بسم الله الرحمن الرحيم

Sterilization and disinfection:

Sterilization: it indicate a procedure which will completely kill all living organisms including bacteria, vegetative bacteria and viruses in any given set of condition . sterilization should be done to prevent the cross infection between patients there are very dangerous diseases like viral hepatitis and AIDS transmitted by dental instruments. Disinfection: it indicate aprocedure affording a valuable measure of control of infection, but definitely inferior to sterilization, in particular bacterial spores and many vegetative organism and viruses may not be killed.

Methods of sterilization: 1-Physical methods 2-chemical methods 3- combination between both

Physical methods: 1-boiling water: its economic method, boiling water does not kill spores and can not sterilize instruments. The disadvantage of boiling water is rusting of the instrument in addition to dulling the sharp one. to minimize this disadvantage can use rust inhibitor such as sodium bicarbonate. Boiling is a method of high level disinfection that is useful when actual sterilization can not be achieved. Well-cleaned items must be completely submerged and allowed to boil at 100C° for 10-30 minutes this may kill many of microorganism, but most viruses will not be killed.

Physical methods: 2- Dry heat sterilization: Hot air oven widely used in dentistry because of its efficient and economic and instrument are not going to rust. Two points should be taken in consideration: the temperature and the time. The recommended temperature is 160 C° which should be held of minimum time of 60 minutes. The time required to sterilize can be reduced by raising the temperature. Disadvantages of dry heat method: the high temperature will affect the sharpness of instruments, and the process is slow.

Physical methods: Short-Cycle, High-Temperature Dry Heat Ovens: A rapid high-temperature process that uses a forced-draft oven (a mechanical convection oven that circulates air with a fan or blower) It reduces total sterilization time to 6 minutes for unwrapped and 12 minutes for wrapped instruments these short-cycle high temperature dry heat ovens operate at approximately370° to 375° F. (185C°)

Physical methods: 3- Pressure steam sterilization “autoclaving”: In this method moist heat in form of super heated under pressure is one of the most effective in destroying microorganisms including viruses, fungi and spores in relatively short time, to ensure sterilization; instruction related to time, temperature, and pressure must be followed carefully. (For light load of instrument the use of 20 pounds/inch3 the time should be 20minutes the temperature 170C0 is enough to kill all M.O) Disadvantage is rusting of the instrument to minimize this instrument must be put in 1% sodium nitrate solution before autoclaving for 2minutes.

Physical methods: 4- Hot oil method: this can be used for sterilization of endodontic instruments and hand pieces, the temperature .about 150C° and time for 15 minutes.

Physical methods: 5- Ultrasonic vibration method: We use it especially for reamers, files and burs. The advantages of this method are: *16 times more efficient than hand scraping ** reduce erosion of the instruments *** reduce puncturing wounds

Physical methods: 6- Radical sterilization: its efficient method but expensive we use ultra violet light , gamma, beta rays. we use this method to sterilize disposable needles and drugs.

Physical methods: 7- Gas methods: Ethylene oxide is used which is highly bactericidal, Ethylene oxide sterilization is the best method for sterilizingcomplex instruments and delicate materials. hand pieces are sterilized by this method.

Chemical methods: All chemical disinfectants are poor alternative to proper physical sterilizing procedure. Disinfectant antiseptics do not kill all spores , the ways that these disinfectant acts are: 1-react with the cell protein of the bacteria 2-react with the enzyme system of the bacteria 3- cause disruption of the cell wall of the bacteria

Chemical methods: properties of ideal antiseptic: they must destroy the M.O. it should penetrate deeply through bacterial cell. Rapid in action Doesn’t damage material or living tissue when coming in contact. Return its potency Soluble in water Non corrosion and doesn’t stain the instrument

Chemical methods: Some points should be taken in consideration concentration: we should follow the instruction of each agent before using as a general rule temperature : higher temperature more efficient sterilization P.H.: each agent act perfectly at certain P.H

Chemical methods: Examples of chemicals used widely in dentistry: eugenol : eugenol is pal yellow solution and goes darker with time. Eugenol is protoplasmic poison (antiseptic) Alcohol: methylated spirit its protoplasmic poison , its most effective at concentration of 70%.

Chemical methods: C.M.C.P: (camphorated Para mono chlorophynol) Use it in root canal its powerful bactericidal so kill the bacteria in the canal. Chlorhexidine : use especially as mouth wash and hand wash at concentration of 0.12% .its bactericidal against G+ and G- bacteria but viruses are resistant to it. Hydrogen peroxide: (H2O2) its mild anti bacteria it librated O2 rapidly it helps for cleaning pus and debris so can be used in R.C.T Sodium hypochlorite: powerful germicidal and good solvent for necrotic tissue so use it in R.C.T

Combination between chemical and physical methods CHEMICAL VAPOR PRESSURE STERILIZATION (CHEMICLAVING) Sterilization by chemical vapor under pressure is performed in a Chemiclave. Chemical vapor pressure sterilizers operate at 270° F (131° C) and 20 pounds of pressures. They are similar to steam sterilizer’s and have a cycle time of approximately half an hour.

Combination between chemical and physical methods Advantages of Chemiclaves: sterilized instruments without rust or corrosion. Disadvantages of Chemiclaves: Items sensitive to The elevated temperature will be damaged. Towels and heavy cloth wrappings of surgical instruments may not be penetrated to provide Sterilization.

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