Contamination zones

Work surfaces should be defined as zones of high or low contamination.

Surfaces liable to become contaminated with body fluids or infected matter should be identified and designated high contamination zones. These areas benefit from impervious disposable coverings that can be changed and the surface beneath cleaned between patients. All disposable and sterilizable instruments and trays fall within this area (Fig. 6.5).

Low contamination zones include all other areas that, during normal clinical procedures, are not expected to become coated with infected material. In these areas, procedures should be adopted to limit the number of surfaces touched each time a patient is treated. The operator should be aware that their hands are generally contaminated and hand-washing techniques have gained a high priority in helping to eliminate serious infection spread in hospitals. Figure 6.6 shows bacterial growth on agar plates from hand prints before and after hand washing using Hibiscrub hand cleanser.

Water supplies

All waterlines and airlines should be fitted with antiretraction valves to help prevent contamination of the lines. Water retraction valves may aspirate infected material back into the tubing. Hand-pieces with water sprays should be allowed to discharge water into the sink for 20–30 seconds after each patient. Overnight microbial accumulation can be reduced if the hand-piece is run for two minutes at the beginning of each day. Many units now have a bottled water system, disinfectants advised by the manufacturer may be run through the system at the end of each day to reduce the microbial load and prevent the build-up of biofilm. Specific agents, such as Alpron (Fig. 6.7) are now available to eradicate biofilms in dental unit water lines (Fig. 6.8).

The basic instrument pack

A presterilized basic pack (Fig. 6.9) is required for all routine root canal procedures. The pack contains:

Use of the front surface mirror overcomes the problems associated with double images, which are produced when the reflecting surface is beneath a layer of glass. The endodontic locking tweezers allow small items to be gripped safely and transferred between assistant and operator (Fig. 6.10). They are particularly useful when handling gutta-percha points, paper points and cotton-wool pledgets. The tips of the beaks should be blunt and grooved. A Mitchell’s trimmer may be used to remove cement and either temporary or permanent crowns. The canal probe or DG 16 should be long, fine, sharp and strong. It is used to feel the floor of the pulp chamber when locating canal orifices. A Briault probe is used to feel for overhangs when removing the roof of the pulp chamber and to check the internal margins of any restorations. Two other probes, although not included in the basic kit, are useful in periodontal assessment: the explorer EXD3CH (Fig. 6.11) (used to examine restorations, such as bridges), furcation probe with markings (for measuring the extent of periodontal furcation involvement in posterior teeth); and a pocket measuring probe with a fine shank, blunt end, and millimetre markings (as illustrated in Chapter 11). Long-shanked excavators (Fig. 6.12) come in a range of designs to allow access to the pulp chamber. These are used for scooping out the remains of the pulp and excess gutta-percha; also for flicking away pulp stones. The flat plastic assists in placement of inter-appointment provisional restorations. The ruler is used to measure and set instrument lengths. The nurse can provide initial measurement but the operator may wish to use a finger-ring held ruler for checking or fine adjustments.

Operation microscope

There are many brands of Dental Operating Microscopes available on the market. They vary by the optical system; a continuous zoom versus series of steps of magnification (3.4×, 5.1×, 8.5×, 13.6×, 21.3×); fixed versus inclinable binoculars; halogen, Xenon or LED illumination; and manual versus foot pedal for hands-free operation. Installation of video camera and monitor or assistant scope could facilitate four-handed endodontic practice. The former set-up would allow the dental assistant to carry out other tasks and for documentation purposes. The type of microscope and installation (ceiling mounts, wall mounts, floor-stands, custom-mounts) may be limited by the size of the dental surgery and the quality of the ceiling and walls. An optimal mounting arrangement would facilitate easy access and positioning, as well as make best use of the available surgery space (Fig. 6.13).

X-ray machine

All medical devices, including X-ray machines, purchased for use in countries within the European Union should have acquired CE (stands for Communauté Européenne, i.e. European Community) marking according to the Medical Devices Regulations 2002. The wiring must comply with BS 7671: 2008, 17th edition. Each newly installed X-ray machine must receive a Critical Examination (IRR99 reg 31) by the installer confirming the correct function of safety systems, leakage exposure rates and in-beam dose. An acceptance test must be performed prior to clinical use and, thereafter, routine tests at suitable intervals.

Current dental X-ray machines are normally microprocessor-controlled digital devices with touch contact keyboards to set the exposure time and area to be exposed. The tube voltage of most current machines is 70 kV and must comply with a suitable British or international standard for construction. Most current machines are suitable to be used with conventional and digital radiographic techniques.

Dental X-ray machines come in a variety of configurations including mobile units or wall, floor column or dental unit mounted machines. Recently, a number of cordless hand-held dental X-ray machines with high-frequency, 60 kV DC X-ray generator have become available (Fig. 6.14). The advantages of these hand-held units include flexibility in positioning, spacing saving and economy as a single device can serve multiple surgeries. However, the X-ray tube, X-ray control circuitry, and high voltage generator (transformer) contained in a single, lead shielded housing may increase the risk of operator exposure to radiation as a result of tube leakage and radiation back scatter. The back scatter can be reduced by a properly deployed lead acrylic disc surrounding the exposure aperture cylinder to absorb and limit this unnecessary dose. A theoretical increase in patient dose from these units could result from repeated exposure required due to operator/patient movement.

Operation of the dental X-ray machine should comply with current legislations governed by:

A dental practice must draft Written Procedures for the use of dental X-ray equipment including:

Each employer is responsible for ensuring that all Practitioners, Referrers and Operators are suitably trained. Normally, a practice should appoint a Radiation Protection Supervisor. Persons responsible for exposing X rays should be suitably trained, a record of current training should be recorded and regular refresher training scheduled and audited by the employer.

X-ray viewer

Radiographic viewers or computer monitor connecting to a digital system should also be sited within easy reach. They may be placed on a nearby work surface, or on a mounted, adjustable arm (Fig. 6.15).