The concept of asepsis and its role in the prevention of infection was put forward nearly 2 centuries ago. The general principles for asepsis were laid down by Hungarian abstetrician, Ignaz semmelweiss in europe in early 1850’s and Oliver Holmes in USA. These principles were accepted after Joseph Lister’s studies on prevention of wound infection carried out between 1865-91. Lister, working on antisepsis, initially used phenol (dilute carbolic acid) for contaminated wounds, later applied it in all surgical wounds, also in operating room by nebulization of the solution. Further developments occurred with the introduction of steam sterilization surgical masks, sterile gloves, sterile gowns and drapes etc.
In present days certain guidelines and regulations are recommended by accepted bodies, which have to be followed in dental practice and up graded in every general body meeting.
CLASSIFICATION OF METHODS OF STERILIZATION
Factors influencing sterilization by heat are : –
A. DRY HEAT
Killing is due to :
Example : inoculating wires, needles, forceps etc.
b. Flaming : The article is passed over flame without allowing it to become red hot.
Example : Glass plates, Cotton wool plays and glass slides.
c. Hot Air Oven: It is used to sterilize items, which do not get damaged by high temp. such as laboratory glass wave, flasks, scissors, impression trays (metal), all stainless steel instruments with sharp cutting edges, (preferred) B.P. handles, Dapen dishes, mouth mirrors and poles. Hot air is poor conductor of heat and poor penetrating capacity. So grease, oils, powders plastics, rubber-containing substances should be sterilized by other methods. High temp. can damage fabrics or melt them.
Temp. & Time: The sterilization is complete if these two factors are achieved throughout the load.
Sterilization Control of Hot Air Oven
GLASS BEADS STERILIZER:
This method employs a heat transfer device. The media used are glass beads, molten metal and salt. The temperature achieved is of 220oC. The method employs submersion of small instruments such as endodontic files and burs, into the beads; and are sterilized in 10 seconds provided they are clean. A warm-up time of at least 20 minutes is recommended to ensure uniform temperatures in these sterilizers.
Some hand piece can be sterilized by dry heat. The hand pieces should be carefully cleaned and lubricated with special heat resistant oils.
B. MOIST HEAT:
Effective by denaturation and coagulation of proteins.
a. Temperature below 100oC.
b. Temperature at 100oC
c. Temperature above 100oC
These are three major factors required for effective autoclave :
Example: Diagnostic and prognostic Instruments, plastic filling Instrument, impression trays, laboratory equipments, surgical instruments etc. Higher temperature and greater pressure shorter the time required for sterilization.
Time required to sterilize for a particular item also varies with the amount of material for the thickness of the wrap.
Radiation used for sterilization is of two types
It is effective for heat labile items. Bellamy (1959) reported that it has great penetrating properties. It is commonly used by the industry to sterilize disposable materials such as needles, syringes and swabs.
The lethal action of this radiation is believed to be due to its effect on the DNA of nucleus and on the other vital cell components. There is no appreciable rise in temperature. High energy gamma rays from cobalt-60 are used to sterilize such articles.
Two types of non-ionizing radiations are used for sterilization:-
It is absorbed by proteins and nucleic acids and kills microorganisms by the chemical reactions it sets up in the bacterial cell. It has low penetrating capacity and its main application is purification of air in operating rooms; viz, to reduce the bacteria in air, water and on the contaminated surfaces. All forms of bacteria and viruses are vulnerable to ultraviolet rays below 3000 atmospheric pressure. Excessive exposure of skin can produce serious burns. Care must be taken to protect the eyes while using U-V radiation for sterilization.
It is another form of dry heat sterilization. It is most commonly used to purify air, such as in the operating room. Infrared is effective, however, it has no penetrating ability.
Several studies have shown that, when performed correctly, ultrasonic cleaning will remove dried serum, whole blood, plaque, zinc phosphate cement, and polycarboxylate cement from instruments, metal surfaces and dentures. It has been found to be more effective than manual cleaning.
Ultrasonic cleaning minimizes the handling of contaminated instruments by the nurse and reduces the chance of injuries from sharp, contaminated instruments.
Instruments are loaded into a metal basket, which is then placed into the ultrasonic bath. The unit is activated for the time recommended by the manufacturer (usually about 6 minutes). Instruments, which are contained in cassettes, are cleaned for 12 minutes.
After the cleaning cycle is complete, the basket is taken to the sink and the instruments are carefully and thoroughly rinsed under tap water. The instruments are checked for residual debris, which may be safely removed manually.
Instruments are taken to the packaging area, where they are unloaded from the baskets onto a thick disposable paper towel. The instruments are thoroughly ‘pat’ dried using strong paper towels. Drying is important.
Small rotary and Endodontic instruments should be held in beakers of ultrasonic cleaning solution which are suspended in the cleaning bath
ULTRASONIC CLEANERS AND SOLUTIONS
The Clinical Research Associates (CRA) recommended the following ultrasonic cleaners:
BIOSONIC – Whaledent
T33C – Health Sonics Group
CLOSTER 3 – Provides ultrasonic clean, rinse and dry, but is noisy
Details of these cleaners are given in the report.
They are used to disinfect the skin of a patient prior to surgery, and to disinfect the hands of the operator. No available chemical solution will sterilize instruments immersed in it. Secondly, there is a risk of producing tissue damage if residual solution is carried over into the wound while it is being used. The chemicals used are
i. Formaldehyde: This is a broad-spectrum antimicrobial agent, which is used for disinfection. It is a hazardous substance, inflammable and irritant to the eye, skin and respiratory tract. This is used to upto 500c and has limited sporicidal activity. It is used for large heat-sensitive equipment such as ventilators and suction pumps excluding rubber and some plastics.
ii. Glutaraldehyde: It is toxic, irritant and allergenic. It is a high level disinfectant. It is applicable where heat cannot be used. It is active against most vegetative bacteria (including M. Tuberculosis) and some viruses (including HIV and HBV), fungi and bacterial spores. It is frequently used for heat sensitive material. A solution of 2 percent glutaraldehyde (Cidex), requires immersion of 20 minutes for disinfection; and 6 to 10 hours of immersion for sterilization. Stonehill et al (1963) reported that glutaraldehyde kills vegetative bacteria, spores, fungi and virus by alkylation on a 10-hour contact. The Centre for Disease Control includes it in the list of effective agents against hepatitis viruses. It is also toxic and irritating, and hence, not used on certain surfaces such as furniture, walls and floors. It can be safely used on metal instruments (for less than 24 hours), rubber, plastics and porcelain. It is activated by addition of sodium bicarbonate, but in its activated form in remains potent only for 14 days
Ethanol and isopropyl alcohols are frequently used as antiseptic. Alcohols possess some antibacterial activity, against some Gram-positive and negative bacteria, and especially against M tuberculosis. Alcohols act by denaturing proteins. They are not effective against spores and viruses.
The alcohol must have a 10 minute contact with the organisms. Solutions of 70 percent alcohol are more effective than higher concentrations, as the presence of water speeds up the process of protein denaturation as reported by Lawrence and Block (1968). The alcohols do not function as disinfectants when instruments, hand pieces, or other equipment are simply wiped with them, since they evaporate quickly. Alcohols can dissolve cements holding instruments together, and plastics may harden and swell in their presence.
They are frequently used for skin antisepsis prior to needle puncture. They are good organic solvents. Their benefit is derived primarily in their cleansing action. The alcohols must have a prolonged contact with the organisms to have an antibacterial effect. This contact is prevented due to its rapid evaporation. Alcohol is sometimes used as a rinse following a surgical scrub. Its effectiveness lies in the solvent action and not in its antibacterial properties. Ethanol (Ethyl alcohol) is employed in the concentration of 70 percent as a skin antiseptic. It has poor activity against bacterial spores, fungi, and viruses. It is used in the concentration of 60 to 70 percent v/v, for disinfection of skin. The alcohols do not have reliable sporicidal, virucidal, or fungicidal action; hence, they are not useful for sterilizing surgical instruments.
Phenol itself toxic to skin and bone marrow. The phenolic compounds were developed to reduce their side effects but are still toxic to living tissues. These compounds, in high concentration, are protoplasmic poison, and act by precipitating the proteins and destroy the cell wall.
Lawrence and Block (1968) reported that their spectrum of activity includes lipophilic viruses, fungi and bacteria but not spores. Hence these are approved by ADA for use as surface or immersion disinfectant.These compounds are used for disinfection of in animate objects such as walls, floors and furniture. They may cause damage to some plastics, and they do not corrode certain metals, such as brass, aluminium and carbon steel.
AQUEOUS QUARTERNARY AMMONIUM COMPOUNDS
Benzalkonium chloride (Zephiran) is the most commonly used antiseptic. Its spectrum of activity is primarily Gram-positive bacteria. It is well tolerated by living tissues. It is not widely used because of its narrow spectrum of activity.
Many studies have shown, that, iodophor compounds are the most effective antiseptics,. Iodine is complexed with organic surface-active agents, such as, polyvinylpyrrolidone (Betadine, Isodine). Their activity is dependent on the release of iodine from the complex. The surface agent is film forming; this prevents the solution form staining clothes or skin.
These compounds are effective against most bacteria, spores, viruses, and fungi. These are the most commonly used surface disinfectants along with hypochlorite. Concentrated solutions have less free ioidine. Iodine is released as the solution is diluted. An appropriate dilution is 1 : 2 : 3 parts of iodophor and distilled water, respectively.
Geraci (1963) reported that these compounds build up on the skin after successive scrubs, and that this provides long la
STORAGE OF STERILE GOODS
Literature reported that the storage of instruments is also a problem. The pattern of storage varies from place to place. They are either stored in drawers, or in containers, in packs or sterilized trays. The maintenance of sterility during transportation and storage is of utmost importance.
Packs should be stored with the following considerations
alcohol as disinfactant ASEPSIS betadine CHEMICAL STERILIZATION CLASSIFICATION OF METHODS OF STERILIZATION CLASSIFICATION OF STERILIZATION DISINFECTION DRY STERILIZATION formaldehyde glass bead sterilization glutaraldehyde hot air oven INFECTION CONTROL INFRA RED STERLIZATIO ionizing radiation irradiation METHODS OF STERILIZATION MOIST STERILIZATION non-ionizing radiation PHYSICAL STERILIZATION RRADIATION STERILIZATION ULTR SONIC STERILIZATION STERILIZATION sterilization by means of alcohol sterilization of glass storage of sterile instruments ULTR SONIC STERLIZATION