This document discusses sterilization and disinfection in dentistry. It defines sterilization as removing all microorganisms and disinfection as removing pathogens. It describes various sterilization methods like heat, radiation, filtration and chemicals. Heat methods include dry heat using devices like hot air ovens and moist heat using autoclaves. Proper sterilization of dental instruments and impressions is important to prevent infection.

1. STERILIZATION AND
DISINFECTION IN DENTISTRY
Dr Purva Pihulkar
Assistant Professor
Dr HSRSM Dental College and Hospital

2. INTRODUCTION
 Sterilization
It is defined as the process by which an
article, surface or medium is freed of all living
microorganisms either in vegetative or spore
state.
 Disinfection
It is destruction or removal of all pathogenic
organisms or organisms capable of producing
infections but not necessarily spores.

3.  Disinfectant
Products used to kill microorganisms on
nonliving objects or surfaces.
 Antiseptic
They are chemical disinfectants that can be
safely applied on skin or mucous membrane
and are used to prevent infection by
inhibiting the growth of bacteria.

4. METHODS OF STERILIZATION
1. Physical methods
 Sunlight
 Heat
-Dry
-Moist
 Radiation
 Filtration
2. Chemical Methods

5. 1) Sunlight
- The microbicidal activity of sunlight is mainly due to
the presence of ultra violet rays in it.
- It is responsible for spontaneous sterilization in
natural conditions.
- In tropical countries, the sunlight is more effective
in killing germs due to combination of ultraviolet
rays and heat.
- By killing bacteria suspended in water, sunlight
provides natural method of disinfection of water
bodies such as tanks and lakes.

6.  Semple and grieg showed that in india,
typhoid bacilli exposed to sun on pieces of
white drill cloth were killed in 2 hours,
whereas contols kept in dark were alive after
6 days.
 Bacteria suspended in water are readily
destroyed by exposure to sunlight.

7.  2) Heat
- Heat is considered to be most reliable
method of sterilization of articles.
- It is of types
- A) dry heat
- B) moist heat

8. Dry heat sterilization
 The temperature required is usually higher
than 356° F or 180 °C.
 Thus Dry heat acts by protein denaturation
and oxidative destruction.
 Articles that are heavily contaminated
require higher temperature or prolonged
exposure.
 More the number of microorganisms, higher
the temperature or longer the duration
required.

9.  Moist heat sterilization
 Moist heat penetrates materials much more
rapidly than dry heat because water
molecules conduct heat better than air.
 Thus moist heat is superior to dry heat in
action.
 Lower temperatures and a shorter exposure
time are therefore required than for dry heat.
 Mode of Action: Moist heat kills
microorganism by denaturing their proteins.

10. Dry Heat Sterilization
 Following procedures are used for
sterilization of dry heat:-
1. Flaming
2. Incineration
3. Hot air oven

11. 1) Flaming
o In flaming, Glass slides, scalpels,tip of
forceps, inoculating loops and mouths of
culture tubes are passed through bunsen
flame.
o inoculating loops carrying infective material
may be dipped in disinfectant before
flaming to prevent spattering.

12.  2) Incineration
 This is a method of destroying contaminated
material by burning them in incinerator.
 Articles such as soiled dressings; animal
carcasses, pathological material and bedding
etc should be subjected to incineration.

13.  This technique results in the loss of the
article, hence is suitable only for those
articles that have to be disposed.
 Burning of plastic emits dense smoke, and
hence they should not be incinerated.

14.  3) Hot Air Oven
• This method was introduced by Louis
Pasteur.
• Articles to be sterilized are exposed to high
temperature (160º C) for duration of one hour
in an electrically heated oven.
• Since air is poor conductor of heat, even
distribution of heat throughout the chamber
is achieved by a fan.
• The oven should be fitted with a thermostat
control, temperature indicator, meshed
shelves and must have adequate insulation.

15.  Principle of HOT AIR OVEN
 Sterilization by dry heat is accomplished by
conduction.
 The heat is absorbed by the outside surface
of the item, then passes towards the centre
of the item, layer by layer.
 The entire item will eventually reach the
temperature required for sterilization to take
place.

16.  Sterilization process:
 Articles to be sterilized must be perfectly dry
before placing them inside to avoid breakage.
 Articles must be placed at sufficient distance
so as to allow free circulation of air in
between.
 Mouths of flasks, test tubes and both ends of
pipettes must be plugged with cotton wool.
 Articles such as petri dishes and pipettes may
be arranged inside metal canisters and then
placed.
 Individual glass articles must be wrapped in
kraft paper or aluminum foils.

17.  Sterilization cycle:
 Different temperature-time relations for
holding time are
 60 minutes at 160ºC
 40 minutes at 170ºC
 20 minutes at 180ºC.

19. Hot air oven used for sterilization of
1. Glass wares like glass syringes, petridishes,
flasks,pipettes and test tubes.
2. Surgical instruments like scalpels,
scissors,forceps,mouth mirrors,probes.
3. Chemical like liquid paraffin,fats,
sulphonamides powders.

20.  Sterilization control:
 ƒ
Physical:Temperature chart recorder and
thermocouple. ƒ
 Chemical: Browne’s tube (green spot, color
changes from red to green)

21.  Biological:
 Clostridium tetani on paper strips are placed
inside envelopes and then placed inside the
hot air oven.
 Upon completion of sterilization cycle, the
strips are removed and inoculated into
thioglycollate broth or cooked meat medium
and incubated at 37oC for 3-5 days.
 Proper sterilization should kill the spores and
there should not be any growth

22.  Advantages: It is an effective method of
sterilization of heat stable articles.
 The articles remain dry after sterilization.
 This is the only method of sterilizing oils and
powders.
 Disadvantages: ƒ
Since air is poor conductor of
heat, hot air has poor penetration.
 ƒ
Cotton wool and paper may get slightly
charred. ƒ
 Glasses may become smoky. ƒ
 Takes longer time compared to autoclave

23.  Precautions
1. It should not be overloaded
2. Rubber materials or inflammable materials
should not be kept inside oven.
3. Oven must allowed to cool for two hours
before opening the doors,since the
glasswares may crack by sudden cooling.

24. Moist heat sterilization
 Used at temperatures as follows:-
1. At a temperature below 100ºC
2. At a temperature of 100ºC
3. At a temperature above 100ºC

25. 1) At a temperature below 100ºC
a) Pasteurisation
 It uses heat at temperatures sufficient to
inactivate harmful organism in milk.
 when heat-treated milk become denatured
and stop the enzymes from functioning.This
helps to stop pathogen growth by stopping
the functionality of the cell.
 Holder method 63 for 30 min
 Flash method 72 for 20 sec

26.  B) Inspissation
 This is a technique disinfect egg and serum containing
media.
 The medium containing serum or egg are placed in an
inspissator and heated at 80-85º C for 30 minutes on
three successive days.
 Proteins in the serum will coagulate at higher
temperature.
 On the first day, the vegetative bacteria would die and
those spores that germinate by next day are then killed
the following day.

27. C)Vaccine bath
-The contaminating bacteria in a vaccine
preparation can be inactivated by heating in a
water bath at 60ºC for one hour.
-Only vegetative bacteria are killed and
spores survive.

28. 2) At a temperature of 100 C
a) Boiling
-Boiling water (100ºC) kills most vegetative
bacteria and viruses immediately.
-When absolute sterility is not required,
certain metal articles and glasswares can be
disinfected by placing them in boiling water
for 10-20 minutes.

29.  2)Tyndallization
-steam at 100 for 20 min on 3 successive days is
used.
-The principle is that 1st exposure kills
vegatative forms in intervals between
heatings the remaining spores germinate into
vegetative forms which are killed on
subsequent heatings.
-used for sterilization of culture media.

30. 3) At a temperature above 100°C
Autoclave
 Standard sterilization method in hospitals.
 The Autoclave works under the same
principle as the pressure cooker where water
boils at increased atmospheric pressure.

31.  The autoclave is a double walled chamber in
which air is replaced by pure saturated steam
under pressure.
 The air in the chamber is evacuated and filled
with saturated steam.
 The chamber is closed tightly the steam
keeps on filling into it and the pressure
gradually increases.

32. Autoclave

33.  The items to be sterilized get completely
surrounded by saturated steam (moist heat)
which on contact with the surface of material
to be sterilized condenses to release its latent
heat of condensation which adds to already
raised temperature of steam so that
eventually all the microorganisms in what
ever form are killed.

34.  The usual temperature achieved is 121 °C at a
pressure of 15 ppsi. at exposure time of only
15-20 mins.
 By increasing the temperature, the time for
sterilizing is further reduced.

35.  Uses
1. To sterilize culture media,rubber material,
gowns, dressing, gloves.
2. Surgical instruments like forceps,
scapels,mouth mirrors,probes,etc.
3. use the power of steam to kill bacteria,
spores and germs resistant to boiling water
and powerful detergents.

36.  Precautions
1. The air must be allowed to escape from
chamber as temperature of air steam
mixture is lower than that of pure steam.
2. Materials should be arranged in such a
manner as to ensure free circulation of
steam inside chamber.

37.  Advantage:Very effective way of
sterilization, quicker than hot air oven.
 Disadvantages: Drenching and wetting or
articles may occur, trapped air may reduce
the efficacy, takes long time to coo

38.  Glass bead sterilizer
 It is mainly used for sterilizing the working ends
of endodontic files and reamers by placing them
in a container containing glass beads heated
upto approximately 225°C (437°F)
 Glass bead sterilizer works on the principle of
intense dry heat.
 intense dry heat damages vegetative and spore
forms of bacteria.

39.  Glass beads should be less than 1mm in size
because larger beads are not effective in
transferring heat due to large spaces between
the beads.
 The instruments to be sterilized are immersed
into heated up glass beads and left for period of
time.
 Glass bead sterilizer has disadvantage that
beads which are less than 1 mm in diameter get
struck in the instruments when they are
introduced into the root canal.

40. Filtration
 Filtration does not kill microbes, it separates
them out.
 Filtration allows for the exclusion of
organisms based upon size.
 Various applications of filtration include
removing bacteria from ingredients of culture
media, preparing suspensions of viruses and
separating toxins from culture, counting
bacteria.

41.  Types of filters
1. Earthenware candles
o These filters are made up of diatomaceous
earth or porcelain.They are usually baked into
the shape of candle.
o Water poured into the upper basin, where
it filters through the candle and collects in the
lower container.
o it physically traps microorganisms and other
suspended contaminants
in its pores.

42.  2) Asbestos disc filters( seitz filter)
 These filters are made from chrysotile type of
asbestos, chemically composed of magnesium
silicate.
 It consists of disc, which is to be used only once.
 This disc absorbs the contaminants and sterilize
the liquid.

43.  3) Sintered glass filter
 These are made from finely ground glass that are fused
sufficiently to make small particles adhere to each other.
 They are usually available in the form of disc fused into a
glass funnel.
 This funnel separates the contaminants and sterilize the
solution.
 They are washed in running water in reverse direction
and cleaned with warm concentrated
H2SO4 and sterilized by autoclaving.

44.  4) Membrane filters
 These filters are composed of cellulose diacetate.
 These membranes have a pore diameter ranging from
0.015 µm to 12 µm.
 The membrane separation process is based on the
presence of semi permeable membranes.
 The principle is quite simple: the membrane acts as a
very specific filter that will let water flow through, while
it catches suspended solids and other substances.

45.  3. Radiation:
- Non Ionising Radiations
 Rays of wavelength longer than the visible light
are non-ionizing.
 Microbicidal wavelength of UV rays lie in the
range of 200-280 nm, with 260 nm being most
effective.
 UV rays are generated using a high-pressure
mercury vapor lamp.
 It is at this wavelength that the absorption by
the microorganisms is at its maximum, which
results in the germicidal effect.
 Microorganisms such as bacteria, viruses,
yeast, etc. that are exposed to the effective UV
radiation are inactivated within seconds.

46.  Since UV rays don’t kill spores, they are
considered to be of use in surface disinfection.
 UV rays are employed to disinfect hospital
wards, operation theatres, virus laboratories,
corridors, etc.
 Disadvantages of using uv rays include low
penetrative power, limited life of the uv bulb,
organic matter and dust prevents its reach, rays
are harmful to skin and eyes.
 It doesn't penetrate glass, paper or plastic.

47. - Ionizing radiation
• X-rays,gamma rays and cosmic rays are
highly lethal to DNA and other vital
constituents.
• They have high penetrative power.
• Used mainly in industrial facilities e.g.
sterilization of disposable plastic syringes,
gloves, specimens containers,Petri Dishes,
oils,greases,fabrics and metal foils.

48. Instruments for sterilization
are classified as follows:

49.  Endodontic Instrument Sterilization:
1. Files must be sterilized before use.
ANSI/ADA Specification 28 recommends:
2. Scrub the instruments with soap and warm
water.
3. Rinse thoroughly with distilled water.
4. Allow to air dry.

50. 5) Place the instruments, unwrapped, in the
autoclave tray.
6) Use fresh distilled water.
7) Steam Autoclave at 136° C (plus or minus 2°
C) for 20 minutes.
8) All rotary files are single patient use
instruments.
9) Recommended File Disposal: Place used files
in a Biohazard Sharps container.

51.  ULTRASONICTIPS STERILIZATION:
 Maintain a temperature of at least 136°C
(277°F) for a minimum of 20 minutes per USP
recommendations.

52.  OBTURATORS:
 Disinfect the obturator in a 5.25% sodium
hypochlorite solution (bleach) for one minute.
 Rinse the obturator in 70% alcohol.
 Dry the obturator for several seconds on a
clean work surface to allow evaporation of
excess alcohol.

53.  Handpieces
 Wipe with an alcohol gauze.
 Clean and lubricate handpieces with a cleaner/
lubricant after each use and before autoclaving.
 This will ensure proper operation and a long
service life for your handpiece.
 Do not use a cleaner/ lubricant after autoclaving,
only use before sterilization.
 Follow the instructions provided with the
handpiece purchased for complete maintenance
instructions.

54.  Motors
 The entire motor and cord assembly supplied
with your unit must be surface sterilized by
autoclave.
 sterilize at 132º C (270º F) for 3 minutes.
 Before autoclaving the motor and cord
assembly, always install the autoclaving plug
into the motor and motor connector.
 Motor/handpiece holding cradle is also fully
autoclavable.

55.  Recommended Procedure for disinfecting the
alginate impression
 Rinse the impression thoroughly under
running tap water, shake the impression to
remove excess water.
 Dip the impression in a 1:10 solution of
sodium hypochlorite for several seconds to
ensure maximum contact of undercut with
the disinfectant.
 Wrap the impression in gauze soaked in 1:10
sodium hypochlorite, place in a plastic bag
and seal for 10 minutes.

56.  Remove the impression and rinse thoroughly
under running tap water.
 Dental casts from impressions may harbor
infectious microorganisms or the wax bite
records from the patients may cause dental casts
to become infected.
 Dental casts may be disinfected by adding
disinfectant like iodophor or neutral
gluteraldehyde to dry gypsum during the mixing
process.
 Spraying the dental casts with iodophor or
chlorine products may be recommended.

57. Precautions for HIV patients
 Special precautions for dental care include the
use of gloves, suction tubing and reservoirs when
working inside the mouth and sterilization or
disinfection of instruments and other
contaminated objects.
 Masks and protective eyewear should be used
particularly when the spattering of blood is likely.
 Disposable cups for mouth washing are
advisable.
 Otherwise, glassware should always be
disinfected adequately or autoclaved after each
use.

58.  Needles and other sharp instruments or
materials should be placed in a puncture-proof
container immediately after use and should
preferably be incinerated.
 Liquid wastes such as bulk blood, suction fluids,
excretions and secretions should be carefully
poured down a drain connected to an adequately
treated sewage system, or disposed of in a pit
latrine.
 Solid wastes, such as dressings and laboratory
and pathology wastes, should be considered as
infectious and treated by incineration, burning or
autoclaving.
 Other solid wastes, such as excreta, may be
disposed of in a hygienically controlled sanitary
landfill or pit latrine.

59.  In mega check up camps, instruments are
sterilized using disinfectants like 2%
glutaraldehyde,6% hydrogen peroxide and
99.9% ethyl alcohol.
 Latter they are autoclaved.
 Sometimes, instead of mouth mirrors ice
cream sticks can be used to examine the oral
cavity.

60.  An ideal disinfectant or antiseptic has the
following characteristics:
 1. Ideally, the disinfectant should have a wide
spectrum of antimicrobial activity.
 2. It should act in the presence of organic
matter.
 3. It should not be toxic to human or corrosive.
 4. It should be stable upon storage and should
not undergo any chemical change.

61.  5. It should be odorless or with a pleasant
odor.
 6. It should be soluble in water and lipids for
penetration into microorganisms.
 7. It should be effective in acidic as well as
in alkaline media.
 8. It should have speedy action.
 9. If possible, it should be relatively
inexpensive.

62. 1. Alcohols
 Mode of action: Alcohols dehydrate cells,
disrupt membranes and cause coagulation
of protein.
 Examples: Ethyl alcohol, isopropyl alcohol
and methyl alcohol
 Application:
70% ethyl alcohol (spirit) is used as
antiseptic on skin.

63. o Isopropyl alcohol is used to disinfect
surfaces.
o It disinfects clinical thermometers.
o Methyl alcohol kills fungal spores, hence is
useful in disinfecting inoculation hoods.
 Disadvantages: Skin irritant, volatile
(evaporates rapidly), inflammable

64.  2) Aldehydes
 Mode of action: Acts through alkylation of
amino-, carboxyl- or hydroxyl group, and
probably damages nucleic acids.
 Examples: Formaldehyde, Gluteraldehyde
 Application:
40% Formaldehyde (formalin) is used for surface
disinfection and fumigation of rooms,
chambers, operation theatres, biological safety
cabinets, wards, sick rooms etc.
2% gluteraldehyde is used to sterilize
thermometers, cystoscopes, bronchoscopes,
centrifuges, anasethetic equipments etc.

65.  3) Phenols
 Mode of action: Act by disruption of membranes,
precipitation of proteins and inactivation of
enzymes.
 Examples: 5% phenol, 1-5% Cresol, 5% Lysol,
hexachlorophene, chlorhexidine, chloroxylenol
(Dettol)
 Applications:They act as disinfectants at high
concentration and as antiseptics at low
concentrations.
 They are bactericidal, fungicidal,
mycobactericidal but are inactive against spores
and most viruses.

66.  4) Halogens
 Mode of action:They are oxidizing agents and
cause damage by oxidation of essential sulfydryl
groups of enzymes. Chlorine reacts with water to
form hypochlorous acid, which is microbicidal.
 Examples: Chlorine compounds (chlorine,
bleach, hypochlorite) and iodine compounds
(tincture iodine, iodophores)
 Applications:Tincture of iodine (2% iodine in
70% alcohol) is an antiseptic. For hand washing
iodophores are diluted in 50% alcohol.

67.  5) Oxidising agents
i. Hydrogen peroxide
 Mode of action: It acts on the microorganisms
through its release of nascent oxygen.
Hydrogen peroxide produces hydroxyl-free
radical that damages proteins and DNA.
 Application:
 It is used at 6% concentration to
decontaminate the instruments, equipments
such as ventilators.

68.  7) Surface active agents
 Mode of actions:They have the property of
concentrating at interfaces between lipid
containing membrane of bacterial cell and
surrounding aqueous medium.
They disrupt membrane resulting in leakage
of cell constituents.
 Examples:These are soaps or detergents.
Detergents can be anionic or cationic.

69.  8) Dyes
 Mode of action: Acridine dyes are bactericidal
because of their interaction with bacterial nucleic
acids.
 Examples:Aniline dyes such as crystal violet,
malachite green and brilliant green.
Acridine dyes are acriflavin and aminacrine.
A related dye, ethidium bromide, is also germicidal.
They are more effective against gram positive
bacteria than gram negative bacteria and are more
bacteriostatic in action.

70.  Applications:
 They may be used topically as antiseptics to
treat mild burns.
 They are used as paint on the skin to treat
bacterial skin infections.
 The dyes are used as selective agents in
certain selective media

71.  9) Gases
 Mode of action: It is an alkylating agent. It acts by
alkylating sulfydryl-, amino-, carboxyl- and hydroxyl-
groups.
 Properties: It is a cyclic molecule, which is a
colorless liquid at room temperature. It has a sweet
ethereal odor, readily polymerizes and is flammable.
 Application: It is a highly effective chemisterilant,
capable of killing spores rapidly. It requires presence
of humidity.

72.  It is used to sterilize heat labile articles such as
bedding, textiles, rubber, plastics, syringes,
disposable petri dishes, complex apparatus like
heart-lung machine, respiratory and dental
equipments.
 Disadvantages: It is highly toxic, irritating to
eyes, skin, highly flammable, mutagenic and
carcinogenic.

74. Conclusion
 “Prevention is better than cure” a proverb
well suited to sterilization.
 Thorough understanding of the application
of sterilization will help ensure safety from
the invisible but deadly world of microbial
pathogens.
 Hence utilization of proper sterilization,
disinfectants and aseptic procedures help us
achieve the safety of our professional
demands.

75.  References
 Textbook of microbiology Anantnarayan
 Textbook of microbiology C P Baveja
 Sterilization and Disinfection - Sridhar Rao P.N
 Sterilization Protocols in Dentistry – A Review
 Lakshya Rani et al /J. Pharm. Sci. & Res.Vol. 8(6),
2016, 558-564
 Endodontic Sterilization Guide
 Infection Control in Orthodontics Dr Shilpa Kalra,
DrTulikaTripathi , Dr Priyank Rai Journal of
Orthodontics and Endodontics 2015Vol. 1