Sterilization

sterilization techniques

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2. STERILIZATION SEMINAR-5 Presented by Akhil C A First Year PG Dept. Of Public Health Dentistry SCB Dental College, Cuttack 2

3. CONTENTS INTRODUCTION TERMINOLOGIES HISTORICAL BACKGROUND METHODS OF STERILIZATION STERILIZATION IN DENTAL SETTING CONCLUSION REFERENCES 3

4. INTRODUCTION Microorganisms are ubiquitous. They are found in the surroundings, on inanimate objects and on the surface of the human body. Since they cause contamination, infection and decay, it becomes necessary to remove or destroy them. Methods to remove or kill microorganisms are known as sterilization. The methods of sterilization used depend on the purpose for which it is carried out, the material to be sterilised and the nature of the microorganisms to be removed or destroyed . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 4

5. TERMINOLOGIES Disinfectant : Usually a chemical agent (but sometimes a physical agent) that destroys disease causing pathogens or other harmful microorganisms, but might not kill bacterial spores . It refers to substances applied to inanimate objects. Disinfection : Thermal or chemical destruction of pathogen and other types of microorganisms. Disinfection is less lethal than sterilization because it destroys most recognized pathogenic microorganisms but not necessarily all microbial forms (e.g., bacterial spores). Sterilization : Validated process used to render a product free of all forms of viable microorganisms including bacterial spores. Sterilizer is the apparatus used to sterilize medical devices, equipment or supplies by direct exposure to the sterilizing agent . Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 5

6. Antiseptic : Substance that prevents or arrests the growth or action of micro-organisms by inhibiting their activity or by destroying them. The term is used especially for preparations applied topically to living tissue. Asepsis : Prevention of contact with micro-organism. Sanitizer : Agent that reduces the number of bacterial contaminants to safe levels as judged by public health requirements . Commonly used with substances applied to inanimate objects. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 6

7. Sterile : State of being free from all living microorganisms . Germicide : Agent that destroys micro-organisms, especially pathogenic organisms Detergent : Surface cleaning agent that makes no antimicrobial claims on the label. They comprise a hydrophilic component and a lipophilic component. It acts by lowering surface tension e.g. soap which removes bacteria along with dirt. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 7

8. HISTORICAL BACKGROUND Ignaz Semmelweis in Vienna, Austria (1818-1865) in 1847 demonstrated the value of handwashing with antiseptic solutions, when he obtained considerable reduction in the death rate from puerperal fever . He is also called the “ Father of infection control” and “ Saviour of mothers.” Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 8

9. Joseph Lister (1827-1912) was also successful in reducing the number of wound infections by prophylactic application of an antiseptic (carbolic acid) to wounds . In 1865, after some doubtful beginnings,  he managed for the first time to heal without infection the open leg fracture of a child hit by a car. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 9

10. From then on, Lister laid out a protocol to sterilize the surgical instruments, the hands of the surgeon, the dressings and the wounds with solutions of carbolic acid, and even designed a sprayer to diffuse the substance in the air of the operating room. 10

11. When he  died at the age of 84 on February 10, 1912, he left behind a drastic reduction in the mortality of surgical patients due to infections.  According to statistics collected by himself, the decrease went from almost 50% of those operated on to only 15%. 11

12. METHODS OF STERILIZATION Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 12

13. A.Physical methods 1. S unlight 2. H eat ( a ) Dry heat ( b) Moist heat 3. O zone 4. F iltration 5. R adiation to a level that is no longer harmful to health. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 13

14. B.Chemical Methods Phenol and related compounds Quaternary ammonia compounds Halogens and their compounds Alcohols Formaldehyde Oxidizing agents Metals Lime Ethylene oxide Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 14

15. 1 . Sunlight Sunlight has an active germicidal effect due to its content of ultraviolet rays. It is a natural method of sterilization in cases of water in tanks, rivers and lakes . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 15

16. 2. Heat Heat is the most reliable and commonly employed method of sterilization . It should be the method of choice unless contraindicated. Two types of heat are used- D ry heat M oist heat Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 16

17. Principle (i ) Dry heat kills the organisms by denaturation of bacterial protein, oxidative damage and by the toxic effect of elevated levels of electrolytes . The possibility of DNA damage is also incriminated as one of the mechanisms of inactivations of microbes . (ii) Moist heat kills the microorganisms by denaturation and c oagulation of proteins . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 17

18. Factors influencing ( i) Nature of heat : Dry heat or moist heat (ii) Temperature and duration: The time required for sterilization is inversely proportional to temperature to which organisms are exposed. (iii) Characteristic of microorganisms and spores present : Bacterial spores are killed by moist heat at 121 ° C for 15 minutes. Most vegetative bacteria, fungi and viruses are killed in 30 minutes at 65°C by moist heat. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 18

19. (iv) Type of material: A high content of organic substances tend to protect the vegetative form and spores against the lethal action of heat. Materials containing organic substances require more time for sterilisation . Proteins, sugars, fats and starch are some of the organic substances. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 19

20. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 20

21. 1. Red heat Inoculating wires or loops ,tips of forceps and needles are held in the flame of a bunsen burner till they become red hot. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 21

22. 2.flaming Glass slides,scalpels and mouths of culture tubes are passed through bunsen flame without allowing them to become red hot. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 22

23. 3.Incineration By this method, infective material is reduced to ashes by burning. Instrument named incinerator may be used for this purpose. soiled dressin g s animal carcasses, bedding and pathological materials are dealt with this method. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 23

24. 4.Hot air oven Most commonly used method of sterilization by dry heat . The oven is electrically heated and is fitted with a fan to ensure adequate and even distribution of hot air in the chamber. It is also fitted with a thermostat that maintains the chamber a chosen temperature Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 24

25. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 25

26. Temperature and time 160° for 2 hrs (holding time) is required for sterilization ( previously it was 160°C for one hour). However, alternative temperatures and holding time include 170°C for one hour and 180°C for 30 minutes. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 26

27. Uses It is used for sterilization of Glasswares like glass syringes , petridishes , flasks , p ipettes and test tubes . Surgical instruments like scalpels,scissors,forceps etc. Chemicals such as liquid paraffin, fats, sulphonamides,powders etc. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 27

28. Precautions It should not be over loaded . The material should he arranged in a manner which allows free circulation of air. Material to be sterilized should be perfectly dr y . Test tubes, flasks etc. shou l d be fitted with cotton Petridishes and pipettes should be wrapped in paper . Rubber materials(except silicone) or any inflammable material should not be kept inside the oven . The oven must be allowed t o cool Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 28

29. Sterilization control The spores of Bacillus subtilis subsp. niger are kept inside the oven.These spores should be destroyed if the sterilization is proper. Thermocouples may also be used. B rowne‘s tube with red spot is available. After proper sterilisation a green color is produced (after two hours at 160°c.) Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 29

30. This method of sterilization may be used at different temperatures as follows. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 30

31. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 31

32. a) Pa steurisation of milk Two types of method Holder method (63°C for 30 minutes) Flash method ( 72°C for 20 seconds followed by cooling quickly to 1 3°C or lower) are used. All non- sporing pathogens such as mycobacteria , brucellae and salmonellae are killed except Coxiella burnetii which being relatively heat resistant may survive in holder method. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 32

33. (b) Inspissation Some serum or egg media , such as Lowenstein-Jensen's and Loeffier's serum, are rendered sterile by heating at 80-85°C temperature for half an hour daily on three consecutive days. This process of sterilization is called inspissation . The instrument used is called inspissator . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 33

34. (c)Vaccine bath Bacterial vaccines are sterilized in special vaccine baths at 60°C for one hour. Serum or body fluids can be sterilized by heating for one hour at 56°C in a water bath on several successive days. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 34

35. (d)Low temperature steam formaldehyde ( LTSF) sterilisation In this method steam at sub-atmospheric pressure at the temperature of 75°C with formaldehyde vapour is used. Bacillus stearothermophilus has been used as biological control to test the efficacy of LTSF sterilisers . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 35

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37. Boiling Boiling for 10 to 30 minutes may kill most of the vegetative forms but many spores withstand boiling for a considerable time. When better methods are not available, boiling may be used for glass syringes and rubber stopper. It is not recommended for the sterilization of instruments for surgical procedures . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 37

38. ( b)Tyndallisation (fractional sterilization ) Steam on three successive days is known as tyndallisation or intermittent sterlization . The principle is that the first exposure kills all the vegetative forms , and in the intervals between the heatings the remaining spores germinate into vegetative forms which are killed on subsequent heating. It is used for sterilization of egg, serum or sugar containing media which are damaged at higher temperature of autoclave.The instrument commonly used is Koch's or Arnold's steam steriliser. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 38

39. (c) Steam steriliser at 100°C for 90 minut es Koch's or Arnold's steam steriliser . U sually used for media which are decomposed at high temperature of autoclave. The articles are kept on a perforated tray through which steam can pass. They are exposed to steam at atmospheric pressure for 90 minutes. Most of the vegetative forms are killed by this method except thermophiles. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 39

40. (3) At a Temperature above 100°C (under pressure) AUTOCLAVE Principles: Steam above100°C or saturated steam has a better killing power than dry heat. Bacteria are more susceptible to moist heat as bacterial protein coagulates rapidly . Saturated steam can penetrate porous material easily. When steam comes into contact with a cooler surface it condenses to water and liberates its latent heat to that surface. The large reduction in volume sucks in more steam to the same site and the process continues till the temperature of the article is raised to that of steam. The condensed water produces moist conditions for killing the microbes present . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 40

41. Components of autoclave Autoclave is a modified pressure cooker or boiler. It consists of a vertical or horizontal cylinder of gunmetal or stainless steel in a supporting iron case. The lid is fastened by screw clamps and rendered air tight by an asbestos washer. The lid bears a discharge tap for air and steam , a pressure gauge and a safety valve . Heating is generally done by electricity. The steam circulates within the jacket and is supplied under high pressure to the inner chamber where materials are kept for sterilisation Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 41

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43. Sterilization conditions Temperature - 121 ° C Chamber pressure - 15 lbs per square inch - Holding time - 15 minutes These conditions are generally used, however, sterilization can also be done at higher temperatures, at 126°C - 20 lbs -10 minutes or 133°C- 30 lbs - 3 minutes . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 43

44. Uses To sterilize culture media ,rubber material, gowns, dressing , gloves etc. It is particularly useful for materials which cannot withstand the higher temperature of hot air oven . For all glass syringes, hot air oven is a better sterilizing method. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 44

45. Precautions The air must be allowed to escape from the chamber as temperature of air-steam mixture is lower than that of pure steam . Materials should be arranged in such a manner as to ensure free circulation of steam inside the chamber. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 45

46. Sterilization control (i) Thermocouple - It is to record the temperature directly by a potentiometer . ( ii) Bacterial spores- Spores of b acillus stearo thermophilus are used as the test organism. This organism has an optimum growth temperature of 55- 60 °C and its spores are killed in 12 minutes at 121 °C. ( iii) Chemical indicators - Browne's tube contains red solution which turn green, when exposed to temperature of 121 °C for 15 minutes in autoclave. ( iv) Autoclave tapes Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 46

47. Sterilization controls 47

48. 3. Ozone Low Temperature sterilization by ozone- Ozone sterilizer uses oxygen, water and electricity to produce ozone within the sterilizer and provide sterilization without producing toxic chemicals. It runs at lower temperature ie . 25°C-35 ° In this device, oxygen molecules (0 2 ) are separated into atomic oxygen (0) in the presence of intense electrical field. This atomic oxygen (0) combines with other oxygen molecules (0 2 ) to form ozone ( 3 ). Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 48

49. 4. Filtration This method of sterilization is useful for substances which get damaged by heat process e.g. sera, sugars, antibiotic solutions etc . Uses of filtration To sterilize sera, sugars and antibiotic solutions. Separation of toxins and bacteriophages from bacteria . To obtain bacteria free filtrates of clinical samples for virus isolation. Sterilization of hydatid fluid. Filter discs retain the organism which can then be cultured e.g. testing of water samples for Cholera vibrios or typhhoid bacilli. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 49

50. Types of filters 1)Candle filters are manufactured in different grades of porosity and have been used widely for the purification of water for industrial and drinking purposes. They are of two types - unglazed ceramic filters (for example, Chamberland and Doulton ) and Diatomaceous earth filters (for example, Berkefeld and Mandler ). 2)Sintered glass filters are prepared by heat-fusing finely powdered glass particles of graded sizes . They have low absorptive property and can be cleaned easily, but are brittle and expensive. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 50

51. 3)Membrane filters made; of cellulose esters or other polymers have largely replaced other types of filters. They are routinely used i n water purification and analysis , sterilization and sterility testing, and for the preparation of solutions for parenteral use. They come in a wide range of average pore diameters (APD) , the 0.22µm size being the most widely used for sterilization . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 51

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53. 4)Air filters - These filters are used to deliver clean bacteria-free air to a cubicle or a room. High efficiency particulate air HEPA filters are used in air filtration in laminar air flow system in microbiology laboratories. HEPA filters can remove particles of 0.3 μm or larger. 5)syringe filters- Syringes fitted with membrane of different diameters are available. For sterilisation , the fluid is forced through the disc (membrane ) by pressing the piston of the syringe. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 53

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55. 5. Radiations Two types of radiations - ionising and non-ionising radiations. Ionising radiations include gamma rays, X-rays and cosmic rays. They have very high penetrating power . They are highly lethal to all cells including bacteria. They damage DNA by various mechanisms. Gamma radiations from a Cobalt 60 source are commercially used in sterilisation of disposable items such as plastic syringes,swabs , culture plates, cannulas,catheters . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 55

56. This method is also known a cold sterilization b ecause there is no appreciable increase in temperature. The advantages of this method include speed , high penetrating power (it can sterilize materials, through outer packages and wrappings), and the absence of heat. Bacillus pumilis has been used for testing the efficacy of ionising radiations. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 56

57. Non - ionising radiations These include infrared and ultraviolet (UV) radiations. Infrared is used for sterilization of syringes and catheters. Uv radiation with wavelength of 240 to 280 nm has marked b actericidal activity. It acts by denaturation of bacterial protein and interference with DNA replication. UV radiation is used for disinfecting enclosed areas such as bacteriological laboratory , inoculation hoods, and operation theatres. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. 57

58. B Chemical Methods Desired qualities of an ideal disinfectant Have wide spectrum of activity and effective against all microorganisms including bacteria ( both vegetative and spore forms), viruses, protozoa and fungi . A ct in the presence of organic matters. H ave high penetration power and quick action. S table and effective in acidic as well as in alkaline conditions. Should not corrode metals. 58

59. Be compatible with other disinfectants. Should not cause local irritation. Should not be toxic if absorbed into circulation. Should be safe and easy to use. Should be easily available and cheap. Articles which cannot be sterilized by boiling or autoclaving may be immersed in chemical disinfectants 59

60. Chemical Methods Phenol and related compounds Quaternary ammonia compounds Halogens and their compounds Alcohols Formaldehyde Oxidizing agents Metals Lime Ethylene oxide Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 60

61. 1. Phenol and related compounds (1) Phenol : Pure phenol or carbolic acid is the best known member of this group. Pure phenol is not an effective disinfectant. It is used as a standard to compare the germicidal activity of disinfectants. ( 2) Crude phenol : M ixture of phenol and cresol. It is a dark oily liquid. It is effective against gram positive and gram negative bacteria , but only slowly effective against spores and acid-fast bacteria . It is also effective against certain viruses . N ot readily inactivated by organic matter . In 5 % strength , it may be used for mopping floors and cleaning drains.Aqueous solutions of 0 .2 - 1 % are bacteriostatic . Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 61

62. (3) Cresol : Cresol is an excellent coal-tar disinfectant. It is 3 to 10 times as powerful as phenol , yet no more toxic.Cresol is best used in 5 to 10 % strength for disinfection of faeces and urine.Cresol is an all purpose general disinfectant. ( 4) Cresol emulsions : Cresol emulsified with soap is known as " saponified cresol". Lysol,izal and cyllin are cresol emulsions. Lysol contains 50- 60 % cresol . They are very powerful disinfectants. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 62

63. (5) Chlorhexidine ( hibitane ) : This is one of the most useful skin antiseptics. Highly active against vegetative grampositive organisms , and moderately active against grampositive microbes. It is soluble in water and alcohol. It is inactivated by soaps and detergents. 0.5 % alcoholic or aqueous solutions can be used as effective hand lotions . Creams and lotions containing 1 % chlorhexidine are recommended for burns and hand disinfection Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 63

64. 6) Hexachlorophane : This antiseptic is highly active against gram-positive organisms, but less active against gram negative organisms . It is slow in action , but shows a cumulative effect on the skin and is compatible with soaps. Thus it may be incorporated in soap preparations without loss of activity . (7) Dettol : Dettol ( chloroxylenol ) is a relatively non-toxic antiseptic and can be used safely in high concentrations . It is more easily inactivated by organic matter than many other phenolic disinfectants. It is active against streptococci, but worthless against some gram negative bacteria. Dettol (5%) is suitable for disinfection of instruments and plastic equipment; a contact of at least 15 minutes will be required for disinfection. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 64

65. 2. Quaternary ammonia compounds (1) Cetrimide : It is manufactured under the trade name " cetavlon ". It is actively bactericidal against vegetative gram-positive organisms, but much less so against gramnegative organisms. Cetavlon is soluble in water; it has a soapy feel. It may be used in 1-2 % strength. ( 2) Savlon : Savlon is a combination of cetavlon and hibitane . Plastic appliances may be disinfected by keeping them in normal strength savlon for 20 minutes. Savlon 1 in 6 in spirit is more effective than savlon 1 in 20 aqueous solution. Clinical thermometers may be best disinfected in savlon 1 in 6 in spirit in just under 3 minutes. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 65

66. 3. Halogens and their compounds a. Chlorine and chlorine compounds : They are potent bactericidal , fungicidal , sporicidal, tuberculocidal and virucidal . Since long time chlorine has been used as disinfectant in water treatment. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 66

67. (1) Bleaching powder : Bleaching powder or chlorinated lime (CaOCl2) is a white amorphous powder with a pungent smell of chlorine . A good sample of bleaching powder contains about 33 % of "available chlorine" . It kills most of the organisms when used in the strength of 1 to 3 %. Bleaching powder is widely used in public health practice in India for disinfection of water, faeces and urine; and as a deodorant . A 5% solution is suitable for disinfection of faeces and urine allowing a period of one hour for disinfection. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 67

68. (2) Hypochlorites : Hypochlorites are the most widely used chlorine disinfectant , available as liquid ( e.g . sodium hypochlorite ) or solid (e.g. calcium hypochlorite). The most prevalent chlorine products are aqueous solutions of 5.25- 6.15 % of sodium hypochlorite, usually called household bleach. They have a broad spectrum of antimicrobial activity, do not leave toxic residues, are unaffected by water hardness, are inexpensive and fast acting , remove dried or fixed organisms and biofilms from surfaces . Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 68

69. (3) Chlorine tablets : Under various trade names (viz. , halazone tablets) they are available in the market. They are quite good in disinfecting small quantities of water . ( 4) Alternative compounds that release chlorine and are used in the health-care setting include demand release chlorine dioxide, sodium dichloro isocyanurate , and chloramine-T . The advantage of these compounds over hypochlorites is that they retain chlorine longer and so exert a more prolonged bactericidal effect. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 69

70. b. Iodine ( 1) Iodine solutions or tinctures have been used as antiseptic on skin or tissue since long time. Iodine is bactericidal, fungicidal, virucidal and lethal to spore-bearing organisms. Iodine is cheap, readily available and quick in action. ( 2) Iodophores : An iodophore is a combination of iodine and a solubilizing agent or carrier; the resulting complex provides a sustained-release reservoir of iodine and releases small amounts of free iodine in aqueous solution . Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 70

71. The best known and most widely used iodophore is povidone -iodine ( Betadine ). They are non-irritant and do not stain the skin. Besides their use as an antiseptic, iodophores have been used for disinfecting blood culture bottles and medical equipment. 71

72. 4. Alcohols Ethyl and isopropyl alcohols are commonly used as antiseptics and disinfectants. Ethyl alcohol in the form of industrial methylated spirit is the alcohol most commonly used for skin disinfection and hand washing. Pure alcohol has no powers of disinfection but when diluted with water to 60- 90 % vol / vol , it is potent bactericidal, fungicidal,virucidal and tuberculocidal , but does not destroy bacterial spore. Its activity decreases rapidly below 50 per cent concentration . 70 per cent alcohol is lethal in a period of seconds to all types of non- sporing bacteria. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 72

73. 5. Formaldehyde More commonly known in solution as formalin ,formaldehyde is a highly toxic and irritant gas which precipitates and destroys protein. It is effective against vegetative bacteria, fungi and many viruses but only slowly effective against bacterial spores (e.g. , tetanus spores) and acid-fast bacteria. It does not injure fabrics and metals. It may be used as a 2-3 % solution (20- 30 ml of 40 percent formalin in one litre of water) for spraying rooms, walls and furniture. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 73

74. Formaldehyde gas is most commonly used for disinfection of rooms. The gas is most effective at a high temperature and a relative humidity of 80-90 %. The gas may also be used for disinfection of blankets, beds, books and other valuable articles which cannot be boiled. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 74

75. Glutaraldehyde : When buffered with sodium bicarbonate to pH 7.5–8.5, this has potent bactericidal, mycobactericidal , sporicidal , fungicidal, and virucidal action. The buffered solutions should be used within 2 weeks of preparation. It is available under the brand name Cidex . A 2 % solution provides a high level of disinfection, which approximates sterilization . It is the only disinfectant that can be reused . It is less toxic than formaldehyde 75

76. 6. Oxidizing agents a. Potassium permanganate : It is a purplish black crystalline powder that colours everything it touches through strong oxidizing action, which limits its use. It is used to disinfect aquariums and is also widely used in community swimming pools to disinfect ones feet before entering the pool. It is also used to disinfect fruits and vegetables. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 76

77. (b)Hydrogen peroxide Hydrogen peroxide is bactericidal , virucidal , sporicidal and fungicidal. It is used in hospital setting to disinfect surfaces. It is used as solution alone or in combination with other chemicals as a high level disinfectant. A 0.5 % accelerated hydrogen peroxide demonstrated bactericidal and virucidal activity in 1 minute and mycobactericidal and fungicidal activity in 5 minutes. A 3 % solution is also used as an antiseptic and for cleaning wounds and discharging ulcers. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 77

78. ( c) Peracetic acid It is a disinfectant produced by reacting hydrogen peroxide with acetic acid. It is broadly effective against microorganisms and is not deactivated by catalase and peroxidase , the enzymes that break down hydrogen peroxide . It inactivates gram-positive and gram-negative bacteria , fungi and yeast in less than 5 minutes at less than 100 ppm . In the presence of organic matter, 200- 250 ppm is required . For viruses, the dose range is wide ( 12- 2250 ppm ). Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 78

79. 7. Metals as microbicides Anti-infective activity of some heavy metals has been known since antiquity. Heavy metals such as silver have been used for prophylaxis of conjunctivitis of the new-born, topical therapy for burn wounds, and bonding to indwelling catheters. Metals such as silver, iron, and copper could be used for environmental control, disinfection of water or reusable medical devices, or incorporated in to medical devices. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 79

80. 8. Lime Lime is the cheapest of all disinfectants. It is used in the form of fresh quick lime or 10-20 % aqueous suspension known as "milk of lime". As lime wash, it is used for treating walls. As a deodorant, lime is sprinkled in cattle sheds and stables and in public places where urinals and latrines are located. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 80

81. 9. Ethylene oxide Heat-sensitive articles may be sterilized at 55-60 C by ethylene oxide which kills bacteria, spores (e.g. , tetanus spores ) and also viruses. Ethylene oxide is explosive , therefore , it is mixed with carbon dioxide (12 %). Water vapour is also often added to the mixture ( relative humidity 33 %) since it increases the efficiency of the gas. Ethylene oxide has been effectively used to sterilize fabrics , plastic equipment, cardiac catheters, books, etc ; but the process is difficult to control. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 81

82. Factors affecting the efficacy of sterilization 1. Cleaning Failure to adequately clean instruments results in higher bioburden, protein load , and salt concentration. These will decrease sterilization efficacy . 2. Pathogen type Spore-forming organisms are most resistant to sterilization. However, the contaminating microflora on surgical instruments consists mainly of vegetative bacteria. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 82

83. 3. Biofilm accumulation Biofilm accumulation reduces efficacy of sterilization by impairing exposure of the sterilant to the microbial cell . 4. Lumen length and lumen diameter Increasing lumen length and decreasing lumen diameter impairs sterilant penetration . May require forced flow through lumen to achieve sterilization. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 83

84. 5. Restricted flow Sterilant must come into contact with microorganisms . Device designs that prevent or inhibit this contact ( e.g. sharp bends, blind lumens) will decrease sterilization efficacy . 6. Device design and construction Materials used in construction may affect compatibility with different sterilization processes. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 84

85. STERILIZATION IN DENTAL SETTING 85

86. Categories of Patient-Care Items Critical . Semicritical . Noncritical. Based on intended use and the potential risk of disease transmission Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 86

87. Critical Items Penetrate soft tissue or contact bone, enter into or contact the vascular system or other normally sterile tissue. Greatest risk of transmitting infection. Must be heat sterilized between use, or sterile single-use, disposable devices must be used. Examples: surgical instruments and periodontal scalers . Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 87

88. Semicritical Items Contact mucous membranes or non-intact skin (e.g., exposed skin that is chapped, abraded, or has dermatitis). Lower risk of transmission. Should be heat sterilized or high-level disinfected. Examples: mouth mirrors, amalgam condensers, and reusable impression trays. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 88

89. Dental Handpieces Follow manufacturer’s instructions to safely reprocess dental handpieces and accessories (e.g., low-speed motor, reusable prophylaxis angles). Clean and heat sterilize between patient uses. Do not subject the handpiece to high-level disinfection and do not simply wipe the surface with a low-level disinfectant. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 89

90. Digital Sensors Follow manufacturer’s instructions to safely reprocess digital radiography equipment . Ideally, barrier protection should be used, followed by cleaning and heat sterilization or high-level disinfection between patients . If the item cannot tolerate these procedures, then at minimum, barrier protection should be used, followed by cleaning and disinfection with an intermediate-level disinfectant between patients. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 90

91. Noncritical Items Contact intact skin. Barrier protect or clean and disinfect (if visibly soiled) using a low to intermediate-level (i.e., tuberculocidal ) disinfectant. Examples: x-ray head or cone, facebows , blood pressure cuff. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 91

92. Single-Use (Disposable) Devices Intended for use on one patient during a single procedure. Usually not heat-tolerant. Cannot be reliably cleaned. Do NOT reprocess . Examples: syringe needles, prophylaxis cups, and plastic orthodontic brackets. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 92

93. Methods for Sterilizing and Disinfecting Patient-Care Items and Environmental Surfaces 93

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95. The preferred methods of sterilisation in a dental office Steam pressure sterilization (autoclave ) Unsaturated chemical vapor pressure sterilization( chemiclave ) Dry heat sterilization( dryclave ) Other Methods of Sterilization - Liquid chemical germicides:  - Ethylene oxide gas (ETG ) - Bead sterilizers Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 95

96. Heat sterilization methods are for several reasons: Effective. Relatively easy to use. Comparatively inexpensive. Readily monitored for effectiveness . Liquid chemical disinfectants/ sterilants should be used only when heat will damage an item. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 96

97. Unsaturated chemical vapour sterilization Unsaturated chemical vapour sterilization involves heating a chemical solution of primarily alcohol with formaldehyde in a pressurized chamber. This method of sterilization is ideally suited to carbon steel instruments (e.g. dental burs) because the low level of water present during the cycle results in less corrosion than might be expected with steam sterilization . Instruments must be dry before sterilization Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 97

98. Advantages of chemical vapour sterilization Is relatively quick. Does not rust or corrode metal items. Is very reliable. Can be used with packaged items (paper packaging only). Can be monitored for effectiveness. Disadvantages of chemical vapour sterilization Requires good ventilation owing to fumes. Won't penetrate fabric- wrapped packs. Damages some plastics. Requires replacement of special solution, increasing cost. Requires hazardous waste disposal of the sterilizing solution. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 98

99. Bead sterilizers: Historically , bead sterilizers have been used in dentistry to sterilize small metallic instruments (e.g. endodontic files). This method employs a heat transfer device. The media used are glass beads or salt and the temperature achieved is 220°C. The method employs submersion of small instruments such as endodontic files and burs into the beads; they are sterilized in 10 seconds provided they are clean. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 99

100. Sterilisation process Accomplished by the following steps Presoaking :  A presoaking solution (phenolic compounds) prevents drying of debris, helps to dissolve or soften organic debris and sometimes helps in microbial killing. Cleaning :  Cleaning can be done either by hand, scrubbing or with the use of ultrasonic devices. Corrosion control and lubrication :  Instruments must be dried prior to sterilization to decrease chances of corrosion.The non-stainless steel instruments should be coated with a rust inhibitor. Packaging :  The instruments can be packed individually or in small groups and distributed on sterile or disposable disinfected trays for use at chair side .. See- through polyfilm bags or pouches facilitate instrument identification. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 100

101. Sterilization :  Autoclaving is the most accepted method of sterilization of surgical instruments as it eliminates bacteria, viruses, fungi and spores. Dry heat ovens or the unsaturated chemical vapour sterilizers are the other means of sterilization . Handling sterile instruments :  Post sterilization procedures involve drying, cooling, storage and distribution. As far as possible the sterile packages or trays should not be handled, till required for use, to reduce recontamination . Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 101

102. Storage :  Sterile packs and trays should be kept in dry, low dust, low traffic areas away from sinks and sewer of water pipes, at least a few inches above the floor. Distribution :  Sterilized packs can be placed on sterile, disposable trays for use at chair side. Placing unwrapped or wrapped instruments in drawers for direct use at chair side is not recommended. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 102

103. Sterilization Monitoring: Types of Indicators Mechanical :Measures time, temperature, and pressure. Chemical :Change in color when physical parameter is reached. Biological (spore tests):Uses biological spores to asses the sterilization process directly. Indicators are specific to the type of sterilization used. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 103

104. Mechanical Monitoring Monitor each load with mechanical (physical) indicators : Time . Temperature. Pressure. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 104

105. Chemical Monitoring Use an internal chemical indicator in every package. If the internal indicator is not visible from the outside, then also use an external indicator. Chemical indicators may be integrated into the package design. Inspect indicator(s) after sterilization and at time of use. If the appropriate color change did not occur, do not use the instruments. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 105

106. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 106

107. Biological Monitoring Assess sterilization process directly by killing known highly resistant microorganisms. Use biological indicators (spore tests) at least weekly. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings . 2003 . MMWR 2003[cited 2021Apr22 ]. Available from: https://www.cdc.gov/mmwr/index.html 107

108. CONCLUSION To conclude, sterilization, disinfection, and cleaning are the mainstay of hospital infection control activities. When properly used, disinfection and sterilization can ensure the safe use of invasive and noninvasive medical devices. The method of disinfection and sterilization depends on the intended use of the medical device: critical items (those that contact sterile tissue) must be sterilized prior to use; semicritical items (those that contact mucous membranes or nonintact skin) must undergo high-level disinfection; and noncritical items (those that contact intact skin) should undergo low-level disinfection . Cleaning should always precede high-level disinfection and sterilization. Current disinfection and sterilization guidelines must be strictly followed. Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. Rutala WA, Weber DJ. Disinfection and Sterilization in Health Care Facilities: What Clinicians Need to Know. Clinical Infectious Diseases. 2004;39(5):702–9. 108

109. REFERENCES Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017 . Ananthanarayan R. Textbook of microbiology. 10th ed. Hyderabad: University Press ; 2016. Baveja CP. Textbook of microbiology. 5th ed. New Delhi: Arya Publications; 2005. Morbidity and Mortality Weekly Report (MMWR) [Internet]. Guidelines for Infection Control in Dental Health-Care Settings — 2003. MMWR 2003[cited 2021Apr22]. Available from: https://www.cdc.gov/mmwr/index.html 109

110. Rutala WA, Weber DJ. Disinfection and Sterilization in Health Care Facilities: What Clinicians Need to Know. Clinical Infectious Diseases. 2004;39(5):702–9. Appendix C: Methods for Sterilizing and Disinfecting Patient-Care Items and Environmental Surfaces [Internet]. Centers for Disease Control and Prevention .[ cited 2021Apr22]. Available from:https ://www.cdc.gov/mmwr/preview/mmwrhtml/rr5217a4.htm WHO Guidelines on Hand Hygiene in Health Care: First Global Patient Safety Challenge Clean Care Is Safer Care [Internet]. National Center for Biotechnology Information. U.S. National Library of Medicine; [cited 2021Apr22]. Available from: https://pubmed.ncbi.nlm.nih.gov/23805438/ 110

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113. 3 main classes of autoclaves you can choose from: Class N (the most compact small autoclaves) Class B (nicknamed “big small”, or “medium” autoclaves) Class S (all other types of autoclaves, including the largest steam sterilizers) Class N steam sterilizers are essentially small dental autoclaves, that are perfect if you’re looking for the most space saving solution, and you only need to sterilize certain materials. The “N” stands for “naked solid product”, so be wary, as these dental steam sterilizers cannot be used to treat fabrics such as textiles. These machines also don’t always make use of the vacuum described above.  Class S covers a much less defined category of autoclaves, where the details are mostly found in the technical descriptions provided by the manufacturer. The letter “B” stands for “big small”, meaning that despite their smaller size (which is also perfect if you don’t work at a huge dental clinic),they can provide an excellent performance.  113

114. checklist Flush devices connected to dental unit air and water system for 20- 30 seconds between patients. Flush dental waterlines at the beginning and at the end of the day. Insert only sterile needles and syringes into multi-dose vials. Clean and disinfect blood spills immediately. Dispose of all single-use devices after use on patient. Use sterilized instruments for every patient. Decontaminate or properly contain and label extracted teeth. Properly dispose of extracted teeth containing amalgam. Heat sterilize extracted teeth before using them in educational settings. Disinfect dental prostesis and impressions before sending to the laboratory. 114

115. DENTAL RADIOGRAPHY CDC(MMWR),dec19,2003vol.52 • Contamination of working area occurs from saliva. • X-ray tube head, exposure selector and timer button are likely to get contaminated by saliva. • Precaution to be taken up : 1. Put on gloves. 2. Place the film packets and film holders in special tray. 3. Contaminated films(exposed films) to be placed in separate tray. 54 55.  4. Film holding device to be rinsed in running water to remove saliva. 5. Metallic part to be autoclaved. 6. Plastic attachments to be kept in chlorhexidine solution. 7. Wipe the x-ray tube head, exposure selector, timer button and film packets with detergents. 8. Tube can be wrapped in disposable plastics. 9. Film packets to be discarded in yellow bags. 115

116. ROTARY INSTRUMENTS - BURS  Diamond and carbide burs: After use they are placed in 0.2% gluteraldehyde and sodium phenate ( Eg . Sporicidin ) for at least 10 minutes, cleaned with a bur brush or in an ultrasonic bath. Sterilize in an autoclave or dry heat  Steel burs: May get damaged by autoclaving. Can be sterilized by using a chemical vapor sterilizer or glass bead sterilizer at 2300C for 20-30 seconds. 62 63.  ENDODONTIC INSTRUMENTS CDC(MMWR),dec19,2003vol.52 • Glass Bead or salt sterilizer is the best option, but they do not sterilize the handle. • Sterilization achieved in 10 seconds • Dry heat is used, with instruments in closed metal or perforated metal boxes. • Sterilization achieved at 218oC for 15 seconds • Gutta percha points are pre-sterilized. • Contaminated points are sterilized by 5.25% sodium hypochlorite.(1 min immersion). • Then rinse with hydrogen peroxide & dry it. 6 116

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120. HISTORICAL BACKGROUND In the mid-1800s, studies by Ignaz Semmelweis in Vienna, Austria , and Oliver Wendell Holmes in Boston, USA, established that hospital-acquired diseases were transmitted via the hands of HCWs . He also noted that doctors and medical students often went directly to the delivery suite after performing autopsies and had a disagreeable odour on their hands despite handwashing with soap and water before entering the clinic. He hypothesized therefore that “ cadaverous particles ” were transmitted via the hands of doctors and students from the autopsy room to the delivery theatre and caused the puerperal fever . As a consequence, Semmelweis recommended that hands be scrubbed in a chlorinated lime solution before every patient contact and particularly after leaving the autopsy room . Following the implementation of this measure , the mortality rate fell dramatically to 3% in the clinic most affected and remained low thereafter. 120

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122. Clinical hand washing, since then, has prevented millions of deaths of humankind. In the present times too, his idea of hand hygiene plays a central role in COVID-19 pandemic management. Authors present a brief account of life and work of this maverick genius, who was born “too early in the darkness.” He is also called the “Father of infection control” and “Savior of mothers.” 122

123. When surgeon  Joseph Lister  died at the age of 84 on February 10, 1912, he left behind  a drastic reduction in the mortality of surgical patients due to infections.  According to statistics collected by himself, the decrease went from almost 50% of those operated on to only 15 %. 123

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125. In 1864, while practicing as a professor of surgery at the University of Glasgow, Lister discovered the work of  a French chemist named Louis Pasteur . When he read in  Recherches sur la putrefaction  that fermentation was due to germs, microbes invisible to the eye, he sensed that the same cause could explain the infection of wounds. 125

126. Following the ideas of Pasteur,  Lister looked for a chemical substance with which to annihilate the germs.  After several tests he arrived at carbolic acid (now called phenol), a compound extracted from creosote that was then used to prevent the rotting of railway sleepers and the wood of ships, and which was also applied to the wastewater of cities. In 1865, after some doubtful beginnings,  he managed for the first time to heal without infection the open leg fracture of a child hit by a car. 126

127. From then on, Lister laid out a protocol to sterilize the surgical instruments, the hands of the surgeon, the dressings and the wounds with solutions of carbolic acid, and even designed a sprayer to diffuse the substance in the air of the operating room, which was definitely not pleasant. But the results made up for the inconvenience, and in 1867 Lister was able to publish his findings and his antiseptic method in a series of  articles in the magazine  The Lancet . 127

128.  From our current perspective, we might be surprised by the generous use of the corrosive and toxic phenol, which nowadays is handled in laboratories with special care. But from Lister, today we have his revolutionary idea that drew the line between old-fashioned surgery and its modern incarnation. And we have Listerine. 128

129. 10. Miscellaneous inactivating agents Pasteuri.zation MicrowC1ve : Microwaves are used in medicine for disinfection of soft contact lenses, dental instruments, dentures , milk, and urinary catheters for intermittent selfcatheterization . However, microwaves must only be used with products; that are compatible (e.g., do not melt). 129

130. Microwaves are radio-frequency waves, which are usually used at a frequency of 2450 MHz. The microwaves produce friction of water molecules in an alternating electrical field. The intermol12cular friction derived from the vibrations generates hea1t . The microwaves produced by a " hometype “ microwave oven (2.45 GHz) completely inactivate bacterial cultures, mycobacteria viruses, and G. stearothermophilus spores within 60 seconds to 5 minutes depending on the challenge organism. 130

131. Flushing and Washer Disinfectors : Flushing and washer- disinfoctors are automated and closed equipment that clean and disinfect objects from bedpans, urinals and washbowls to surgical instruments and anesthesia tubes. They have a short cycle of a few minutes. They clean by flushing with warm water, possibly with a detergent, and then disinfect by flushing the items with hot water or with steam. Because this machine empties, cleans, and disinfects, manual cleaning is eliminated, fewer disposable items are needed , and fiewer chemical gemicides are used. 131

132. Ultraviolet radiation : The wavelength of UV radiation ranges from 328 nm to 210 nm. Its maximum bactericidal effect occurs at 240-280 nm . Mercury vapour lamps emit more than 90 per cent of their radiation at 253. 7 nm, which is near the maximum microbicidal activity (155). UV radiation has been employed in the disinfection of drinking water , air, titanium implants and contact lenses . Bacteria and viruses are more easily killed by UV light than the bacterial spores. 132

133. Ozone : Ozone has been used for years as a drinking water disinfectant. Ozone is produced when 0 2 is energized and split inito two monatomic (01) molecules. The monatomic m,ygen molecules then collide with 0 2 molecules to form ozone·, which is 0 3 • Ozone is a powerful oxidant that destroys microorganisms but it is highly unstable (i.e. halflife of 22 minutes of room temperature). 133

134. Steam Sterilization Among sterilization methods, steam sterilization is the most widely used for wrapped and unwrapped critical and semicritical items that are not sensitive to heat and moisture. When using an autoclave, the load must be placed so that steam can circulate freely around each item, because steam must be able to reach all instrument surfaces at a required temperature and pressure for a specified time in order to kill all microorganisms and achieve sterilization. Be sure to follow the autoclave manufacturer's operating instructions The majority of tabletop sterilizers used in dental practice are gravity displacement sterilizers, although prevacuum sterilizers are becoming widely available. Prevacuum sterilizers are fitted with a pump to create a vacuum in the chamber and to ensure air removal from the sterilizing chamber before the chamber is pressurized with steam. Relative to gravity displacement, this procedure allows faster and more positive steam penetration throughout the entire load. Autoclave An autoclave is a self locking machine that sterilizes with steam under pressure, achieved by the high temperature. Autoclaves are the universally accepted means for sterilization. It is generally accepted that an autoclave chamber must reach at least 121°C at 15 Psi for a minimum of 30 minutes to ensure adequate sterilization. Sterilization time may vary depending on the quantity and density of items in the autoclave chamber. Overloading must be avoided. Instruments and materials for sterilizing in the autoclave are usually enclosed in the muslin wrappers as surgical packs. These packs should be porous to allow steam to penetrate and reach the instruments. The autoclave is employed for the sterilization of the instruments, extraction forceps, surgical instruments, explorers etc. The sterilized instruments should remain wrapped until next used . 134

135. Testing of efficacy Autoclave indicator tape and autoclave indicator bags change colour when the proper temperature has been reached. While the indicator tape quick-check should be conducted with every load, it must be supplemented periodically by use of a biological indicator (such as Bacillus spores) buried in the center of a load to confirm the sterilization. Advantages of steam sterilization Is quick and easy to use. Allows loads to be packaged, making it easier to maintain items in a sterile state. Penetrates fabric and paper wrappings. Can be readily monitored for effectiveness. Is economical and very reliable. Disadvantages of steam heat sterilization May cause rust and corrosion (corrosion inhibitors such as sodium nitrite are available that may reduce this problem). May damage plastics. May blunt certain sharp items. 135

136. Dry Heat Sterilization Dry heat is used to sterilize materials that might be damaged by moist heat (e.g. burs and certain orthodontic instruments). Although dry heat has the advantages of low operating costs and being non-corrosive, it is a prolonged process and the high temperatures required are not suitable for certain patient care items and devices with temperatures ranging from 300 degrees F (149 degrees C) and upward can be used for sterilization. Dry heat sterilizers used in dentistry include static-air and forced-air types. The static-air type is commonly called an oven-type sterilizer. The forced-air type is also known as a rapid heat transfer sterilizer. Heated air is circulated through the chamber at a high velocity, permitting more rapid transfer of energy from the air to the instruments, thereby reducing the time needed for sterilization compared to the oven-type sterilizer. Advantages of dry heat sterilization Is very reliable. Rust and corrosion are not a problem, provided that items are dry prior to sterilization. Is easy to use and requires little maintenance. Can be readily monitored for effectiveness. Disadvantages of dry heat sterilization Usually requires longer processing times than do steam sterilization or unsaturated chemical vapour . Damages some plastics. Requires careful loading. May char fabric. High temperatures may prohibit use with some materials and may melt or destroy some metal or solder joints . 136

137. Other Methods of Sterilization Liquid chemical germicides: Heat-sensitive critical and semicritical instruments and devices can be sterilized by immersing them in liquid chemical germicides. However, items sterilized in this manner can require approximately 12 hours of complete immersion. Additionally items sterilized in this manner must be rinsed with sterile water to remove any toxic or irritating residues, handled using sterile gloves and dried with sterile towels, delivered to the point of use in an aseptic manner and then used immediately. Because of these limitations, they are almost never used to sterilize instruments. Rather, these chemicals are more often used for high-level disinfection of heat-sensitive semicritical instruments and devices. Shorter immersion times (12-90 minutes) make high-level disinfection more practical than sterilization; however, instruments and devices disinfected in this manner must still be handled as if sterile (e.g. rinsed with sterile water, dried with sterile towels, etc.) and used immediately. Chemical sterilants (e.g. glutaraldehyde , peracetic acid, hydrogen peroxide) are powerful, sporicidal chemicals and are highly toxic. Instruments can be sterilized by placing them in a 2% solution of glutaraldehyde for 6-10 hours. The chemical sterilants must only be used according to manufacturer's instructions and for those applications indicated on their label. Misapplications include use as an environmental surface disinfectant or instrument holding solution. Alcohols are effective as skin antiseptics.Usually a 50% to 80% ethyl alcohol solution is recommended. In general, use of heat-sensitive semi- critical items that must be processed with liquid chemical germicides is discouraged; heat-tolerant or disposable alternatives are available for the majority of such items. 137

138. Dental prosthesis, impressions, orthodontic appliances and other prosthodontic materials (e.g. occlusal rims, temporary prosthesis, bite registrations) should be thoroughly rinsed under gentle running water to remove blood, saliva or debris. The disinfection can be done by a short-term immersion in 0.5% or 1% sodium hypochlorite. In addition, immersion in glutaraldehydes , povidone -iodine diluted in water or halogenated phenol has no apparent effect on the dimensional stability of rubber materials. The best time to clean and disinfect the impressions, prosthesis or appliances is as soon as possible after removal from the patients mouth, before drying of blood and saliva. 138

139. (5) The microbicidal activity of a new disinfectant, " superoxidized water" has been examined. The concept of electrolyzing saline to create a disinfectant or antiseptic is appealing because the basic materials of saline and electricity are inexpensive and the end product (i.e. , water) does not damage the environment. The main products of this water are hypochlorous acid (e.g ., at a concentration of about 144 mg/L) and chlorine. Park K. Park's textbook of Preventive and social medicine. 25 th ed. India: Bhanot Publishers; 2017. 139

140. Multiple semicritical dental devices that touch mucous membranes are attached to the air or waterlines of the dental unit. Among these devices are high and low-speed handpieces , prophylaxis angles, ultrasonic and sonic scaling tips, air abrasion devices and air and water syringe tips. These devices have the potential for retracting oral fluids into their internal compartments. Restricted physical access limits their cleaning. This indicates that retained patient material can be expelled intraorally during subsequent uses. Any dental device connected to the dental air/water system that enters the patient's mouth should be run to discharge water, air or a combination for a minimum of 20- 30 seconds after each patient. This procedure physically flushes out patient material that might have entered the turbine, air and waterlines. Heat methods can sterilize dental handpieces and other intraoral devices attached to air or waterlines. Proper scrubbing with detergent, water and drying followed by wiping with a suitable chemical disinfectant is essential for those ultrasonic scalers , handpieces and air syringes that cannot be sterilized. For processing any dental device that can be removed from the dental unit air or waterlines, neither surface disinfection nor immersion in chemical germicides is an acceptable method. Manufacturer's instructions for cleaning, lubrication and sterilization should be followed to ensure both the effectiveness of the process and the longevity of handpieces . Some components of dental instruments are permanently attached to dental unit waterlines and although they do not enter the patient's oral cavity, they are likely to become contaminated with oral fluids during treatment procedures. Components (e.g. handles or dental unit attachments of saliva ejectors, high- speed air evacuators and air/water syringes) should be covered with impervious barriers that can be changed after each use. If the item becomes visibly contaminated during use, dental practitioner should clean and disinfect with a disinfectant (intermediate- level) before use on the next patient. 140

141. First , formaldehyde-alcohol has been deleted as a recommended chemical sterilant or high-level disinfectant because it is irritating and toxic and not commonly used. Second , several new chemical sterilants have been added, including hydrogen peroxide, peracetic acid 58, 69, 70, and peracetic acid and hydrogen peroxide in combination. Third , 3% phenolics and iodophors have been deleted as high-level disinfectants because of their unproven efficacy against bacterial spores, M. tuberculosis, and/or some fungi. 55, 71 Fourth , isopropyl alcohol and ethyl alcohol have been excluded as high-level disinfectants 15 because of their inability to inactivate bacterial spores and because of the inability of isopropyl alcohol to inactivate hydrophilic viruses (i.e., poliovirus, coxsackie virus).72 Fifth , a 1:16 dilution of 2.0% glutaraldehyde-7.05% phenol-1.20% sodium phenate (which contained 0.125% glutaraldehyde , 0.440% phenol, and 0.075% sodium phenate when diluted) has been deleted as a high-level disinfectant because this product was removed from the marketplace in December 1991 because of a lack of bactericidal activity in the presence of organic matter; a lack of fungicidal, tuberculocidal and sporicidal activity; and reduced virucidal activity.49, 55, 56, 71, 73-79 Sixth , the exposure time required to achieve high-level disinfection has been changed from 10-30 minutes to 12 minutes or more depending on the FDA-cleared label claim and the scientific literature. 27, 55, 69, 76, 80-84 A glutaraldehyde and an ortho-phthalaldehyde have an FDA-cleared label claim of 5 minutes when used at 35°C and 25°C, respectively, in an automated endoscope reprocessor with FDA-cleared capability to maintain the solution at the appropriate temperature. 85 141