Review of Surface Disinfection Protocols in Dentistry: a 2019 Update

GENERAL DENTISTRY Review of surface disinfection protocols in dentistry: a 2019 update

Mel Mupparapu, DMD/Karaan Raj M. Kothari

Disinfection is a crucial aspect of patient care in dentistry. In most trusted form of clinical sanitization. This article explores the pre-19th century era, natural elements like acids, sulfur, the history as well as the current practice of disinfection in the mercury, and various alkaline metals were valued for their abil- dental profession and further explores the variations in the ity to obliterate pathogens. More recently aerosols, sprays, and use of surface disinfection based on the published literature. disinfectant wipes with more powerful chemicals including The current practice guidelines as recommended by agencies quaternary ammonium compounds and aldehydes have be- like Centers for Disease Control (CDC) were studied and come popular. As aerosols fall out of favor due to their health summarized for this review. (Quintessence Int 2019;50:58–65; and environmental risks, disinfectant wipes are becoming the doi: 10.3290/j.qi.a41337)

Key words: alcohol, Centers for Disease Control, dental chair disinfection, disinfectant wipes, gluteraldehyde, surface disinfection

Dental operatory has three basic classifications for surfaces to the proper care of a mop may increase the likelihood of a that need to be disinfected or sterilized; critical, semi-critical, spread of germs. Therefore the cleaning solution should be and noncritical. Critical objects are defined by the CDC1 as changed on average between every three to four rooms, or in items that “confer a high risk for infection if they are contami- increments of sixty minutes. The other alternative is to use sin- nated with any microorganism.” These objects include surgical gle-use disposable disinfectant wipes with a special holder. implements, dental tools, and ultrasound probes. All items It was observed in studies that the disinfection practices of labeled as critical must be sterilized, most commonly with dentists are not desirable and there is a clear need to educate heat. Heat-sensitive operatories can be treated with a liquid dental practitioners and raise their awareness in order to chemical sterilant which must include specific concentrations improve the safety of patients seeking care at the dental office.2 of disinfectants including glutaraldehyde, phenol solutions, It is known that transmission of infection in a medical setting3 hydrogen peroxide, and peracetic acid. Semi-critical articles1 is often caused by the residue of endogenous flora, or bacteria include machinery that comes in direct contact with either living on a patient’s body. When this endogenous flora encoun- mucous membranes or nonintact skin. Semi-critical objects ters inanimate surfaces and medical or dental machinery that rarely require the use of high-level disinfectants. Noncritical1 is not disinfected properly, it can create a breeding ground for describes any operatory item that encounters intact skin. many viruses and bacteria. It was suggested4 that disinfection Some examples of this classification include computers, coun- is extremely important in a medical setting in order to fight tertops, and floors. The use of mops and disinfectant wipes against microbes that can arise from anatomical cavities. suffices for the disinfectant processes of noncritical areas. Similar recommendations were in place in dental practice.5 On-contact disinfection requires single-use disposable wipes, Blancou’s research6 on the history of traditional disinfectant and flooring of noncritical areas usually requires the use of a methods revealed that the term “disinfect” was contrived in the mop and a water-disinfectant material. However, negligence 17th century to describe the act of warding off mysterious

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Table 1 A list of the pre-19th century disinfection techniques

Method Action Historical uses

Acidic rinses Visible corrosion of acid on various hard substances and the 3000 BC. Ancient Egypt: embalmers rinsed the abdominal preserving action of vinegar on vegetables suggest the use of vinegar cavities of cadavers prior to embalming. as a disinfectant.

Sulfuric fumigation Easily combustible and pungent in odor. Lethal effect on plants and 4th century India: placed in surgical operatory rooms for animals due to exposure suggest killing. purification. Mercury derivatives Direct observation of corrosive effects on living creatures. 1429 Italy: combated an outbreak of syphilis. Alkaline rinses Sodium, which is classified as an alkali metal, when introduced to 1715 Italy: during cattle plague, troughs and fountains organic matter visibly cleanses and leaves behind white traces of lime. were rinsed in a concentrated soda lime solution. The result of the reaction verifies their antiseptic use together.

effusions through the burning of various chemicals. Scientific of mercuric chloride as an antiseptic considering that it effi- knowledge of the origins of infections was not available until ciently killed more bacterial spores than any of the other solu- the 19th century. Traditional processes of disinfection were tions present in the experiment. However, the use of mercuric mostly based on the effects of various solutions on living chloride diminished in the 1950s due to new studies on the mul- things. Medical professionals considered liquids with the most tiple health risks of exposure to the substance.6 lethal effect on plants and animals as the most effective for kill- Findings from the Lenntech Water Treatment plant9 re- ing off diseases. Some of these methods included acidic rinses, vealed that numerous acids have antiseptic properties. One sulfur fumigations, mercury deposits, and alkaline rinses. such acid is peracetic acid, which is a mixture of acetic acid and Acids are some of the first antibacterial products used by hydrogen peroxide. Peracetic acid, or peroxyacetic acid, has ancient people that are still in use today. In the 1st century AD, been frequently used since the 1950s to sanitize medical sup- physician Aulus Celsus reported the healing effects of washing plies. The New Jersey Department of Health and Human Ser- wounds in vinegar.6 Burning sulfur creates sulfur dioxide, which vices (DHHS) 1998 fact sheet10 reveals that high exposure to was heavily used as a disinfectant throughout the great plagues peracetic acid may cause pulmonary edema, a medical emer- of the Middle Ages. When contacted with ample moisture, sul- gency with severe shortness of breath, and in many cases it fur dioxide creates a gaseous substance that can attack bacteria. should be disposed of as hazardous waste. Peracetic acid is a A review of chemical preservation and disinfection7 reveals highly reactive chemical and has the potential for dangerous that mercury was discovered in the 4th century. Arabic medical explosion hazard. professionals realized the antiseptic abilities of mercuric chlor- Some man-made chemicals that are popular in today’s dis- ide and began to use it as a disinfectant. The original use of infection world include hydrogen peroxide, glutaraldehyde, alkaline metals, primarily lime, as disinfectants began in 1509 by and quaternary ammonium compounds. The purpose of this Arabic scientists (Table 1).6 The discovery of chemical bleaches review is to study the trends in the surface disinfection in the was due to the work of three scientists in the 18th and 19th cen- dental profession, and review the disinfection guidelines for turies. A Swedish scientist named Carl Wilhelm Scheele discov- dental operatories recommended by the Centers for Disease ered chlorine. It is now well known that the chemical sodium Control (CDC) in the United States. hypochlorite contains chlorine. A French scientist named Claude Berthollet was the first person to make the solution sodium Method and materials hypochlorite, which he named it as “Eau de Javel” or Javel water, named after the work place in Paris where Berthollet completed Electronic searching and data extraction his study.8 Another French scientist named Antoine Germain Labarraque discovered that hypochlorites could act as disinfec- To identify published works that could be valuable for this tants. In 1881, physician Robert Koch completed a study on 70 review, search strategies were developed. The search strategies compounds and their antiseptic properties. He affirmed the use compiled a combination of controlled vocabulary and free-text

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terms. Electronic searches were explored using the following more to suppress any other living material. Although seem- databases: PubMed, Scopus, Embase, Cinahl, and Google ingly tedious, the “spray-wipe-spray” technique was necessary Scholar. The keywords used were “dental disinfection,” “dental considering that outdated dental machinery contained infection control,” “disinfection,” “inhalation,” “pathogens,” grooves and irregular surfaces that could only be cleaned effec- “asthmatic attacks,” “infection,” “clinical disinfection,” “disin- tively with anti-bacterial sprays.14 In various medical settings fectant chemicals,” “aerosols,” “disinfectant wipes,” and “history today, the use of aerosols for disinfection purposes has declined of disinfection.” After removing duplicates, the full-text pub- due to its negative effects on the environment and the body. lished articles and Manufacturer Safety Data Sheets, formerly Nelson’s study15 of the emissions of aerosol sprays explains that known as Material Safety Data Sheets (MSDS), were reviewed. although the chemicals that deplete the ozone layer (chloroflu- Data were collected from these articles using a standardized orocarbons), have been banned since the 1970s, aerosols still data extraction form: author’s first and last names or the name generate a myriad of other toxins that cause climate change of the agency, year of publication, study location, whether or and pollution. Essentially, aerosols are cans of compressed not the information presented was researched prior to publica- chemicals that not only release disinfectants but also can tion, whether or not a government agency was involved in the potentially trigger an asthmatic attack. Vacik’s research16 on the distribution of information, information extracted from the topic of asthmatic attack noted that the sheer mist that is cre- hazardous substance fact sheets, etc. The information so ated from the spray of these aerosols is inhaled deep into the obtained was carefully reviewed by the authors and discussion lungs when sprayed in a poorly ventilated area. In addition, the was built based on the information obtained. Historical data on mist can linger in the air leading to over-exposure, which can disinfection in dental settings were obtained from print text- also lead to asthma. The process begins with the inhalation of books that are available either at the University library or on the compressed chemicals which enter the lungs through the worldwide web. Non-indexed references, for instance the bronchi and bronchioles. An immune response is triggered MSDS, were also consulted as the information is specific to the which releases leukotrienes and histamines, which both cause industry and the disinfectant studied. Tables were developed inflammation in the lungs. As a result, the body dispatches by listing the chemicals and their categories and uses. more immune cells to the area that produce a surplus of mucus in an attempt by the body to eradicate the chemical from the lungs. This process is exhibited through a demonstration of Discussion wheezing, shortness of breath, and other common symptoms Although the possibility of transmission of infections from the of asthma. Constant and long-term exposure to aerosolized dental operatory settings to the patient is considered to be a chemicals can create an accumulation of chemicals in the lungs low risk, it nevertheless exists. To minimize the risk, emphasis that can lead to asthma. Today, newly designed dental technol- should be placed on adherence to recommended infection ogy allows for easier disinfection, as well as heavier reliance on control strategies, including the use of protective barriers, best disinfecting wipes, which are saturated with the same sanitiz- available surface disinfection, and sterilization techniques.11 ing chemicals as spray aerosols, without the risk for asthma and Several studies were conducted and published on the topics of inhalation.16 air syringe contamination and disinfection, bacterial contami- Hypochlorites (Table 2), the most widely used of the chlor- nation and dental unit disinfection,12 and disinfection of pri- ine disinfectants, are available as both liquid (eg, sodium hypo- mary impression materials,13 but there were very few that chlorite) and solid (eg, calcium hypochlorite). Chlorine prod- focused on surface disinfection protocols, especially related to ucts that are available in the United States are aqueous dental operatory surfaces. One reason for this could be the cat- solutions of 5.25% to 6.15% sodium hypochlorite, also known egorization of the operatory surfaces by the CDC as noncritical as household bleach. They are broad-spectrum antimicrobial since there is no direct contact between the surfaces and oral agents, do not leave toxic residues, are inexpensive, fast-acting, cavity. However, the CDC developed guidelines for dental and not affected by water hardness. They also remove dried or health care personnel (DHCP) for surface disinfection to pre- fixed organisms and biofilms from surfaces, and are least vent cross-contamination. The CDC previously mandated the toxic.17-19 “spray-wipe-spray” method which was coined to describe the Hydrogen peroxide (Table 2), when used for antiseptic pur- act of spraying a surface with an anti-bacterial aerosol, then poses, produces destructive hydroxyl radicals that are capable proceeding to wipe it dry, and finally spraying the surface once of obliterating DNA, and other crucial anatomical organs of a

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Table 2 A list of chemicals in the commonly used disinfectant products and their uses

Chemical name Mode of disinfection Effectiveness/uses

Quaternary ammonium compounds (Group I). Quaternaries inactivate enzymes, denature cell Widely used in disinfectant products due to Alkyl or hydroxyl substituted Quats proteins, and interfere with a pathogen’s cell compatibility with common disinfectant membrane. ingredients. Effective against most vegetative bacteria and some fungi. N-alkyl dimethyl ethyl benzyl ammonium One hydrogen group of the ammonium is replaced Widely used in disinfectant products including both chloride (quaternary ammonium compounds by a long carbon-chain alkaline which is effective in wipes and sprays. Groups II and III) disinfection. N-alkyl dimethyl benzyl ammonium chloride Attacks pathogens by tampering with their cell Widely used in disinfectant products including both (quaternary ammonium compound Groups II membrane and lipid bi-layers, which is fatal for an wipes and sprays. and III) organism. Isopropyl alcohol (alcohol) Denatures vital parts of the protein and lipids in a cell. Marginally more efficient than ethanol in bactericidal situations. Also effective in killing viruses, including hepatitis B and Herpes simplex. Ethanol (alcohol) Uses dehydration to denature bacterial cells. Less effective than a mixture of alcohol and water because denaturation is executed more quickly with the assistance of water. Methanol (alcohol) Disinfects through the process of denaturation. Rarely used in clinical disinfections due to its weak bactericidal ability. Hydrogen peroxide Creates hydroxyl radicals which destroy crucial parts Effective against many microorganisms, including of a pathogen’s anatomy. bacteria, viruses, yeasts, spores, and fungi. Formaldehyde (aldehyde) Deactivates microorganisms by alkylating amino and Active in the disinfection of viruses including sulfhydryl groups in the proteins of pathogenic cells. tuberculosis and Salmonella; however, it is less effective in the eradication of spores than glutaralde- hyde. Glutaraldehyde (aldehyde) Comparable to the disinfectant process of formalde- High-level disinfectant that protects against fungi, hyde, glutaraldehyde uses alkylation to alter the RNA, bacteria, and spores. DNA, or amino groups in microorganisms. Hypochlorites (chlorine and chlorine The specific method that makes chlorine an effective Lower concentrations have a biocidal effect on compounds) disinfectant is still unidentified. vegetative bacteria. Higher concentrations can kill tuberculosis. Absolute chlorine can kill Bacillus atrophaeus spores within the span of 5 minutes. Iodine solutions (iodophors) Able to penetrate the pathogen’s cell wall rapidly. Studies report that iodophors are bactericidal, Killing of the cell is believed to result from the mycobactericidal, and viricidal; however, they may disarrangement of the proteins and nucleic acids require more time for on-contact disinfection. structure. Ortho-phthalaldehyde The lipophilic nature of ortho-phthalaldehyde can More micro bactericidal that glutaraldehyde. assist in the removal of outer layers in a micro bacteria’s anatomy. Peracetic acid The mode of action for peracetic acid is unidentified; Able to disinfect both gram-positive and -negative however, it denatures proteins, and disrupts the bacteria, fungi, and yeasts. ability of the cell wall’s permeability. Phenol solutions (phenolics) Phenol lethally penetrates the cell wall causing an Reportedly bactericidal, fungicidal, viricidal, and inactivation of enzyme systems and a leakage of tuberculocidal. metabolites from the cell wall.

pathogen’s cell.17-19 Hydrogen peroxide has good antibacterial fungi, bacteria, and spores. For disinfection purposes, medical properties that fight against a multitude of bacteria and viruses. tools should be immersed in a dilute solution of glutaralde- The CDC reported that 6% concentration of hydrogen peroxide hyde and water for 20 to 30 minutes. Although formaldehyde is more effective as a high-level disinfectant than the compara- is powerful and arguably the most well-known aldehyde, glu- ble 2% concentration of glutaraldehyde. taraldehyde is reportedly three times as effective in the disin- Glutaraldehyde (Table 2) is a high-level disinfectant and is fection process.17-19 The CDC states that glutaraldehyde does part of the aldehyde family. Aldehydes can protect against not corrode metal or destruct other non-metal instruments.

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Fig 1 A radiology operatory with a panoramic dental x-ray unit and a table. White arrows indicate surfaces that need disinfection and blue arrows show the areas that need a removable plastic barrier.

1

Glutaraldehyde should only be used sparingly on critical sur- lipid bilayers, which halts cellular interactions inside the organ- faces because of its toxicity and high price.20 Special care is ism. Other disinfectant wipes contain between 5% to 10% by needed for the disposal of glutaraldehyde. Proper handling of weight diethylene glycol monobutyl ether and about 3% to 7% this chemical is elucidated in the Hesperian Health Guides;21 by weight tetrasodium ethylenediaminetetraacetate. They may glutaraldehyde must first be diluted with a sodium hydroxide contain trace amounts of nitrilotriacetic acid, a chemical known solution and left for at least 7 hours. Once diluted it is safe to to cause cancer, birth defects, or other reproductive harm as per pour the mixture into a leach pit, which is a trench made of rock the US State Regulations in California.23 An attack on the cell to prevent any leaking into the water stream. membrane is fatal to an organism.24 It is well known that alco- Quaternary ammonium compounds (Table 2) (quaternaries hols are effective disinfectants.19,24 Ethanol and isopropyl alcohol or quats) are widely used in disinfectant products due to their are both members of the alcohol family and have similar disin- palpable affinity in working with other common disinfecting fectant properties. Isopropyl alcohol, also known as isopropanol chemicals. Quaternaries are low-level disinfectants that have (IPA), is not as effective at dehydrating living tissues as ethanol. strong surface activity. Quaternaries can be effective against Ethanol (C2H5OH), also known as pure grain alcohol, as a disin- most vegetative bacteria and some fungi. However, quaternary fectant works by denaturing proteins and dissolving lipids, ammonium compounds are not effective on bacteria less than effectively destroying many types of bacterial and viral cells.24 zero grams, or microorganisms.21 Methyl alcohol (methanol) has the weakest bactericidal action Currently, the standard of disinfection is the use of hospital- of the alcohols and thus rarely is used in health care settings. The grade wipes and aerosol sprays which encompass multiple Food and Drug Administration (FDA) has not cleared any liquid antibacterial chemicals in their product. According to Kennedy- chemical sterilant or high-level disinfectant with alcohol as the Jangraw,22 the major chemicals in disinfectant wipes include main active ingredient.19 These alcohols are rapidly bactericidal n-alkyl dimethyl ethyl benzyl ammonium chloride, n-alkyl rather than bacteriostatic against vegetative forms of bacteria. dimethyl benzyl ammonium chloride, and isopropyl alcohol. Alcohols are tuberculocidal, fungicidal, and viricidal but are inef- N-alkyl dimethyl ethyl benzyl ammonium is a quaternary ammo- fective against spores. Their cidal activity drops sharply when nium compound in which the four hydrogen groups of ammo- diluted below 50% concentration, and the optimum bactericidal niums are replaced by organic groups. One of the hydrogens is concentration is 60% to 90% solutions in water (volume/vol- replaced by a long carbon-chain alkaline that is efficient in dis- ume).18,19 In conclusion, if alcohol has to be used for disinfecting infection. N-alkyl dimethyl benzyl ammonium chloride, also surfaces, both ethanol and isopropyl alcohol are nearly equally known as benzalkonium chloride, is another part of the quater- effective.24 Ethanol may be used in purely surface-cleaning nary ammonium compound family. Benzalkonium chloride applications as a surface disinfectant but IPA can also double as affects pathogens by tampering with the cell membrane and an antiseptic and is often used in hospitals.24

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Summary of disinfection recommendations for face, and after drying uses another wipe to disinfect the dental practices surface. The common chemicals that are used to saturate the wipes are those recommended by the CDC, including a ■ Dental practices should develop a written infection-control combination of n-alkyl dimethyl ethyl benzyl ammonium protocol that includes surface disinfection and barrier pro- chloride, n-alkyl dimethyl benzyl ammonium chloride, and tection. isopropyl alcohol. Another common quaternary ammo- ■ There are several techniques for isolation of noncritical ar- nium compound is N-alkyl dimethyl benzyl ammonium eas without disinfection by surface barrier techniques, for chloride, also known as benzalkonium chloride. Several example: headrest covers, sleeves for bite blocks, computer combinations of these compounds exist combined with ISP key board covers, computer mouse covers, sleeves for side alcohol for better effectiveness. bars in panoramic and cone beam computed tomography ■ Hospital grade disinfectants must be Environmental Pro- x-ray machines, barrier tapes with adhesives (sticky plastic tection Agency (EPA)-registered. Typically low level (HIV tape) and plastic bags (Fig 1). These can be used typically in and hepatitis B level claims) can be used for most noncrit- areas where wiping is not very effective; for instance light ical surfaces but intermediate level (tuberculocidal claim) switches, headlights, water spray handles. Surface barriers can be used to disinfect surfaces visibly contaminated are used to protect surfaces that are hard to clean. They with blood.25 must be changed between patients and are typically used ■ Radiography equipment such as the radiographic tube to speed up operatory turnaround. head/cone/arm and control panel should be protected with ■ Wipes can be used for all surfaces (Figs 2 and 3) like counter- surface barriers that are changed after each patient or dis- tops, instrument trays, side tables that are used for placing infected using CDC-recommended and EPA-registered hos- dental instruments, x-ray shields, and other noncritical den- pital grade disinfectant wipes using the wipe-dry/dis- tal equipment or location within the operatory. There should card-wipe technique. Alternatively, equipment that has be a written protocol for all critical areas and instruments come into contact with gloved hands of dental health care that must adhere to the guidelines proposed by the CDC. personnel or contaminated film packets should be cleaned ■ “Wipe-dry-wipe or wipe-discard-wipe,” also proposed by and then disinfected after each patient use. Digital radio- the CDC, is a standard disinfection practice in the modern graphic sensors are considered semi-critical and should be dental operatory. The user uses one wipe to clean the sur- protected with an FDA-cleared barrier to reduce contami-

Fig 2 A typical dental operatory with a computer monitor, a Fig 3 A standard dental operatory with a dental chair and keyboard, and a mouse. This is a thin client and hence a separate accessories. Note the x-ray apron hung on the wall. White arrows Central Processing Unit (CPU) is not shown. Blue arrows indicate areas indicate the surfaces that need standard disinfection and that need barriers and the white arrow shows the countertop that blue arrows show areas that need a disposable barrier. needs standard disinfection.

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nation during use, followed by cleaning and high-level dis- ■ Proper protection for operators during disinfection proto- infection between patients. If the item cannot tolerate cols: Due to the risks associated with exposure to chemical these procedures then, at a minimum, it should be pro- disinfectants and contaminated surfaces, the CDC recom- tected with an FDA-cleared barrier and cleaned and disin- mends25 that dental health care personnel (DHCP) should fecte,ediate-level (ie, tuberculocidal claim) activity, be- wear appropriate personal protective equipment (PPE) to tween patients.25,26 prevent exposure to infectious agents or chemicals. PPE in- ■ Floors, walls, and sinks can be disinfected with detergent and cludes gloves, gowns, masks, and eye protection. Chemical- water or an EPA-registered hospital disinfectant used when and puncture-resistant utility gloves off er more protection a visibly soiled surface is noted. The dental personnel should than patient examination gloves when using hazardous prepare EPA-registered disinfecting solutions daily and as chemicals. The CDC adds, “DHCP should follow manufac- instructed by the manufacturer. Walls, blinds, and window turer instructions and review the manufacturer Safety Data curtains in patient care areas must be cleaned periodically Sheet regarding correct procedures for handling or work- with detergent and water or a hospital disinfectant.25,26 ing with hazardous chemicals.”25

References 1. American Dental Association. Sterilization 10. New Jersey Department of Health and 18. CDC. Guidelines for infection control in and disinfection of dental instruments. Senior Services: Hazardous Substance Fact dental health-care settings, 2003. MMWR https://www.ada.org/~/media/ADA/Member Sheet – Peroxyacetic Acid. Revised 2004. 2003;52(RR-17):1–61. %20Center/FIles/cdc_sterilization.ashx. https://www.nj.gov/health/eoh/rtkweb/ 19. CDC. Summary of infection prevention Accessed 24 August 2018. documents/fs/1482.pdf. Accessed 22 August practices in dental settings. Basic expecta- 2. Matsuda JK, Grinbaum RS, Davidowicz 2018. tions for safe care. Atlanta: Centers for Disease H. The assessment of infection control in 11. Araujo MW, Andreana S. Risk and Control and Prevention, US Department of dental practices in the municipality of São prevention of transmission of infectious Health and Human Services, 2016;Oct:1–44. Paulo. Braz J Infect Dis 2011;15:45–51. diseases in dentistry. Quintessence Int 20. Jeff rey DJ. Chemicals used as disinfec- 2002;33:376–382. 3. Collins AS. Preventing health care- tants: active ingredients and enhancing associated infections. In: Hughes R (ed). 12. Williams HN, Johnson A, Kelley JI, et al. additives. Rev Sci Tech 1995;14:57–74. Patient Safety and Quality: An evidence- Bacterial contamination of the water supply 21. Hesperian health guides. Safe disposal based handbook for nurses. Rockville: in newly installed dental units. Quintessence of chemical waste. http://en.hesperian.org/ Agency for Healthcare Research and Quality Int 1995;26:331–337. (US) 2008;2:547–575. hhg/A_Community_Guide_to_Environmen- 13. Bock JJ, Fuhrmann RA, Setz J. The tal_Health:Safe_Disposal_of_Chemical_ 4. Block SS. Disinfection, Sterilization, and infl uence of diff erent disinfectants on Waste. Accessed 13 August 2018. Preservation. 5th ed. Philadelphia: Lippincott primary impression materials. Quintessence Williams & Wilkins, 2001:135-473. Int 2008;39:e93–e98. 22. Kennedy-Jangraw L. The science be- hind household cleaners. https://owlcation. 5. Walter C. Sterilization and disinfection in 14. Govoni M. To Spray of not to spray. com/stem/The-Science-Behind-House- dental practice. Quintessence Int (Berl) Dental Economics, 1 January 2012. https:// hold-Cleaners. Accessed 22 August 2018. 1971;2:11–13. www.dentaleconomics.com/articles/print/ 6. Blancou J. History of disinfection from volume-102/issue-1/practice/to-spray-or- 23. CRC Industries, Pennsylvania (USA). early times until the end of the 18th century. not-to-spray.html. Accessed 14 August 2018. Material Safety Data Sheet (MSDS). http:// docs.crcindustries.com/msds/4101.pdf. Rev Sci Tech 1995;14:21–39. 15. Nelson J. What you need to know Accessed 22 August 2018. 7. Hugo WB. A brief history of heat and about aerosol sprays. https://www.mnn. chemical preservation and disinfection. com/lifestyle/responsible-living/stories/ 24. HealthE. Alcohol as disinfectants. J Appl Bacteriol 1991;71:9–18. what-you-need-know-about-aerosol-sprays. http://www.nzhealthe.co.nz/knowledge/ alcohol-as-disinfectants. Accessed 13 August 8. Crampton L. How bleach works: Accessed 14 August 2018. 2018. Disinfection, stain removal and dangers. 16. Vacik S. Aerosol sprays and asthma. https://owlcation.com/stem/How-Bleach- http://www.bellaonline.com/articles/ 25. CDC. Oral Health. https://www.cdc. Works-Disinfection-and-Stain-Removal. art182807.asp. Accessed 14 August 2018. gov/oralhealth/infectioncontrol/questions/ Accessed 22 August 2018. 17. CDC. Guideline for Disinfection and sterilization/cleaning.html. Accessed 9. Lenntech.com. Disinfectants Peracetic Sterilization in Healthcare Facilities (2008). 23 August 2018. acid. https://www.lenntech.com/processes/ https://www.cdc.gov/infectioncontrol/guide- 26. Molinari JA, Polenik CJ. Environmental disinfection/chemical/disinfectants-peracetic- lines/disinfection/disinfection-methods/ surface infection control, 2003. Compend acid.htm. Accessed 13 August 2018. chemical.html. Accessed 13 August 2018. Contin Educ Dent 2004;25:30,32–34,36–37.

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Mel Mupparapu Professor and Director of Radiology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA, USA Karaan Raj M. Kothari Research Assistant, Department of Oral Medicine, University of Pennsylvania School of Dental Medicine, Philadelphia, PA, USA.

Mel Mupparapu Karaan Raj M. Kothari

Correspondence: Professor Mel Mupparapu, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104, USA. Email: [email protected]

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