Key features of ancillary equipment

In this step I’m going to take you through the key features of the main ancillary equipment associated with the use of dental x-ray sets. Ancillary equipment is the equipment needed to capture and display the radiographic image. We look at the digital imaging systems, as well as film processing and viewing systems. When I’m referring to digital imaging systems, this is a term that covers both systems that are used. Computed radiography, usually abbreviated to CR, and direct radiography abbreviated to DR. Computed radiography involves the use of phosphor plates, and direct radiography, the use of sensors. Panoramic, cephalometric, and cone beam CT radiography are based on direct radiography. Whereas intraoral radiography may be based on either computed or direct radiography systems.

The images produced from both these systems have an algorithm applied to the given data to produce an optimum image, before being presented to the viewer on the computer screen. The resultant image can then also be manipulated manually, by the person viewing the radiograph, using the imaging software. I’ll start by describing the key features of computed radiography systems, as this is now the most commonly used type of imaging system for intraoral radiography. In general, phosphor plate systems, used for intraoral radiography, are faster than conventional dental film. This means that usually around 10% less radiation exposure is required to produce an optimum image, compared to f-speed film, the fastest currently on the market. However, not all computed radiography systems are the same.

And there are some on the market with a much poorer dose response, requiring exposures at the level used for d-speed film to produce an optimum image. You should always get expert advice when selecting a computed radiography system.

Computed radiography systems will produce a clinically useful image over a wide latitude, or range, of radiation exposures. But these exposures tend to be higher than those required for use with direct digital systems. In preparation for use, the phosphor plates are usually placed inside a folded piece of card, to protect the plate from being bitten or otherwise damaged. The plate and the cardboard are then placed inside a plastic sheath for infection control purposes. After exposure, the plate is removed from the plastic sheath and card protector, and is fed into a reader. This uses a laser beam to read the image data on the plates and then clears any remaining image, ready for the plates next use.

It is advisable to read phosphor plates as soon as possible after exposure, as the image on the plate can fade very quickly after exposure. After as little as 10 minutes, diagnostic information may be lost from the image. Following their exposure to x-rays, phosphor plates should not be exposed to light, other than their removal from the sheathing and insertion into the reader. As this will cause some erasure of the image on the plate. Care of phosphor plates should also be considered very carefully, as they are easily prone to damage by scratching or overzealous cleaning, resulting in the phosphor layer being damaged or peeling.

Direct digital systems have solid state sensors usually linked directly to the imaging software on a computer. For equipment used with intraoral x-ray sets, the link is usually through a cable. Although there are some wireless versions available. For panoramic, cephalometric, and cone beam CT equipment, the direct digital system is integrated into the x-ray set. In general, direct digital systems used for intraoral radiography are the fastest of the dental imaging systems. Typically requiring approximately 50% less radiation exposure than the fastest film. And approximately 60% of the exposure required by computed radiography systems. Again, though not all systems are the same, and some do not perform as well as others.

Although these systems are generally faster than computed radiography, they operate over a narrow range of radiation exposures. In preparation for use, the sensors are placed in a plastic sheath for infection control purposes. And very soon after exposure the image can be viewed on the computer screen.

The sensors are less prone to damage than phosphor plates, but the cable connecting the sensor to the computer can be easily damaged, leading to splitting of the protective covering. Direct digital sensors are generally less favoured because, due to their rigidness and the size of the sensor, there is an increased chance of inducing a gagging reflex in patients. The screens used for viewing digital radiographs are a key piece of equipment in the clinical evaluation of images. For most dental use, a standard computer screen will suffice for this. But the screen must be of a sufficient standard to be able to meet the basic quality assurance requirements, which some cheaper screens may not meet.

A computer screen should always be used in its native resolution for viewing patient’s radiographs, to reduce the chance of the images being distorted. A dental practice should consider having a separate dedicated screen for reporting on patient’s radiographs, if the required settings conflict with settings for other software, such as patient management programmes. Film is still used at some dental practices. Intraoral film is available in a range of speeds, the fastest being f-speed film. Panoramic and cephalometric film is used in conjunction with intensifying screens, which must be spectrally matched with the film being used. The processing facilities associated with film use could either be manual or automatic.

In a manual system, the person carrying out the processing needs to check the chemical concentrations, the temperature of the developing and fixing solutions, and determine the time that films are required to be in the individual chemical solutions. Whereas an automatic processor heats the solutions to a predetermined level, the films are fed into the machine at one end, and come out fully processed and dry at the other end. The stripping of wrapping around the film, and the loading and unloading of film cassettes, is carried out either in a darkroom or in a glove box attached to the side of an automatic processing unit. There is also a self developing film. This is supplied with individual sachets of processing solutions.

However, they should only be used in specific situations where access to processing facilities is not possible. Dental practices that continue to use film should view their radiographs on light boxes. These incorporate a bright light, which can be collimated to the size of the film being observed. Sometimes a magnifier is used to increase the size of the image.