Dental clinics have been a focus of attention as dental instruments are possible agents for pathogenic transmission from patient to patient, from patient to doctor and vice versa. With the increasing risk of cross infections by Hepatitis B and HIV viruses, the dental facilities are bound to observe the same stringent rules in sterilization of instruments, and disinfection/maintenance of the operatories.
Prevention of parasitic involvement is the purpose of sterilization. Sterilization should be thoroughly understood before we falsely delude ourselves into believing that all sterilization attempts result in true sterilization. Dental professionals are exposed to infection during their work because of the many potential sources of infection in dental practice, such as the wide variety of microorganisms in the blood and saliva of patients. The infection could be direct infection, contact infection, smear infection, droplet infection or cross infection. The incidence of hepatitis B and the prevalence of the carrier state are increasing. It is believed that in the United Kingdom general dental practitioners treat as many as 250 carriers each day, and in many cases these carriers are not identified.
In the Middle East and Africa, the percentage of hepatitis B virus (HBV) carriers ranges from 20% to 30%, and hepatitis C virus (HCV) carriers form 20% of new cases.
There is a large and growing amount of literature on the hazards of cross infection from contaminated and inadequately sterilized instruments in dental practice. It is the duty of all the members of a dental team to ensure that all the necessary procedures (thorough sterilization) are taken to protect themselves and their patients from cross infection. In dental practice, true sterilization of the general dental armamentarium is probably unobtainable because there are too many variables in most offices to permit such a desirable state. Fortunately, this makes little difference, for the oral environment is a populous bacterial milieu that remains in fairly stable balance and which seems to tolerate and control any transient invasion of organisms brought on by unclean eating utensils, social amenities or dental instruments. However, this state of affairs does not entitle the practitioner to refer to nothing more than instrument sanitizing efforts as true sterilization, and, in addition, to believe it himself.
Sterilization implies that all forms of life have been destroyed. This is a bit difficult to accomplish through use of boiling water or the currently available chemical disinfectants. Saturated steam under pressure is probably the most effective method of bringing about sterilization. This is accomplished, of course, with an autoclave. And yet it is continually heard that instruments are rendered sterile by "cold sterilization solution" or by boiling in water. The medical classification of inanimate objects in a dental clinic is:

The CDC (Center for Disease Control) U.S.A. has proposed certain guidelines for preventing cross infection in a dental clinic setup:
Amend Section 1005 of Division 10 Title 16 of the California Code of Regulations to read as follows:
(1) Health care workers shall wear surgical facemasks in combination with either chin length plastic face shields or protective eyewear when treating patients whenever there is potential for splashing or spattering of blood or OPIM. After each patient and during patient treatment if applicable, masks shall be changed if moist or contaminated. After each patient, face shields and protective eyewear shall be cleaned and disinfected, if contaminated.
(2) Health care workers shall wear reusable or disposable protective attire when their clothing or skin is likely to be soiled with blood or OPIM. Gowns must be changed daily or between patients if it should become moist or visibly soiled. Protective attire must be removed when leaving laboratories or areas of patient care activities.
(3) Hand Hygiene: Health care workers shall wash contaminated or visibly soiled hands with soap and water and put on new gloves before treating each patient. If hands are not visibly soiled or contaminated an alcohol based hand rub may be used as an alternative to soap and water.
(4) Healthcare workers who have exudative lesions or weeping dermatitis of the hand shall refrain from all direct patient care and from handling patient care equipment until the condition resolves.
(5) Gloves: Medical exam gloves shall be worn whenever there is a potential for contact with mucous membranes, blood or OPIM. Gloves must be discarded upon completion of treatment and before leaving laboratories or areas of patient care activities. Healthcare workers shall perform hand hygiene procedures after removing and discarding gloves. Gloves shall not be washed before or after use.
(6) Sterilization and Disinfection: Heat stable critical and semi-critical instruments shall be cleaned and sterilized before use by using steam under pressure (autoclaving), dry heat, or chemical vapor. FDA cleared chemical sterilants/disinfectants shall be used for sterilization of heat-sensitive critical items and for high level disinfection of heat-sensitive semi-critical items.
(7) Critical and semi-critical instruments or containers of critical and semi-critical instruments sterilized by a heat or vapor method shall be packaged or wrapped before sterilization if they are not to be used immediately after being sterilized. These packages or containers shall remain sealed unless the instruments within them are placed onto a setup tray and covered with a moisture impervious barrier on the day the instruments will be used and shall be stored in a manner so as to prevent contamination.
(8) All high-speed dental hand pieces, low-speed hand piece components used intraorally, and other dental unit attachments such as reusable air/water syringe tips and ultrasonic scaler tips, shall be heat-sterilized between patients.
(9) Single use disposable instruments (e.g. prophylaxis angles, prophylaxis cups and brushes, tips for high-speed evacuators, saliva ejectors, air/water syringe tips) shall be used for one patient only and discarded.
(10) Needles shall be recapped only by using the scoop technique or a protective device. Needles shall not be bent or broken for the purpose of disposal. Disposable needles, syringes, scalpel blades or other sharp items and instruments shall be placed into sharps containers for disposal according to all applicable regulations.
(11) Proper functioning of the sterilization cycle shall be verified at least weekly through the use of a biological indicator (such as a spore test).
(12) Irrigation: Sterile coolants/irrigants shall be used for surgical procedures involving soft tissue or bone. Sterile coolants/irrigants must be delivered using a sterile delivery system.
(13) Facilities: If items or surfaces likely to be contaminated are difficult to clean and disinfect they shall be protected with disposable impervious barriers.
(14) Clean and disinfect all clinical contact surfaces that are not protected by impervious barriers using a Cal-EPA registered, hospital grade low- to intermediate-level disinfectant after each patient. The low-level disinfectants used shall be labeled effective against HBV and HIV. Use disinfectants in accordance with the manufacturer’s instructions.
(15) Dental unit water lines shall be anti-retractive. At the beginning of each workday, dental unit lines shall be purged with air, or flushed with water for at least two (2) minutes prior to attaching handpieces, scalers and other devices. The dental unit line shall be flushed between each patient for a minimum of twenty (20) seconds.
(16) Contaminated solid waste shall be disposed of according to applicable local, state, and federal environmental standards.
(17) Lab Areas: Splash shields and equipment guards shall be used on dental laboratory lathes. Fresh pumice and a disinfected, sterilized, or new ragwheel shall be used for each patient. Devices used to polish, trim or adjust contaminated intraoral devices shall be disinfected or sterilized.
(18) Intraoral items such as impressions, bite registrations, prosthetic and orthodontic appliances shall be cleaned and disinfected with an intermediate-level disinfectant before manipulation in the laboratory and before placement in the patient’s mouth. Such items shall be thoroughly rinsed prior to placement in the patient’s mouth.
Steps to follow in a clinical setup are:
1. CLEANING :
Manual Cleaning: Scrubbing with a brush and a surfactant or detergent with water removes debris and contaminants. If critical and noncritical items cannot be cleaned immediately after use, they should be placed in a puncture-proof, covered container and soaked in a detergent, disinfectant/detergent or an enzymatic cleaner (holding solution) until the soil is dissolved and removed. High-level disinfectants/ sterilants are not appropriate for presoaking instruments. Automated Cleaning: UItrasonic cleaners or washer-disinfecting units are safer and are recommended because they do not require presoaking or the manual scrubbing of instruments and therefore, minimize the exposure to blood and body fluids.(fig 1)
2. CORROSION CONTROL:
Always dry the cleaned instruments as it reduces the chances of corrosion. A rust inhibitor can be applied to the instruments before autoclaving.
3. PACKAGING:
Instruments should be pre-packaged before sterilization to protect against contamination after sterilization. Use proper packaging material according to the method of sterilization. Too thin a wrap may cause sharp instruments to tear the wrap.
4. STERILIZATION:
Heat: Heat sterilization is most commonly used in dental settings; however, steam and chemical vapor sterilization units are also used. High temperature methods include steam, dry heat and unsaturated chemical vapor while low temperature automated sterilization involves ethylene oxide (ETO) and plasma sterilization. Of these methods the autoclaves is the most preferred method in a dental setup. Autoclave is a self locking setup based on the efficacy of steam under pressure of 121 degree Celsius for 15 minutes and 15 pounds pressure. Another method is that of “Flash Sterilization” for unwrapped instruments using 270 degrees Fahrenheit at 30 pounds pressure for 4 – 7 minutes.
Hot air ovens are electrical devices used in sterilization. The oven uses dry heat to sterilize articles. They do not require water and there is not much pressure build up within the oven, unlike an autoclave, making them safer to work with. They can be more rapid than an autoclave and higher temperatures can be reached compared to other means. As they use dry heat instead of moist heat, some organisms like prions, may not be killed by them every time. The standard settings for a hot air oven are:
• 1.5 to 2 hours at 160 °C (320 °F)
• 6 to 12 minutes at 190 °C (374 °F)
These are widely used to sterilize articles that can withstand high temperatures and not get burnt, like glassware and powders. Linen gets burnt and surgical sharps lose their sharpness.
Liquid Sterilants used for "cold sterilization" are intended only for the reprocessing of heat-sensitive instruments and devices. If the critical or semicritical item is heat sensitive, it should be immersed in a liquid sterilant. Glutaraldehyde is a dialdehyde that is slightly acidic in its natural state. In a buffered (pH balanced) alkaline solution, it is a highly effective microbicidal agent. Glutaraldehyde is corrosive to metal instruments and is not to be used as a holding solution prior to instrument cleaning and sterilization. It is widely used in the cold sterilization of dental items, such as suction hoses. Glutaraldehyde is usually a clear liquid that turns green when activated. It has a strong odor and is an irritant to the skin, eyes, and respiratory system. It can cause allergic reactions in some individuals. The chemical should be used in separate areas where there is control over ventilation and occupational exposure.
Ortho-phthalaldehyde (OPA) is a chemical sterilizing agent used in a 0.55% solution, OPA shows better myco-bactericidal activity than glutaraldehyde. It also is effective against glutaraldehyde-resistant spores. OPA has superior stability, is less volatile, and does not irritate skin or eyes, and it acts more quickly than glutaraldehyde. On the other hand, it is more expensive, and will stain proteins (including skin) gray in color.
Ethylene oxide is a colorless gas used at room temperature to kill micro-organisms by chemical reaction. As it is toxic & irritating to skin & mucous membrane so it can only be used in an aerated & well ventilated room. The two most important ethylene oxide sterilization methods are: (1) the gas chamber method and (2) the micro-dose method. Ozone is used in industrial settings to sterilize water and air, as well as a disinfectant for surfaces. It has the benefit of being able to oxidize most organic matter. On the other hand, it is a toxic and unstable gas that must be produced on-site, so it is not practical to use in many settings.
Ultraviolet light irradiation (UV, from a germicidal lamp) is useful only for sterilization of surfaces and some transparent objects. Many objects that are transparent to visible light absorb UV. UV irradiation is routinely used to sterilize the interiors of biological safety cabinets between uses, but is ineffective in shaded areas, including areas under dirt (which may become polymerized after prolonged irradiation, so that it is very difficult to remove). It also damages some plastics, such as polystyrene foam if exposed for prolonged periods of time.
5. STORAGE & SHELF LIFE: All sterile items should be stored in an area and manner whereby the packs or containers will be protected from dust, dirt, moisture, animals and insects. Packs and containers with sterile (or high-level disinfected) items should be stored 20–25 cm (8–10 inches) off the floor, 45–50 cm (18–20 inches) from the ceiling and 15–20 cm (6–8 inches) from an outside wall. The shelf life of an item after sterilization is event-related. The item remains sterile until something causes the shelf life of sterilization depends on the following factors:
Quality of the wrapper or container Number of times a package is handled before use Number of people who have handled the package Whether the package is stored on open or closed shelves Condition of storage area (e.g., humidity and cleanliness) Use of plastic dust covers and method of sealing

6. MONITORING STERILIZATION PROCEDURES:
Sterilization procedures can be monitored routinely using a combination of biological, chemical and mechanical indicators as parameters. The biological indicator types Steam sterilizers: Bacillus stearothermophilus, weekly and as needed.Fig (2 and 3) Dry-heat sterilizers: Bacillus subtilis, weekly and as needed(fig 4) Chemical indicators include indicator tape or labels, which monitor time, temperature and pressure for steam sterilization, and time and temperature for dry-heat sterilization. These indicators should be used on the inside and outside of each package or container.
Mechanical indicators for sterilizers provide a visible record of the time, temperature and pressure for that sterilization cycle. This is usually a printout or graph from the sterilizer, or it can be a log of time, temperature and pressure kept by the person responsible for the sterilization process that day.

REFERENCES:
1. Walker W.V., Sterilization of dental instruments. The Journal of The American Dental Society of Anesthesiology, Vol. 12(1), 2006.
2. Technical bulletin, Disinfection & sterilization of dental instruments & materials, Dept. of Army, Washington D.C. 1995.
3. Centers for Disease Control and Prevention (CDC). 2002. Questions and answers regarding Creutzfeldt-Jakob disease infection-control practices. Available at: (http//www.cdc.gov/ncidod/diseases/cjd/cjd_inf_ctrl_qa.htm).
4. Curtis P. Hamann, How to clean, disinfect, and sterilize a dental operatory, Dental Assistant, Nov-Dec, 2004