Case Studies in Infection
Training in Infection Control
The Bug Blog
Page updated 9 October 2006
All instruments selected for use even if they were not actually used must be cleaned and sterilized. Steam sterilisation is the most practicable method for sterilizing reusable
dental devices because it has high lethality, is rapid and non-toxic. The need for cold sterilisation has almost disappeared in the dental surgery, as most items of equipment can now be steam sterilized or have been replaced with single use disposable items.
There are three stages in the decontamination of dental instruments and equipment:
If instruments are not clean they cannot be sterilized effectively. Cleaning lowers the bacterial load on a used instrument by log 10 3-4 i.e. by a thousand fold. Cleaning may be done either manually or by machine using an ultrasonic bath and/or a thermal washer disinfector. Best practice is to use an automated washing process. The BDA, Department of Health Estates & Facilities Directorate and the Medicines and Healthcare products Regulatory Agency (MHRA) all recommend automated cleaning whenever practical with a thermal washer/disinfector, as it is reproducible, and more easily controlled and validated than manual cleaning. Studies have demonstrated that washer/ disinfectors are more efficient at reducing the bacterial load during pre-sterilisation cleaning than either ultrasonic cleaning or hand cleaning of dental instruments. Staff safety is enhanced as handling of sharp contaminated instruments is significantly reduced, as instruments do not need to be scrubbed so there is less exposure to microorganisms and noxious chemicals. Furthermore, productivity is increased as more time becomes available for clinical activities. However, depending on the cycle time of the thermal washer disinfector the turn round time for instruments may be increased and additional instruments may therefore be required. The approximate down time for instruments cleaned in a thermal washer disinfector and sterilized in a vacuum sterilizer is 2 hours. If possible, when purchasing new items of equipment select devices that can be machine cleaned and thermally disinfected and sterilized .
Staff should be provided with a written policy for manual cleaning and trained appropriately. Instruments should be cleaned as soon as possible after use. If saliva and blood are allowed to dry on instruments, the cleaning process becomes more difficult. Blood is corrosive to stainless steel instruments and will cause pitting and rusting if left for any length of time. Damaged and pitted instruments are more difficult to clean effectively and corrosion may reduce the life of the instrument. If it is not practical to clean the instruments immediately then pre-soak them in a non-ionic or enzymatic detergent solution, or pre-cleaning foam.
A dedicated deep sink (not a hand basin) should be used for decontamination of instruments preferably with a separate sink for rinsing. Manual cleaning should be undertaken in a safe and effective manner. Always take great care with sharp instruments. Before cleaning the instruments the member of staff should put on the following protective clothing:
To clean instruments safely and effectively use the following method:
Ultrasonic cleaning baths offer an effective method for cleaning intricate, jointed or serrated stainless steel and metal instruments and items that are heavily soiled e.g. with cement. Plastic instruments are not successfully cleaned by this method as they absorb the ultrasonic energy . Remember the ultrasonic bath only cleans, it will not disinfect instruments. The following are some key guidelines: -
Small benchtop versions suitable for use in dental surgeries can be loaded with instruments in cassettes, trays or baskets and come supplied with connectors for a pressure flush of dental handpieces. The size, model and type chosen depend on the practice's workload, number of instruments, throughput volume and time requirements, as well as available space. Domestic dishwashers are not an acceptable alternative. They do not perform to the same specifications as washers/ disinfectors, may not adequately clean the inner surface of hollow or lumened instruments, and nor are they capable of validation in accordance with HTM 2030 (see www.dh.gov.uk for additional guidance on validation testing and protocols).
The washer disinfector cycle includes a cool -prewash (below 35 O C to prevent protein coagulation and remove debris) main wash, rinse, thermal disinfection and post- disinfection rinse. Thermal disinfection is achieved by the use of hot water (set between 80-90 O C) coming into in direct contact with the instruments and equipment for a specified period of time. This reduces the number of viable microorganisms contaminating the devices but may not necessarily inactivate some viruses and bacterial spores, so instruments are not sterile.
Thermal washer disinfectors are required to operate to HTM2030 specifications and Model Engineering Specifications C31. Machines are designed with independent monitoring or "watchdog circuits" that are separate from the machine control system. Watchdog circuits monitor the detergent dosing verification, detergent cleaning cycle and thermal disinfection cycle and will alert the operator of any failures or malfunctions, either on the display screen and/or on the print out; and will abort the cycle if errors are detected. Models should be fitted with a printer (and some also have computer links) for maintaining a permanent record of the operation parameters and performance indicators of the disinfection cycle. The detergent formulation and concentration is critical and the washer disinfector must be capable of detecting any deviations and altering the operator to a failed cycle. The cycle must include a drying stage. Quarterly performance and function testing is performed by Competent Test person.
Pre-sterilisation dental handpiece cleaning machines
Pre-sterilisation dental handpiece cleaning machines are recommended by the BDA. These devices vary in design and sophistication but all clean and lubricate the internal components of the handpiece. A typical machine cleans the air and water channels with the aid of a detergent spray solution, followed by cleaning and lubricating the bearings and gears with oil, and finally the excess oil is purged and the interior dried with compressed air. The process takes about 35-40 seconds. Manufacturer's advice on which type of detergent is compatible with their handpiece equipment should be sought prior to using the cleaning machine. Some models also include a handpiece vacuum sterilisation stage.
Thermal washer/disinfector safe handpieces
Many of the contralateral, straight and turbine handpieces currently available are thermal washer/disinfector safe. Only instruments designated by the manufacturer as being suitable for cleaning in a washer disinfector and carry the washer-disinfector symbol can be processed in a thermal washer disinfector. Remember to lubricate with service oil after the thermal washer disinfector stage.
Manual cleaning of dental handpieces
A suggested manual cleaning procedure is set out below. Manufacturers may offer different advice for their equipment, which should be followed, and will vary according to the age and design of the handpiece. Wear protective clothing e.g. heavy-duty gloves, goggles/visor, and a mask. Handpieces run by an electric motor do not require oil lubrication .
External cleaning of handpiece
Internal cleaning of handpiece
Instruments should be function tested as part of the decontamination process. Instruments that are damaged should be repaired or taken out of service. Instruments that develop or sustain surface damage due to general wear, pitting or corrosion encourage dirt and bacteria to accumulate and are more difficult to clean and sterilize effectively. Furthermore they may be more prone to failing during function and could potentially harm patients or staff.