radiographic asepsis, (7) safe handling of dental waste, and (8) immunization.


Prevention of Contamination

The three basic steps in the development of an infectious disease are (1) contamination (a portion of the body is exposed to microorganisms), (2) infection (the microorganisms survive and grow on or in the body), and (3) disease (growth of the microorganisms causes damage to our body).12

Preventing or reducing contamination interferes with the initial step in the development of an infectious disease. It is always best to prevent contamination (when possible) than to rely totally on the body’s resistance to a given disease agent. One of the important approaches in attempts to accomplish this is the use of approved PPE, such as gloves, protective eyewear, masks, face shields, and protective clothing, to prevent or reduce exposure to potentially infectious materials. Many blood-borne pathogens prevention standards indicate that PPE is to be provided by an employer to any employee who may have potential for exposure to human body fluids at work. Also, the employer must maintain, clean, launder, and properly dispose of soiled PPE and provide alternatives (eg, latex-free gloves) when necessary (eg, Occupational Safety and Health Administration, US Department of Labor13).


Gloves not only protect the hands of dental personnel from direct or indirect contact with patients’ saliva and blood but also protect the patient from contamination with microorganisms on the hands of dental personnel.

Gloves must be worn by the dental team where there is the potential to have direct contact with blood, saliva, other potentially infectious body fluids, mucous
membranes, and nonintact skin, and when handling items or surfaces soiled with blood or other potentially infectious materials (OPIM).3,13 Disposable gloves must be replaced when torn or punctured or when their ability to function as a barrier is compromised. A fresh pair of gloves is to be used for each patient. Thus, gloves must not be washed or disinfected for reuse on another patient. In restricted conditions, heavy utility gloves may be cleaned and disinfected for reuse if the integrity of the glove is not compromised, but they should be discarded if they are cracked, peeling, discolored, torn, punctured, or exhibit other signs of deterioration.

Because the use of powder on medical gloves presents numerous risks to patients and HCWs, including inflammation, granulomas, and respiratory allergic reactions, the US Food and Drug Administration (FDA) has banned the sale of powdered surgeon’s gloves and powdered examination gloves.14 This rule became effective January 2017 and includes powdered latex and nonlatex gloves.

Sterile surgeon’s gloves are to be worn when performing oral surgical procedures.3 The sterile latex surgeon’s gloves offer the best fit, with half-sizes and right and left thumb orientation. Nonsterile latex, nitrile, and vinyl examination gloves are adequate for nonsurgical intraoral procedures. Heavy utility gloves should be worn during operatory cleanup when disinfecting surfaces, handling other chemicals, and handling contaminated instruments (eg, during cleaning). Heat-resistant gloves should be worn when working with heat-based sterilizers.

Reactions to Gloves

One study of dental and other HCWs reported that 19% had some type of reaction to gloving and 3.8% reported having a latex allergy.15 Another study involving testing of dental workers for latex allergy indicated that 6.2% were positive.16 Reports for the general population range from 0.12% to 6%.17,18

There are three types of reactions to gloves: irritant contact dermatitis, allergic contact dermatitis, and latex allergy.19 Irritant contact dermatitis is the most common and results from a nonimmunologic irritation of the skin from chemicals in the gloves or powder. Allergic contact dermatitis is an immunologic reaction to one of the many nonlatex chemicals in gloves. This reaction is the same in those sensitive to the poison ivy plant. Latex allergy is an immunoglobulin E (IgE)-mediated immunologic response to the protein allergens in latex. Latex allergy may not only result in skin reactions of hives, redness, burning, or itching but may also involve respiratory symptoms with difficulty breathing and, more rarely, anaphylactic shock. The protein allergens involved are not only present in the latex glove material but are also absorbed into cornstarch powder from the glove. During donning and removing of powdered gloves, the powder becomes airborne and can be widely distributed through a health care facility. If inhaled, it may cause respiratory symptoms in the allergic and possibly enhance sensitization to latex proteins in others. Thus, as mentioned earlier, FDA has instituted a ban on powdered gloves to help reduce these potential reactions.

In the United States, both sterile surgeon’s and nonsterile patient examination gloves are medical devices regulated by the FDA.20 Accepted quality levels with respect to inherent perforations are actually 4.0% and 2.5% (maximum percentage of gloves with defects) for examination and sterile surgeon’s gloves, respectively.

Gloving and Personal Protection

Small cuts and abrasions on the hands and fingers may serve as a route through which pathogenic microorganisms enter the body. A study of 26 second-semester senior dental students who did not routinely wear gloves at chairside revealed a total of 101 areas of trauma (cuts and abrasions) on their hands.21 Twelve percent of these areas became painful on swabbing with alcohol, suggesting an open epidermis. Of interest was that a few additional alcohol-induced painful responses were detected in visually intact areas between the fingernail and peripheral epidermis, including the subungual area. This indicates that even a close visual inspection of the hands may not detect areas that could serve as a portal of entry for microorganisms into the body.

Wearing gloves provides a physical barrier over such portals of entry for pathogenic organisms from the saliva or blood of dental patients. The lack of routine gloving may have been a major contributing factor to the once alarmingly high occurrence of hepatitis B among dental personnel.2 Like hepatitis B, herpetic whitlow (herpes simplex infection of the hands) is also an occupational disease of dental personnel.22,23,24 Gloving prevents the occurrence of herpes simplex infections on the fingers acquired through direct contact with lesions or contaminated saliva.

Another personal protection aspect of wearing gloves involves providing a barrier against contact with contaminated inanimate objects or with irritating chemicals used in the office. For example, office staff responsible for post-treatment operatory cleanup or use of disinfecting or sterilizing solutions should wear heavy, chemical-resistant utility gloves. This reduces chances of accidental instrument puncture or direct contact with agents that may cause skin irritations or allergic reactions.

Hand Hygiene and Gloving for Protection of Patients

Besides offering personal protection to members of the dental team, gloves also provide an important measure of protection to patients. Hands have long been known to be one of the most important sources of nosocomial infection, and hand hygiene is generally considered the single most
important procedure for preventing such infections.25,26,27 There are two approaches to hand hygiene. Hand washing with plain or antimicrobial soap suspends dirt and microbes that are removed by thorough rising with water. When hands are not visibly soiled an alcohol hand rub can be used.3,28 Hand hygiene facilities are recommended to include liquid soaps in no-touch dispensers, no-touch faucets, and disposable paper towels.

Although proper hand hygiene can remove/kill the transient skin flora, which is the most important in disease spread, no hand washing procedure sterilizes the skin, not even properly performed surgical scrubs with antiseptic agents.29,30 Thus, sterile gloving is used to prevent transmission of organisms not removed by hand washing. Surgical hand scrubbing is a standard procedure, but hand hygiene should also be performed before routine nonsterile gloving to reduce the number of skin microbes that can multiply under the gloves and cause skin irritation. Hands also need to be washed after removing gloves to remove perspiration, materials that may have come through glove defects/punctures/tears, and microbes that may have multiplied beneath the gloves. Recognized antiseptic hand washing agents that have residual activity on the skin (long-lasting effect) include biocides such as chlorhexidine gluconate or parachlorometaxylenol.31

Ungloved hands of dental personnel become contaminated with potentially infectious materials from patients’ mouths. Blood impaction under the fingernails does occur, and this material may be retained for several days after treating a patient.21 This occult (concealed) blood could serve as a source of infection for subsequent patients through a leaching process. Routine gloving prevents blood or saliva impaction in those parts of the hands that are difficult to clean, such as under the fingernail or areas of dermatitis.

Microorganisms that might be present in the blood periodically contaminate the hands and fingers as a result of blood or serum leaking through small cuts or abrasions. This process may be enhanced if the site of the cut or abrasion is kept moist, as when performing barehanded dentistry. This seems to be a likely route of HBV and other pathogen transmission from carrier dentists to their patients.

The eight reported instances of HBV transmission from dental personnel to patients resulted in numerous cases of the disease.2,32,33 Most of the implicated dental personnel acquired subclinical infections and became chronic carriers of the virus; none had worn gloves, and some had skin lesions or dermatitis on their hands. Although intact gloves would protect patients from this route of disease transmission, other routes of disease transmission from carrier dental personnel to patients clearly do exist.

The report of an outbreak of herpes simplex virus type I gingivostomatitis in a dental hygiene practice also offers a vivid line of evidence for the role of contaminated hands in disease transmission.8 A hygienist with dermatitis on her ungloved hands contracted a herpes infection on her hands after treating a patient with active herpes labialis. Before vesicles developed in the areas of chronic dermatitis on her hands, she unknowingly transmitted the virus to other patients, resulting in gingivostomatitis in 20 of 46 patients treated over the next few days with ungloved hands. When the herpes vesicles appeared on her hands she began to wear gloves, and this prevented further spread of the virus.

Surgical Masks

Surgical masks covering the mouth and nose were originally developed for the protection of the patient from respiratory organisms of health care personnel. This is an important reason to use surgical masks in dentistry, but equally important in dentistry is that surgical masks help protect the dental staff from the patient’s microorganisms. They reduce the number of infectious particles that may enter the mouth or nose while the staff person performs techniques that generate dental spatter (the larger particles of oral fluids). Respirators (eg, N95 respirator) are needed to protect against inhalation of the smaller aerosol-type particle that cause airborne infections (eg, the causative agents of tuberculosis, measles, and severe acute respiratory syndrome [SARS]). Patients with many high-risk infections may need to be treated in specialized facilities. Respirators are not part of the normal PPE needed in dental offices. Masks made of glass fiber or synthetic fiber mats are more efficient in filtering bacteria than gauze or paper masks.34

For FDA clearance, mask manufacturers are required to submit performance data that includes fluid resistance, particulate filtration efficiency, bacterial filtration efficiency, differential pressure (degree to which the passage of air is impeded through the mask material and flammability).35 Surgical masks are available that claim at least a 99% bacterial filtration efficiency against particles that are 3 to 5 µm in diameter, as determined by the modified Greene and Vesley method.36 The filterability of any mask is destroyed if the mask does not fit well, however; this permits excessive contaminated air to leak around the edges of the mask.37 A key feature of a mask is that it must be comfortable to wear, and the mask should fit snugly over the bridge of the nose to reduce fogging of the protective eyewear from exhaled air.

Masks are single-use disposable items and should not be reused with another patient and should be changed when wet.

Protective Eyewear

Protective eyewear can reduce the chance of physical and microbial injury to the eyes.38 Microorganisms may contact the eye by aerosol spray or droplet deposition.
Tooth or restorative material expelled from the mouth also may be contaminated with potentially pathogenic microorganisms.

Usually, the eye eliminates transient infections, but if the contamination is heavy, if a highly virulent organism is involved, or if physical damage accompanies the contamination, serious disease may result. Of particular concern is a herpesvirus infection of the eye that may recur and produce increasing ocular damage. Hepatitis B infection may also develop after initial contamination of the eye with the virus.39,40

Review of a report of 10 cases of ocular injuries sustained in dental offices demonstrates a compelling need for protective eyewear for both patients and dental personnel.41 The cases included impalement of a patient’s eye by an excavator, corneal abrasions in patients from an exploding anesthetic carpule or a piece of acrylic denture tooth, subconjunctival hemorrhage after a dentist hit a patient’s eye with his or her thumb, corneal abrasions and hemorrhage in dental assistants’ eyes by projectiles emitted from patients’ mouths during operative procedures, and damage to an assistant after splashing varnish into his or her eyes while working in the laboratory.

Protective eyewear should be worn at chairside, in the laboratory, in darkrooms, in the use of chemical disinfectants, and in the sterilization area when mixing and using chemicals. The OSHA blood-borne pathogens standard as well as the CDC require protective eyewear to have side shields.3,13

Face Shields

Plastic face shields have become more popular for use at chairside during procedures that generate salivary droplets. Face shields protect the skin, eyes, and mucous membranes of the mouth and nose from potentially infectious droplets but offer little protection from inhalation of aerosols. Thus, masks need to be worn beneath face shields.

Protective Clothing

Dental procedures generate salivary droplets, particularly during the use of handpieces, ultrasonic scalers, and air/water syringes. Protective clothing should be worn to protect underlying work clothes, street clothes, undergarments, and skin.3,13 Protective clothing worn at work should be changed before leaving for home, and this clothing is not to be taken home for laundering. Disposable gowns are available for use at chairside or reusable protective clothing may be worn. A laundry service may be used for reusable clothing or laundering may be performed in the office with a washer and dryer. As a related precaution, work shoes should be kept at work or at least out of reach of small children at home because at work the shoes are constantly in contact with salivary spatter that rapidly settles to the floor.

Donning and Doffing PPE

The CDC recommends the following sequence for putting on and removing PPE to avoid unnecessary spread of contaminants.42 For donning (1) protective clothing, (2) mask, (3) protective eyewear, and (4) gloves. For doffing: (1) gloves, (2) protective eyewear, and (3) gown, and (4) mask.


The goal of instrument reprocessing is to prevent transfer of infectious agents to patients from contaminated dental hand instruments and handpieces and, at the same time, to protect the staff who must handle these items. The steps in this process involve instrument transport, presoaking, cleaning, packaging, sterilization, monitoring, storage, and distribution, as summarized in Table 51.1. Heavy utility gloves, protective clothing, a mask, and protective eyeglasses should be worn during the cleaning and disinfection of instrument processing to help protect against sharps injuries, direct contact with contaminated surfaces, and splashing of chemicals or contaminated fluids. Following thermal disinfection, devices are considered safe for handling, but critical and semicritical devices are required to be sterilized prior to patient use. Processing dental handpieces is described at the end of this section.

The central processing area should be divided physically or, at a minimum spatially, into distinct areas for (1) receiving, cleaning, and decontamination; (2) preparation and packaging; (3) sterilization; and (4) storage.3 This helps prevent the intermingling of contaminated with sterile instruments. The responsibility for reprocessing dental instruments needs to be assigned to personnel with the appropriate training, and the manufacturers’ instructions for reprocessing instruments/equipment are to be readily available, ideally in or near the reprocessing area.3

Instrument Transport

Contaminated instruments should be transported to the processing area in a manner that minimizes the risk of exposure to people and the environment. This includes the use of covered, rigid, leak-proof containers or carts that are appropriately marked with biohazard symbols. The containers used for these sharp contaminated instruments must not permit a person to reach into them without being able to see the instruments. It is considered best practice to not allow soil to dry on devices prior to cleaning, but if this occurs, then instrument presoaking is recommended prior to cleaning (see in the following text). This may be achieved such as cleaning solution,
transportation gel or foam, or water. The containers or carts used during transport (where applicable) need to be decontaminated (cleaning and disinfected with an environmental surface disinfectant) between each use and should be indicated as “contaminated” or “sterile.”

TABLE 51.1 Critical dental instrument reprocessing

1. Transport

Separate and dispose all single-use devices and materials. Transport contaminated reusable instruments to a defined decontamination area so that exposure of staff and the environment are minimized. It is best practice not to allow soil to dry on devices prior to cleaning.

2. Presoak and rinse

If used (eg, if soil has dried on devices), submerge in pH neutral to mild alkaline detergent in accordance with manufacturer’s instructions.

3. Clean, rinse, and dry

Carefully remove gross soil using a cleaning solution in compliance to manufacturer’s instructions, ensuring cleaning of any restricted access device features (eg, brushing of lumens, articulating moving parts). Ultrasonic cleaning systems may be used and devices may also be cleaned and/or disinfected in a washer or washer-disinfector.

4. Inspection and maintenance

Dry devices using a drying over or lint-free materials.

Inspect devices to ensure they are clean and undamaged. Lubricate any devices in accordance to manufacturer’s instructions.

5. Package

Include any applicable biological or chemical indicators to test for steam sterilization. Package in an approved sterilization wrap, bags, pouches, or rigid containters.

6. Sterilize and monitor

Steam sterilization is preferred, unless the devices are heat sensitive. Ensure to check all indicators used to test the sterilization process, including mechanical gauges or monitors (eg, temperature and pressure). Ensure packaging is dry prior to storage. Record results of monitoring.

7. Store or distribute

Sterilized cassettes or packages are ready for storage or use at chairside. Store in a dry place in a manner that does not allow for accidental damage of the packaging material.

Instrument Presoaking

If saliva and blood on instruments are allowed to dry, the cleaning process becomes more difficult. This occurrence is not uncommon because seldom, is it possible in a busy practice to clean instruments immediately after use. Thus, contaminated instruments can be presoaked in a pH neutral to mild alkaline detergent solution (which may or may not include enzymes) until time is available for full cleaning. The manufacturer’s instructions for use (IFU) need to be followed, including not only those provided with the instruments but also the cleaning chemistries or other equipment used for reprocessing. This process also is referred to as instrument holding and is most effective when it begins immediately after the patient is dismissed. This step in instrument processing prevents drying of blood and saliva and actually begins the cleaning process. Some enzyme- or alkaline-based detergents designed to break down proteins may facilitate this process, but such detergents should be labeled for use on medical or dental instrumentation. The use of environmental disinfectants (eg, bleach solutions), saline or antiseptic formulations (eg, chlorhexidine- or iodine-based soaps) are not appropriate and can even damage devices. Instruments should not be presoaked for more than a few hours, for the longer the instruments remain wet, the greater the chances for corrosion of stainless steel and other metals, as well as the risk of bacterial growth.

If ultrasonic cleaning is used, gross contamination should be manually removed, and the contaminated instruments then placed in the ultrasonic cleaning basket or the cassettes in a cassette rack, and the basket or rack placed in the presoak solution. This reduces the direct handling of the contaminated instruments. If the clinician uses “plastic-type” instrument cassettes that retain the instruments during use at chairside and during ultrasonic cleaning, the manufacturer of the cassettes should be consulted as to which type of presoak solution will not damage the cassette. After the presoak period, the instruments should be carefully rinsed under running tap water with minimal splashing.

Instrument Cleaning

One approach to instrument cleaning is hand washing, which includes manual cleaning of exposed and restricted access parts of the devices. It is particularly important to ensure that any restricted access device features are manually cleaned (eg, brushing of lumens, articulating moving parts). However, hand scrubbing is directly contrary to one of the dogmas of infection prevention—reduce direct contact with contaminated surfaces as much as possible. Hand scrubbing increases such contact and involves the added danger of handling sharp and pointed objects.43
If an item must be hand scrubbed, then heavy-duty utility gloves, mask, protective eyewear, and clinic attire must be worn and spattering must be avoided by scrubbing the item while it is submerged under water using a long-handled brush.

Approved automated cleaning (or cleaning-disinfection) equipment should also be considered.3 Ultrasonic cleaning or using an instrument washer or washer/disinfector is effective and generally much safer than hand scrubbing. It is, however, important to understand the limitations of such equipment depending on their IFU. For example, gross soiling should be removed prior to ultrasonics and lumens (or other device restricted access features) may not be adequately cleaning by such equipment. Several brands of ultrasonic cleaners are available in a variety of sizes.1 A metal cleaning basket or cassette rack and a lid over the tank always should be used, and the IFU followed for optimal results. An ultrasonic cleaning detergent solution should be used that is specifically recommended for use with medical/dental instruments in sonic cleaners.

For ultrasonic cleaning, the rinsed instruments contained in the cleaning basket are submerged into the cleaning solution. The basket suspends the instrument in the tank. Loose instruments should not be placed on the bottom of the tank because this usually results in less effective cleaning. Place the lid on the bath and operate the unit in accordance with manufacturer-validated instructions (eg, for 6 to 10 min or until no visible debris remains). Note that the efficiency of ultrasonic cleaning will depend on the equipment device, ultrasonic energy, and cleaning detergent solution. If the instruments are to be in cassettes, it may be recommended to increase cleaning time to 15 minutes.44 Cleaning time in these cases is not time lost because other tasks can be performed during this process. After cleaning, thoroughly rinse the instruments while they are still in the cleaning basket or cassette rack to remove dislodged debris, microorganisms, and residual cleaning solution.

Instrument washers that automatically clean and rinse instruments and cassettes are becoming more popular in group practices and large clinics. They operate somewhat like a home dishwasher but are much more sophisticated and are specifically designed for processing medical/dental instruments. Washer-disinfectors may also be used and are recommended to be compliant to International Organization for Standardization (ISO) 15883-1.45 These typically have separate phases to validated cycles to include cleaning, thermal disinfection (to render devices safe for handling), and drying. It is important that such equipment is calibrated and maintained in accordance with manufacturer’s instructions.

Cleaned instruments should be visually inspected for cleanliness and carefully dried before packaging and sterilization.3 If nonstainless steel instruments are to be sterilized in a steam autoclave, a rust inhibitor (dip or spray) such as sodium nitrite should only be applied to the instruments after cleaning if recommended by the device manufacturer. Other instrument maintenance recommendations may be appropriate at this time, such as handpiece lubrication. Only approved lubricants should be used that are compatible with subsequent steam sterilization.

Ultrasonic cleaners, instrument washers, and washer-disinfectors may be excellent for cleaning but are not sterilizers. Thus, the cleaned and rinsed instruments (but not thermally disinfected) are still considered biohazardous and must be handled only while wearing protective gloves. The used cleaning solution in ultrasonic cleaning tanks is also contaminated.46 Use of the ultrasonic cleaning basket or cassette rack with handles avoids excessive contact with this solution, and rinsing after cleaning reduces this contamination on the instruments. The ultrasonic cleaning solution should be changed periodically, some suggest every use, by someone wearing gloves, protective clothing, eyewear, and a mask. At the end of the day, the ultrasonic cleaner tank should be cleaned, disinfected (eg, using alcohol), rinsed (if appropriate for the disinfectant type), and dried.

Note that the quality of water use during reprocessing can also be an important consideration due to the potential presence of chemical, microorganisms, and other contaminants in water. Tap water, for example, may be suitable for cleaning, but a higher purity of water is generally recommended for final rinsing and, for example, in the generation of steam for sterilization. Guidelines from the Association for the Advancement of Medical Instrumentation (AAMI), such as AAMI TIR34, can provide useful discussions on the impact and safety requirements for water used during device reprocessing.47


Wrapped Instruments

Packaging cleaned instruments in an appropriate microbial barrier material before sterilization will help protect the instruments from recontamination after removal from the sterilizer. The instruments may be packaged in functional sets and then opened when required for patient use at chairside, or they may be packaged individually or in smaller groups and then distributed at chairside on sterile or disposable trays intended for use at chairside.

A variety of packaging materials are available for this purpose including peel pouches of plastic or paper, sterilization wraps (including woven or unwoven materials), and sterile rigid containers. In choosing the appropriate packaging material, they should be designed and labeled for use for the type of sterilization process and used in accordance to the manufacturer’s claims. Packaging materials should be compliant to the appropriate standards, such as ISO 1160748,49 and may need to be cleared for such uses in certain countries (as in the United States by the FDA).3,50 Some types of materials may not be appropriate
in certain cases, such as thin material bags through which pointed instruments may protrude. “See-through” bags and pouches facilitate instrument identification. One type is provided as a clear tubing of different widths on a roll that is cut and heat sealed. These are available for steam or dry-heat sterilization, and self-sealing paper/“plastic” pouches are also available for use in the steam autoclave or chemical gas sterilizers.1 Sterilization paper wrap may be used for dry-heat processes as long as protrusion of sharp instruments is prevented. Each package to be sterilized should be labeled with the sterilizer used, the cycle or load number, and the date of sterilization. Use a writing device that does not run or fade during sterilization, and do not penetrate the packaging material with the writing device. Some permanent markers can be used on the plastic of paper/plastic pouched. Labels can be used on other types of packaging material.

Instruments in Trays or Cassettes

One option in this approach involves using a cassette that retains the instruments at chairside and during ultrasonic cleaning, rinsing, and subsequent sterilization.44 This maintains the instruments in functional sets and minimizes potentially dangerous handling of the contaminated instruments during the cleaning or distribution process. After ultrasonic cleaning and rinsing, sterilizable supply items may be added to the cassette, and the cassette is wrapped, sterilized, and stored or used immediately.

The other option in this approach involves placing the cleaned instruments in one of several types of sterilizable trays.1 Some types of solid metal trays with lids, that are designed and labeled to provide a sterile barrier, need no additional wrapping and can be used in standard dry-heat sterilization. However, their suitability as sterilization containers needs to be confirmed by proper sterilization monitoring using chemical and biological indicators as described later. “Plastic-type” or metal trays for steam or chemical vapor sterilization must have no lids or be perforated to permit penetration of the steam or chemical vapors. These trays, like cassettes, must be wrapped in an appropriate sterile barrier material before sterilization.

The use of sterilizable trays requires sterilizers with adequate chamber size to accommodate the trays. Larger size office sterilizers are available.

Unwrapped Instruments (Special Circumstances Only)

This approach should be used only in special circumstances, such as when one or a very small number of instruments are needed quickly on an emergency basis, and a short-time, high-temperature steam autoclave cycle is to be used. This is sometimes referred to as flash or immediate-use sterilization. This involves sterilizing previously cleaned and unpackaged instruments that will be used immediately after sterilization, if they do not become contaminated with blood or saliva from hands, surfaces, or aerosols before use. An aseptic protocol must be established for handling these instruments after sterilization, during conveyance from sterilizer to chair-side. For example, this might include using sterile tongs to place the instruments in sterile bags for transport. It is recommended that these procedures are only used under emergency situations.

Sterilization Versus Disinfection

Sterilization is defined as a validated process that kills all microorganisms, as verified by demonstrating the kill of highly resistant bacterial spores. Sterilization is the highest level of microbial kill. If a process can be routinely shown to kill bacterial spores, then it is correctly assumed that the process can kill all other microorganisms, yielding sterilization. Disinfection is considered a less lethal form of microbial killing, usually involving the use of heat (eg, hot water) or a liquid disinfectant at room temperature. Disinfection can be achieved at different levels depending on the process or product claims (see chapter 2). Disinfection processes are directed at pathogenic microorganisms and are considered less lethal than sterilization. Unfortunately, the level of killing that does occur with liquid disinfectants in particular cannot be easily verified during actual use. On the other hand, the level of killing that occurs in a heat-based sterilizer can be monitored parametrically (eg, based on temperature, pressure, and time monitoring) and/or the routine use of chemical and biological indicators. Thus, the safest approach to preventing disease transmission by contaminated instruments is to sterilize them rather than disinfecting them.

All items used in the mouth must be cleaned, packaged, and sterilized before they are reused on another patient. For example, the CDC recommendations for infection prevention in dentistry indicate that surgical and other instruments used to penetrate soft tissue or bone and those that do not penetrate soft tissues or bone but contact oral tissues should be heat sterilized routinely between uses using steam under pressure (autoclave), dry heat, or chemical vapor.3,51

The only exceptions are disposable items that are used with only one patient and items that can be covered with a barrier that prevents contamination, such as light-curing devices and some camera lens probes and x-ray sensors. In these latter cases, equipment can be periodically disinfected using an approved environmental disinfectant.

Sterilization Processes

Sterilization equipment should be approved for use and used in accordance with equipment manufacturers requirements.3 In dentistry, the three most commonly used
forms of heat sterilization of instruments in the United States are (1) steam sterilizers (also known as autoclaves), (2) unsaturated chemical vapor sterilizers, and (3) dry heat. A fourth form of sporicidal disinfection in the United States involves submerging items in a liquid sterilant (eg, properly prepared glutaraldehyde or hydrogen peroxide solutions) often for extended contact times (eg, 3-10 h) followed by rinsing to remove toxic residuals; however, this method cannot be verified by spore testing and should be reserved for plastic and other items that are incompatible in the heat systems. Alternative low-temperature gaseous sterilization processes (such as those based on ethylene oxide or hydrogen peroxide gas) may be used as alternatives. The use of ethylene oxide gas sterilizers are reliable methods of low-temperature sterilization that can be verified with spore testing but requires special safety and postprocess aeration time (to remove toxic residuals). This method is primarily used in hospitals, some universities, and industry however, with only minimal use in dental offices. These low-temperature processes are described in more details in other chapters (see chapters 31 and 32).

TABLE 51.2 Comparison of heat-sterilization methods with small office sterilizers


Sterilizing Conditionsa



Spore Testing

Steam autoclave

15-30 min at 121°C (250°F) or 3.5-10 min at 132°C (270°F)

Time efficient Good penetration

Some materials can corrode or be damaged. Items can be wet after normal cycle and require extended drying afterward.

Do not use nonvented, closed containers.

May damage plastic and rubber items Use of hard water may leave deposits (white spotting).

Geobacillus stearothermophilus strips or vented vials

Unsaturated chemical vapor

20 min at 132°C (270°F)

Time efficient Less corrosion risk Items typically dry after cycle.

Must use special solution

Ventilation must be adequate.

Predry instruments.

May damage plastic and rubber items

Do not use closed, nonvented containers.

May not be appropriate for handpiecesb

Devices must be compatible with the heat/chemical process.

Do not use absorptive materials.

G stearothermophilus strips

Dry heat (oven type)

60-120 min at 160°C (320°F)

No corrosion Items dry after cycle. Closed containers may be used.c

May damage plastic and rubber items Predry instruments.

Long cycle time

May not be appropriate for handpiecesb

Bacillus atrophaeus strips

Dry heat (rapid heat transfer)

12 min at 190°C (375°F)

No corrosion Items dry after cycle. Time efficient

May damage plastic and rubber items Predry instruments.

May not be appropriate for handpiecesb

B atrophaeus strips

a These cycle times are representative; they do not include warm-up times, and they may vary with the brand of sterilizer. Some sterilizers will include drying phase, whereas others will not. Follow the sterilizer manufacturer’s directions for using the sterilizer, sterilizing conditions, and confirming kill by spore testing.

b Check with handpiece manufacturer.

c Use spore tests to confirm appropriate kill in closed containers.

Microorganisms are rapidly killed after they come in direct contact with a heat-sterilizing agent (steam, chemical vapor, air) that is at the proper temperature. Thus, time, temperature, and exposure are the minimum three key factors. The actual surfaces of the instruments must be exposed to the agent for the appropriate time, and the sterilizing agent must be at an appropriate temperature. Anything that interferes with exposure or temperature may prevent the sterilization or extend the time required for sterilization.52 This will include trapped air (prevent steam or chemical penetration) or the presence of residual soil (due to inadequate cleaning or rinsing). An example is that device packages need to be loaded in sterilizers loosely and in accordance with device manufacturer’s instructions so as not to impede contact with the sterilizing agent.

A comparison of the three heat-sterilization methods appears in Table 51.2. Each of the three methods, when performed properly, yields sterilization. Special care must be taken to follow the sterilizer manufacturer’s IFU. Moreover, the manufacturer’s IFU for the type of
wrapping material to use must be followed, and the sterilizing process should be routinely monitored, as described later.

Steam Autoclave

Steam autoclaves are the most popular sterilizers in dental settings. A variety of models are available and should be approved for use.1 Minimal features to look for are a temperature gauge independent of the pressure, an automatic timer that begins once the sterilizing temperature has been reached, and a print-out that documents the sterilizing conditions. Local recommendations for the use of steam sterilizers in dental facilities have been made such as in the United States by the AAMI ST79:2017,53 and in the United Kingdom by Health Technical Memorandum 01-05:2013.54 There are also local (eg, AAMI,55 American National Standards Institute56) and international standards57 describing the requirements for equipment and sterilization processes, respectively. Follow the manufacturer IFU for proper sterilization. Be sure to dry the packages either during or following sterilization to avoid damage to the packaging material when handling and to avoid wicking, the drawing through of microbes from the outside of paper packaging.

Unsaturated Chemical Vapor Sterilizer

The unsaturated chemical vapor sterilizer is a noncorrosive form of sterilization because of the low level of water present during the cycle. The sterilizing agent is mainly heated alcohol-formaldehyde vapor that is generated from the special solution added to the sterilizer for each cycle. Instruments need to be dry before sterilizing and compatible with the process. This keeps the presence of water at a minimum, so the noncorrosive environment can be maintained. Further information about the unsaturated chemical vapor sterilizer is available.58,59

Dry-Heat Oven

More and more dry-heat ovens are being used in dental offices to sterilize items as alternatives to steam autoclave. Smaller models are available through dental and scientific supply companies. The instruments must be dry before sterilizing. Care should be taken during use of the dryheat sterilizer not to open the door until the entire cycle is completed. Opening the door reduces the chamber temperature and requires that the sterilizing cycle be started again.

An example of a new type of dry-heat sterilizer is called a rapid heat-transfer unit, with claims of sterilization after 12 minutes at a chamber temperature of 190°C (375°F) with wrapped instruments. Further information about dry-heat sterilizers is available (see chapter 28 and AAMI60). There is also an international standard for the requirements for dry-heat sterilization.61

Sterilization Monitoring

Monitoring the sterilization process is one of the few standard quality-assessment procedures available in infection control. The three forms of monitoring can include

  • Mechanical monitoring: observation of read-outs, dials, and/or gauges (monitors sterilizer functioning such as time, temperature, pressure)

  • Biological monitoring: spore-based biological indicator testing, a main guarantee of sterilization

  • Chemical monitoring: color or physical change chemical indicators that monitor exposure to sterilizing agents or conditions

Proper monitoring typically can involve all three forms and includes keeping records of the results.58 At least weekly biological monitoring (spore testing) of the use and functioning of dental office sterilizers is recommended by the CDC.3 Some states in the United States also require that dental sterilizers be spore tested at least weekly. Spore testing should also be performed at certain times in addition to routine testing (Table 51.3). AAMI guidelines recommend that biological monitoring should be performed at least weekly but preferably every day that a sterilizer is used.53

Biological indicators (spore strip or vial) should always be placed inside packages, bags, or trays next to the instruments themselves just before placing the items into the sterilizer. Sterilization monitoring services that function through the mail are available at a few dental schools and from some companies.63 Most of these services can test steam autoclaves, unsaturated chemical vapor sterilizers, dry-heat sterilizers, and ethylene oxide sterilizers. Some also provide infection control newsletters, certificates of participation, and an available contact person to answer questions about infection control. The necessary supplies and instructions are sent, and the processed biological indicators are mailed back to the service for culturing, analysis, and return of a testing report. Although a mail-in spore testing service requires a delay in culturing the biological indicators, a study has shown that immediate and delayed culturing of biological indicators yields comparable results in relation to detection of sterilization failures.64 Alternatively, steam autoclaves can be tested in the office with purchase of spore vials and an appropriate 56°C incubator for culturing. In-office testing of other types of sterilizers is more difficult.58 Modern self-contained and rapid read-out biological indicators can be easily incubated and evaluated on site.

The CDC recommends monitoring each sterilizer load with mechanical and chemical indicators (CIs).3 Mechanical monitoring consists of observing the gauges on the sterilizer and checking the timer to make sure the unit appears to be working properly. The CIs are generally recommended to be placed inside each package to be sterilized. If that internal indicator is not visible from the outside of the package, a second CI is to be placed
on the outside. Chemical monitoring of dental office sterilizers involves use of color change or other indicators (eg, autoclave tape, special markings on bags, strips, and packets). These CIs, which can range in labeling and sensitivity (eg, from class 1 to Class 6 CIs in accordance with ISO 11140-1:2014),62 are available for most types of sterilizers and give immediate indication that the items have at least been exposed to the sterilizing agent or to defined sterilizing conditions.

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May 9, 2021 | Posted by in MICROBIOLOGY | Comments Off on Sterilization, Disinfection, and Asepsis in Dentistry
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